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Ecosystems Research Division Publications: 2000
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This page lists publication titles, citations and abstracts produced by NERL's Ecosystems Research Division for the year 2000, organized by Publication Type. Your search has returned
94 Matching Entries.
See also Ecosystems Research Division citations with abstracts:
1999,
2000,
2001,
2002,
2003,
2004,
2005,
2006,
2007,
2008
Technical Information Manager: Janice Sims - (706) 355-8011 or sims.janice@epa.gov
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Presented/Published |
| BOOK CHAPTER |
UV Radiation Effects on Microbes and Microbial Processes |
04/01/2000
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Moran, M. A. AND R. G. Zepp. UV Radiation Effects on Microbes and Microbial Processes. Chapter 7, D.L. Kirchman (ed.), Microbial Ecology of the Oceans. John Wiley & Sons Incorporated, New York, NY, 201-228, (2000).
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The ultraviolet (UV) region of solar radiation is defined as wavelengths in the range of 200 to 400 nm. In contrast to visible radiation (400 - 800 nm), which has a well-defined role as the energy source for most of the Earth's primary production, the effects of UV radiation on biological processes in the ocean include an assortment of both positive and negative aspects, the balance of which is not readily understood. Recent increases in components of UV radiation reaching the ocean surface due to stratospheric ozone depletion makes comprehending, and ultimately predicting, the effects of UV radiation on the ocean ecosystem an especially important task. Understanding the ecological effects of UV radiation in the ocean requires sufficient knowledge of a least three factors. First, information on the number of photons of light reaching the surface of the ocean for each individual wavelength in the UV range is required. Since photons at 310 nm are likely to inflict microbial damage whereas photons at 380 nm can stimulate repair of such damage, the spectrum of UV radiation reaching the seawater surface is an important determinant of its effect on marine microbes. Second, information on the penetration of UV radiation into seawater at each individual wavelength is required. UV wavelengths are differentially absorbed by seawater constituents and therefore penetrate (and have the potential to affect biological processes) to different depths within the water column. Third, information on the effectiveness of each photon surviving to a given depth to bring about photobiological or photochemical changes is required. Molecules in both living cells and non-living organic matter are susceptible to modification by UV light, and the outcome is highly dependent on wavelength. This chapter is organized as a step-wise progression through each of these important factors.
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| BOOK CHAPTER |
Analysis of Chiral Pesticides and Polychlorinated Biphenyl Congeners in Environmental Samples |
11/01/2000
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Garrison, A. W. Analysis of Chiral Pesticides and Polychlorinated Biphenyl Congeners in Environmental Samples. , R.A. Myers (ed.), Encyclopedia of Analytical Chemistry. John Wiley & Sons, Ltd., Chichester, Uk, 6147-6158, (2000).
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Over 25 % of pesticides and other toxic organic pollutants are chiral, as are 19 of the 209 polychlorinated biphenyl (PCB) congeners; that is, they exist as two mirror image species called enantiomers (PCB enantiomers are called atropisomers). The enantiomers of a chiral compound have identical physical and abiotic chemical properties, but usually differ in biological properties such as microbial degradation, uptake and transport across membranes, metabolism rate, and toxicity. Chirality in the environment has become recognized as an important phenomenon since the mid-1980s, and related research has centered on the need to understand the environmental fate and effects of pesticides and PCBS. This article provides a brief back- ground on chiral chemistry in general and the importance of chirality in the drug industry, followed by a summary of examples of the enantioselectivity ofpesticide and PCB occurrencesand degradation in the environmentasgleaned from the scientific literature. The main emphasis is on the analysis of these compounds, with the primary focus on chiral separations. Chiral separations are generally performed by gas chromatography (GC) orhigh-performance liquid chromatography (HPLC) using chiral columns, or, to a lesser extent, by capillary electrophoresis (CE) using cyclodextrin (CD) or other chiral selectors in the run buffer. Summaries of these three separation methods are provided, with figures giving examples of pesticide and PCB enantiomeric separations. Finally, to show the usefulness of these separation methods, applications to several environmental chemistry problems involving chiral pesticides and PCBs are described and illustrated.
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| BOOK CHAPTER |
Hydrolysis |
07/01/2000
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Wolfe, N. L. AND P. M. Jeffers. Hydrolysis. , Chapter 13, R.S. Boethling and D. Mackay (ed.), Handbook of Property Estimation Methods for Chemicals: Environmental and Health Sciences. Lewis Publishers, Boca Raton, FL, 311-333, (2000).
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Hydrolytic processes provide the baseline loss rate for any chemical in an aqueous envi- ronment. Although various hydrolytic pathways account for significant degradation of certain classes of organic chemicals, other organic structures are completely inert. Strictly speaking, hydrolysis should involve only the reactant species water provides - that is, H+, OH-, and H20 - but the complete picture includes analogous reactions and thus the equivalent effects of other chemical species present in the local environment, such as SH- in anaerobic bogs, Cl- in sea water, and various ions in laboratory buffer solutions.Methods to predict the hydrolysis rates of organic compounds for use in the environmental assessment of pollutants have not advanced significantly since the first edition of the Lyman Handbook (Lyman et al., 1982). Two approaches have been used extensively to obtain estimates of hydrolytic rate constants for use in environmental systems. The first and potentially more precise method is to apply quantitative structure/activity relationships (QSARs). To develop such predictive methods, one needs a set of rate constants for a series of compounds that have systematic variations in structure and a database of molecular descriptors related to the substituents on the reactant molecule. The second and more widely used method is to compare the target compound with an analogous compound or compounds containing similar functional groups and structure, to obtain a less quantitative estimate of the rate constant.
Predictive methods can be applied for assessing hydrolysis for simple one-step reactions where the product distribution is known. Generally, however, pathways are known only for simple molecules. Often, for environmental studies, the investigator is interested in not only the parent compound but also the intermediates and products. Therefore, estimation methods may be required for several reaction pathways. Some preliminary examples of hydrolysis reactions illustrate the very wide range of reactivity of organic compounds. For example, triesters of phosphoric acid hydrolyze in near-neutral solution at ambient temperatures with half-lives ranging from several days to several years (Wolfe, 1980), whereas the halogenated alkanes pentachloroethane, carbon tetrachloride, and hexachloroethane have "environmental" (pH = 7, 25 degrees C) half-lives of about 2 hr, 50 yr, and 1000 millennia, respectively (Mabey and Mill, 1978; Jeffers et al., 1989). On the other hand, pure hydrocarbons from methane through the PAHs are not hydrolyzed under any circumstances that are environmentally relevant.
Hydrolysis can explain the attenuation of contaminant plumes in aquifers where the ratio of rate constant to flow rate is sufficiently high. Thus 1,1,1-trichloroethane (TCA) has been observed to disappear from a mixed halocarbon plume over time, while trichloroethene and its biodegradation product 1,2-dichloroethene persist. The hydrolytic loss of organophosphate pesticides in sea water, as determined from both laboratory and field studies, suggests that these compounds will not be long-term contaminants despite runoff into streams and, eventually, the sea (Cotham and Bidleman, 1989). The oceans also can provide a major sink for atmospheric species ranging from carbon tetrachloride to methyl bromide. Loss of methyl bromide in the oceans by a combination of hydrolysis and Cl- for Br- exchange constitutes a significant contribution to the total degradation and is a key factor in modeling atmospheric concentrations and balance schemes. It is therefore an important part of the assessment of stratospheric ozone depletion potential.
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| BOOK CHAPTER |
Identification of New Drinking Water Disinfection By-Products Formed in the Presence of Bromide |
07/01/2000
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Richardson, S. D., A. D. Thruston Jr., T. V. Caughran, P. H. Chen, T. W. Collette, K. M. Schenck, AND B. W. Lykins Jr. Identification of New Drinking Water Disinfection By-Products Formed in the Presence of Bromide. , Chapter 26, Barrett, S.E., Krasner, S.W., and Amy, G.L. (ed.), Natural Organic Matter and Disinfection By-Products Characterization and Control in Drinking Water. American Chemical Society, Washington, DC, 389-402, (2000).
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Using a combination of mass spectrometry and infrared spectroscopy, disinfection by-products (DBPs) were identified in ozonated drinking water containing elevated bromide levels, and in ozonated water treated with secondary chlorine or chloramine. Only one brominated by-product-dibromoacetonitrile-was found in the water treated with only ozone. Many more by-products were identified when secondary chlorine or chloramine was applied after ozonation. A number of these by-products have not been reported previously. When comparing low-bromide water to water with elevated bromide, a tremendous shift in speciation was observed for samples treated with secondary chlorine or chloramine. Without high bromide levels, chlorinated species dominate (e.g., chloroform, trichloroacetaldehyde, tetrachloro-propanone, dichloroacetonitrile, trichloronitromethane); with elevated bromide levels (I mg/L), these shift to brominated species (e.g., bromoform, tribromoacetaldehyde, tetrabromopropanone, dibromo-acetonitrile, tribromonitromethane). An entire family of bromo- and mixed chlorobromopropanones was identified that were not present in library databases, and have not been reported previously. They were observed mainly in the ozone- chlorarnine samples, but were also present in ozone-chlorine-treated water. These brominated by-products were also observed in water treated with only chloramine or chlorine.
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| BOOK CHAPTER |
Identification of Polar Drinking Water Disinfection By-Products Using Liquid Chromatography Mass Spectrometry |
07/01/2000
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Richardson, S. D., T. V. Caughran, F. G. Crumley, T. Poiger, AND Y. Guo. Identification of Polar Drinking Water Disinfection By-Products Using Liquid Chromatography Mass Spectrometry. , Chapter 25, Natural Organic Matter and Disinfection By-Products Characterization and Control in Drinking Water. American Chemical Society, Washington, DC, 374-388, (2000).
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A qualitative method using 2,4-dinitrophenylhydrazine (DNPH) derivatization followed by analysis with liquid chromatography (LC)/negative ion-electrospray mass spectrometry (MS) was developed for identifying polar aldehydes and ketones in ozonated drinking water. This method offers advantages over the currently accepted method using pentafluorobenzylhydroxylarnine (PFBHA) derivatization and gas chromatography/mass spectrometry (GC/MS) analysis, in that it allows for the detection of highly polar carbonyl compounds (with multiple polar substituents) and produces mass spectra and chromatographic behavior that can be used to distinguish between aldehydes and ketones in ozonated water. Results for many polar-substituted aldehyde and ketone standards are presented, as well as the identification of polar disinfection by-products (DBPs) in ozonated drinking water from full-scale plants and laboratory-scale ozonations of hurnic acid.
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| EPA PUBLISHED PROCEEDINGS |
Fish Physiology, Toxicology, and Water Quality |
04/15/2000
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Thurston, R. V. Fish Physiology, Toxicology, and Water Quality. Proceedings of the Fifth International Symposium, Kowloon, Hong Kong, November 10-13, 1998. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-00/015 (NTIS PB2000-107439), 2000.
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Scientists from ten countries presented papers at the Fifth International Symposium on Fish Physiology, Toxicology, and Water Quality, which was held on the campus of the city University of Hong Kong on November 10-13, 1998. These Proceedings include 23 papers presented in sessions convened over 4 days. Papers addressed effects of metals on the physiology of fishes and aquatic invertebrates, effects of ammonia on fishes, effects on fishes of toxicants from oil shale and coal gasification effluents, thermal effects on fishes, effects of pollutants on reproduction of fishes, bioaccumulation and physiological effects on fishes of xenobiotics, and the use of semi-permeable membrane devices to monitor xenobiotics. Water quality papers included discussions on hypoxia, metal ecotoxicology, metals on sediments, methodologies to evaluate the health of riparian and wetland environments, risk management of metal pollution, remedial strategies to reduce impacts on a watershed of metal mine wastes, watershed modeling, and strategies for developing nutrient and sediment load allocations for water quality protection.
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| JOURNAL |
Phytodegradation of P,P'-Ddt and the Enantiomers of O,P'-Ddt |
05/01/2000
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Garrison, A. W., V. Nzengung, J. Avants, J. J. Ellington, W. J. Jones, D. Rennels, AND N. L. Wolfe. Phytodegradation of P,P'-Ddt and the Enantiomers of O,P'-Ddt. ENVIRONMENTAL SCIENCE 34(9):1663-1670, (2000).
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There is no abstract available for this product. If further information is requested, please refer to the bibliographic citation and contact the person listed under Contact field.
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| JOURNAL |
Diel Temperature Effects on the Exchange of Elemental Mercury Between the Atmosphere and Underlying Waters |
04/01/2000
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Loux, N. T. Diel Temperature Effects on the Exchange of Elemental Mercury Between the Atmosphere and Underlying Waters. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY 19(4):1191-1198, (2000).
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There is no abstract available for this product. If further information is requested, please refer to the bibliographic citation and contact the person listed under Contact field.
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| JOURNAL |
Analysis of Anionic Metallized Azo and Formazan Dyes By Capillary Electrophoresis/Mass Spectrometry |
07/21/2000
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Poiger, T., S. D. Richardson, AND G. L. Baughman. Analysis of Anionic Metallized Azo and Formazan Dyes By Capillary Electrophoresis/Mass Spectrometry. JOURNAL OF CHROMATOGRAPHY A 886(1-2):259-270, (2000).
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Capillary electrophoresis-mass spectrometry was applied to the separation of several anionic dyes containing copper(II), chromium(III), or cobalt(III) as part of the dye molecule. The dyes were separated using a 110 cmX50 mu m uncoated fused-silica capillary and a 5 mM ammonium acetate buffer (pH 9) containing 40% acetonitrile. Excellent separationefficiencies (N = 500 000 plates/column) and low detection limits of 20-50 pg (selected ion monitoring, S/N = 10) were achieved. Mass spectra were acquired at different cone voltages. At low cone voltages (low collision energies), sensitivity was maximized and the mass spectra contained only signals of the (multiply charged) molecular ions and low levels of sodium ion
and proton adducts. At higher cone voltages, the 2:1 (ligand:metal) chromium and cobalt dyes showed losses of one of the two dye ligands, accompanied by a reduction of the metal. The copper dyes showed signals due to loss of SO2 and SO3- but no release of metal. Azo cleavage, otherwise typical of azo dyes, was not observed with the metallized dyes.
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| JOURNAL |
Identification of Reactive Dyes in Spent Dyebaths and Wastewater By Capillary Electrophoresis/Mass Spectrometry |
07/21/2000
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Poiger, T., S. D. Richardson, AND G. L. Baughman. Identification of Reactive Dyes in Spent Dyebaths and Wastewater By Capillary Electrophoresis/Mass Spectrometry. JOURNAL OF CHROMATOGRAPHY A 886(1-2):271-282, (2000).
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Capillary electrophoresis with diode array detection and mass spectrometry combined with solid-phase extraction were employed for the identification of reactive vinylsulfone and chlorotriazine dyes and their hydrolysis products in spent dyebaths and raw and treated wastewater. Recoveries of dyes from treated wastewater as their tetrabutylammonium ion-pairsusing C-18 reversed-phase cartridges ranged from 81 to 121%. Detection limits in sewage effluent of the different dyes and hydrolysis products ranged from 23 to 42 mu g/l. The method was successfully applied to the detection of the hydrolysis products of five reactive dyes in influents and effluents of a municipal wastewater treatment plant receiving dyehouse effluents.
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| JOURNAL |
Ozone Depletion and the Air-Sea Exchange of Greenhouse and Chemically Reactive Trace Gases |
04/01/2000
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Erickson, D. J., R. G. Zepp, AND E. Atlas. Ozone Depletion and the Air-Sea Exchange of Greenhouse and Chemically Reactive Trace Gases. CHEMOSPHERE - GLOBAL CHANGE SCIENCE 2(2):137-149, (2000).
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One of the most important aspects of global change is that of stratospheric ozone depletion and the resulting increase in UV radiation reaching the surface of the Earth. Some 70% of the Earth surface is covered by water containing an extremely complicated milieu of organic and inorganic chemical species. The photochemical production and transformation of variousgreenhouse and chemically reactive gases in the ocean has been a focus of much study over the last century. We assess the implications of increased UV radiation on aquatic and marine boundary layer biogeochemistry with a focus on trace gases that exchange between the ocean and the atmosphere. CO2, DMS, CO, OCS, CH4, N2O, non-methane hydrocarbons (NMHCs) and organohalogens are considered within the context of changing surface ocean UV fluxes and various feedbacks upon the integrated climate system. Links between the upper ocean photochemical environment and the lower atmosphere are stressed. Once in the atmosphere, these gases each play a different role in modulating several aspects of atmospheric chemistry and by implication atmospheric circulation and climate dynamics such as precipitation patterns, surface temperatures and surface atmosphere substance exchange. We augment the conceptual models proposed with new observational data on surface ocean concentrations from the southern hemisphere obtained under a range of UV exposures.
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| JOURNAL |
Environmental Mass Spectrometry |
09/15/2000
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Richardson, S. D. Environmental Mass Spectrometry. ANALYTICAL CHEMISTRY 72(18):4477-4496, (2000).
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In many ways, environmental chemistry would appear to be a mature field, in that many of the same types of chemicals and pollutants continue to be of interest. Those most commonly measured include pesticides, surfactants, textile dyes, chlorinated alkanes, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), dioxins, nutrients, heavy metals, and other toxic inorganics, such as arsenic species. Although these types of chemicals have held the interest of the environmental community for several years, the types of methods and measurements have advanced. Improved low- or no-solvent extraction techniques, such as solid-phase microextraction (SPME), have become more important as researchers and regulators seek environmentally friendly and more rapid methods. There has also been an increase in the use of on-line separation techniques with mass spectrometry, including liquid chromatography (LC)/MS, supercritical fluid chromatography (SFC)/MS, ion chromatography (IC)/inductively coupled plasma (ICP)-MS, IC/electrospray ionization (ESI)-MS, capillary electrophoresis (CE)/MS, and CE/ICP-MS. ESI-MS and atmospheric pressure chemical ionization (APCI)-MS have also been extremely beneficial for the measurement of highly polar pesticides, such as diquat and paraquat. Before the advent of LC/MS techniques, these types of polar compounds were difficult, and sometimes impossible, to measure. Now, they can be measured at very low detection levels. ESI-MS has also enabled the identification of DNA and protein adducts, and other biomarkers of human exposure to chemical pollutants, which has enabled researchers to begin to understand some of the mechanisms involved in the toxicity of the pollutants. In addition, matrix-assisted laser desorption ionization (MALDI)-MS and ESI-MS have enabled pathogenic microorganisms to be measured and identified. This is an important advance because pathogenic microorganisms have entered drinking water supplies and have caused several outbreaks of illness in recent years. Toxin-producing microorganisms have also adversely impacted ecosystems and have been responsible for illness in swimmers. There is also increased field-portable/mobile mass spectrometry instrumentation, which allows samples to be analyzed quickly at the site of contamination, enabling more thorough site characterizations and enabling environmental processes to be studied in real-time. Therefore, although many of the environmental pollutants of interest have not changed much through the years, the type and amount of information that can be obtained has changed and is enabling a better understanding of environmental processes.
