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2003 Progress Report: Contaminant Release During Removal and Resuspension
EPA Grant Number: R828773C004Subproject: this is subproject number 004 , established and managed by the Center Director under grant R828773
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: HSRC (2001) - South and Southwest HSRC
Center Director: D. Reible, Danny
Title: Contaminant Release During Removal and Resuspension
Investigators: Tomson, Mason B. , Kan, Amy T. , Thibodeaux, Louis J. , Valsaraj, Kalliat T.
Institution: Rice University , Louisiana State University - Baton Rouge
EPA Project Officer: Lasat, Mitch
Project Period: October 1, 2001 through September 30, 2006 (Extended to September 30, 2007)
Project Period Covered by this Report: October 1, 2002 through September 30, 2003
Project Amount: Refer to main center abstract for funding details.
RFA: Hazardous Substance Research Centers - HSRC (2001)
Research Category: Hazardous Waste/Remediation
Description:
Objective:Rice University Portion
During resuspension, generally, the largest physical-chemical effect with respect to heavy metal sorption is the change in redox of the freshly disturbed sediments. At the point of dredging, the sediments are suspended in the river bottom, and there is an immediate increase in solid surface area and corresponding immediate change in the physical-chemical parameters that characterize the water. Following these immediate changes, there will be several time scales that are applicable: (1) the slower redox processes; (2) the desorption kinetics; (3) the kinetics of iron oxide precipitation and fines production; and (4) the relative rates of redeposition of the fine particles. The objective of this portion of the research project is to understand the dynamics and kinetics of heavy metal release processes during sediment resuspension events.
Louisiana State University Portion
The Louisiana State University (LSU) group is attempting to develop a theory-based simple and practical model to track the metal release process kinetics. Data generated by the Rice University group will be utilized by the LSU group in model development, refinement, and testing. The objective of this portion of the research project is to develop an algorithm to estimate metal concentrations in solution emanating from the mud clouds produced during dredging. Being able to predict the concentrations of metals is key in evaluating aquatic organism exposure levels and uptake quantities both in the water column and in the bed-sediment surface layers.
Progress Summary:LSU Portion
A biphasic empirical model for organic chemicals released from suspended particles, first proposed by Karickhoff in 1980, has been used successfully by numerous investigators to interpret the release fractions and kinetics. A theory-based version of the biphasic model referred to as the "hockey stick model" was developed and is being used to interpret the empirical one.
Rice University Portion
In resuspension of contaminated sediments, heavy metals such as Pb, Cd, Cu, and As represent several special challenges and will be the focus of this Hazardous Substance Research Center (HSRC) research. Mercury (Hg) will not be a focus of this research for two reasons: (1) the U.S. Environmental Protection Agency (EPA) and others have several major research thrusts explicitly on the fate of mercury, and these efforts will be followed in this project; and (2) the chemistry of Hg is different from other heavy metals and should be studied separately. DiGiano, et al. observed that the dredging elutriate test (DRET) protocol corresponds reasonably well to field dredge tests for polychlorinated biphenyls (PCBs) and for other organic contaminants during dredging, but not for the heavy metals. This notion was further explained by Myers, et al.: "…but this approach is not recommended for application to release of dissolved metals during dredging because the rapid and pronounced change in redox and the complicated environmental chemistry of metals make equilibrium approaches highly unreliable and uncertain."
The overall objective of this research is to determine and quantify the processes responsible for heavy metal release during resuspension events based on key physical and physical-chemical variables such as particle size, aggregation status, total dissolved solids, total suspended solids (TSS), pH, redox, acid volatile sulfide (AVS), solution composition, and organic matter content in the sediment and overlying water. Five specific testing hypotheses are proposed:
1. Sorption and desorption of heavy metals from natural sediments are not the reverse of each other (i.e., sorption/desorption of toxic metals exhibits hysteresis),
2. Although there is a number of unique combinations of sediments, it is possible to identify a few key parameters that can be used to predict heavy metal release and thereby the potential for ecological exposure. We will simulate resuspension events in the laboratory, study the kinetics of heavy metal release during resuspension, and identify a few key parameters controlling contaminant transportation.
