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Novel and Nontraditional Use of Stable Isotope Tracers To Study Metal Bioavailability from Natural Particles

U.S. Geological Survey, MS 496, 345 Middlefield Road, Menlo Park, California 94025, United States
Environ. Sci. Technol., 2013, 47 (7), pp 3424–3431
DOI: 10.1021/es400162f
Publication Date (Web): March 4, 2013
Copyright This article not subject to U.S. Copyright. Published 2013 by the American Chemical Society
OpenURL UNIV OF NORTH TEXAS

 Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Abstract

Abstract Image

We devised a novel tracing approach that involves enriching test organisms with a stable metal isotope of low natural abundance prior to characterizing metal bioavailability from natural inorganic particles. In addition to circumventing uncertainties associated with labeling natural particles and distinguishing background metals, the proposed “reverse labeling” technique overcomes many drawbacks inherent to using radioisotope tracers. Specifically, we chronically exposed freshwater snails (Lymnaea stagnalis) to synthetic water spiked with Cu that was 99.4% 65Cu to increase the relative abundance of 65Cu in the snail’s tissues from ∼32% to >80%. The isotopically enriched snails were then exposed to benthic algae mixed with Cu-bearing Fe–Al particles collected from the Animas River (Colorado), an acid mine drainage impacted river. We used 63Cu to trace Cu uptake from the natural particles and inferred their bioavailability from calculation of Cu assimilation into tissues. Cu assimilation from these particles was 44%, indicating that 44% of the particulate Cu was absorbed by the invertebrate. This demonstrates that inorganic particulate Cu can be bioavailable. The reverse labeling approach shows great potential in various scientific areas such as environmental contamination and nutrition for addressing questions involving uptake of an element that naturally has multiple isotopes.

Introduction

Tracers are invaluable tools to investigate the fate of minerals and trace elements in various biological systems such as cell cultures, animals, and humans.(1-3) In environmental toxicology, nutrition, and biomedicine, tracers are commonly used to characterize the absorption, excretion, transport, and transformation of trace metals,(2-10) major cations, and nutrients.(1, 11-13) The most common types of tracers are radioisotopes(14) and enriched stable isotopes.(15) Both share similar advantages such as low detection limits and the possibility to discriminate tracer from background and to work with multiple isotopes for some elements. However, only γ-emitting radiotracers allow for the repeated measurement of the tracer on the same unit (e.g., cell, individual) as analyses are nondestructive. However, complicated logistics, handling, and waste issues limit their use to laboratories that have trained handlers and can maintain permits. In addition to health and safety hazards associated with radioactivity, the lack of suitable radioisotopes can be a problem for the study of elements such as Cu for which radioisotopes either are too difficult to prepare (e.g., 67Cu) or have half-lives too short (e.g., 64Cu t1/2 = 12.7 h) for proper study design (see Croteau et al.(2) for more detailed comparison of advantages and disadvantages of both tracer approaches). Enriched stable isotopes have the potential to overcome many of the shortcomings of radioactive tracers. Their application is growing rapidly as a result of new developments in mass spectrometric instrumentation, especially inductively coupled plasma mass spectrometry (ICP-MS).(2, 4, 7, 8, 10, 15)
In most applications of tracers in biological systems, however, the proper labeling of the substance under study is complex. For example, a major challenge to studying the bioavailability of metals from natural particles is posed by the difficulty to properly label natural particles. Typically, labeling time is short, which favors sorption of the label onto particle surfaces.(16) But the chemical speciation and physical location of metals within a particle can vary greatly. In addition to sorption, metals can be coprecipitated with manganese and/or iron oxides, occluded in aggregates of colloidal particles, incorporated into mineral structures, or trapped under layers of organic matter. Systematically labeling each of these geochemical phases is impossible, yet they can all influence metal bioavailability. Moreover, the age of the metal–particle association plays a crucial role in controlling metal bioavailability as metals can redistribute over time to more resistant phases.(17) Aggregation of colloids over time can also limit the rate of desorption of metals.(18) Equilibration time further determines the partitioning of metals between sediment particles and the dissolved phase. For example, short equilibration time and high spiked metal concentrations can alter metal exposure pathways, resulting in flawed estimations of metal bioavailability.(19) Whether an added tracer and the background metal it represents are similarly distributed among binding sites also remains uncertain in most cases. For example, high concentrations of an enriched stable metal isotope tracer might shift the distribution of metals from its native state and as such misrepresent metal bioavailability. Thus, unless synthetic particles are prepared using a tracer to assess the influence of a specific geochemical phase (e.g., 65Cu bound to colloidal hydrous ferric oxides(8)) or natural particles are allowed to age in the presence of a tracer for a period of time representative of the metal–particle contact time in nature, the most basic assumption of a tracer study is rarely met. That is, a tracer must behave in exactly the same way as the natural metal it is intended to represent.(14)
To circumvent these problems, we devised a novel tracing approach that involves enriching test organisms with an isotope of low natural abundance of the element under study prior to the onset of an experiment. Conceptually, the procedure reverses the labeling from the “source” to the “recipient”, such that the test organism is artificially enriched with a rare isotope of the element under study. The source is not altered by labeling and thus is studied in its natural state. Subsequent exposure to the element from the source shifts the isotopic ratio of the element in the test organism toward its natural isotopic ratio. Here we demonstrate the technique for copper (Cu) and show its application to characterize Cu bioavailability from natural inorganic particles. Specifically, we chronically exposed freshwater snails to enriched 65Cu to artificially increase the abundance of the less common Cu isotope (65Cu) in the snail’s soft tissues to a point where most of the snail’s background Cu is 65Cu instead of 63Cu. The relative abundances of Cu natural isotopes are 0.692 for 63Cu and 0.309 for 65Cu in the standard reference material NIST 976 (commercial metal).(20) We first show that the reverse labeling has no measurable effect on growth. We then show that following a pulse-chase exposure to environmentally relevant concentrations, Cu uptake from natural inorganic particles induces detectable changes in the Cu isotopic ratios of soft tissues of isotopically enriched test animals. We provide equations to convert isotope ratios into accumulated metal concentrations, which were then used to determine biokinetic rate constants and infer Cu bioavailability. This novel “reverse labeling” technique provides a means to simply and directly assess the bioavailability of unaltered natural inorganic particles, which addresses a long-standing uncertainty in the literature.