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| JOURNAL |
Determination of Perchlorate at Parts-Per-Billion Levels in Plants By Ion Chromatography |
11/17/2000
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Ellington, J. J. AND J. J. Evans. Determination of Perchlorate at Parts-Per-Billion Levels in Plants By Ion Chromatography. JOURNAL OF CHROMATOGRAPHY A 898(2):193-199, (2000).
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A method for the analysis of perchlorate in plants was developed, based on dry weight, and applied to the analysis of plant organs, foodstuffs, and plant products. The method reduced greatly the ionic interferences in water extracts of plant materials. The high background conductivity, due to the plant matrix, was reduced sufficiently to allow quantitation of perchlorate with little or no matrix interference. Ion chromatography (IC) on a microbore AS16 anion-exchange column and a conductivity detector was used for separation and detection of perchlorate from the ionic plant extract. The extract was heated to precipitate proteins, centrifuged, exposed to alumina, and filtered through a cartridge filled with divinylbenzene to yield a water clear extract for IC analysis, even from highly colored solutions. Heating the extract and treatment with alumina reduced substantially the ionic content of the extracts without loss of perchlorate.
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| JOURNAL |
Uptake and Phytotransformation of Organophosphorus Pesticides By Axenically Cultivated Aquatic Plants |
12/15/2000
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Gao, J., A. W. Garrison, C. S. Mazur, N. L. Wolfe, AND C. F. Hoehamer. Uptake and Phytotransformation of Organophosphorus Pesticides By Axenically Cultivated Aquatic Plants. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 48(12):6114-6120, (2000).
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The uptake and phytotransformation of organophosphorus (OP) pesticides (malathion, demeton-S-methyl, and crufomate) was investigated in vitro using the axenically aquatic cultivated plants parrot feather (Myriophyllum aquaticum), duckweed (Spirodela oligorrhiza L.), and elodea (Elodea canadensis). The decay profile of these OP pesticides from the aqueous medium adhered to first-order kinetics. However, extent of decay and rate constants depended on both the physicochemical properties of the OP compounds and the nature of the plant species. Malathion and demeton-S-methyl exhibited similar transformation patterns in all three plants: 29-48 and 83-95% phytotransformation, respectively, when calculated by mass recovery balance during an 8-day incubation. No significant disappearance and phytotransformation ofcrufomate occurred in elodea over 14 days, whereas 17-24% degraded in the other plants over the same incubation period. Using enzyme extracts derived from duckweed, 15-25% of the three pesticides were transformed within 24 h of incubation, which provided evidence for the degradation of the OP compounds by an organophosphorus hydrolase (EC 3.1.8.1) or
multiple enzyme systems. The results of this study showed that selected aquatic plants have the potential to accumulate and to metabolize OP compounds; it also provided knowledge for potential use in phytoremediation processes.
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| JOURNAL |
Uptake and Phytotransformation of O,P'-Ddt and P,P'-Ddt By Axenically Cultivated Aquatic Plants |
12/15/2000
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Gao, J., A. W. Garrison, C. S. Mazur, N. L. Wolfe, AND C. F. Hoehamer. Uptake and Phytotransformation of O,P'-Ddt and P,P'-Ddt By Axenically Cultivated Aquatic Plants. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 48(12):6121-6127, (2000).
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The uptake and phytotransformation of o,p'-DDT and p,p'-DDT were investigated in vitro using three axenically cultivated aquatic plants: parrot feather (Mariophyllum aquaticum), duckweed (Spirodela oligorrhiza), and elodea (Elodea canadensis). The decay profile of DDT from the aqueous culture medium followed first-order kinetics for all three plants. During the 6-day incubation period, almost all of the DDT was removed from the medium, and most of it accumulated in or was transformed by these plants. Duckweed demonstrated the greatest potential to transform both DDT isomers; 50-66% was degraded or bound in a nonextractable manner with the plant material after the 6-day incubation. Therefore, duckweed alsoincorporated less extractable DDT (32-49%) after 6 days than did the other plants. The capacity for phytotransformation/binding by elodea is between that of duckweed and parrot feather; similar to 31-48% of the spiked DDTwas degraded or bound to the elodea plant material. o,p'-DDD and p,p'-DDD are the major metabolites in these plants; small amounts of p,p'-DDE were also found in duckweed (7.9%) and elodea (4.6%) after 6 days. Apparently, reduction of the aliphatic chlorine atoms of DDT is the major pathway for this transformation. This study, which provides new information on plant biochemistry as related to pollutant accumulation and phytotransformation, should advance the development of
phytoremediation processes.
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| JOURNAL |
Carbon Loss and Optical Property Changes During Long-Term Photochemical and Biological Degradation of Estuarine Dissolved Organic Matter |
09/01/2000
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Moran, M. A., W. Sheldon, AND R. G. Zepp. Carbon Loss and Optical Property Changes During Long-Term Photochemical and Biological Degradation of Estuarine Dissolved Organic Matter. LIMNOLOGY AND OCEANOGRAPHY 45(6):1254-1264, (2000).
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Terrestrially derived dissolved organic matter (DOM) impacts the optical properties of coastal seawater and affects carbon cycling on a global scale. We studied sequential long-term photochemical and biological degradation of estuarine dissolved organic matter from theSatilla River, an estuary in the southeastern United States that is dominated by vascular plant-derived organic matter. During photodegradation, dissolved organic carbon (DOC) loss (amounting to 31% of the initial DOC) was much less extensive than colored dissolved organic matter (CDOM) or fluorescent dissolved organic matter (FDOM) loss (50% and 56% of the initial CDOM and FDOM), and analysis of kinetics suggested a reservoir of DOC that was resistant to
photodegradation. In contrast, CDOM photodegradation closely followed first-order kinetics over two half-lives with no indication of a nondegradable component. FDOM loss was slightly biased toward fluorophores considered representative of terrestrial humic substances. Additional changes in optical properties included increases in spectral slope and shifts in fluorescence excitation/emission maxima that were generally consistent with previous observations from field studies of photobleached DOM. Biological degradation of photobleached DOM was more rapid than that of unbleached material, and this net positive effect was evident even for extensively photodegraded material. Bacterial degradation caused shifts in the opposite direction from photochemical degradation for both spectral slope and
excitation/emission maxima and thus dampened but did not eliminate changes in optical properties caused by photobleaching.
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| JOURNAL |
Surface Finishes on Stainless Steel Reduce Bacterial Attachment and Early Biofilm Formation: Scanning Electron and Atomic Force Microscopy Study |
12/01/2000
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Arnold, J. W. AND G. W. Bailey. Surface Finishes on Stainless Steel Reduce Bacterial Attachment and Early Biofilm Formation: Scanning Electron and Atomic Force Microscopy Study. POULTRY SCIENCE 79(12):1839-1845, (2000).
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Three common finishing treatments of stainless steel that are used for equipment during poultry processing were tested for resistance to bacterial contamination. Methods were developed to measure attached bacteria and to identify factors that make surface finishes susceptible or resistant to bacterial attachment and biofilm formation. Samples of the treated surfaces (sand-blasted, sanded, and electropolished) were exposed to natural bacterial populations from chicken carcass rinses to allow growth of bacteria and development of biofilms on the surfaces. The kinetics of bacterial growth during surface exposure was followed by UV-visible spectrophotometry, and counts of bacteria and early biofilm formation were measured following scanning electron microscopy (SEM). The surface morphology of the samples was analyzed by atomic force microscopy (AFM) with samples from each of the batches of treatments used in the SEM studies. Relative differences in the surface morphology, including fractal dimensions, Z ranges, roughness, and other measurements corresponded by treatment with the differences in reduction of bacterial counts shown by SEM. The surface types varied in affinity for bacteria, and both physical and electrochemical treatments improved resistance of stainless steel to bacterial attachment. Electropolished stainless steel was the least rough surface and showed significantly fewer bacterial cells and beginning biofilm formations than the other treated surfaces. Food safety could be improved if bacterial populations could be reduced during processing by increasing the use of materials that are resistant to bacterial contamination. These findings will aid equipment manufacturers and processors in selecting materials and finishes that are most resistant to bacteria and biofilm formation.
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| JOURNAL |
Effect of Redox Zonation on the Reductive Transformation of P-Cyanonitrobenzene in a Laboratory Sediment Column |
09/01/2000
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Simon, R., D. Colon, C. L. TebesStevens, AND E. J. Weber. Effect of Redox Zonation on the Reductive Transformation of P-Cyanonitrobenzene in a Laboratory Sediment Column. ENVIRONMENTAL SCIENCE & TECHNOLOGY 34(17):3617-3622, (2000).
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The reductive transformation of a model compound, p-cyanonitrobenzene (pCNB), was investigated in a laboratory sediment column that had been characterized with respect to redox zonation. Characterization of the redox zones was assessed by measurement of the solution phase concentrations of NO3-, NO2-, Mn(ll), Fe(ll), and SO42-. Monitoring iron concentrations over time showed that the redox zones were not under steady-state conditions. The iron-reducing zone migrated in the direction of the flow at an initial rate of about 0.2 cm per pore volume resulting in more oxidizing conditions with time, pCNB was rapidly reduced at the head of the column to p-cyano-N-hydroxylaniline (pCNH), which was reduced further top-cyanoaniline (pCNA) in the iron-reducing zone. The same reaction-product distribution was observed in batch experiments with Fe(ll)/goethite. Modeling of the column reaction kinetics demonstrated, however, that reduction of pCNB occurred at least an order of magnitude faster on the column than predicted by reaction parameters from the batch experiment. Aging of the
column had a significant effect on the reduction kinetics of pCNB. After elution of 240 pore volumes, pCNB underwent facile reduction directly to pCNA under nitrate-reducing conditions suggesting a change in reaction mechanism from a chemical to a biological process. After elution of 283 pore volumes, the column was completely oxic, and reduction of pCNB was no longer observed.
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| JOURNAL |
Phytotransformations of Perchlorate Contaminated Waters |
09/01/2000
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Susarla, S., G. Harvey, S. C. McCutcheon, AND S. T. Bacchus. Phytotransformations of Perchlorate Contaminated Waters. ENVIRONMENTAL TECHNOLOGY 21(9):1055-1065, (2000).
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There is no abstract available for this product. If further information is requested, please refer to the bibliographic citation and contact the person listed under Contact field.
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| JOURNAL |
The Contribution of Microarthropods to Above Ground Food Webs: A Review and Model of Below Ground Transfer in a Coniferous Forest |
01/31/2000
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Johnston, J. M. The Contribution of Microarthropods to Above Ground Food Webs: A Review and Model of Below Ground Transfer in a Coniferous Forest. AMERICAN MIDLAND NATURALIST 143(1):226-238, (2000).
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Although belowground food webs have received much attention, studies concerning microarthropods in nondetrital food webs are scarce. Because adult oribatid mites often number between 250,000-500,000/m(2) in coniferous forests, microarthropods are a potential food resource for microarthropods and vertebrate predators of the forest floor. Although thecontribution of microarthropods to aboveground food webs has received little attention, sufficient data concerning macroarthropods and vertebrate predators were available at the Savannah River Site (SRS. Aiken. South Carolina) to construct a food web model of the various trophic interactions. To supplement this analysis, literature of microarthropod
predation by arthropods and vertebrates was reviewed. This information was incorporated with the existing data to produce a model for taxa occurring in coniferous forests at the SRS. Because of the diversity and natural history of microarthropod predators, both vertebrate and invertebrate, the resulting web is quite connected and included transfers to many trophic levels. The diets of arthropods and vertebrates are variable; yet feeding patterns reflect the relative abundance of prey at a place and time. Also many predators feed on members of their own group. These factors suggest that belowground transfers are deserved of more attention in these and other forest food webs where substantial numbers of detritus feeding invertebrates
inhabit the soil/litter interface and are available as prey items. More over, this model can be generalized to describe the dynamics of arthropod and vertebrate communities in other coniferous forests. The functioning of terrestrial ecosystems is dependent upon the interrelationships between aboveground and belowground food webs, and transfers of biotic components of the decomposer subsystem to aboveground consumers connect the two subsystems. It is hoped that those consumers traditionally associated with foliage-based food webs be reconsidered, as they may be gaining a proportion of their nutrition from organisms in the detrital pathway.
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| JOURNAL |
Vulnerability of Ecosystems of the Mid-Atlantic Region, USA, to Climatic Change |
04/01/2000
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Lassiter, R. R., E. O. Box, R. G. Wiegert, J. M. Johnston, J. Bergengren, AND L. A. Suarez. Vulnerability of Ecosystems of the Mid-Atlantic Region, USA, to Climatic Change. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY 19(4):1153-1160, (2000).
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| Abstract:
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Changes in the distribution of vegetation in the mid-Atlantic region of the United States were explored for two climate-change scenarios. The equilibrium vegetation ecology (EVE) model was used to project the distribution of life forms and to combine these into biomes for a doubled-CO2 scenario generated by the GENESIS earth system model. The species model, a climate-envelope model, was used to project the distribution of 200 woody plant species for a climate-change scenario with mean 2 degrees C warming, enhanced winter warming, and no net evapotranspiration. Results from EVE suggest a considerable northward shift of both northern and southern boundaries of the biomes that occur in the mid-Atlantic region. The species model, using the climate scenario with no net evapotranspiration, more closely examines the isolated effect of temperature. This model predicts that most species will persist in their present location, with considerable expansion northward and with a small fraction of the species throughout the region experiencing dieback. Present-day ranges of several vertebratespecies, considered with anticipated climatic changes, suggest that animal range changes will also occur.
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| JOURNAL |
Multimedia Integrated Modeling for Environmental Protection: Introduction to a Collaborative Framework |
07/01/2000
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Johnston, J. M., J. H. Novak, AND S. R. Kraemer. Multimedia Integrated Modeling for Environmental Protection: Introduction to a Collaborative Framework. ENVIRONMENTAL MONITORING AND ASSESSMENT 63(1):253-263, (2000).
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| Abstract:
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The EPA's Office of Research and Development is embarking on a long term project to develop a Multimedia Integrated Modeling System (MIMS). The system will have capabilities to represent the transport and fate of nutrients and chemical stressors over multiple scales. MIMS will be designed to improve the environmental management community's ability to evaluate the impact of air and water quality and watershed management practices on stream and estuarine conditions. The system will provide a computer-based problem solving environment for testing understanding of multimedia (atmosphere, land, water) environmental problems, such as the movement of chemicals through the hydrologic cycle, or the response of aquatic ecological systems to land-use change, with initial emphasis on the fish health endpoint. The design will attempt to combine the state-of-the-art in computer science, system design, and numerical analysis (i.e. object oriented analysis and design, parallel processing, advanced numerical libraries including analytic elements) with the latest advancements in process level science (process chemistry, hydrology, atmospheric and ecological science). The problem solving environment will embrace the watershed/airshed approach to environmental management, and build upon the latest technologies for environmental monitoring and geographic representation. The MIMS team will promote a common and open modeling framework for the university and government modeling communities, and be open to cooperative arrangements with private partners where appropriate.
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| JOURNAL |
Application of Dnph Derivatization With LC/MS to the Identification of Polar Carbonyl Drinking Water Disinfection By-Products in Drinking Water |
12/31/2000
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Richardson, S. D., T. V. Caughran, T. Poiger, Y. Guo, AND F. G. Crumley. Application of Dnph Derivatization With LC/MS to the Identification of Polar Carbonyl Drinking Water Disinfection By-Products in Drinking Water. OZONE: SCIENCE & ENGINEERING 22(6):653-675, (2000).
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A qualitative method using 2,4-dinitrophenylhydrazine (DNPH) derivatization followed by analysis with liquid chromatography (LC)/negative ion-electrospray mass spectrometry (MS) was developed for analyzing and identifying highly polar aldehydes and ketones in ozonated drinking water. Using this method, aldehydes could be easily distinguished from ketones by differences in their mass spectra and chromatographic behavior. Results for many polar-substituted aldehyde and ketone standards are presented, as well as the identification of polar disinfection by-products (DBPs) in ozonated drinking water from full-scale plants and laboratory-scale ozonation of humic acid. One polar DBP identified has not been previouslyreported. This method could also potentially be used as a tool to identify carbonyl-containing DBPs from disinfectants other than ozone. However, the detection limits for the DNPH-LC/MS method are not as low as for the pentafluorobenzylhydroxylamine (PFBHA)-gas chromatography (GC)/MS method (LC/MS is typically not as sensitive as GC/MS). Therefore, it is not recommended that this method replace the PFBHA-GC/MS method, but be used as a
supplement to enable the identification of highly polar carbonyl-containing DBPs that would not be possible by GC/MS.
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| JOURNAL |
Identification of Drinking Water Disinfection By-Products from Ozone, Chlorine Dioxide, Chloramine, and Chlorine |
11/30/2000
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Richardson, S. D., A. D. Thruston Jr., T. V. Caughran, P. H. Chen, T. W. Collette, K. M. Schenck, B. W. Lykins Jr., C. RavAcha, AND V. Glezer. Identification of Drinking Water Disinfection By-Products from Ozone, Chlorine Dioxide, Chloramine, and Chlorine. WATER, AIR, AND SOIL POLLUTION 123(1-4):95-102, (2000).
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Many drinking water treatment plants are currently using alternative disinfectants to treat drinking water, with ozone, chlorine dioxide, and chloramine being the most popular. However, compared to chlorine, which has been much more widely studied, there is little information about the disinfection by-products (DBPs) that these alternative disinfectants produce. Thus, itis not known if the DBPs from alternative disinfectants are safer or more hazardous than those formed by chlorine. To answer this question, we have set out to comprehensively identify DBPs formed by these alternative disinfectants, as well as by chlorine. The results presented here represent a compilation of the last 8 years of our research in identifying new DBPs from
ozone, chlorine dioxide, chloramine, and chlorine. We also include results from recent studies of Israel drinking water disinfected with both chlorine dioxide and chloramine. Over 200 DBPs were identified, many of which have never been reported. In comparing by-products formed by the different disinfectants, ozone, chlorine dioxide, and chloramine formed fewer halogenated DBPs than chlorine.
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| JOURNAL |
Phyto-Removal of Trinitrotoluene from Water With Batch Kinetic Studies |
07/01/2000
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Medina, V. F., S. L. Larson, A. E. Bergstedt, AND S. C. McCutcheon. Phyto-Removal of Trinitrotoluene from Water With Batch Kinetic Studies. WATER RESEARCH 34(10):2713-2722, (2000).