3. Heavy metal release has been found to be multiphasic, with one set of processes controlling the early resuspension and a completely different set of processes important at times in excess of a few hours. Both rate processes need further study.
4. Particle fines are released upon initial resuspension. These fines do not resettle rapidly, yet they contain many times the heavy metal load on a mg/g basis. These fines will facilitate the migration of many of the most dangerous heavy metals. Furthermore, these fines will impact the existing organisms. Understanding these issues will be a priority.
5. Lastly, the possibility to identify a potential remediation plan that can be used to prevent heavy metals release during resuspension events and dredging also will be investigated. Attention has been and will continue to be focused on the impacts of resuspension on fines versus settleable particles and short versus long time frames.
Approach
LSU Portion. This hockey stick model is a lumped-parameter version of the more complex model being developed by Center researchers Reible-Fleeger. The progress achieved in development and testing of the hockey stick model is presented as a meeting poster (Birdwell/Thibodeaux), and a manuscript is in the final stages of preparation (Birdwell, et al., 2003). Much is known about the aquatic chemistry behavior of halogenated organic compounds (HOCs); they are suspected to have simple and traceable desorption kinetics and thermodynamics of release. A model based on this suite of compounds provides a basis upon which to build a metal release kinetic process. The latter is suspected to be much more complex for the individual metals and may vary considerably between metals.
Rice University Portion. Most work has been conducted on Trepangier and Anacostia River sediments. Both sediments have been characterized for their reactive metal contents, metal distribution in various fractions by sequential extractions, AVS, and organic carbon (OC) analyses (see Table 1 and Figure 1). Both sediments contain significant concentrations of Zn, Cu, Ni, and Pb. Trepangier sediments also contained significant concentration of As. The Pb concentration in Trepangier sediment is 2.2 times greater than the EPA sediment quality guideline's probably effect concentration ([PEC], i.e., above which harmful effects are likely to be observed). Laboratory-scaled resuspension experiments were conducted, where pH, dissolved oxygen (DO), and microbial activities were either monitored or controlled, and the release of heavy metals in solution and suspended solids were analyzed to identify the cause and effect of various factors that control the release of heavy metals into the water body. The microbial activity was controlled by the addition of 0.01 M NaN3, and the anoxic condition was controlled by purging the sediment suspension with N2. Resuspension experiments, similar to the DRET, also were performed with various resuspension time of aeration and metal concentration in both the solution and suspended solids were analyzed to compare the heavy metal concentration in water column after 1 hour of settlement. Various anionic, nonionic, and cationic polymers were tested to study their effect on heavy metal release and fines settlement. The heavy metal release was tested with widely different pH, Eh profiles: (1) Trepangier, aerated (varying both Eh and pH); (2) Trepangier, anoxic (low Eh and neutral pH); (3) Trepangier, no microbes (varying Eh, neutral pH); (4) Trepangier, anoxic and pH adjusted (low Eh, varying pH); and (5) Anacostia, aerated (varying Eh, neutral pH).
| Sediments | Trepangier | Anacostia | Sediment Quality Guidelineb (mg/g) | ||
| Ions | Conc. (µg/g) |
Conc. (µmol/g) |
Conc. (µg/g) |
Conc. (µmol/g) |
|
| Fe | 88,296.5 | 1,582.4 | 16,647.4 | 298.34 | |
| Ca | 8,778.9 | 219.5 | 3,774.1 | 94.35 | |
| Mn | 862.2 | 15.7 | 252.3 | 4.60 | |
| Zn | 196.4 | 3.0 | 336.6 | 5.15 | 459 |
| Co | 7.6 | 0.1 | 16.9 | 0.29 | |
| Ni | 17.0 | 0.3 | 31.8 | 0.54 | 48.6 |
| Cu | 23.0 | 0.4 | 79.0 | 1.24 | 149 |
| Pb | 281.3 | 1.4 | 116.3 | 0.56 | 128 |
| S | 15,274.3 | 477.3 | 734.1 | 22.94 | |
| As | 22.3 | 0.3 | 1.5 | 0.02 | 33 |
| P | 6,799.8 | 219.3 | 1,747.5 | 56.37 | |
| AVS | 130.0 | 5.00 | |||
| OC (%) | 8.1 | 3.70 | |||
| a Sediments were digested with 1 N HCl for 24 hours. Amorphous and crystalline
Fe and Mn oxyhydroxides, carbonate, and hydrous aluminosilicates should have
been dissolved by this digestion procedure. b The values are sediment quality guidelines determined by the U.S. EPA (U.S. EPA 905/R-00/007, June 2000) that reflect PECs. |
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Figure 1. Plot of the Fractional Distribution of Metal Ions, Sulfur, and As in Exchangeable, Carbonate, Oxide, and Organic Matter Phases
Outputs/Accomplishments
LSU Portion. Based on published material, an extensive database exists for the desorption kinetics on numerous HOCs and application or the empirical biphasic model. Detailed results of the analysis of these data are presented in the Birdwell/Thibodeaux poster. Key findings are: (1) The range of numerical values of the fast and slow desorption rate constants are very different numerically, but are remarkably uniform. They appear to be independent of the sediment particle sizes and chemical KOC. (2) The fraction desorbed that is loosely bound or tightly bound appears to be very sediment specific.