Materials and Methods

Isotopically Enriched Snails
Freshwater snails (Lymnaea stagnalis) were reared in the laboratory in a 40 L glass tank filled with 20 L of moderately hard (MOD) water.(21) Eight weeks prior to experiments, snails of a restricted size range (i.e., soft tissue dry weight of <1 mg) were transferred to an 8 L glass aquarium filled with MOD water spiked with isotopically enriched 65Cu (99.4% Trace Sciences) to achieve a total Cu concentration of 10 μg L–1. Snails were fed lettuce ad libitum during the exposure period. Medium was replaced every 11–12 days.
Animas River Particles (ARP)
Particles were harvested in September 2006 from the Animas River (Colorado) ∼0.8 km downstream of its confluence with Cement Creek by concentrating the particulate fraction from 35 L of river water to 1 L by tangential flow ultrafiltration using a 10 kDa filter (2 nm effective pore size).(22) In samples collected from Cement Creek upstream of the confluence at this time, ∼50% of the total Fe was in the particulate phase, with little measurable Al (∼4%) and no Cu in the particulate phase (>10 kDa). After mixing and neutralization of Cement Creek water (pH 4.1) with circumneutral Animas River (pH 7.5) during transport to the sampling point, metal concentrations in the ultrafiltrate indicate that precipitation of the remaining dissolved Fe, nearly complete precipitation of Al, and ∼50% sorption of Cu to colloidal phases had occurred (Table S1, Supporting Information). Cement Creek comprises about 22% of the discharge to the Animas River and about 87, 95, and 71% of the total load of Fe, Al, and Cu, respectively. A detailed description of this site and colloid formation in the confluence can be found in Schemel et al.(22)
Particles were transported on ice to the laboratory where they were concentrated by settling and centrifugation and then stored at 4 °C. Total metal concentrations of the ARP were determined by ICP-OES analysis of a split of the recovered particles after drying and digestion in nitric acid (Table S1, Supporting Information). Prior to the uptake experiments, the particles were resuspended in 30 mL of the ultrafiltrate. The suspension was subsampled and diluted with MOD water to achieve a Cu concentration of 720 μg L–1.
Uptake Experiments
To characterize the uptake of Cu from particles entrained with food, we used the benthic diatom Nitzschia palea as a food source. Algae were grown axenically in an S-diatom medium.(23) They were harvested onto 1.2 μm Isopore membrane filters (Millipore) and washed with soft (SO) water(21) to make algal mats. We employed the protocol described by Croteau et al.(24) to present the algae in the form the snails would ingest. Briefly, algae were resuspended into a 50 mL acid-washed Falcon tube filled with MOD water amended with different volumes of ARP. After a short gentle mixing (<1 min), the diatoms mixed with the ARP were harvested onto 1.2 μm Isopore membrane filters. Analysis of filtrates showed that the majority of ARP was retained on the filters (73–100% recovery of the Cu and Fe initially added). Small sections of the filters holding the diatoms mixed with the ARP were sampled, dried for 24 h at 40 °C, and weighed prior to metal analysis (Table S2, Supporting Information). The weight of diatoms was corrected for the mass of ARP on the filters to get Cu (μg) per gram of diatoms. The remaining filters were offered as food to L. stagnalis.