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A series of batch reactor studies were conducted to obtain kinetic data for optimizing phyto-treatment of water contaminated with trinitrotoluene (TNT). A plant screening study indicated that stonewort and parrotfeather were the most effective among the plants tested; parrotfeather being chosen for further testing because it is heartier and easier to cultivate than stonewort. Treatment was reproducible under similar conditions, and sequential formation and breakdown of aminodinitrotoluene (ADNT) and diaminonitrotoluene (DANT) were observed in the aqueous phase. TNT removal rates increased with increased plant density, and removal kinetics increased with increasing temperature up to 34? C. Michaelis?Menton kinetics applied to the phyto-removal of TNT. At concentrations less than 5.5 mg/l TNT, a pseudo-first-order approximation of the Michealis-Menton equation was used with acceptable deviation. Prior exposure to TNT did not appear to have a significant effect on phyto-transformation rates, suggesting that the mechanisms for removal were not induced. Small concentrations ofADNT were found in the plant material, however, TNT was not detected. The results indicated that optimized reactors for the phyto-treatment of contaminated wastewater and groundwater are feasible, increasing degradation rates and decreasing reactor
volumes.
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| JOURNAL |
The Possible Role of Volcanic Aquifers in Prebiologic Genesis of Organic Compounds and Rna |
02/01/2000
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Washington, J. W. The Possible Role of Volcanic Aquifers in Prebiologic Genesis of Organic Compounds and Rna. ORIGINS OF LIFE AND EVOLUTION OF THE BIOSPHERE 30(1):53-79, (2000).
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In a volcanic aquifer, a wide range of physical and chemical conditions are not merely possible, but to be expected: relatively oxidizing and reducing environments both are present; hot and moderate temperatures can be expected; distillation and reflux conditions are probable to allow concentration of reactants, stimulation of reaction and fractionation of isotopes; apatite, hydroxides, clays and sulfide minerals are present to act as chromatographic media for separating compounds, to serve as catalytic surfaces and to provide potential energy sources; supersaturated precipitation of optically active crystals is reasonable, allowing for chromatographic separation of racemic mixtures by the resulting fixed chiral phase; and saturated and unsaturated conditions both are present for promotion of constructive reactions and inhibiting destructive hydrolysis reactions. Because the multitude of physical-chemical environments makes the setting robust with respect to circumventing commonlyidentified problems in origin-of-life theories, even if objections to details proposed herein are identified, the setting is favorable for devising alternatives. This paper describes a theory for the genesis of organic compounds, including RNA, in the mixing zone of juvenile and meteoric
waters above a leaky semi-confined aquifer. Starting with basic reactants for best-guess conditions on Archean Earth, parallel sequences of specific reactions are proposed that culminate with RNA oligonucleotides, key molecules in contemporary life. All proposed reactions, or close analogues, are experimentally confirmed and all are set in plausible Archean conditions. Calculations indicate that the proposed reactions would yield C isotopic compositions that are consistent with observed biologic C.
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| JOURNAL |
Enantiomer Separation of Polychlorinated Biphenyl Atropisomers and Polychlorinated Biphenyl Retention Behavior on Modified Cyclodextrin Capillary Gas Chromatography Columns |
01/15/2000
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Wong, C. S. AND A. W. Garrison. Enantiomer Separation of Polychlorinated Biphenyl Atropisomers and Polychlorinated Biphenyl Retention Behavior on Modified Cyclodextrin Capillary Gas Chromatography Columns. JOURNAL OF CHROMATOGRAPHY A 886(2):213-220, (2000).
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Seven commercially-available chiral capillary gas chromatography columns containing modified cyclodextrins were evaluated for their ability to separate enantiomers of the 19 stable chiral polychlorinated biphenyl (PCB) atropisomers, and for their ability to separate these enantiomers from achiral congeners, necessary for trace environmental analysis of chiral PCBs. The enantiomers of each of the 19 chiral PCBs were at least partially separated on one or more of these columns. Enantiomeric ratios of eleven atropisomers could also be quantified on six columns as they did not coelute with any other congener containing the same number of chlorine atoms, so could be quantified using gas chromatography-mass spectrometry. Analysis of a lake sediment heavily contaminated with PCBs showed enantioselective occurrence of PCB 91, proof positive of enantioselective in situ reductive dechlorination at the sampling site.
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| JOURNAL |
Inland Dissolved Salt Chemistry: Statistical Evaluation of Bivariate and Ternary Diagram Models for Surface and Subsurface Waters |
10/01/2000
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Baca, R. M. AND S. T. Threlkeld. Inland Dissolved Salt Chemistry: Statistical Evaluation of Bivariate and Ternary Diagram Models for Surface and Subsurface Waters. JOURNAL OF LIMNOLOGY 59(2):156-166, (2000).
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We compared the use of ternary and bivariate diagrams to distinguish the effects of atmospheric precipitation, rock weathering, and evaporation on inland surface and subsurface water chemistry. The three processes could not be statistically differentiated using bivariate models even if large water bodies were evaluated separatefrom small water bodies. Atmospheric precipitation effects were identified using ternary diagrams in water with total dissolved salts (TDS) <25 mg r' dominated by SO4(-2), Ca(+2) and (Na+ + K), though water whose inorganic chemistry was dominated by atmosfheric precipitation were few. Waters affected by weathering had TDS of 15 to 1, 000 mg and were dominated by (HC03- + CO 3(-2) and Ca(+2). The effects of rock weathering on ion chemistry were the dominant mechanism influencing water chemishy. The contribution ofsilicates, carbonates, and evaporites to ions in weathering were distinguished using ternary diagrams. Weathering of silicates was evident in low TDS waters, while weathering of carbonates and evaporites was evident in moderate and high TDS waters, respectively. Evaporation effects were first obvious in water around 1, 000 mg TDS as a shift towards higher S04(-2), Cl, and (Na+ + K+). At higher TDS, Cl became the dominant anion while (Na+ + K+) remained the dominant cation. The general patterns were consistent in lakes, rivers, and subsurface water bodies, although sub- surface waters did not show an influence due to ionsfrom atmospheric precipitation. While several of the TDS size classes separated statistically into distinct groups, there was wide variation in the pattern of inorganic ions within a TDS size class, especially when TDS > 1000 mg. A principal components analysis showed that the variability in the relative proportions of the major ions was related to atmospheric precipitation, weathering, and evaporation. About half of the variation in the distribution of inorganic ions was related to rock weathering. By considering most of the important inorganic ions, ternary diagrams are able to distinguish the contributions of atmospheric precipitation, rock weathering, and evaporation to inland water chemishy.
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| JOURNAL |
Computational Electrochemistry: Aqueous One-Electron Oxidation Potentials for Substituted Anilines |
03/01/2000
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Winget, P., E. J. Weber, C. J. Cramer, AND D. G. Truhlar. Computational Electrochemistry: Aqueous One-Electron Oxidation Potentials for Substituted Anilines. PHYSICAL CHEMISTRY CHEMICAL PHYSICS 2(6):1231-1239, (2000).
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| Abstract:
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Semiempirical molecular orbital theory and density functional theory are used to compute one-electron oxidation potentials for aniline and a set of 21 mono- and di-substituted anilines in aqueous solution. Linear relationships between theoretical predictions and experiment are constructed and provide mean unsigned errors as low as 0.02 V over a training set of 13anilines; the error rises to 0.09 V over a test set of eight additional anilines. A good correlation is also found between oxidation potential and a simple computed property, namely the energy of the highest occupied molecular orbital for neutral anilines in aqueous solution. For the particular case of the substituted anilines, a strong correlation between oxidation potential and pK(a)
is found, and a still stronger correlation between oxidation potential and physical organic descriptors for aromatic substituents is also found, albeit over a reduced data set.
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| PRESENTATION |
The on-Site on-Line Tool for Site Assessment Calculations |
03/10/2000
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Weaver, J. W. The on-Site on-Line Tool for Site Assessment Calculations. Presented at Georgia Ground Water Association Meeting, Doraville, GA, March 10, 2000.
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| Abstract:
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State and Federal Agency personnel often receive modeling reports with undocumented parameter values. The reports give parameter values, but often no indication if the value was measured, taken from the literature, the result of calibration, or some type of estimate. Recent examples from leaking underground storage tank sites included a retardation factor of 10 for benzene, bulk density of 2.65 g/cm3 in a sandy aquifer, recharge rate of 2 ft/d, and longitudinal dispersivity of 1/2 the plume length. These values should raise red flags but unfortunately in some cases they were accepted at face value. On the other side of the coin, even experienced modelers appreciate the convenience and efficiency of prepackaged calculations, particularly for some less well known parameters. From these needs, a set of "calculators" were developed to provide formulas and data for performing a suite of site assessment calculations. The calculators run over the Internet and the user only needs Internet access and a JavaScript-enabled browser (Netscape4+or Internet Explorer4+ both work fine). Three kirids of calculations are provided: Formulas--gradient, retardation factor, seepage velocity and travel time, effective solubility, etc. Models-1 D constant source, 1 D fuel source, (3D and others under development), Unit Conversions-hydraulic conductivity, henry's law, flow rates, half lives, dates- to-days. The calculators can be found at www.epa.gov/athens/software/trainining/WebCourse by following the link to the "calculators". The web pages for the calculators give background information, suggestions for using the calculators and examples of their use. The presentation will highlight uses of the calculators by evaluating a case study.
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| PRESENTATION |
Techniques for Analyzing Complex Mixtures of Drinking Water DBPs |
04/11/2000
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Richardson, S. D. Techniques for Analyzing Complex Mixtures of Drinking Water DBPs. Presented at Analytica Conference 2000, Munich, Germany, April 11-14, 2000.
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Although chlorine has been used to disinfect drinking water for approximately 100 years, there have been concerns raised over its use, due to the formation of potentially hazardous by-products. Trihalomethanes (THMs) were the first disinfection by-products (DBPs) identified and shown to cause cancer in laboratory animals, and are regulated by many countries. Recently, there has also been concern about haloacetic acids, which will be regulated in the United States following the promulgation of the Disinfectants/Disinfection By-product Rule in 1998. As a result of tightening regulations and increased concerns over chlorine DBPs, many drinking water treatment plants have changed their mode of disinfection to alternative disinfectants, including ozone, chlorine dioxide, and chloramine. However, DBPs from these disinfectants have not been thoroughly characterized, so it is not known whether these alternative disinfectants are safer or more harmful than chlorine. To solve this issue, the U.S. Environmental Protection Agency's (EPA's) National Exposure Research Laboratory has been applying a variety of analytical techniques to identify these unknown DBPs--with a focus on the alternative disinfectants (for which less is known), but also including chlorine DBPs. One reason that many DBPs have not been previously identified is that their spectra are often not found in the spectral libraries, such as the NIST or Wiley databases. Spectral matching against one of these databases is the easiest and most common way of identifying an unknown compound. But, when compounds are not present in the libraries, additional spectral information is required to solve their structures. Because drinking water extracts typically contain over 300 detectable compounds, a separation device (such as a gas chromatograph or liquid chromatograph) is beneficial to allow pure spectra to be obtained for these unknowns. For those compounds that can be extracted into an organic solvent, we use a combination of gas chromatography/mass spectrometry (GC/MS) techniques and GC/infrared (IR) spectroscopy. High resolution mass spectrometry limits the number of choices of possible atom combinations and typically points to a single empirical formula assignment for the unknown DBPs. Chemical ionization mass spectrometry is used to provide molecular weight information when molecular ions are not present in the electron ionization (EI) mass spectra. And, finally, GC/IR is used to provide functional group information for the unknown compounds. For example, we may know that an oxygen is present in the structure from high resolution EI-MS information, but we may not be sure whether the compound is a ketone, an alcohol, or an aldehyde. GC/IR will usually point to a definitive functional group, which aids in determining the exact structure of the compound. Another reason for the lack of information on DBPs is that many are believed to be polar in nature and cannot be easily extracted from water or analyzed by GC. To identify these compounds, we have utilized liquid chromatography (LC)/MS, in addition to using derivatizing agents such as pentafluorobenzylhydroxylamine (PFBHA) with GC/MS. Initially, capillary electrophoresis/MS was also investigated as a tool because it has been shown to work well for ionic and polar compounds. However, we found the separations to be poor, due to interfering salts from the drinking water. Conventional LC/MS, utilizing electrospray or atmospheric pressure ionization, presented difficulties also, as chemical backgrounds were difficult to overcome in the low molecular weight range that the DBPs are usually found. One solution we found for analyzing polar carbonyl DBPs was to first derivatize the drinking water sample with 2,4-dinitrophenylhydrazine (DNPH), then use solid phase extraction (which concentrates the trace levels of DBPs and removes salts), and analyze the unknown DBPs with LC/MS (with electrospray). We were successful in identifying a number of highly polar DBPs that were not easily analyzed by other methods. We are currently continuing to apply new derivatizing agents in order to broaden the classes of structures that can be identified. Using all of the spectroscopic techniques discussed, we have been able to identify more than 100 DBPs that were not previously known. Preliminary toxicity screening is now being conducted on those DBPs that were determined to be possible adverse health risks, and a U.S. nationwide occurrence study will provide occurrence and concentration information on those high-priority DBPs.
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| PRESENTATION |
Comparative Evaluation of Mtbe Sites on Long Island |
02/02/2000
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Weaver*, J. W., J. E. Haas, AND C. B. Sosik. Comparative Evaluation of Mtbe Sites on Long Island. Presented at US Environmental Protection Agency Methyl Tert-Butyl Ether (MTBE) Biodegradation Workshop, Cincinnati, OH, February 1-3, 2000.
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| Abstract:
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The aquifers of Long Island serve as the sole-source drinking water supply for approximately 3 million people. About 20 percent of this population obtains drinking water directly from the water table aquifer (Upper Glacial) whereas the remainder obtain their drinking water from deeper aquifers (Mahothy and Lloyd). High population density assures a large number of gasoline stations and numerous fuel releases which directly impact the water table aquifer. Thin surface soils (less than 2 feet) overlie the coarse sands and gravels of the Upper Glacial aquifer through this area, leaving the aquifer particularly vulnerable to contamination. This paper summarizes observations from four gasoline release cases investigated by the New York State Department of Environmental Conservation. Since all the sites are on Long Island, they share some common general characteristics, namely similar climate and geology. Differences in the geometry of the observed plumes result from the differences in timing and volume of the releases, prior release history and the chemical properties of benzene, toluene, ethylbenzene and the xylenes (BTEX) and methyl tert-butyl ether (MTBE), rather than dramatic hydrogeologic variation among the sites. At the East Patchogue and Riverhead sites, the MTBE plume is moving as a detached pulse ahead of the benzene and other plumes. This appears largely due to high ground water velocity and high recharge rate causing relatively rapid dissolution of MTBE from the gasoline at East Patchogue. One of the two plumes at Riverhead had extensive source removal, but the distribution of MTBE suggests that the majority of MTBE leaching had already occurred when the excavation was done. In contrast, at Uniondale and Lindenhurst, the MTBE plume is continuous with the source. Although the ground water velocity and recharge at Uniondale and Lindenhurst are also high, the releases are positively dated to a later time than those at East Patchogue and Riverhead. Thus these plumes have had less time to evolve. The sites also have less disturbance and remain paved, reducing any flushing of the source area by rainfall. For each of four sites, however, the highest MTBE concentrations were observed in the downgradient portion of the plumes.
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| PRESENTATION |
Fish Communities and Human Disturbance in the Albemarle-Pamlico Basin of North Carolina and Virginia |
08/06/2000
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Baca, R. M. Fish Communities and Human Disturbance in the Albemarle-Pamlico Basin of North Carolina and Virginia. Presented at Ecological Society of America Meeting, Snowbird, UT, August 6-10, 2000.
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| Abstract:
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Data on fish abundance, diversity, and habitat quality from the USGS and EPA were analyzed for patterns in the regional fish communities of the Albemarle-Pamlico drainage basin. The basin covers approximately 72,500 square kilometers and four physiographic provinces in Virginia and North Carolina, which includes the watersheds of the Chowan, Roanoke, Tar-Pamlico, and Neuse Rivers. The fish communities were analyzed using cluster analysis and various gradient analysis techniques. Cluster analysis was used to parse the data set prior to gradient analysis, as it seemed unlikely that environmental gradients would organize the fish communities over such a large and ecologically diverse area. Canonical correspondence analysis was then used to find patterns between human influences in the region and fish community structure. Measures of human influence, such as density of roads, density of human population, and land use characterization were used in addition to water quality measurements as explanatory variables in the canonical correspondence analysis. Since human disturbance in this region is very large due to extensive agriculture, measures of a variety of human influences may better explain patterns in the fish communities than water quality variables alone. This research is part of a larger research initiative at EPA modeling how fish populations in the Albemarle-Pamlico basin may respond to changes in land-use patterns by humans over the next 50 years, and provides initial empirical relations between regional patterns in fish and human populations for the model.
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| PRESENTATION |
Abiotic Redox Transformation of Organic Compounds at the Clay-Water Interface |
03/06/2000
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Yan, L. AND G. W. Bailey. Abiotic Redox Transformation of Organic Compounds at the Clay-Water Interface. Presented at Bouyoucos Conference on Environmental Chemistry at the Clay-Water Interface, Honolulu, HI, March 6-9, 2000.
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| Abstract:
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The interactions of clay, water and organic compounds considerably modify the structural and physico-chemical properties of all components and create a unique domain for biological and chemical species in environments. Previous research indicates that the nature and properties of this interfacial region control both abiotic and biotic reactions. Under anoxic conditiorLT nitroaromatics and aromatic azos are reduced primarily by abiotic processes. These compounds, therefore, should serve as suitable probes to follow interfacial redox reactions and help define the reaction mechanism.
Structural or exchangeable transition metals cations in clays act as a carrier in either forward or reverse electron transfer in both abiotically and microbially mediated redox reactions. The intervalence Fe2-+ Fe 3+ charge transfer (Fe2+-to-02- -to-Fe 3+electron transfer) process is proposed as the mechanism for the solid state electron transfer to the basal surfaces and/or edges of Febearing phyllosilicates. To evaluate this hypothesib chemically reduced nontronite was reacted with nitrobenzene and the reduction product(s) were followed using HPLC. Nitrosobenzene and hydroxyarnine are reaction intermediates; aniline is the main reduction product and was found to be the major product in our study.
Two pathways are proposed forthe interfacial electron transfer: (1) interfacial coordination complex formation and (2) hydroxyl radical (-OH) formation. Nitrobenzene forms a charge transfer complex via sorption with smectite accepting electrons from the clay lattice; the excess electrons in the crystal layer structural Fe of reduced phyllosilicate migrate to the surface/edges and are transported to organic compounds in the interfacial region. Further research is needed to define the efficiency and rate of electron transfer at the clay-water interface before predictive relationship are possible.