Key developments of the hockey stick model are as follows: (1) A two-adsorbent patch chemical release model comprised of adsorbate diffusion correctly mimics the general shape of the biphasic model. (2) Both solid phase diffusion and the porewater diffusion mechanism seemed to be involved in the release kinetics process. Their relative roles and the importance of the equilibrium desorption is still under investigation.
Rice University Portion. From several testings, we have concluded that heavy metal release is driven by a complicated sequence of reactions, redox, biological activities, pH-driven desorption/dissolution, precipitation of iron oxide and fines productions, and readsorption of certain heavy metals. The following is a summary of key findings:
• It appears that there are three distinct categories of heavy metals (1: Mn, Zn, Ni, Co; 2: Fe, Pb, As; and 3: Cu) with respect to release profile during aeration versus acid dissolution to a final pH of 4.6. The different fate of these heavy metals is related to the relative affinity of heavy metals to iron oxide and/or organic matter after oxidation. This classification is consistent with the fractional distribution of the sequential extraction.
• Microbial activities significantly enhanced AVS oxidation kinetics during aeration and accelerated Mn, Zn, Ni, and Co release. However, Pb, Cu, and As release may be quenched by the iron oxide fine precipitation.
• Higher Pb concentration was observed in the unsettled suspended fines.
• Some polymers effectively reduced suspended fines in solution and could significantly reduce both heavy metals and organic pollutant exposure during resuspension events such as dredging.
In Figure 2, the changes in pH, Eh, and heavy metal releases during resuspension under anaerobic versus aerated condition at a sediment concentration of 10 g/L are compared. When Trepangier sediment was resuspended in anoxic conditions, heavy metal release was negligible. However, when the Trepangier sediment suspension was exposed in air, a dramatic increase in heavy metal release was observed after 2 days of aeration. Simultaneously, we observed a drastic change in solution pH and Eh (see Figure 2). Along with the changes in redox and pH was the dissolution of Fe, Mn, Zn, Ni, Co, Cu, Pb, and As. However, Fe was subsequently oxidized and precipitated as iron oxide. Presumably, because of adsorption to the newly formed iron oxide phase, the dissolved Pb, Cu, and As concentrations also were reduced drastically from the solution phase following the reduction of Fe concentration.
Figure 2. Comparison of pH, Eh, Fe, Mn, Heavy Metals, and As Release Under Aerobic Versus Anoxic Conditions. The sediment is from Trepangier Bayou, and the sediment concentration is 10 g/L. The anoxic condition is controlled by N2.
It was later observed that the drastic change in pH and Eh after 2 days of aeration was because of microbial activities as shown in Figure 3, where the sediment concentration was 20 g/L. When Trepangier sediment suspension was aerated in the presence of a bacteria inhibitor, NaN3 (0.01 M), little changes in pH and a moderate change in Eh occurred, but large changes in pH and Eh were observed after 1 day in the system aerated in the absence of NaN3 (see Figure 3). Note that the pH and Eh change is more drastic than that shown in Figure 2, presumably because of higher sediment concentration. Apparently, the presence of Fe- and S-oxidizing bacteria accelerate the AVS oxidation kinetics during aeration, and the induction time for the microbial activity is between 1 to 2 days. The microbial activity was accompanied by the reduction of dissolved total organic carbon concentration (TOC). With the microbial activity, the large release of group one metals (Mn, Zn, Ni, and Co) was observed. Contrary to the first group of heavy metals (Mn, Zn, Ni, and Co), more Pb and Cu were desorbed into the microbial-free condition than in the presence of microbial activity during the first 4 days of resuspension. This is probably because of the adsorption of Pb and Cu onto the newly formed iron oxide at around 2-3 days, when microbes are present. Pb concentration in the case of microbes eventually exceeded that in the case of no microbes activity. This is likely because of Pb desorption at the lower pH. However, Cu concentration remained high for the no-microbes case. Because Cu is known to form a strong complex with dissolved organic matter, it is proposed that Cu complexation with TOC contributed to the higher Cu concentration in solution in the absence of microbes.
Figure 3. Comparison of pH, Eh, Fe, S, TOC, Heavy Metal and As Release Kinetics in the Presence and Absence of Microbial Activities and Aerobic Condition. The sediment is from Trepangier Bayou, and the concentration is 20 g/L. The microbial activity is inhibited with NaN3 in the no-microbe case.
It is proposed that the lower pH, instead of further oxidation, because of microbial activity contributed to the dramatic increase in heavy metal concentration. Another set of experiments was conducted by comparing a set of anoxic resuspension experiments, whereby the pH was artificially lowered by HCl to the aerated system, and the pH was naturally reduced by the coupled redox/microbial activity (see Figure 4). In Figure 4, the Eh, Fe, Mn, Zn, Ni, Co, Pb, As, and Cu versus pH solution of the anoxic and aerated systems were plotted. In the anoxic condition, iron oxide precipitation is minimized. Interestingly, a significant amount of Mn, Zn, Ni, Co, and As are dissolved at the lower pH in both the aerated and anoxic conditions. However, Fe concentration is significantly lower in the aerated system, presumably because of oxidation and precipitation of iron oxide. Both Pb and Cu are dissolved to a higher concentration at neutral pH in the aerated system than in the anoxic condition, indicating that Pb and Cu dissolution are more strongly influenced by redox at neutral pH. However, Pb, As, and Cu are strongly adsorbed to iron oxide in the aerated system, which causes their concentration to reduce at lower pH. Furthermore, in a well-buffered system, oxidation of AVS alone during sediment resuspension does not induce heavy metal dissolution. An example of such a system is the Anacostia River sediment. The Anacostia sediment contains less sulfur-containing mineral, and the suspension is well buffered. Little heavy metal is released upon the aeration of the resuspended Anacostia (see Figure 5).
Figure 4. Comparison of Eh, Fe, Heavy Metal and As Release Kinetics as a Function of pH During Resuspension Experiments Where the pH Was Either Controlled by the Addition of HCl in the Anaerobic Condition or by Coupled Redox/Microbial Activities in the Aerated Condition. Trepangier sediment (10 g/L) was used in the resuspension experiment.
Figure 5. Comparison of Heavy Metal Release From Trepangier and Anacostia Sediments Under Aerated Resuspension Experiments
During sediment resuspension, a large amount of suspended fines are either mobilized because of disturbance or are formed during oxidation. These fine particles often are a source of elevated heavy metal concentration because of their high surface area and more reactive surfaces. Therefore, controlling fine settlement should be important in the study of sediment resuspension and its impact on the water column quality. We observed that Fe colloids were formed during the oxidation process. Further resuspension experiments, using a DRET-type protocol, were conducted where aeration was performed for 1 hour, 24 hours, and 3 days. The sediments were allowed to stand for 1 hour before aqueous samples were measured for both the amount of TSS and the aqueous and TSS phase heavy metal composition. In Table 2, the TSS heavy metals and As concentrations in the water column are listed. As expected, most of the water column heavy metal concentrations are contributed by that associated with TSS. In Figure 6, the heavy metal concentrations in TSS versus the heavy metal concentration in the bulk sediment are compared, where the ratios of heavy metal in TSS and bulk sediment are plotted. Some of the heavy metal concentrations in TSS are similar to that of bulk sediments. During short resuspension between 1 to 24 hours, Pb, Cu, Ni, and Zn concentrations in TSS could be enriched by a factor of 1.5. In Figure 7, the Pb concentration of the bulk Trepangier and Anacostia sediments and the Pb concentrations of the various TSS preparations are plotted. The horizontal line is the EPA sediment quality guidelines (SQG). As noted, the Pb concentration in the TSS is enriched above SQG for Anacostia sediments, although the bulk sediment Pb concentration is below SQG. Note that TSS is expected to have much higher surface area than bulk sediment, and the heavy metals on TSS are presumably bioavailable. Pb bioavailability in TSS could be much higher than that defined in SQG.