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| PRESENTATION |
Drinking Water Disinfection By-Products: What Is Known |
05/07/2000
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Richardson, S. D. Drinking Water Disinfection By-Products: What Is Known. Presented at International Workshop on Exposure Assessment for Disinfection By-Products in Epidemiologic Studies, Ottawa, Canada, May 7-10, 2000.
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| Abstract:
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Chlorine, ozone, chlorine dioxide, and chloramine are currently the major disinfectants being used to disinfect drinking water. Although the alternative disinfectants (ozone, chlorine dioxide, and chloramine) are increasing in popularity in the United States, chlorine is still used at most treatment plants, with an estimated 150 million people in the U.S. drinking chlorinated water. Following the discovery of chloroform as a chlorination disinfection by-product (DBP) in 1974, researchers began to identify disinfection by-products. Of the disinfectants, chlorination by- products have been the most studied, and, as a result, over 300 chlorine DBPs have been reported in the literature (Richardson, 1998). Fewer studies have been carried out for the alternative disinfectants; however, there is some information known about their by-products. It should be noted that, even for chlorine, not all by-products have been identified and reported. In studying chlorine as a secondary disinfectant, our research group has identified several new by-products of chlorine that have never been reported. It is likely that the lack of available spectroscopic tools limited earlier researchers in their efforts to identify these by-products. Another limitation is the inability to extract highly polar DBPs from water. Derivatization is one way to overcome this limitation. For example, derivatization with pentafluorobenzylhydroxylamine (PFBHA) has allowed a subset of ozonation DBPs--polar aldehydes and ketones--to be extracted and identified. However, it is believed that a large fraction of highly polar DBPs are still not identified. As analytical techniques are developed to address these polar by-products, and derivatization methods are discovered, it is likely that the more polar DBPs will be identified. As with any other chemicals, the knowledge of DBPs will be driven by the analytical techniques that are available. A summary of what is currently known about the DBPs from the major disinfectants and their combinations will be presented. Some were identified in actual drinking water samples, others from reaction of the disinfectant with isolated humic or fulvic acids.
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| PRESENTATION |
Models and Methods for Petroleum Hydrocarbon Risk Assessment: Onsite, Lustrisk, and Hssm |
03/21/2000
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Weaver*, J. W. AND M. Small. Models and Methods for Petroleum Hydrocarbon Risk Assessment: Onsite, Lustrisk, and Hssm. Presented at 12th National Underground Storage Tank Conference, Portland, OR, March 21-23, 2000.
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| Abstract:
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U.S. EPA has developed three tiers of models for analysis of fuel releases from underground storage tank (UST) systems: 1) OnSite; 2) LUSTRisk, and 3) the Hydrocarbon Spill Screening Model (HSSM). The tiered approach to modeling allows users to select a model based upon the amount of data available at the site and the complexity of analysis required for the simulation. All of these models incorporate improved description of the source area by considering the presence of light non-aqueous phase liquids (LNAPL). The first tier, OnSite, is analogous to a "back of the envelope calculation," and runs interactively from a web site. OnSite consists of a collection of on-line calculators for solving basic contaminant fate and transport equations, simple models and unit conversion factors. Calculations include groundwater gradients, retardation factors, effective solubilities from fuels, plume diving and simple transport models where the source is defined by a fuel-contaminated zone. This collection of calculators is intended to be used by state regulators to evaluate modeling reports, by consultants for analysis of site data, and as a site assessment tool in its own right. Only Internet access and a JavaScript-enabled browser (current or recent versions of Netscape Navigator or Internet Explorer, for example) are required. The web site includes a tutorial and case study to give concrete examples of OnSite usage. (http://www.epa.gov/athens/software/training/WebCourse/part-two/onsite/index.html).The second tier, LUSTRisk, provides a more sophisticated model and a more highly integrated user interface. The LUSTRisk model allows computation of risks associated with petroleum hydrocarbon lenses in contact with ground water. LUSTRisk performs iterative dissolution and transport simulations for multiple chemicals (e.g. BTEX and MTBE) migrating from a single petroleum release. Two-dimensional fate and transport is computed, comparisons are made to site data, and risks associated with ingestion of ground water are calculated. LUSTRisk is implemented as a set of Microsoft Excel spreadsheets, which provide a convenient interface for data input, calculation, and graphically analyzing results. LUSTRisk is currently undergoing peer review and is available in beta version only. The third tier, HSSM is the most sophisticated model of the group. HSSM is a stand-alone modeling system that includes extensive input guidance for unfamiliar input parameters, online databases of parameter values, automatic report generation, comparison against field data and more. HSSM simulates the emplacement of the petroleum during a defined release scenario, formation of the lens of fuel in the subsurface, dissolution in groundwater, as well as fate and transport in a shallow aquifer. HSSM allows simulation of long duration releases where petroleum continually is added to the source. Estimation of source volume from field data and various release scenarios are provided to assist with difficult inputs. Graphical and textual output from the model is written to HTML files which are viewed with a standard Internet browser. This material is formatted as a pre-written report that contains a narrative description of the problem simulated, description of the sources of input parameters, and model results. These are provided for partially for convenience, but more importantly to encourage proper documentation of modeling studies. All of the above software will be available on a CD at the meeting.
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| PRESENTATION |
Photochemical Alteration of Dissolved Organic Matter: Effects on the Concentration and Acidities of Ionizable Sites in Dissolved Organic Matter in the Satilla River of Georgia, USA |
07/24/2000
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Xie, H., Y. Wang, W. J. Cai, O. C. Zafiriou, AND R. G. Zepp. Photochemical Alteration of Dissolved Organic Matter: Effects on the Concentration and Acidities of Ionizable Sites in Dissolved Organic Matter in the Satilla River of Georgia, USA. Presented at 10th International Meeting of the International Humic Substance Society, Toulouse, France, July 24-28, 2000.
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The acid-base properties of humic substances, the major component of dissolved organic matter (DOM), area major control on the alkalinity, or acid neutralizing capacity of freshwater systems. Alkalinity is one of the fundamental parameters measured in aquatic sciences, and is an important index for water quality. At the molecular level, the number and pKa values of charged sites of humic substances profoundly influence their physico-chemical properties, such as aggregation and disaggregation, hydrophobic binding, trace metal binding, etc. It has been reported that major proton-binding sites in DOM consist of carboxyl, phenolic, and amine groups. Numerical models which describe the charge sites with these functional groups can reasonably simulate the titration curves of DOM and constrain the concentrations and pKa values of each charge group. Humic substances in natural waters are subjected to photochemical degradation by solar radiation, producing both reactive transient intermediates (e.g. hydroxyl radicals) and relatively long-lived photoproducts, such as carbon monoxide (CO), dissolved inorganic carbon (DIC), and hydrogen peroxide (HOOH). It has been suggested that photoproduction of DIC may be related to destruction of carboxylgroups in humic substances. Phenolic groups are well known for their high photochemical reactivity, and they may thus be chemically altered during photolysis of humic substances. Photo-degradation ofDOM also produces non-humic low-molecular-weight carboxylic acids, including oxalic, formic, acetic, and malonic acids. Therefore, photochemical processes in natural waters may significantly influence the proton and metal binding properties of charge sites in DOM. In this paper, we present the results of a preliminary study on the effects of photo-oxidation of DOM on the concentrations and acidities of proton-binding sites in DOM, employing acid-base titration and numerical modeling approaches. We also explored the role of iron in modifying the acid-base properties of DOM, since iron has been shown to be capable of catalyzing photo-decomposition of DOM.
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| PRESENTATION |
A Quantum Mechanical Study of the Protonation and Covalent Hydration of Quinazoline in the Presence of Metal Cations |
08/20/2000
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Sawunyama, P. AND G. W. Bailey. A Quantum Mechanical Study of the Protonation and Covalent Hydration of Quinazoline in the Presence of Metal Cations. Presented at 220th American Chemical Society National Meeting, Washington, DC, August 20-24, 2000.
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We have investigated the protonation and reversible covalent hydration of quinazoline in the presence of Li+, Na+, and Ca2+ ions using ab initio quantum mechanical calculations at the MP2/6-31G**//HF/6-31G*level of theory. Proton affinities, enthalpies of hydration at 298.15K (DH298), and activation energies for several species that are considered to be present in acidic aqueous solutions of quinazoline as well as DH298 for the metal cations were obtained. Protonation of quinazoline results in three stable species whose relative stability is in the order; N1-N3 dication > N3 cation > N1 cation. The energy difference between the N3 and N1 species is ~0.57 kcal mol-1. DH298 values range from 0.40 kcal mol-1 for neutral quinazoline to -11.09 kcal mol-1 and -10.05 kcal mol-1 for N1 and N3 cations, respectively. DH298 values for the metal cations are approximately 3 - 6 fold larger than those for the quinazoline cation species. Thus, in the presence of metal cations a local competition for water occurs leading to the inhibition of hydration of quinazoline cation species. Overall, our findings are crucial to the understanding of the mechanisms of organic compound hydration at the clay-water interface, processes of major significance in the prediction of the fate and transport of organic pollutants in the ecosystems.
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| PRESENTATION |
Effect of Temperature on the C Isotopic Value of Microbial Lipids Applied to Determine C Usage in Microbial Communities |
05/21/2000
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Molina, M., R. A. Burke Jr., AND J. E. Cox. Effect of Temperature on the C Isotopic Value of Microbial Lipids Applied to Determine C Usage in Microbial Communities. Presented at American Society for Microbiology Annual Meeting, Los Angeles, CA, May 21-25, 2000.
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The combination of compound specific stable isotopic analysis with phospholipid fatty acid (PLFAS) analysis is useful in determining the source of organic carbon used by groups of a microbial community. Determination of the effect of certain environmental parameters is important when interpreting C sources utilized by the microbial community in complex ecosystems. In this research, we studied the effects of temperature, substrate, and incubationtime on the abundance and isotopic fractionation of PLFAS. Lipids were extracted from pure bacterial cultures and salt marsh sediments incubated at 10, 20, and 28 degrees C for 5, 10, 15, and 25 days. PLFAs were 2 to 8 per mil more depleted in 13C relative to the substrate, with the cultures grown at 10 degrees C showing the largest fractionation. For instance, Pseudomonas and Mycobacterium lipids were 2 and 4 per mil more depleted in 13C when grown at 10 degrees C than when grown at 28 degrees C. In general, C16:0 showed the greatest fractionation in almost all the cases, while C16:lw7c and C18:lw7c showed the least and were sometimes enriched relative to the substrate. However, there was no consistent trend in the 13C values among the individual lipids extracted from a given bacterial species. Differences in substrates did not affect the "C fractionation. The isotopic values of most PLFAs extracted from the environmental samples indicated that the fractionation was smaller (less than or equal to 4 per mil) than in the pure cultures. In addition, C16:0 was not the most depleted lipid. The results suggest that when using PLFAs to determine the sources of organic C utilized by the microbial community, it is important to consider the effect of temperature on the 13C fractionation of the lipids. Specifically, the effect that lower temperatures may cause greater isotopic fractionation. Although there are significant differences in the lipid isotopic values from pure cultures grown at different temperatures, such a strong temperature dependence is not observed in the environmental samples. Therefore, results from pure laboratory cultures should be applied cautiously when interpreting environmental data.
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| PRESENTATION |
Molecular Dynamics Modeling of Sorption of Pesticides Onto the Surfaces of Kaolinite |
08/20/2000
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Yan, L. AND G. W. Bailey. Molecular Dynamics Modeling of Sorption of Pesticides Onto the Surfaces of Kaolinite. Presented at 220th American Chemical Society National Meeting, Washington, DC, August 20-24, 2000.
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To accurately predict the fate of contaminants in the environment and to make sound decisions about environmental remediation, we must accurately understand sorption mechanisms and surface reactivity of environmental particles. Sorption of selected pesticides on kaolinite surfaces was simulated with molecular dynamics. The kaolinite model was built based on crystallographic data, the model humic acid, and four types of lignin oligomers were constructed to study the effect of various functional groups. Electrostatic potential-derived charge was determined by ab initio quantum mechanical calculations to assign the atomic charges for both the kaolinite crystal structure and for the pesticide molecules. The Gasteiger-HUckel method was used to calculate the atomic charges for the humic acid and the oligomers. Simulated annealing and energy The association energy for 2,4-D [(2,4-dichloro)phenoxyacetic acid], atrazine [(2-chloro-4- ethylamino-6-isopropylamino-1,3,5-triazine)], hydroxyatrazine [(2-hydroxy-4-ethylamino-6- isopropylamino-1,3,5-triazine)] and metolalachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2- methoxy-l-methylethyl)acetamide] for the Al-OH octahedral surfaces of kaolinite was higher than for the Si-O tetrahedral surfaces. Alachlor [(2-chloro-N-(2,6-diethylphenyl)-N- (methoxymethyl)acetamide)] has a lower association energy on the Al-OH surface. Humic acid and negatively charged organic oligomers were more strongly bonded to the Al-OH surfaces than to Si-O surfaces. Sorption energies for humics varied from 37 to -84 kcals mole-'; for thevarious oligorners, it varied from -16 to -269 kcals mole- . The electrostatic energy component dominates the adsorption energy, therefore, the charge properties of both the mineral and humic acid/oligomers play a critical role in determining the environmental fate of pesticides.
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| PRESENTATION |
An Individual-Based Model of Cottus Population Dynamics |
05/20/2000
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Rashleigh, B. AND G. Grossman. An Individual-Based Model of Cottus Population Dynamics. Presented at Ethology, Evolutionary, Ecology of Fishes Meeting, Athens, GA, May 20-24, 2000.
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We explored population dynamics of a southern Appalachian population of Cottus bairdi using a spatially-explicit, individual-based model. The model follows daily growth, mortality, and spawning of individuals as a function of flow and temperature. We modeled movement of juveniles and adults among discrete habitat patches according to length-based ideal despotic distribution rules. Abundance, length, and weight of juveniles and adults were calibrated to 10 years of bi-yearly sampling data from Ball Creek, North Carolina, USA. Model results for abundance were in good agreement with observed values. Simulated mean lengths and weights were within the range of field data but the model was not able to reproduce all of the observed temporal patterns in these variables. Population dynamics in the model appear to be influenced by competition for patches, density-dependent juvenile mortality, and variations in hydrology. Although the model contains many simplifying assumptions, it may be a useful tool in understanding the regulation of natural populations.
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| PRESENTATION |
Ground Water and Watersheds and Environmental Protection |
05/30/2000
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Hamilton, J. A., S. R. Kraemer, W. J. Ryan, W. Melgin, K. L. Schroer, D. Long, AND C. Chesney. Ground Water and Watersheds and Environmental Protection. Presented at American Geophysical Union Meeting, Washington, DC, May 30-June 2, 2000.
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Effective watershed management has the potential to achieve both drinking water and ecological protection goals. However, it is important that the watershed perspective be three- dimensional and include the hidden subsurface. The subsurface catchment, or groundwatershed, is geohydrologicafly defined, and this catchment may or may not correspond to the topographically defined watershed. The waters of the subsurface catchment, and their associated chemical loads, are in exchange with the baseflow in the river. In the evaluation of stream assimilative capability and the calculation of TMDLs (total maximum daily loads), the subsurface catchment should be evaluated, especially for nitrogen assessments. Public water supply wells located near streams often induce recharge, and thus the source water area includes the topographically defined stream catchment. A public water supply well would be under the direct influence of surface water if virus transport from the stream to the well was demonstrated based on hydrologic and residence time arguments. These, and other examples, will be discussed.
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| PRESENTATION |
Identification of Chlorine Dioxide Drinking Water Disinfection By-Products Formed at High Bromide Levels |
06/11/2000
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Richardson, S. D., A. D. Thruston Jr., C. RavAcha, AND V. Glezer. Identification of Chlorine Dioxide Drinking Water Disinfection By-Products Formed at High Bromide Levels. Presented at 48th American Society for Mass Spectrometry Conference, Long Beach, CA, June 11-15, 2000.
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Due to concern over the potential adverse health effects of trihalomethanes (THMs), haloacetic acids, and other chlorinated by-products in chlorinated drinking water, alternative disinfection methods are being explored. Chlorine dioxide is a popular alternative, with over 500 drinking water treatment plants currently in operation in the U.S. However, there is little known about the disinfection by-products (DBPS) that are produced when chlorine dioxide is used to treat drinking water. And, there is nothing known about the formation of DBPs in the presence of high bromide levels. Bromide is naturally present in many source waters across the U.S. and other parts of the world, and when it is present, it causes an increase in bromine-containing DBPs (for chlorine, chloramine, or ozone disinfection). Because bromine-containing compounds are generally the most hazardous of the DBPs that have been investigated, the U.S. Environmental Protection Agency is interested in discovering what DBPs are formed by chlorine dioxide under these high bromide conditions. Drinking water in Israel was chosen to be the water studied because its source water (the Sea of Galilee) is among the highest in the world in natural levels of bromide (2-3 mg/L), and chlorine dioxide is used for disinfection.
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| PRESENTATION |
Applications of Capillary Electrophoresis to the Study of Chiral Environmental Pollutants: Enantiomer Separation and Measurements of Enantioselectivity |
05/08/2000
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Garrison, A. W. Applications of Capillary Electrophoresis to the Study of Chiral Environmental Pollutants: Enantiomer Separation and Measurements of Enantioselectivity. Presented at EnviroAnalysis 2000, Ottawa, Canada, May 8-11, 2000.
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CE is rarely used for routine environmental analysis of organic pollutants -- certainly not to the extent of gas chromatography or high pressure liquid chromatography. There are advantages to CE, however, that belie this lack of application. For example, CE is preferred over GC for ionic organic analytes, even if the pH has to be adjusted to accommodate the analyte pKa, because no derivatization is required. This is especially true for ionic analytes with aromatic or other types of chromophores that absorb readily in the UV, but can be true even when indirect detection has to be used for adequate sensitivity. In addition, CE may be the preferred technique for any chiral analyte, even neutral ones, when enantiomers are to be separated and measured because of the facility with which chiral selectors can be used in CE. These advantages can be negated, of course, when sensitivity is an issue. However, for studies of pollutant fate in laboratory systems, CE with UV detection generally provides adequate sensitivity. Our laboratory has applied CE to enantiomeric separations of ionic and neutral chiral analytes in a routine mode for several years with the object of measuring enantiomeric ratios and respective enantiomer degradation rates in environmental matrices. Examples to be shown include the microbial transformation of.- 1) bromochloroacetic acid, a chiral drinking water disinfection byproduct, in surface waters; 2) ruelene (crufomate), a neutral organophosphorus pesticide, in soil-water matrices; and 3) dichlorprop, a phenoxyacid herbicide, in soil-water matrices. Enantioselectivity was observed in most of these cases; for BCAA the same enantiomer always degraded preferentially, but for ruelene and dichlorprop, enantiomer preference depended upon the characteristics of the matrix.