Table 2. pH, Eh, TSS Concentration, and Selected Heavy Metal and As Concentrations in the Water Column After 1 Hour Settling Time Following a DRET Procedure
| Sediment | Aeration time (hour) | Settling time (hour) | TSS (g/L) |
pH | Eh (mv) |
Zn (mg/L) |
Co (mg/L) |
Ni (mg/L) |
Cu (mg/L) |
Pb (mg/L) |
As (mg/L) |
| Anacostia | 1 | 1 | 0.672 | 7.51 | -217.8 | 213.27 | 11.47 | 30.82 | 62.59 | 67.66 | 2.03 |
| Anacostia | 24 | 1 | 2.079 | 7.52 | -223.7 | 841.46 | 37.98 | 69.25 | 222.33 | 368.97 | 1.94 |
| Anacostia | 72 | 1 | 2.353 | 7.35 | -205.0 | 1,016.69 | 42.09 | 79.28 | 241.41 | 431.05 | 2.08 |
| Anacostiaa | 1 | 1 | 0.0146 | 7.41 | -259.0 | 7.03 | 1.15 | 0.39 | 2.23 | 1.99 | 1.17 |
| Trepangier | 1 | 1 | 1.143 | 7.46 | -236.8 | 300.40 | 9.35 | 33.65 | 40.42 | 241.60 | 27.18 |
| Trepangier | 24 | 1 | 2.169 | 6.34 | -225.0 | 528.13 | 18.34 | 38.70 | 75.66 | 697.63 | 37.16 |
| Trepangier | 72 | 1 | 0.424 | 4.25 | -133.0 | 1,280.40 | 32.91 | 48.57 | 16.44 | 117.59 | 7.27 |
| Trepangiera | 1 | 1 | 0.183 | 7.48 | -268.9 | 55.37 | 7.43 | 1.97 | 9.98 | 43.64 | 6.32 |
| a2.2 ppm of PDDAC was added to the Anacostia sediment, and a mixture of 6 ppm polyacrylamide and 5 ppm of PDDAC is added to the Trepangier sediment. | |||||||||||
Figure 6. Plots of the Ratios of the Metal and As Concentration on TSS to Bulk Sediment Concentrations at Three Resuspension Times of 1 Hour, 1 Day, and 3 Days Using a DRET Test
Figure 7. Comparison of Pb Concentration in Bulk Sediments and in TSS After 1 to 3 Days of Aeration of Trepangier and Anacostia Sediments. The horizontal line is the EPA sediment quality guideline limit for Pb concentration (PEC).
To control fine migration during dredging, we have studied the effect of polymers on fine control. We have observed that a polyacrylamide (150,000,000 MW) at as low as 2.5 mg/L causes the accelerated sedimentation of suspended fines after resuspensions of oxic sediment. The polymer has been tested with three sediments (Utica, Trepangier, and Anacostia) and several ionic strengths. A flocculation rate of approximately 1.28 mm/second is observed with 2.5 mg/L polyacrylamide. The flocculation rate is at least three orders of magnitude (103 x) faster with polymer than without polymer. The primary impact of the polymer is in the reduction of suspended fines, although it also has some effect on the complexing and removal of Pb and Cd from the solution phase. The heavy metal concentration in suspension can be reduced significantly by settling the resuspended particles quickly with the aid of a polymer. In Figure 8, the water column Pb concentrations of four experiments are plotted, where the aeration time is 1, 24, and 72 hours and settling time is 1 hour. In one of the 1-hour experiments, 2.2 ppm of poly(dialyl dimethyl ammonium chloride) (PDDAC) was added to the Anacostia sediment, and a mixture of 6 ppm polyacrylamide and 5 ppm of PDDAC was added to the Trepangier sediment. The TSS concentration was reduced by more than 6 and 40 times in the presence of polymers for Trepangier and Anacostia sediments, respectively. Note that the selection of polymers and concentrations have not been optimized. Such techniques might be very useful for dredge material confinement and management.
Figure 8. Comparison of Pb Concentration in the Water Column Following 1, 24, and 72 Hours Aeration and 1 Hour Settling. One set of data included experiments amended with polymers to enhance settling, where 2.2 ppm PDDAC is used for the Anacostia sediment and 6 ppm polyacylamide and 5 ppm PDDAC are used for the Trepangier sediment.
Last year, several papers and conference proceedings were submitted for publication in Environmental Science and Technology, Ground Water, and Ground Water Monitoring Review. Two manuscripts have been accepted by Environmental Science and Technology and Ground Water for publication. In the Environmental Science and Technology paper, the adsorption/desorption of heavy metal on sediment was reported. It is observed that a small fraction (~ 0.5 mg/g) of adsorbed Pb and Cd does not desorb reversibly, similar to what we have observed for the organic contaminants.
In conclusion, we have observed that the relative composition of FeS, calcite, and Fe- and S-oxidizing bacteria are significant in controlling various heavy metal release during sediment resuspension. Most of these impacts are more important to long-term exposure in a stagnant water body than to the short-term resuspension that occurs in a time frame of a few minutes to hours. Nevertheless, it is important to understand their interrelationship to better understand the fate of heavy metal during resuspension and dredge operations. A paper to summarize these observations will be ready in the near future.
References:
Saulnier I, Mucci A. Trace metal remobilization following the resuspension of estuarine sediments: Saguenay Fjord, Canada. Applied Geochemistry 2000;15(2):203-222.
Future Activities:More work is needed to determine the generality of the metal classifications. We have observed rather slow release of most heavy metals in the presence of high AVS-containing sediments, but others (e.g., Saulnier and Mucci, 2000) have observed release times of a few hours or less for lower AVS-containing sediments ratios. This might suggest that as sediments are suspended and diluted in a water body, the more diluted sediments might release heavy metals on the time scales of dredging and resettling. We have observed that polymers that worked for the oxic sediment behave differently for the anoxic sediment and for different sediments. When anoxic sediments were used, we observed that a 2.2 ppm of PDDAC is better for Anacostia sediment, while a mixture of 6 ppm polyacrylamide and 5 ppm of PDDAC is needed to cause TSS to settle in Trepangier sediment. Very little information regarding polymer sediment interaction is understood, and the area of research appears to have considerable benefit to control dredging in an environmentally safe manner.
Proposed Efforts Over the Next Year
LSU Portion. The plan for 2003 is to focus on the short-term release
process. We will apply the hockey stick model to the kinetic data for the 
24
hour time period when pH remains fairly uniform and conditions are aerobic.
A working hypothesis at this juncture is that the quick release/mixing of particles
and water near the dredge head and in the departing mud cloud maintains near
constant (i.e., background water) pH and O2 conditions.
Data for anionic conditions will be factored in as well. The outcome of using
this data will be more or
less a "litmus test" for the appropriateness of the hockey stick
model for use in metals release. However, a review of the available short-term
release data appears to support the general hockey stick model approach. In
conjunction with the Rice University group, the development of a modified DRET
test will be explored. The buildup of the "chemical soap" in the
DRET test solution does not truly mimic the continuing mixing/dilution of freshwater
with the particle mass. In other words, dilution occurs with time as the mud
cloud moves downstream; it does not in the DRET experiment. Providing an infinite
metal co-ion/counter ion sink by introducing an ion exchange resin into the
DRET protocol may mimic this dilution process and yield more realistic release
kinetics while maintaining a fixed solids-to-water (s/w) source strength ratio.