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| PRESENTATION |
Comparison of Scanning Electron and Atomic Force Microscopy of Surface Finishes on Stainless Steel That Reduce Bacterial Attachment |
05/09/2000
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Arnold, J. W. AND G. W. Bailey. Comparison of Scanning Electron and Atomic Force Microscopy of Surface Finishes on Stainless Steel That Reduce Bacterial Attachment. Presented at Scanning 2000 Meeting, San Antonio, TX, May 9-12, 2000.
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Bacteria adhere to food products and processing surfaces that can cross-contaminate other products and work surfaces (Arnold, 1998). Using materials for food processing surfaces that are resistant to bacterial contamination could enhance food safety. Stainless steel, although susceptible to bacterial attachment, is the most frequently used material for construction of equipment used for food processing. Treatments of stainless steel were evaluated foreffectiveness in improving the resistance of the surface finish to bacterial attachment. Two methods of microscopy were partnered to correlate form and function of surface finishes.
Relative differences in the topography and morphology of surface finishes were measured by atomic force microscopy (AFM) and compared with changes in bacterial attachment and early biofilm. formation as shown by scanning electron microscopy (SEM). Natural bacterial populations collected frqrn the food processing environment were assessed for their affinity to attach to surfaces. Aliquots (I - ml) of meat rinses were incubated in trypticase soy broth 18 hr, 3 7'C. Then the culture was diluted in broth to Absorbance (41 Onm) of .3 as measured by spectrophotometry. Stainless steel disks (I -cm diameter) were added, and the cultures were grown to an Absorbance of .6, 37'C. The disks were removed from the bacterial suspensions, rinsed in 0. 1 M sodium cacodylate buffer, and fixed for 2 h in 2% glutaraldehyde, 2% paraformaldehyde in buffer. After rinsing in buffer, the samples were dehydrated in 50
to 100% ethanol and critical point dried. The disks were mounted on aluminum stubs, sputter- coated with gold-palladium, and examined in a JEOL 6400V SEM at an accelerating voltage of
5 W. Triplicate counts of bacterial cells on micrographs were taken from each of two trials covering 10 random fields of view. Beginning biofilm was measured as clumps of cells that showed extensive intercellular fibrils at high magnification SEM (Arnold and Shinikets, 1988a).
After the finishing treatments the surfaces could be distinguished visually. For example, the untreated surface of the 304 stainless steel was smooth and light gray, the sandblasted surface was a darker gray and uniformly pitted, and the electropolished surface was mirror-like and very smooth and shiny. The differences in the surface finishes were confirmed by SEM. Bacteria readily attach to the untreated surface (Fig. a). As bacteria accumulated on the untreated stainless steel, they exhibited typical phenotypic properties of biofilm formation. The sandblasting pitted the surface, and with SEM the pit-marks seen by visual observation appeared as "craters" to which bacteria attached even more frequently (Fig. b). The steel-ball burnished surface was much smoother, but was not the least resistant to bacteria (Figure c). Stainless steel that had been electropolished showed significantly fewer bacterial cells and beginning biofilm formations than the other treated surfaces. The electropolished surface was difficult to image with SEM because the surface was so smooth and featureless (Fig. d). Surface morphological characteristics are determinants for the attachment of bacteria (Arnold and Shimkets, 1988b). Measurements of the surface topography by AFM confirmed and extended the SEM data. The disks for each finishing treatment analyzed by AFM were stamped from the same sheets used for SEM. Disks were removed from the bacterial suspensions described above and examined directly. Changes in AFM surface measurements had the same relative differences as the data from the bacterial counts for the SEM studies, with the electropolished finish showing the most reduced roughness parameters. These data demonstrate that AFM can predict the potential for bacteria to attach and form biofilms on surfaces, without the time-consuming preparations and tedious counting required for SEM.
Appropriate finishing treatments on stainless steel surfaces can improve the resistance to bacterial contamination and thereby enhance food safety during processing. Of course, final selection of surface finishes would be influenced by ftinction and economy. This research has shown that AFM is a rapid method to predict the potential resistance of a surface to bacterial contamination. Further analysis with AFM could enable a manufacturer to develop specifications for production with maximum and minimum tolerances for components at particular locations. In future work, the AFM might be used to determine the importance of bacterial morphology and chemistry for the pathogens associated with surface biofilms. To understand these processes will enable us to develop interventions that enhance plant sanitation and pathogen control.
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| PRESENTATION |
Investigation of Disinfection By-Products in Drinking Water Using Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry |
06/11/2000
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Pastor, S. J., S. W. Krasner, H. Weinberg, AND S. D. Richardson. Investigation of Disinfection By-Products in Drinking Water Using Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry. Presented at 48th American Society for Mass Spectrometry Conference, Long Beach, CA, June 11-15, 2000.
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Disinfection by-products (DBPs) result from the interaction of natural organic matter and bromide with chemical disinfectants, such as chlorine, added to drinking water to inactivate disease-producing microorganisms. These DBPs are monitored and regulated because of their possible adverse health effects. Historically, DBP monitoring focused on the volatile andnon-polar DBPs. Because extraction of polar compounds from a polar water matrix is a non-trivial task, new analytical methods are being developed that aid in identifying new DBPs that have yet to be discovered in drinking water.
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| PRESENTATION |
Solid Phase Microextraction for Trace Level Analysis of Disinfection By-Products |
06/11/2000
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Gonzalez, A. C., S. W. Krasner, H. Weinberg, AND S. D. Richardson. Solid Phase Microextraction for Trace Level Analysis of Disinfection By-Products. Presented at 48th American Society for Mass Spectrometry Conference, Long Beach, CA, June 11-15, 2000.
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This presentation focuses on the development of a solid-phase microextraction (SPME)-gas chromatography (GC)/ion trap mass spectrometry (MS) method for the analysis of semivolatile disinfection by-products (DBPs) in drinking water in the low ug/L range. These DBPs were selected from approximately 600-700 DBPs that have been reported in the literature,due to their possible adverse health effects, as judged by expert toxicologists.
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| PRESENTATION |
Survey of Halonitromethanes and Iodomethanes: Disinfection By-Products in Drinking Water |
06/11/2000
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Thruston Jr., A. D., S. D. Richardson, C. RavAcha, AND V. Glezer. Survey of Halonitromethanes and Iodomethanes: Disinfection By-Products in Drinking Water. Presented at 48th American Society for Mass Spectrometry Conference, Long Beach, CA, June 11-15, 2000.
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This project involves the study of two classes of chemicals, halonitromethanes and iodomethanes, which have been found to be drinking water disinfection by-products (DBPs). Both have been predicted to have toxicity. In toxicity screening tests, bromonitromethanes have been shown to be mutagenic in both bacterial and in mammalian cell assays.Halonitromethanes and iodomethanes were measured in drinking water from Louisiana and Israel. Louisiana drinking water samples were treated with ozone followed by chlorine or chloramine. Israel samples were treated with chlorine dioxide. lodomethanes are also associated with drinking water taste and odor problems.
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| PRESENTATION |
Role of Humic Substances on the Photochemical Reduction of Mercury |
08/20/2000
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Ravichandran, M., R. Araujo, AND R. G. Zepp. Role of Humic Substances on the Photochemical Reduction of Mercury. Presented at 220th American Chemical Society National Meeting, Washington, DC, August 20-24, 2000.
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Solutions containing mercury and fulvic acids (isolated from the Florida Everglades) were exposed to simulated sunlight from a 1000-W Xenon lamp. In the ensuing reaction, ionic mercury was reduced to elemental mercury, which was collected on a gold trap and measured on a cold vapor atomic fluorescence detector. The amount of reduced mercury increased linearly with time in the absence of organic matter, whereas the rate was log-linear in the presence of organic matter. After 60 minutes of irradiating a solution containing 100 ng/L Hg, 5 mg C/L fulvic acid, and pH 6, about 56% of mercury was reduced to elemental Hg, while only about 7.2% was reduced in the absence of organic matter. The amount of Hg reduced remained nearly constant under varying DOC concentrations (1-40 mg C/L), while elemental Hg production was limited by the total amount of Hg in solution.
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| PRESENTATION |
The Near-Equilibrium of Microbially Mediated Redox Couples in Reducing Groundwater Environments |
08/20/2000
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Washington, J. W. The Near-Equilibrium of Microbially Mediated Redox Couples in Reducing Groundwater Environments. Presented at 220th American Chemical Society National Meeting, Washington, DC, August 20-24, 2000.
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Redox couples are commonly held to be in disequilibrium among each other in most natural waters. To evaluate this view for microbially mediated, reducing, groundwater environments, monitoring data were examined for several couples under conditions ranging from nitrate-detectable to sulfide-precipitating. For these data, iron and sulfur redox couples show close consistency. Several samples were in approximate equilibrium with goethite, siderite and mackinawite, a condition that is promoted by oxidation of organic material via a negative feedback in the reaction stoichiometry. The ammonia/nitrate redox couple generally equated to redox values inconsistent with those of iron and sulfur. The Mn2+/Mn-oxide couple gave redox values that are inconsistent with the iron, sulfur and nitrogen couples. Analysis of previously published literature shows approximate consistency for redox couples involving Fe, S, H2 and CH4 for microbially mediated groundwater environments in many areas. Hence, it appears that reducing groundwater environments often reach near-equilibrium with a common effective redox state for several redox couples.
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| PRESENTATION |
Comparison of Hydrogen Concentrations in Pce-Dehalogenating and Sulfate-Reducing Estuarine Sediments |
08/20/2000
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Mazur, C. S. AND W. J. Jones. Comparison of Hydrogen Concentrations in Pce-Dehalogenating and Sulfate-Reducing Estuarine Sediments. Presented at 220th American Chemical Society National Meeting, Washington, DC, August 20-24, 2000.
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The primary transformation pathway for PCE in anoxic environments is through sequential reductive dehalogenation, and information concerning dehalogenation processes that occur in environments containing alternative electron acceptors (sulfate) is limited. Hydrogen is postulated as a key electron donor during PCE transformation, and the "hydrogen threshold"concept suggests that microorganisms that utilize an energetically more favorable electron acceptor will maintain a lower hydrogen threshold. We compared the hydrogen concentrations in unamended and PCE-amended estuarine sediment slurries. A significantly lower hydrogen concentration (0.42-0.47 nM) was observed and maintained in PCE-amended sediment microcosms compared to sulfate-reducing sediments (0.6-0.7 nM). Our findings provide evidence that a lower hydrogen threshold exists in anoxic estuarine sediment slurries with PCE serving as a terminal electron acceptor compared to sediment slurries in which sulfate-reduction is the predominant electron accepting process.
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| PRESENTATION |
QSAR Analysis of Sorption-Corrected Rate Constants for Reductive Biotransformation of Halogenated Aromatics |
08/20/2000
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TebesStevens, C. L. AND W. J. Jones. QSAR Analysis of Sorption-Corrected Rate Constants for Reductive Biotransformation of Halogenated Aromatics. Presented at 220th American Chemical Society National Meeting, Washington, DC, August 20-24, 2000.
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The inherent coupling among geochemical and microbial reactions may have significant effects on the environmental fate of a containinant. For example, sorption processes may decrease the concentration of an organic compound in solution, thereby reducing the biodegradation rate of the compound. In order to conduct meaningful comparisons of biodegradation rates in systems with different organic carbon concentrations or sediment-to-solution ratios, the observed biotransforrnation rate constants must be corrected to obtain a more "intrinsic" rate constant for an equivalent sediment-free system. In this study, a set of literature rate constants for reductive dehalogenation of halogenated aromatics were corrected for hydrophobic partitioning. The sorbed fractions of the target compounds were assumed to be unavailable for biodegradation, and the sorption process was assumed to be at equilibrium. Multivariate statistical analyses demonstrated that the correlation of the sorption-corrected rate constants to physicochemical and molecular descriptors of the compounds was stronger than that of the observed rate constants.
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| PRESENTATION |
Speciation of Complex Organic Contaminants in Water With Raman Spectroscopy |
06/11/2000
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Collette, T. W. AND T. L. Williams. Speciation of Complex Organic Contaminants in Water With Raman Spectroscopy. Presented at 30th Annual International Symposium on Environmental Analytical Chemistry, Espoo, Finland, June 11-18, 2000.
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Pesticides and industrial chemicals are typically complex organic molecules with multiple heteroatoms that can ionize, tautomerize, and form various types of hydrates in water. However, conceptual models for predicting the fate of these chemicals in the environment ignore these complex forms and, instead, assume that each chemical exists exclusively as a simple isolated neutral specie. This oversight is primarily due to the lack of experimental data on speciation of complex organics in water. It is clear that this erroneous assumption contributes large uncertainty in chemical exposure assessments when one considers the degree to which chemical behavior (e.g., sorption to soil) differs for different ionization species of the same chemical (e.g., a cation versus a neutral). Unfortunately, it has heretofore been prohibitively difficult to study organic chemical speciation in water; particularly when multiple species exist with the same net ionization charge (such as with zwitterions and tautomers).We have recently developed an experimental and mathematical method, based on Raman spectroscopy, by which simultaneously occurring site-specific "micro-equilibrium" constants (such as with zwitterions and tautomers) can be determined with confidence. The method involves nonlinear regression modeling of temperature-variant spectral data according to the Gibbs-Helmholtz equation. Success of the method depends on capturing small changes in the observed series of spectra that are due to a systematic change (as a function of temperature) in relative concentration of the species that compose the equilibrium "mixture".
In order to glean the requisite information from our chemical systems, it is critical that the measurement method not perturb the equilibrium under study. Therefore, invasive techniques can not be considered. For example, methods that involve measurements at surfaces (such as infrared spectroscopy via attenuated total reflectance) can not be employed due to the possibility of surface affinity for one species over the other. Also, chromatographic separation of species is not feasible because equilibration times are too fast. We hope to illustrate that a modern dispersive Raman spectrometer is the ideal tool for this type of environmental investigation because measurements of bulk solutions can be made without contacting or perturbing the sample in any significant way. With this technique we can obtain unparalleled information regarding molecular speciation of organics in water. This information will significantly advance our understanding of the behavior complex organic chemicals in the aquatic environment.
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| PRESENTATION |
Reductive Dehalogenation of Halomethanes in Natural and Model Systems: QSAR Analysis |
08/20/2000
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Kenneke, J. F. AND E. J. Weber. Reductive Dehalogenation of Halomethanes in Natural and Model Systems: QSAR Analysis. Presented at 220th American Chemical Society National Meeting, Washington, DC, August 20-24, 2000.
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Reductive dehalogenation is a dominant reaction pathway for halogenated organics in anoxic environments. Towards the goal of developing predictive tools for this reaction process, the reduction kinetics for a series of halomethanes were measured in batch studies with both natural sediments (iron-reducing/methanogenic and sulfate-reducing) and chemical model systems (Fe(II)/goethite, FeS and Fe(O)) to elucidate key system and molecular properties controlling the mechanism and rate of halomethane reduction. The facile reduction of thehalomethanes in the model systems indicates that chemical reduction is a dominant process controlling the loss of these chemicals in the natural sediments. Correlation analysis indicates, however, that the chemical model systems have limited value for predicting rates of reduction for the halomethanes in natural sediments. A significant decrease in the first-order reduction rate constant with increasing substrate concentration in the iron-reducing/methanogenic
sediment suggests that the microbially-mediated regeneration of chemical reductants and/or diffusion to reactive sites becomes the rate controlling process at higher substrate concentrations.
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| PRESENTATION |
Sediment-Associated Reactions of Aromatic Amines: QSAR Development |
08/20/2000
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Weber, E. J., D. Colon, AND G. L. Baughman. Sediment-Associated Reactions of Aromatic Amines: QSAR Development. Presented at 220th American Chemical Society National Meeting, Washington, DC, August 20-24, 2000.
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Despite the common occurrence of the aromatic amine functional group in environmental contaminants, few quantitative structure-activity relationships (QSARs) have been developed to predict sorption kinetics for aromatic amines in natural soils and sediments. Towards the goal of developing successful QSARs, the sorption kinetics for a series of anilines with substituents in the 3- or 4-positions were measured in sediment slurries. Generally, the sorption kinetics of the substituted anilines were characterized by a rapid, initial loss of substrate from the aqueousphase followed by a much slower rate of disappearance. The initial rates of sorption varied with the type and position of the substituent group. Sorption rate constants were correlated with molecular descriptors including ionization constants (pKa's), HOMO energies, E1 and E2 oxidation potentials, and Hammett s-constants. Based on the strength of linear correlations and the availability of data, ionization constants appear to be the most useful molecular descriptor for predicting initial rates of sorption of substituted anilines in natural soils and sediments.
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| PRESENTATION |
Impacts of Land Use Change and Fire on Nutrient and Carbon Cycles and Trace Gas Exchange in Soils of the Cerrado in Central Brazil |
06/26/2000
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Pinto, A., R. Varella, G. Nardoto, L. Viana, L. Andrade, R. Chiba, R. Santos, M. Bustamante, R. A. Burke Jr., M. Molina, R. G. Zepp, K. Kisselle, AND S. P. Opsahl. Impacts of Land Use Change and Fire on Nutrient and Carbon Cycles and Trace Gas Exchange in Soils of the Cerrado in Central Brazil. Presented at First Large Scale Biosphere-Atmospheric Experiment in Amazonia (LBA) Scientific Conference, Belem, Brazil, June 26-30, 2000.
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The Brazilian cerrado is experiencing rapid land use changes that are often accompanied by fire. Here we report initial studies of the effects of fire and land use change on the composition and persistence of litter and soil organic carbon and nitrogen and related changes in the soil-atmosphere fluxes of selected trace gases (C02, CO, N20, NO). The studies are focusing on two classes of cerrado, cerrado stricto senso (20-50% canopy cover) and campo sujo (open, grass-dominated), located in the research and ecological reserve operated by IGBE, located 35 km south of Brasilia and in a 20-year-old cattle pasture at an EMBRAPA Cerrados field research site located 25 km northwest of Brasilia. Variation in N-mineralization rates were determined in both dry and wet season. Pronounced increases were observed at the beginning of the wet season. N-mineralization rates were lowest in the camp sujo and pasture sites. Significant immobilization of N immediately following fire at both classes of cerrado at IBGE. These variations in mineralization indicate that significant changes in soil-atmosphere trace gas fluxes, especially of nitrogen oxides, may occur at the sites. To determine the size and diversity of the soil microbial community at the sites, we are measuring the amount and composition of biomarker compounds in the litter and soil organic matter, particularly phosopholipid ester-linked fatty acids (PLFA) and ergosterol.