Control of this s/w parameter is key for an unambiguous interpretation of the
release kinetics.
Beyond 2003, the LSU Principal Investigators will be involved with the U.S. Army Corps of Engineers in another research project having to do with collecting field data at environmental dredging sites. The focus of this Dredging Operations Environmental Research (DOER) Project is on the emissions of organic chemicals to air generated by the dredging operations and related processes; however, the water column concentration data are a key observable. The chemical release kinetics (particles-to-water) are needed for the DOER work so that the objectives of acquiring field data on metal concentrations in water for the HSRC project in 2003 and 2004 may dovetail nicely into the DOER project plans.
Rice University Portion. The fundamental overall goals of this research remain as stated in the original proposal: to understand the impact of dredging on heavy metal release during resuspension and subsequent settling. The research is designed around three tasks: resuspension experiments, model systems, and controlling contaminant release.
We will conduct resuspension experiments on fresher sediments with distinct variation in sediment character such as AVS, carbonate content, etc. Additional uncontaminated and contaminated sediments are obtained from rivers or bayous in Louisiana coordinated by Louis Thibodeaux. Sediment samples and redox conditions are preserved as undisturbed as possible. Associated or overburden water either will be used directly or will be simulated in the laboratory. The impact of known changes in sediment/solution conditions during resuspension will be simulated with these field sediments, including redox and DO, pH, ionic strength, and temperature. Specifically, the change in composition and quantities of unsettleable fines during resuspension will be characterized thoroughly.
Based on results from the first 2 years of study, emphasis will be placed on the central role of redox processes in controlling the fate of heavy metals during dredging. Specifically, it has been observed that even redox systems release fewer heavy metals when well buffered. Many of the redox processes are subject to cycling from anoxic to aerobic by changes in DO, bacterial activity, and light effects. All of these processes are potentially active in many typical dredging conditions as the sediments migrate up and away from the bottom, are consumed by extant organisms, and possibly resettle. Some of the sediments will spend sufficient time in different environments to cause redox changes and concomitant changes in heavy metal availability. The standard DRET test is still our base test, but added variations designed to simulate a stream, bayou, etc. better also will be conducted.
There has been considerable interest in using AVS as a sole sediment quality guideline for dredging. Our studies have suggested that heavy metals fall into three categories, depending on in which compartment they are contained. We will compare these two classification schemes.
We will model the mobility of heavy metal release during the resuspension event using a few predominant mechanisms. Once the range of interest for a particular contaminant-solid combination has been identified, the method of "constant composition" desorption will be used for a few combinations to obtain precise stoichiometry, kinetics, and equilibrium information at a fixed-chemical potential driving force. Key samples will be used for extensive characterization by modern surface methods such as atomic force microscopy and extended range x-ray absorption fine structure.
More experimental and theoretical modeling will be conducted to examine the impact of biological processes and films on the availability of heavy metals. Some of this work will be conducted in the next task topic of mitigating the release of heavy metals by various methods. This will require both thermodynamic and kinetic models to better understand the induction and inhibition effects.
We will investigate the interactions between polymers and priority contaminants (heavy metals and organic pollutants) and test the potential use of polymers to reduce the mobility of organic and inorganic pollutants during sediment resuspension events. Testing also has demonstrated that several of these additives also can reduce the release of polycyclic aromatic hydrocarbons and other organic contaminants; this will be tested further. It appears that heavy metals in the sediments from Louisiana can be classified as to their predominant compartments for sorption, exchangeable, metal oxide, organic matter, etc. Therefore, more explicit testing will be conducted with respect to the impact of additives on the various compartments and the effect of biological films of this efficacy; it is suspected that some additives will be effective in reducing heavy metal availability in clean sediments, but in the presence of biofilms, other components, such as surfactants, might be needed.
The relative interplay between immediate physical-chemical changes, redox, heavy metal desorption, and redeposition for real sediments will be modeled by changing one parameter at a time. Change in solution and solid-surface redox is expected to be the most important parameter controlling heavy metal release during dredging. How this redox varies and alters the kinetics of heavy metal release is not known, but this is probably related to sediment properties such as sulfide/oxide content and to sediment organic matter. Once key descriptors have been identified, simplified assays and predictors will be developed for routine use. The final hypothesis to be tested is that sorption and desorption of heavy metals can be modeled using readily available or measurable properties of sediments and dredged materials, along with properties of potentially impacted surface water bodies. Understanding the key physical and chemical parameters that affect heavy metal desorption during dredging and resuspension will enable regulators and field practitioners to use only a few key sediment/water parameters and reliably predict the environmental risk in specific dredging operations.
At the end of next year's research, we will be in a position to test our models and best treatment options in the field. Laboratory studies and modeling will be to a point where we will propose to test our physical, chemical, and transport models at a field site. For this reason, effort will be spent identifying such a site with HSRC, Scientific Advisory Committee, and LSU guidance.
Journal Articles on this Report: 5 Displayed | Download in RIS Format
| Other subproject views: | All 21 publications | 6 publications in selected types | All 6 journal articles |
| Other center views: | All 260 publications | 82 publications in selected types | All 61 journal articles |
| Type | Citation | ||
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Cheng X, Kan AT, Tomson MB. Naphthalene adsorption and desorption from aqueous C60 fullerene. Journal of Chemical and Engineering Data 2004;49(3):675-683. |
R828773 (Final) R828773C004 (2003) R831718 (2005) |
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Cong L, Kan AT, Tomson MB. A rapid method to characterize the desorption resistant fraction of sediment-sorbed organic contaminants. Ground Water Monitoring and Remediation. |
R828773C004 (2003) |
not available |
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Gao Y, Kan AT, Tomson MB. Critical evaluation of desorption phenomena of heavy metals from natural sediments. Environmental Science & Technology 2003;37(24):5566-5573. |
R828773 (Final) R828773C004 (2002) R828773C004 (2003) |
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Gao Y, Wahi R, Kan AT, Falkner JC, Colvin VL, Tomson MB. Adsorption of cadmium on anatase nanoparticles—effect of crystal size and pH. Langmuir 2004;20(22):9585-9593. |
R828773 (Final) R828773C004 (2003) R831718 (2005) |
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Kan AT, Fu G, Tomson MB. Effect of methanol and ethylene glycol on sulfates and halite scale formation. Industrial & Engineering Chemistry Research 2003;42(11):2399-2408. |
R828773 (Final) R828773C004 (2003) |
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labile fraction, nonlabile fraction, desorption kinetics, adsorption, desorption, resuspension, heavy metal, pH, redox potential, analytical chemistry environmental microbiology, microbiology, molecular biology, genetics, polymer, contaminated sediments, sediment resuspension, dredge, storm events, waste, water, analytical chemistry, environmental microbiology, microbiology, molecular biology, genetics, hazardous, hazardous waste, atomic force microscopy, AFM, bioavailability, biodegradation, bioremediation, bioremediation of soils, contaminated sediment, contaminated soil, dewatering, dredged sediments, dredging, kinetics, microbial degradation, phytoremediation, resuspension. , Water, Scientific Discipline, Waste, RFA, Analytical Chemistry, Hazardous Waste, Environmental Engineering, Contaminated Sediments, Hazardous, bioavailability, dredged sediments, biodegradation, microbial degradation, phytoremediation, atomic force microscopy, dewatering, kinetcs, contaminated sediment, contaminated soil, bioremediation of soils, bioremediation, resuspension, vegetative dewatering
Relevant Websites:
http://www.hsrc.org
http://www.sediments.org
Progress and Final Reports:
2002 Progress Report
Original Abstract
Main Center Abstract and Reports:
R828773 HSRC (2001) - South and Southwest HSRC
Subprojects under this Center:
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R828773C001 Bioturbation and Bioavailability of Residual, Desorption-Resistant
Contaminants
R828773C002 In-Situ Containment and Treatment: Engineering Cap Integrity
and Reactivity
R828773C003 Phytoremediation in Wetlands and CDFs
R828773C004 Contaminant Release During Removal and Resuspension
R828773C005 HSRC Technology Transfer, Training, and Outreach