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| PRESENTATION |
Phytoremediation Potential of a Chlorinated Solvents Plume in Central Florida |
05/01/2000
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Lewis Hutchinson, S. AND J. W. Weaver. Phytoremediation Potential of a Chlorinated Solvents Plume in Central Florida. Presented at US Environmental Protection Agency Phytoremediation Conference, Boston, MA, May 1-2, 2000.
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The potential for phytoremediation of a shallow chlorinated solvent plume was assessed by application of ground water flow and evapotranspiration (ET) models for a site in Orlando, Florida. The focus of the work was on the hydrologic and hydraulic factors that influence phytoremediation effectiveness. The primary phenomena of concern were observed plume diving, spatially varying recharge and evapotranspiration from existing and candidate trees. The observed contaminant distribution at the site showed sharp plume diving immediately down gradient from the suspect source with partial discharge to a lake approximately 250 feet down gradient. A ground water flow model was developed for the site that included the potential for vertical flow by including detailed bathymetry of the lake. Model results showed that the plume diving is directly attributable to focussing of recharge from paved areas near the source. Since plume diving represents the dominant feature of vertical flow at the site, the design for a phytoremediation system included diverting recharge water from the paved area and planting of trees to further minimize plume diving. Estimates of ET rates were obtained from regional estimates, a simple model of ET and from a previous ET study conducted on site. These estimates provided design parameters for the remediation system and an assessment of the amount of plume control possible at the site.
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| PRESENTATION |
The Science and Practice of Phytoremediation |
05/01/2000
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McCutcheon, S. C. The Science and Practice of Phytoremediation. Presented at US Environmental Protection Agency Phytoremediation Conference, Boston, MA, May 1-2, 2000.
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This presentation will briefly review terminology, and define the types, benefits, and limitations of phytoremediation. A review of where phytoremediation fits in the scheme of hazardous waste management serves as a lead into an overview of the scientific advances on which the practice of phytoremediation is based. This presentation defines broadly the application of phytoremediation as a niche or polishing technology and when the approach can be used as a primary treatment. Secondary benefits for nonpoint source treatment in air and water, effluent treatment, erosion control and site management, and ecosystem restoration will be put into context with the general scientific and ecological engineering knowledge of the art. The fundamental understanding of plant and rhizosphere biochemistry and contaminant fate and transport will be contrasted with the field and pilot studies that represent the current proof of concepts and proof of principles that justify use of phytoremediation. The practice is summarized as those approaches that are ready for application (given the appropriate pilot and feasibility investigations for specific sites), promising treatments expected to be tested soon, and conceivable phytoremediation approaches that require intensive development. Finally, the intrinsic strengths of phytoremediation and future potential for the technology will be reviewed for applications in hazardous waste management.
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| PRESENTATION |
Accumulation and Fate of Perchlorate in Plants |
05/01/2000
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Susarla, S. AND S. C. McCutcheon. Accumulation and Fate of Perchlorate in Plants. Presented at US Environmental Protection Agency Phytoremediation Conference, Boston, MA, May 1-2, 2000.
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Perchlorate, a component of solid rocket fuels, has emerged as a potential threat to surface water and groundwater at several locations in the U.S. Perchlorate levels up to 16 ug/L were detected in Lake Mead and 5-9 ug/L in the lower Colorado River. The water from the Colorado River is used for irrigation to raise food crops each year. One-half of the populations of Nevada, Arizona and California use drinking water from the affected Colorado River. The drinking, and uptake and translocation of Perchlorate through the food chain during irrigation with Perchlorate contaminated waters could represent a human exposure problem. Due to the expense and lack of widespread applicability of the standard treatment methods for Perchlorate (reverse osmosis, ion exchange, and similar approaches), the US Air Force requested that we investigate the phytoremediation of Perchlorate. From the screening of a range plant - 13 trees and terrestrial and wetland herbs - we found that: Poplar and willow trees, French tarragon, and pickleweed (a playa halophyte) actually break down Perchlorate into chloride; willow and eucalyptus stimulate rhizosphere degradation of Perchlorate; lettuce and other plants temporarily accumulate Perchlorate up to 0. 1 8 % in IO days; and some freshwater wetland plants experienced toxic effects, perhaps due to chloride exchange from sand substrates.
Competitive ions (especially chlorides), nutrients, and soil exchange, influence degradation rates, accumulation, and phytotoxicity. Accumulation is focussed in the leaf tips of some plants. Location of the point of degradation awaits radiolabeled mass balance experiments and more complete product analysis in the plant. Once full mass balances and kinetics investigations of irrigation and other water and soil influences are undertaken, discovery of other effects is anticipated.
These preliminary screening results indicate that created wetlands or pumping contaminated ground or surface waters on tree and other plantations may cost effectively remove Perchlorate. However, additional process investigation and then pilot testing is necessary to establish practicality.
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| PRESENTATION |
Remediation of Perchlorate Contaminated Ground Water and Surface Water |
05/22/2000
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McCutcheon, S. C. AND S. Susarla. Remediation of Perchlorate Contaminated Ground Water and Surface Water. Presented at University of Georgia Biological and Agricultural Department and the American Society of Agricultural Engineers, Athens, GA, May 22, 2000.
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There is no abstract available for this product. If further information is requested, please refer to the bibliographic citation and contact the person listed under Contact field.
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| PRESENTATION |
Determination of Perchlorate at Parts-Per-Billion Levels in Plants By Ion Chromatography |
11/12/2000
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Ellington, J. J. AND J. J. Evans. Determination of Perchlorate at Parts-Per-Billion Levels in Plants By Ion Chromatography. Presented at 21st Annual Society of Environmental Toxicology and Chemistry Meeting, Nashville, TN, November 12-16, 2000.
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A standardized method for the analysis of perchlorate in plants was developed, based on dry weight, and applied to the analysis of plant organs, foodstuffs, and plant products. The procedure greatly reduced the ionic interferences in water extracts of plant materials. The high background conductivity increases method detection limits with conductivity detectors. Ion chromatography (IC) on an AS 16 anion exchange column was used for separation of perchlorate from the ionic matrix. The method utilized the seemingly contradictory high water solubility but hydrophobic and unreactive character of the perchlorate anion to greatly reduce the ions in plant extracts without loss of perchlorate. The extract was heated to precipitate proteins, centrifuged, exposed to alumina, and filtered through a cartridge filled with divinylbenzene to yield a water clear extract for IC analysis, even from highly colored solutions. The quantitation limit in lettuce and tomato matrices was determined to be 250 ppb. The method will be described in detail and application to other food matrices and further research to lower the quantitation limit to 100 ppb will also be discussed.
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| PRESENTATION |
Indicators of UV Exposure in Corals: Relevance to Global Climate Change and Coral Bleaching |
10/23/2000
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Anderson, S. L., J. Machula, G. Cherr, R. G. Zepp, D. L. Santavy, L. J. Hansen, AND E. Mueller. Indicators of UV Exposure in Corals: Relevance to Global Climate Change and Coral Bleaching. Presented at Ninth International Coral Reef Symposium, Bali, Indonesia, October 23-27, 2000.
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Increased exposure to solar UV radiation and elevated water temperatures are believed to play a role in the bleaching of corals. To provide additional tools for evaluating the role of UV radiation, we have examined UV-specific effects in coral and have characterized factors that alter the penetration of UV radiation over coral reefs at sites located in the Florida Keys. Using an immunoblotting assay to examine UV-specific lesions (thymine dimers) in coral and zooxanthellae DNA, we observed dose-dependent increases of thymine dimers in purified coral (Porites porites) DNA exposed to UV-C in the laboratory and with live P. porites exposed in a solar simulator. Field studies conducted at the Florida Key (Maryland Shoals and Eastern Sambo) during July 1999 further demonstrated the utility of this technique in evaluating UV exposure of corals. For example, amounts of thymine dimers in P. porites collected at Maryland Shoals at the time of peak UV exposure (1300 hrs) were significantly higher than at 0830 hrs (p=0.04). UV measurements indicated that the coral reefs at Eastern Sambo (at 3-4 meters) were exposed to UV-B radiation that corresponded to 25-30% of surface UV irradiance. However, the water just inside the reef in Hawk Channel and closer to land was considerably more opaque to UV. This water photobleached with loss of UV absorbance and fluorescence when it was exposed to simulated solar radiation. These results indicate that photobleaching of the DOM and transport of near-shore water out over the reefs may play a key role in controlling UV penetration to the reef surface.
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| PRESENTATION |
Formation and Enantioselective Biodegradation of the Enantiomers of Bromochloroacetic Acid |
11/12/2000
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Wong, C. S., A. W. Garrison, W. J. Jones, L. Howell, AND J. Avants. Formation and Enantioselective Biodegradation of the Enantiomers of Bromochloroacetic Acid. Presented at 21st Annual Society of Environmental Toxicology and Chemistry Meeting, Nashville, TN, November 12-16, 2000.
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Bromochloroacetic acid (BCAA) is formed by chlorination of drinking waters containing naturally occurring bromide. This haloacetic acid is a concern to public health because of suspected carcinogenicity and toxicity, and is a potential target of disinfectant byproduct regulations. BCAA is chiral, and its enantiomers may have different biological and toxicological properties from each other. The formation and biodegradation of BCAA in natural waters were studied to determine if these processes are enantioselective. Racemic quantities of BCAA were produced in drinking waters treated by chlorination and ozonation in a pilot drinking water plant, and in chlorinated laboratory waters containing humic acids (e.g., Aldrich, Suwannee) and bromide ions. This result implies that the chiral centers that may be present in humic substances are not involved in the formation of haloacetic acids. The biodegradation of BCAA was studied in laboratory incubations of natural waters from 5 rivers in northeast Georgia, as well as wastewater treatment plant effluent from the city of Athens, GA. BCAA degraded enantioselectively in all natural waters, with the same enantiomer degrading faster in all cases, over times ranging from weeks to several months. The fastest degradation rates were observed in the wastewater effluent. Enantioselective degradation is proof positive of biotransformation; in addition, our results indicate that microbial communities in natural waters have a commonenantioselectivity for the degradation of BCAA.
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| PRESENTATION |
Enzymatic Processes Used By Plants to Degrade Organic Compounds |
05/01/2000
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Wolfe, N. L., O. Prakash, C. F. Hoehamer, AND C. S. Mazur. Enzymatic Processes Used By Plants to Degrade Organic Compounds. Presented at US Environmental Protection Agency Phytoremediation Conference, Boston, MA, May 1-2, 2000.
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This is a review of recent plant enzyme systems that have been studied in uptake and transformation of organic contaminants. General procedures of plant preparation and enzyme isolation are covered. Six plant enzyme systems have been investigated for activity with selected pollutants. A nitroreductase has been isolated and partially characterized that reduces nitroaromatic compounds including the munition TNT to the corresponding amino products. A dehalogenase like compound has been isolated from a large cross section of plants that reduce aliphatic hydrocarbons such as TCE and PCE but not halogenated aromatics. A phosphatase has been isolated from duck weed that degrades selected organophosphate esters by a hydrolysis mechanism. This has been demonstrated for several organophosphate pesticides and chemical warfare agents (surrogates). Three other enzyme systems have been investigated for environmental importance as transformation pathways but they have not been well characterized. They are a family of peroxidases, a nitrilase and an azoreductase.
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| PRESENTATION |
Accumulation of Perchlorate in Tobacco Plants and Tobacco Products |
08/21/2000
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Wolfe, N. L., J. J. Ellington, A. W. Garrison, J. J. Evans, AND J. Avants. Accumulation of Perchlorate in Tobacco Plants and Tobacco Products. Presented at 220th American Chemical Society National Meeting, Washington, DC, August 20-24, 2000.
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Previous field and laboratory studies with vascular plants have shown that perchlorate is transported from perchlorate fortified soils and is accumulated in the plant tissues and organs. This paper reports results of initial investigations on the accumulation of perchlorate in tobacco plants grown in soils amended with Chilean nitrate fertilizers. Methods were developed for the analysis of perchlorate in soils, tobacco leaves, and selected commercial tobacco products based on aqueous extractions from freeze-dried material. Analytical methods based on ion chromatography (IC), capillary electrophoresis (CE), and nuclear magnetic resonance (NMR) spectroscopy were developed for both qualitative and quantitative analyses of perchlorate. Results show that perchlorate is accumulated by tobacco plants into the lamina and midrib of the leaves from soils amended with Chilean nitrate fertilizer containing perchlorate as a natural impurity. Also, perchlorate can persist over an extended period of time and under a variety of industrial processes as shown by its presence in off-the-shelf tobacco products including cigarettes, cigars, and pouch and plug chewing tobaccos in concentrations ranging from 2 to 149 mg/kg on a dry-weight basis.
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| PRESENTATION |
Identification of Chlorine Dioxide and Chloramine Drinking Water Disinfection By-Products |
10/24/2000
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Richardson, S. D., A. D. Thruston Jr., C. RavAcha, AND V. Glezer. Identification of Chlorine Dioxide and Chloramine Drinking Water Disinfection By-Products. Presented at International Society of Exposure Analysis Conference, Monterey, CA, October 24-27, 2000.
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Due to concern over the potential adverse health effects of trihalomethanes (THMs) and other chlorinated by-products in chlorinated drinking water, alternative disinfection methods are being explored. Chlorine dioxide and chloramine are two popular alternative disinfectants, with hundreds of drinking water treatment plants currently using these disinfectants in the U.S. However, there is little known about the disinfection by-products (DBPs) that are produced from these alternative disinfectants. Another important factor is the effect of elevated bromide levels on the formation of DBPs. Bromide is important because it has caused the formation of hazardous bromine-containing DBPs for other disinfectants studied (chlorine and ozone). To investigate the effect on the effect of elevated bromide levels on the formation of chlorine dioxide DBPs, drinking water from Israel was chosen for study, due to their extremely high natural bromide levels (2-3 mg/L). Chlorine dioxide-treated drinking water was collected from two full-scale plants in Israel. To investigate the formation of chloramine DBPs, drinking water was collected from a full-scale plant in Denver, CO, which uses chloramine as its primary disinfectant. High and low resolution gas chromatography/mass spectrometry (GC/MS) (electron ionization and chemical ionization) and liquid chromatography (LC)/MS were used to identify DBPs. Rather than targeting a small group of pre-selected DBPs, we attempted to identify every compound that was detected. In the chlorine dioxide-treated water from Israel, many bromine-containing compounds were identified, including some unusual bromo-aromatic compounds. A DBP of particular interest was 1,1,3,3-tetrabromopropanone. Its chlorinated analog--1,1,3,3-tetrachloropropanone--had been found as one of only two chlorine-containing DBPs identified in a previous chlorine dioxide DBP study in the U.S., where there were not high bromide conditions. In the chloramine-treated drinking water, several halogenated DBPs were found, including some brominated and iodinated compounds.
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| PRESENTATION |
Indicators of UV Exposure in Coral and Their Relevance to Global Climate Change and Coral Bleaching |
06/05/2000
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Anderson, S. L., J. Machula, G. Cherr, R. G. Zepp, D. L. Santavy, L. J. Hansen, AND E. Mueller. Indicators of UV Exposure in Coral and Their Relevance to Global Climate Change and Coral Bleaching. Presented at US Environmental Protection Agency Symposium on Indicators in Health and Environmental Risk Assessment, Research Triangle Park, NC, June 5-6, 2000.
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A compelling aspect of the deterioration of coral reefs is the phenomenon of coral bleaching. Bleaching can destroy large areas of a reef with limited recovery or recruitment, and it may be induced by a variety of stressors ranging from exposure to temperature and salinity extremes, sedimentation, pollution, and ultraviolet light. Under conditions of ocean warming, often associated with calm, stratified waters, photobleaching of UV-absorbing chromophoric dissolved organic matter (CDOM) is increased, and penetrance of both UV-B and UV-A is greatly enhanced. Indices of UV- specific effects in coral tissue are needed to test whether UV increases, associated with global climate change, are harmful to coral. To address this challenge, we have evaluated UV-specific effects in coral and have characterized factors that alter penetrance of UV radiation over coral reefs. An immunoblotting assay was developed to examine UV-specific lesions (thymine dimers) in coral and zooxanthellae DNA. We observed dose-dependent increases of thymine dimers in purified coral (Porites porites) DNA exposed to UV-C in the laboratory and with intact P. porites in a Suntest solar simulator. However, with whole coral, effects were not strictly proportional at the lowest exposure times. Next, the assay was used to determine whether thymine dirners are detected under realistic field conditions (Maryland Shoals, Florida Keys, July 1999). Thymine dimers in P. porites collected at 0830 hrs and 1300 hrs differed significantly (p=0.04). A diurnal variation experiment was conducted in July, 1999 at Eastern Sambo Reef (Florida Keys). Sampling was conducted at multiple timepoints for three days to determine whether thymine dimers follow hypothesized diurnal cycles. Chlorophyll, tissue protein, zooxanthellae counts, and carotenoid pigments will also be analyzed. We are now developing immunofluorescence techniques that will allow us to determine where dimers are localized within coral tissue and zooxanthellae. Results obtained to date indicate that UV-specific effects can be discerned under field conditions and related to exposure dose. Studies now underway will allow us to determine whether these effects are linked to coral bleaching and other indicators of stress in coral. UV measurements were made as part of the experiments conducted during July 1999 at Eastern Sambo reef and nearby sites including profiling along transacts from reef to shore. Results of these analyses indicate that the coral reefs at Eastern Sambo (at 3-4 meters) were receiving UV-B radiation that was equivalent to 25-30% of surface UV irradiance. However, the water just inside the reef in Hawk Channel and closer to land was considerably more opaque to UV. This water photobleached with loss of UV absorbance and fluorescence when it was exposed to simulated solar radiation. These results indicate that photobleaching of the DOM and transport of near-shore water out over the reefs may play a key role in controlling UV penetration to the reef surface.
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| PRESENTATION |
Role of Dom Photoreactions in Controlling UV Exposure of Coral Assemblages in the Florida Keys |
12/14/2000
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Zepp, R. G., E. Davis, S. L. Anderson, D. L. Santavy, L. J. Hansen, AND K. Patterson. Role of Dom Photoreactions in Controlling UV Exposure of Coral Assemblages in the Florida Keys. Presented at The International Chemical Congress of Pacific Basin Societies, Honolulu, HI, December 14-19, 2000.
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Recent studies have indicated that solar LTV radiation is a significant stressor of coral assemblages in tropical and subtropical marine environments. Here evidence is presented that UV exposure of coral reefs in the Florida Keys near Key West is controlled by the colored component of dissolved organic matter, referred to as CDOM, in waters overlying the reefs. Downwelling and upwelling vertical profiles of LTV and visible radiation were obtained and absorption and fluorescence spectra of the filtered water samples were measured. Analyses of the absorption spectral data indicated that they could be closely described by a non-linear exponential function, a(lambda) = a(412)* exp b(412 - lambda), where b ranged from 0.022 up to 0.025. The CDOM photobleached with loss of LTV absorbance and fluorescence when exposed to simulated solar radiation. These results indicate that interactions between photobleaching and transport of the CDOM out over the reefs likely control UV penetration to the reef surface.
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| PRESENTATION |
Perchlorate in Fertilizers?: Analysis By Raman Spectroscopy |
08/21/2000
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Collette, T. W. AND T. L. Williams. Perchlorate in Fertilizers?: Analysis By Raman Spectroscopy. Presented at 220th American Chemical Society National Meeting, Washington, DC, August 20-24, 2000.
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Recently, we and others found perchlorate at high levels (approximately 500 - 8000 mg/kg) in 90+% of 25+ fertilizers (primarily lawn-and-garden products) that are not identified as containing components derived from mined Chile saltpeter, which is known to contain perchlorate as a natural contaminant. These products were acquired over the period of November 1998 to January 1999 at 5 locations across the U.S. However, we have subsequently analyzed 20+ similar products, which were acquired after July 1999. Some of these were the same products (although not the same lots) as those previously sampled. Most of these new products do not contain perchlorate above the ion chromatographic detection level. While our more recent results suggest that the contamination of the earlier products may have been an episodic (if not singular) event, there is an ongoing need for robust analytical methods for rapid and definitive analysis of perchlorate in complex matrices such as fertilizer extracts. We will focus the majority of this talk on the merits of Raman spectroscopy to meet this need.
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| PRESENTATION |
Characterizing the Abiotic Reductants for Nitroaromatic Compounds as a Function of Redox Zonation in Anoxic Sediments |
09/03/2000
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Hoferkamp, L. A. AND E. J. Weber. Characterizing the Abiotic Reductants for Nitroaromatic Compounds as a Function of Redox Zonation in Anoxic Sediments. Presented at Goldschmidt 2000 Conference for Geochemistry, Oxford, UK, September 3-8, 2000.
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Reductive transformation is the dominant reaction pathway for the degradation of nitroaromatic compounds in anaerobic environments (Larson and Weber, 1994). Proposed reductants cover a spectrum ranging from reduced rninerals and organic matter to microbial enzyme systems. Transformation studies carried out in an anaerobic aquifer have implicated specific reductants such as surface-bound Fe(II) and dissolved sulfide species as the primary reducing agents for a series of nitroaromatics (Rugge el al, 1998). The involvement of these various agents in electron transfer can be expected to vary with the redox zonation of a given sediment system. The development of redox zones is associated with sequential utilization of the available electron acceptors by the microbial consortium present in groundwater-infiltrated sediments. At the sediment-water interface dissolved oxygen is the most thermodynamically accessible terminal electron acceptor followed by nitrate, manganese(IV) and iron(III) bearing minerals, sulfate and finally carbon dioxide. The successive reduction of these sediment components results in a series of zones usually associated with depth and identified by variations in concentration of the relevant redox indicators (NO3-, Mn(II), Fe(II), S04 2- and CH4, respectively). With the objective of characterizing the role of chemical reductants as a function of redox zonation, studies were carried out using a representative nitroaromatic compound, p-cyanonitrobenzene (p-CNB) and a river sediment obtained from the Oconee River (OR) in Athens, GA, USA. The mineralogy of this sediment is dominated by quartz, feldspar, kaolinite and iron phases. Electron microprobe examination of representative samples indicated a fine layer of iron oxide on quartz grains. Earlier column studies with OR sediment demonstrated that the reduction kinetics of P-CNB varied as a function of redox zonation as assessed by solution phase concentrations of the redox-active species (Simon et al, 2000). Preliminary experiments in anoxic batch systems designed to monitor the concentration of redox active species were carried out with OR sediment and filtered OR water, with and without 10 MM acetate. These batch studies demonstrated the establishment of a typical series of redox zones over the course of several months. Significant levels of solution-phase FE(II) were detected at 28 days (672 h) in un-amended and 11 days (264 h) in acetate-amended batch systems. Batch studies were also carried out in which additions of P-CNB to un-amended and acetate- amended systems were made initially and changes in the concentrations of P-CNB and its transformation product, cyanoaniline (p-CNA) were monitored as redox zonation progressed. While reduction of the probe compound did occur prior to the establishment of detectable levels of solution-phase ferrous ion in both the amended and un-amended batch systems, a significant increase in the rate of reduction after ~11 days in the batch system containing acetate coincided with a prominent increase in Fe2+ (aq) concentration . These results are consistent with previous studies implicating surface-bound Fe(II) ion as a reductant for xenobiotic species in laboratory columns and model systems.
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| PRESENTATION |
Hydrology and Sediment Modeling Using the Basins Non-Point Source Model |
11/05/2000
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Cyterski, M. J. Hydrology and Sediment Modeling Using the Basins Non-Point Source Model. Presented at 2000 Annual Meeting and International Conference of the American Institute of Hydrology, Research Triangle Park, NC, November 5-8, 2000.
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The Non-Point Source Model (Hydrologic Simulation Program-Fortran, or HSPF) within the EPA Office of Water's BASINS watershed modeling system was used to simulate streamflow and total suspended solids within Contentnea Creek, North Carolina, which is a tributary of the Neuse River. I utilized landuse coverage circa 1996 created by EarthSat Corporation. Hourly meteorological measures (precipitation, pan evaporation, temperature) for 1970-1995 were taken from a weather station at Wilson, NC. Missing meteorological data were supplemented with measures from Raleigh Airport. Time series of observed flow from 1970-1995 gathered by the USGS at Hookerton, NC, and Nahunta Swamp, NC, were used to calibrate/validate the hydrological component of the model. Simulated suspended sediment concentrations were evaluated by comparison to 125 values of TSS measured at Hookerton, NC. Graphical and statistical analyses indicated good model fit to observed flow but observed suspended sediment concentrations were less successfully replicated. Parameter values needed to produce the flow calibration were well within the ranges of values used in other HSPF studies conducted in the Atlantic coastal plain. This was affirmed by reference to the software parameter database HSPFParm, which summarizes previous HSPF studies. Parameter values for sediment simulation were also within the range used by previous investigators in this physiographic province.
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| PRESENTATION |
Testing Linkages Between Groundwater, Watershed, and in-Stream Models in the Contentnea Creek Basin, North Carolina, USA |
11/05/2000
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Kraemer, S. R., E. J. Hayter, AND M. J. Cyterski. Testing Linkages Between Groundwater, Watershed, and in-Stream Models in the Contentnea Creek Basin, North Carolina, USA. Presented at 2000 Annual Meeting and International Conference of the American Institute of Hydrology, Research Triangle Park, NC, November 5-8, 2000.
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Computer modeling provides support for the development of TMDLs (total maximum daily loads) of impaired water bodies. Evaluations of TMDLs for nutrients, especially for nitrogen, benefits from a multi-media assessment (i.e., atmosphere, landscape, subsurface, surface water). In this paper, we evaluate the linkage of a watershed model, subsurface models, and an in-stream model to represent the hydrology/hydraulics of catchments within the Contentnea Creek basin in North Carolina. We represent the subsurface hydrology using the models GFLOW (www.gfiow.com) and MODFLOW (water.usgs.gov/software/rnodflow-96.html). We represent the watershed hydrology using HSPF-Hydrologic Simulation Program Fortran (www.epa.gov/docs/ostwater/BASINS/index.html). We represent the in-stream hyraulics using the EFDC-Environmental Fluid Dynamics Code (Harmick, 1996). Each separate media model supplies additional boundary conditions and calibration targets for the other models through water balance and flux exchanges. The strategy for evaluating sediment and nutrient water quality modeling will be discussed. The evaluation of the linked models provides a foundation for future developments of either fully coupled systems or comprehensive multi-media models.
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| PRESENTATION |
Reactivity of Chemical Reductants as a Function of Redox Zonation |
06/26/2000
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Weber, E. J., J. F. Kenneke, J. W. Washington, AND L. A. Hoferkamp. Reactivity of Chemical Reductants as a Function of Redox Zonation. Presented at Gordon Research Conference 2000 on Environmental Sciences, Plymouth, NH, June 25-30, 2000.
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The incorporation of reductive transformations into fate models continues to be a challenging problem. The occurrence of chemical reductants in anaerobic sediments and aquifers is a result of the reduction of inorganic, electron acceptors coupled to the microbial oxidation of organic matter. Depending on the distribution of thermodynamic conditions, a sequence of redox zones can develop that are characterized by the respective dominant terminal electron accepting process (i.e., nitrate-, manganese-, iron-, sulfate-reducing and methanogenic). It is logical that the dominant chemical reductants in subsurface environments will vary as a function of the redox zonation. To understand this relationship, the reaction kinetics for a series of probe molecules (halogenated methanes and nitroaromatics) have been measured in sediments for which redox conditions have been well characterized. Redox characterization has included quantifying the major redox-active species in sediment pore waters (NO3(-), Mn2+, Fe2+, SO4(2-) and H2) and the use of sequential extractions to determine the major pools of FE(II) and FE(III) associated with the solid phase of the sediments. The results of these studies will be presented showing the relationship between the reaction kinetics of the probe molecules with the redox zonation of natural sediments.
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| PRESENTATION |
Transport |
06/20/2000
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Weaver, J. W. Transport. Presented at US Environmental Protection Agency Methyl Tert-Butyl Ether (MTBE) Scientist-to-Scientist Meeting, Chicago, IL, June 20-21, 2000.
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Presentation outline: transport principles, effective solubility; gasoline composition; and field examples (plume diving). Presentation conclusions: MTBE transport follows from - phyiscal and chemical properties and hydrology. Field examples show: MTBE plumes > benzene plumes; MTBE detachment in certain cases; plume diving. Site characterization is critical for correct interpretation of transport.
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| PRESENTATION |
Identification of New Disinfection By-Products in Drinking Water |
12/06/2000
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Richardson, S. D. Identification of New Disinfection By-Products in Drinking Water. Presented at Southeast/Southwest American Chemical Society Regional Meeting, New Orleans, LA, December 6-8, 2000.
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Due to concern over the potential adverse health effects of trihalomethanes (THMs) and other chlorinated by-products in chlorinated drinking water, alternative disinfectants are being explored. Ozone, chlorine dioxide, and chloramine are popular alternatives, as they produce lower levels of THMs. Millions of people drink water treated with these alternative disinfectants, yet there is still much not known about the disinfection by-products (DBPs) that they produce. Using a combination of mass spectra and infrared techniques, we have identified many new drinking water DBPs from these disinfectants and from chlorine that were not previously known. Drinking water studied includes water from Jefferson Parish, LA (with Mississippi River as the source water); Evansville, IN; Denver, CO; and Israel. These results will be presented, along with recent preliminary health effects research on some new DBPs.
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| PRESENTATION |
Observations from Contaminant Plumes on Long Island |
12/15/2000
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Weaver, J. W. Observations from Contaminant Plumes on Long Island. Presented at American Geophysical Union Fall Meeting, San Francisco, CA, December 15-19, 2000.
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The aquifers of Long Island serve as a sole source drinking water supply for the entirelocal population of about three million people. Where the shallow Upper Glacial Aquifer has been contaminated with petroleum hydrocarbons and methyl tert-butyl ether (MTBE), intensive site investigations have established the vertical and horizontal distribution of contaminants. Plumes and contaminant pulses are the presumed consequences of source emplacement in fairly homogeneous aquifer materials, high recharge and leaching rates through the sources, high ground water velocity, plume diving in the aquifer, and low rates of biodegradation. Detailed vertical characterization of the plumes has revealed orders-of-magnitude variation in concentration in adjacent sample points. Two types of variations have been explored with borehole flowmeter studies. The first type is apparent plume diving associated with changes in
the amount of pervious cover at these locations. The flowmeter studies have show that concentration discontinuities are not associated with observable changes in hydraulic conductivity. Thus the presumed reason for plume diving is enhanced recharge. Additional evidence is supplied by models of vertical flow that confirm the magnitude of vertical displacements caused by infiltrating water. The second type of variation shows concentration discontinuities that are not associated with land use changes. These have been shown not to be associated with observable changes in hydraulic conductivity. Through repeated observations of the plumes the gross motion of the contaminants and some measure of projected contaminant distributions have been determined. Processes controlling fine scale or boundary processes have not been incorporated into site assessments, however, even though in some cases these may have a dominant affect on even the gross features of the contaminant plumes.
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| PRESENTATION |
Interactions of Nutrient and Carbon Cycles and Trace Gas Exchange With Land Use Change and Fire in the Cerrado of Central Brazil |
12/15/2000
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Pinto, A., R. Varella, G. Nardoto, L. Viana, L. Andrade, R. Chiba, R. Santos, M. Bustamante, R. A. Burke Jr., K. Kisselle, M. Molina, AND R. G. Zepp. Interactions of Nutrient and Carbon Cycles and Trace Gas Exchange With Land Use Change and Fire in the Cerrado of Central Brazil. Presented at American Geophysical Union Meeting, San Francisco, CA, December 15-20, 2000.
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Land use changes accompanied by fire frequently occur in the Brazilian cerrado. Here we report measurements in the cerrado of the effects of fire and land use change on the composition and persistence of litter and soil organic carbon and nitrogen and related changes in the soil-atmosphere fluxes of selected trace gases (C02, CO, N20, NO). The studies include two classes of cerrado, cerrado stricto senso (20-50% canopy cover) and campo sujo (open, grass-dominated), located in the research and ecological reserve operated by IGBE, located 35 km south of Brasilia, Brazil and in a 20-year-old cattle pasture at an EMBRAPA Cerrados field research site located 25 km northwest of Brasilia.
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| PRESENTATION |
Impervious Cover as a Regional Indicator |
09/12/2000
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Bird, S. L., S. W. Alberty, AND L. R. Exum. Impervious Cover as a Regional Indicator. Presented at US Environmental Protection Agency Regional Vulnerability Assessment Workshop, Research Triangle Park, NC, September 12-14, 2000.
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Increases in impervious surface area in a watershed gives rise to changes in stream hydrology, stream channel morphology, increased pollutant runoff, and an increase in stream water temperature. These physical changes in the stream systems in turn give rise to impacts on stream biodiversity for both macroinvertebrates and fish species. This poster describes an approach for developing a regional scale indicator based on impervious cover and the collection of a test data set derived from aerial photography to evaluate the uncertainty associated with the application of the indicator.
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| PRESENTATION |
Modeling Consistency, Model Quality, and Fostering Continued Improvement |
11/28/2000
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Frick, W. E., D. J. Baumgartner, L. R. Davis, W. S. Lung, AND P. W. Roberts. Modeling Consistency, Model Quality, and Fostering Continued Improvement. Presented at International Conference of Marine Waste Water Discharges 2000, Genova, Italy, November 27-30, 2000.
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We believe that most contributors to and participants of the International Conference, Marine Waste Water Discharges 2000, "MWWD 2000," could agree that the overarching dream of the conference might be to chart a path the will lead to the best, long-term, applicable water quality science. But how can this dream become a reality when history shows that our actions as a community have frequently diverged from such a path? The reasons for such divergence are complex but the answer may be as simple as periodically meeting, as in MWWD 2000, to reaffirm a commitment to science, despite forces that often divert us from an optimum course.Given the influence of proximity, this is predominantly an American viewpoint, even though our nationalities reflect an international influence. The viewpoints expressed here have a North American focus, but hopefully they can contribute to the larger viewpoint emerging from MWWD 2000. Thus, the opposing values implied by the strengths and weaknesses of limited viewpoints may be ultimately perceived to blur into a holistic entity that contributes to the overall good of the international modeling community. In any case, this work will try honestly to assess major events and ideas with the aim of guaranteeing the long-term vigor of the science embraced and promoted by conferences such as this. In this manner it is appropriate to offer a series of more or less closely related vignettes that can put our experience in perspective, showing where we have seized opportunities for the good of the science, and, also, to explore events and initiatives that have led to missed opportunities, if not outright disasters, and that have sometimes sapped the energy of the community. This work is not an official policy statement, limited time does not allow a development of consensus that would be necessary to formulate an official position. However, as some of us are nearing retirement, if we are not already essentially retired, and as we represent the broad spectrum of interests, at least government, academia, consulting, and industry, it seems pertinent to tell our stories in way to help guide the future of the science that we helped to pioneer and to give the next generation the benefit of this experience and perspective. In that sense, this work will hopefully help shape future directions taken by governments and all entities concerned about the environment.
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| PRESENTATION |
Determination of Newly Identified Disinfection By-Products in Drinking Water |
11/05/2000
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Gonzalez, A. C., S. W. Krasner, H. S. Weinberg, AND S. D. Richardson. Determination of Newly Identified Disinfection By-Products in Drinking Water. Presented at American Water Works Association Water Quality Technical Conference, Salt Lake City, UT, November 5-9, 2000.
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The Metropolitan Water District of Southern California (MWDSC) is investigating the occurrence of 39 newly identified disinfection by-products (DBPs)-which were not included in the Information Collection Rule (ICR)-in drinking waters. Halomethanes (HMs), haloacetonitriles (HANs), haloketones (HKs), haloacetaldehydes (HAs), halonitromethanes (HNMs), and miscellaneous organic compounds listed in Table I comprise the list of target analytes to be measured at MWDSC. This list includes DBPs that were selected by toxicologists from approximately 600 to 700 DBPs reported in the literature that may have possible adverse health effects. The project was done in collaboration with the University of North Carolina (UNC) and the U.S. Environmental Protection Agency (USEPA). Current research at MWDSC focuses on developing analytical methods for the determination of the target analytes in water samples, and on preservation of the analytes between the point of sampling and their analysis at the laboratory. Objectives beyond methods development include the investigation of occurrence of these DBPs in drinking waters; and the determination of the influence of water quality parameters, treatment, and distribution system conditions on their concentrations, persistence and stability.
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| PRESENTATION |
Evolution of An Analytical Method for Halogenated Furanones in Drinking Water |
11/05/2000
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Onstad, G. D., H. S. Weinberg, AND S. D. Richardson. Evolution of An Analytical Method for Halogenated Furanones in Drinking Water. Presented at American Water Works Assoication Water Quality Technical Conference, Salt Lake City, UT, November 5-9, 2000.
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A unified method of detection for seven halogenated furanones present in drinking waters at the ng/L level has been developed. The use of GC/ECD makes this method amenable to manyenvironmental laboratories and water treatment plants in the United States. Detection limits observed using liquid-liquid extraction can be improved significantly by replacing this step with solid phase extraction as a preconcentration method. In order to assess the health risk of halogenated furanones, there is a need to apply this method to real drinking waters and collect occurrence data on the MX-analogues.
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| PRESENTATION |
Perchlorate Accumulation from Fertilizer in Leafy Vegetation |
03/20/2000
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Lewis Hutchinson, S., S. Susarla, N. L. Wolfe, AND S. C. McCutcheon. Perchlorate Accumulation from Fertilizer in Leafy Vegetation. Presented at Association for Environmental Health and Sciences 10th Annual West Coast Conference on Contaminated Soils and Ground Water, Port Hueneme, CA, March 20-23, 2000.
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Perchlorate contaminated water and soil has been identified in many areas of the United States. Previous studies indicated that the primary source of contamination was from industry and military operations that use perchlorate as an oxidzing agent. However, recent studies have found significant quantities of perchlorate in commercial fertilizers, which may be an additional source of perchlorate in the environment. Current studies on vegetation uptake ofperchlorate from fertilizer show that leafy garden crops, lettuce (Lactuca sativa) and mustard (Brassica alba), accumulate perchlorate and its transformation products in their leaves, stems, and roots. Final results have not been tabulated and additional experimental work is needed to confirm preliminary findings.
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| PRESENTATION |
Perchlorate-Crop Interactions from Contaminated Irrigation Water and Fertilizer Applications |
05/22/2000
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Lewis Hutchinson, S., S. Susarla, N. L. Wolfe, AND S. C. McCutcheon. Perchlorate-Crop Interactions from Contaminated Irrigation Water and Fertilizer Applications. Presented at Second International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA, May 22-25, 2000.
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Perchlorate has contaminated water and soils at several locations in the United States. Perchlorate is water soluble, exceedingly mobile in aqueous systems, and can persist for many decades under typical ground and surface water conditions. Perchlorate is of concern because of uncertainties about toxicity and health effects from low levels in drinking water, the impact on ecosystems, and possible indirect exposure pathways for humans from agricultural and other activities. There are very limited data about the possible uptake of perchlorate into agricultural products due to irrigation with contaminated waters or application of fertilizers containing perchlorate. In order, to characterize possible impacts of crop perchlorate interactions, the uptake of perchlorate from fertilizer and contaminated irrigation water in garden crops was investigated by applying a nutrient solution containing perchlorate on lettuce (Lactuca saliva) and mustard (Brassica alba) seedlings based on the recommended application rate for the fertilizer. Four locally purchased fertilizers and an unfertilized control were tested on seedlings grown in 2 different media, washed sand and potting soil. Whole plant samples were taken throughout the growing season. Plant tissues were separated and analyzed for perchlorate and transformation products. The impact of two different irrigation techniques, trickle and sub-irrigation, with contaminated water were analyzed for their affect on rhizosphere conditions and perchlorate interactions.
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| PRESENTATION |
Perchlorate Phytoremediation Using Hardwood Trees and Vascular Plants |
05/22/2000
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Lewis Hutchinson, S., S. Susarla, N. L. Wolfe, AND S. C. McCutcheon. Perchlorate Phytoremediation Using Hardwood Trees and Vascular Plants. Presented at Second International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA, May 22-25, 2000.
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| Abstract:
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Perchlorate has contaminated water and soils at several locations in the United States. Perchlorate iswater soluble, exceedingly mobile in aqueous systems, and can persist for many decades under typical ground and surface water conditions. Perchlorate is of concern because of uncertainties about toxicity and health effects from low levels in drinking water, the impact on ecosystems, and possible indirect exposure pathways for humans from agricultural and other activities. Currently, ion exchange is the most conunon perchlorate remediation technology. However, this technology is very expensive and results in a concentrated waste product. Initial studies at the US EPA Ecosystems Research Division show that several vascular plant species are capable of transforming perchlorate to nontoxic compounds. Studies
are currently underway to assess the phytoremediation potential of several fast growing hardwood trees. Plants are grown hydroponically in 1-2 L reactors containing varying concentrations of perchlorate contaminated water. The reactor weight is monitored to assess plant transpiration and water samples are analyzed daily for perchlorate. After 2 weeks, plants tissues are separated into roots, stems, and leaves, and analyzed for perchlorate and its transformation products.
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| PRESENTATION |
Variable Bound-Site Charging Contributions to Surface Complexation Mass Action Expressions |
03/26/2000
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Loux, N. T. Variable Bound-Site Charging Contributions to Surface Complexation Mass Action Expressions. Presented at 219th American Chemical Society National Meeting, San Francisco, CA, March 26-30, 2000.
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One and two pK models of surface complexation reactions between reactive surface sites (>SOH) and the proton (H+) use mass action expressions of the form: Ka={[>SOHn-1z-1]g>SOH(0-1)aH+EXP(-xeY/kT)}/{[>SOHnz]g>SOH(n)} where Ka=the acidity constant, [ ]=reactive species concentrations, n=the initial number of protons associated withthe site (n=+2 or +1), z=the initial site charge (z=+1, +1/2 or 0), aH+=the chemical activity of the proton, g=an activity coefficient for a bound site, EXP( ) is the exponential to the base of the natural logarithm, e=the electron charge, Y=the surface potential (relative to bulk solution), k=the Boltzmann constant, T=the absolute temperature, and x is a variable commonly given values of either one (with traditional modeling) or two (with expressions derived from chemical potentials of the reacting species. An investigation of bound site charging energies within the context of the Entropic Balanced Surface Potential Model (EBSPM) suggests: 1) charging energies estimated by the expression eY are predicated on an assumed constant value of Y (i.e., creating or eliminating one additional charged site does not significantly alter Y), 2) EBSPM estimated charging energies (at near constant Y) are of the form (1-t)eY where t is the fraction of potential determining ion charge neutralized by counterions in the surface region (t ranges between zero and one) and 3) the EBSPM value for x is (2-t); therefore, EBSPM derived values of x lie in a range between the traditional value of one and the chemical
potential derived value of two. A preliminary assessment using Poisson Boltzmann theory supports these findings.
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| PRESENTATION |
Bathymetric Irregularities, Jet Formation, and Subsequent Mixing Processes |
01/24/2000
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Frick, W. E., S. Emerman, AND A. C. Sigleo. Bathymetric Irregularities, Jet Formation, and Subsequent Mixing Processes. Presented at American Geophysical Union Ocean Sciences Meeting, San Antonio, TX, January 24-29, 2000.
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It is well known that bathymetric contours influence and steer currents and that irregularities in bathymetry contribute to the formation of aquatic non-buoyant jets and buoyant plumes. For example, bathymetric irregularities can channel flow through canyons or accelerate flow over ridges to produce regions of increased kinetic energy density, which is what jets and plumes are, in addition to the latter being buoyant. Considering sufficiently large scales, upon reaching uniform bathymetry, these flows will inevitably mix with ambient fluid. While this mixing effect is well known, and is sometimes called entrainment, the underlying mechanism remains relatively obscure and esoteric. An application of a novel theory for turbulence places an understanding of the basic mixing process within the reach of all researchers and provides a model for turbulent flow that may prove useful for parameterizing turbulence quantitatively in many hydrodynamical models. The basic thesis of the model is that shear between the ambient fluid and the jet helps to transform one-dimensional flow into divergent multi-dimensional flow. Subsequently, the elevated momentum in the jet is available to expand the fluid in the divergent flow region. The main manifestation of this compressible process is not a significant difference in density (however, it is shown that, the pressure gradient term in the so-called incompressible Bernoulli equation is a compressible term) but a reduction in pressure causing the inflow, or entrainment or mixing, of ambient fluid into the jet.
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| PRESENTATION |
Photochemical Production of Reactive Oxygen Species By Constituents of Colored Dissolved Organic Matter and Coastal River Waters in the Southeastern United States |
01/24/2000
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Vaughan, P. P., N. V. Blough, AND R. G. Zepp. Photochemical Production of Reactive Oxygen Species By Constituents of Colored Dissolved Organic Matter and Coastal River Waters in the Southeastern United States. Presented at American Geophysical Union Ocean Sciences Meeting, San Antonio, TX, January 24-28, 2000.
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| Abstract:
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Using a previously developed method to measure OH production, formation rates were obtained for several water systems. Employing an amino-nitroxide probe and DMSO, an actionspectrum for the product consistent with the production of OH by quinone moieties within humic material was observed for Suwannee River fulvic acid. However, model competition
studies with 1,4-benzoquinones indicate that the product formed may not result from the
production of free OH but rather be due to a photosolvate which acts to hydroxylate certain
compounds. The quantum yield for the formation of this intermediate correlates with free
energy values for electron transfer from water to the excited triplet states of substituted
1,4-benzoquinones and 9,10-anthraquinones. This method is further applied to examine OH
production in whole filtered water and size fractionated samples from the Satilla River. The possible involvement of the photo-Fenton reaction in the production of OH will be discussed as it relates to changes in concentrations of hydrogen peroxide, Fe(II) and Fe(III).
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| PRESENTATION |
Photochemical Transformations of Dissolved Organic Matter in a Blackwater River |
01/24/2000
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Opsahl, S. P. Photochemical Transformations of Dissolved Organic Matter in a Blackwater River. Presented at American Geophysical Union Ocean Sciences Meeting, San Antonio, TX, January 24-28, 2000.
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We examined photochemical alterations of dissolved organic matter (DOM) from the Satilla River, a high DOC (10-40 mg/liter) blackwater river of southeast Georgia. Water samples were filtered to remove most organisms, placed in quartz tubes, and incubated under natural sunlight at ambient temperature or 5 degrees Celsius for a period of three weeks. We measured changes in UV/visible absorbance, dissolved oxygen, dissolved inorganic carbon (carbon dioxide and carbon monoxide), dissolved organic carbon, amino acids, and stable carbon isotopes. The DOM was degraded by both sunlight and microorganisms under these conditions and significant changes were observed in all measured parameters. These data will be presented with particular emphasis on the implications for biogeochemical cycling of riverine DOM.
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| PRESENTATION |
Modeling the Interaction of Agrochemicals With Environmental Surfaces |
03/26/2000
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Sawunyama, P. AND G. W. Bailey. Modeling the Interaction of Agrochemicals With Environmental Surfaces. Presented at 219th American Chemical Society National Meeting, San Francisco, CA, March 26-30, 2000.
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The interactions between agrochemicals and organo-mineral surfaces were studied using molecular mechanical conformational calculations and molecular dynamics simulations. Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), 2,4-D (1, 2-dichlorophenoxyacetic acid), and DDT (2,2-bis-(4-chlorophenyl)-1,1,1-trichloroethane) were selected as representative agrochemicals. Model natural organic compounds comprised an oxidized softwood lignin chain (I) generated from eight guaiacyl-propane units connected by b-O-4 bonds, a non-bonded inclusion lignin-carbohydrate complex in which a carbohydrate chain (II) was placed inside the broad helix (I), and b-cyclodextrin. A metal oxide, rutile TiO2, was chosen as the model mineral surface. The electrostatic interactions and hydrogen bonds were accounted for with atomic charges. The results show that the organic coating does not decrease sorption energies although the organic contaminants show a strong tendency to associate with the pristine mineral surface. The proposed binding mechanisms between the agrochemical and the natural organic, the agrochemical and the mineral surfaces and the agrochemical and the organo-mineral aggregate will be discussed.
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| PRESENTATION |
Interactions Between Photochemical and Microbial Decomposition in Modifying the Biological Availability and Optical Properties of Estuarine Dissolved Organic Matter |
01/24/2000
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Zepp, R. G., M. A. Moran, AND W. Sheldon. Interactions Between Photochemical and Microbial Decomposition in Modifying the Biological Availability and Optical Properties of Estuarine Dissolved Organic Matter. Presented at American Geophysical Union Ocean Sciences Meeting, San Antonio, TX, January 24-28, 2000.
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| Abstract:
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Direct photodecomposition and photochemically-mediated bacterial degradation (via photochemical modification of otherwise refractory DOM into biologically labile forms) provideimportant pathways for the loss of dissolved organic matter in coastal waters. Here we report
laboratory studies of the effects of sunlight exposure on the decomposition of DOM from a
coastal estuary in the Southeastern U.S. Results of these studies showed that direct
photodecomposition resulted in significant loss of carbon, absorptivity, and fluorescence, that
was accompanied by consistently positive net effects on biological degradation of the residual
DOM. The efficiency of DOC loss decreased with increasing light exposure, suggesting that a
significant fraction of the DOC may not be readily susceptible to decomposition by solar
radiation. In contrast, the loss efficiency of the UV absorbing component of the DOM(350 nm)
did not detectably decrease with increased light exposure. Direct photodecomposition also
resulted in a general decrease in fluorescence quantum yields and significant changes in the
excitation-emission matrix spectra of the DOM with decreases in the emission and excitation
maxima of the humic component. Biological decomposition following photobleaching at least
partially reversed changes in optical properties caused by direct photodecomposition.
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| PRESENTATION |
The Role of Temperature Disequilibrium in Monitoring Low Volatility Contaminant Migration |
06/25/2000
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Loux, N. T. The Role of Temperature Disequilibrium in Monitoring Low Volatility Contaminant Migration. Presented at Fourth International Symposium of Elements in Biological, Environmental and Toxicological Sciences, Whistler, Canada, June 25-July 1, 2000.
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| Abstract:
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Temperature disequilibrium is a common phenomenon within and among envirornnental media at local regional continental and global scales. The significance of temperature disequilibrium on low vapor pressure environmental contaminant migration has only rarely been addressed in the technical literature. A model describing the effects of diel atmospheric temperature variations on the rates of elemental mercury evasion from natural waters has been developed (Loux, 1999). Among other things, the approach relies on the estimation of non-isothermal Henry's law constants for Quantifying toxicant medium-specific chemical potentials under temperature disequ#ibrium conditions. Although applied to elemental mercury, the thermodynamic framework is applicable to any low volatility compound where sufficient background information is available. Findings from the present work relative to monitoring refractory and labile toxicant air/water exchange and modeling temperature-gradient-mediated contaminant migration will be discussed.
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| PUBLISHED REPORT |
Working With Whaem2000: Source Water Assessment for a Glacial Outwash Wellfield, Vincennes, Indiana. |
05/15/2000
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Kraemer, S. R., H. M. Haitjema, AND V. A. Kelson. Working With Whaem2000: Source Water Assessment for a Glacial Outwash Wellfield, Vincennes, Indiana. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-00/022 (NTIS PB2003-106822), 2000.
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| Abstract:
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This purpose of this document is to introduce the use of the ground water geohydrology computer program WhAEM for Microsoft Windows (32-bit), or WhAEM2000. WhAEM2000 is a public domain, ground-water flow model designed to facilitate capture zone delineation and protection area mapping in support of the State?s Wellhead Protection Programs (WHPP) and Source Water Assessment Planning (SWAP) for public water supplies in the United States. Program operation and modeling practice is covered in a series of progressively more complex representations of the wellfield tapping a glacial outwash aquifer for the city of Vincennes, Indiana. WhAEM2000 provides an interactive computer environment for design of protection areas based on radius methods, well in uniform flow solutions, and geohydrologic modeling methods. Protection areas are designed and overlaid upon US Geological Survey Digital Line Graph (DLG) or other electronic base maps. Base maps for a project can be selected from a graphical index map for the State that is posted on theWorldWideWeb. Geohydrologic modeling for steady pumping wells, including the influence of hydrological boundaries, such as rivers, recharge, no-flow boundaries, and inhomogeneity zones, is accomplished using the analytic element method. Reverse gradient tracelines emanating from the pumping center of known residence time are used to delineate the capture zones. WhAEM2000 has on-line help and tutorials.
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| PUBLISHED REPORT |
Exposure Analysis Modeling System (Exams): User Manual and System Documentation |
09/25/2000
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Burns, L. A. Exposure Analysis Modeling System (Exams): User Manual and System Documentation. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-00/081 (NTIS PB2003-106603), 2000.
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The Exposure Analysis Modeling System, first published in 1982 (EPA-600/3-82-023), provides interactive computer software for formulating aquatic ecosystem models and rapidly evaluating the fate, transport, and exposure concentrations of synthetic organic chemicals - pesticides, industrial materials, and leachates from disposal sites. EXAMS contains an integrated Database Management System (DBMS) specifically designed for storage and management of project databases required by the software. User interaction is provided by a fullfeatured Command Line Interface (CLI), context-sensitive help menus, an on-line data dictionary and CLI users guide, and plotting capabilities for review of output data. EXAMS provides 20 output tables that document the input datasets and provide integrated results summaries for aid in ecological risk assessments. EXAMS core is a set of process modules that link fundamental chemical properties to the limnological parameters that control the kinetics of fate and transport in aquatic systems. The chemical properties are measurable by conventional laboratory methods; most are required under various regulatory authority. When run under the EPA's GEMS or pcGEMS systems, EXAMS accepts direct output from QSAR software. EXAMS limnological data are composed of elements historically of interest to aquatic scientists world-wide, so generation of suitable environmental datasets can generally be accomplished with minimal project-specific field investigations. EXAMS provides facilities for long-term (steady-state) analysis of chronic chemical discharges, initial-value approaches for study of short-term chemical releases, and full kinetic simulations that allow for monthly variation in mean climatological parameters and alteration of chemical loadings on daily time scales. EXAMS has been written in generalized (N-dimensional) form in its implementation of algorithms for representing spatial detail and chemical degradation pathways. This DOS implementation allows for study of five simultaneous chemical compounds and 100 environmental segments; other configurations can be created through special arrangement with the author. EXAMS provides analyses of: Exposure: the expected (96-hour acute, 21-day and long-term chronic) environmental concentrations of synthetic chemicals and their transformation products,Fate: the spatial distribution of chemicals in the aquatic ecosystem, and the relative importance of each transformation and transport process (important in establishing the acceptable uncertainty in chemical laboratory data), and Persistence: the time required for natural purification of the ecosystem (via export and degradation processes) once chemical releases end. EXAMS includes file-transfer interfaces to the PRZM3 terrestrial model and the FGETS and BASS bioaccumulation models; it is a complete implementation of EXAMS in Fortran 90.
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| PUBLISHED REPORT |
Modeling Soil-Water Distribution of Aromatic Amines in Water Saturated Soil Systems |
04/01/2000
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Lee, L. S., C. T. Jafvert, H. Li, AND J. R. FabregaDuque. Modeling Soil-Water Distribution of Aromatic Amines in Water Saturated Soil Systems. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/S-99/005 (NTIS PB2001-101636), 2000.
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| Abstract:
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Research summarized in this report focuses on the abiotic interactions of aromatic amines with whole soils in aqueous systems. This work was initiated to improve our ability to predict the mobility of aromatic amines and their potential to contaminate groundwater, and to improve subsequent remediation of contaminated sites. The results of this work show that interaction of aromatic amines with soils during short times can be adequately predicted on a macro-scale assuming cation exchange as the primary mechanism and utilizing the pKa of the amine, soil cation exchange capacity, and soil-solution pH.
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