For each treatment, eight isotopically enriched 65Cu snails were exposed to diatoms amended with ARP for 6 h in 150 mL acid-washed polypropylene vials partially submerged in a 40 L glass tank. Exposure was shorter than gut residence time (∼22 h).(25) Specifically, the animals were allowed to ingest a mass of food mixed with ARP, then removed, rinsed with MOD water, placed individually in acid-washed enclosures, and fed uncontaminated food (lettuce) ad libitum for 48 h. After depuration, snails were removed from each enclosure and frozen. The feces produced by each snail were collected in acid-washed Teflon vials and dried for 48 h at 40 °C. Aliquots of water (n = 3) were taken immediately after the dietary exposure, as well as at the end of depuration. Water samples were acidified with concentrated nitric acid.
Sample Preparation and Analysis
To minimize inadvertent metal contamination, labware, vials, and Teflon sheeting were soaked for at least 24 h in acid (15% nitric and 5% hydrochloric), rinsed several times in ultrapure water, and dried under a laminar-flow hood prior to use. Partially thawed L. stagnalis were dissected to remove soft tissue, placed individually on a piece of acid-washed Teflon sheeting, and dried at 40 °C for 3 days. Dried snails, feces, and diatoms were weighed and digested in concentrated nitric acid, following the protocol described in Croteau et al.(24) Similar weight samples of the certified reference material TORT-2 (lobster hepatopancreas from the National Research Council Canada) were submitted to the same digestion procedure during each analytical run.
Water and digested samples were analyzed for the naturally occurring stable isotopes of Cu by ICP-MS (Supporting Information). All samples, blanks, and standards were introduced by direct injection (peristaltic pump; spray chamber) into the ICP-MS (single-detector; quadrupole). Analyte analysis for each sample consisted of 20 individual measurements that were averaged. External standards, serially diluted from ultrapure, single-element stock, were used to create calibration curves for each isotope. To account for instrument drift and change in sensitivity, internal standardization was performed by addition of germanium to all samples and standards except the calibration blanks. The method detection limit for 65Cu and 63Cu was 0.03 μg L–1. Measured Cu concentrations in the TORT-2 were consistently within the certified values. We also reanalyzed one of our standards after every 10 samples. Deviations from the standard values were <5% for the analyzed Cu isotopes at all times.
Data Analysis
65/63Cu ratios, Cu concentrations, and Cu burdens in L. stagnalis are the mean of six to seven individual measurements ± standard deviation (SD). Cu concentrations in the diatoms are the mean of three individual measurements ± SD. Treatment differences were tested by ANOVA with Tukey’s post hoc multiple-comparisons test. The effect of reverse labeling on growth was tested by ANCOVA. Differences were considered to be significant at a type I error rate of α = 0.05.

Results

Isotopically Enriching Test Organisms with 65Cu
The 65/63Cu in snails exposed for 8 weeks to 10 μg L–1 of 65Cu increased from 0.48 ± 0.01 to 4.88 ± 0.74, which shifted the relative abundance of 65Cu in the snails soft tissues (psnail65) (eq 1) from 32.2 ± 0.2 to 82.7 ± 2.4%. psnail65 was determined using the net signal intensity for each isotope in the snail’s tissue after the 65Cu exposure:(1)
The total Cu concentration in the isotopically enriched snails ([63Cu] + [65Cu]) averaged 94 ± 9 μg g–1 at the end of the 8 week exposure to 10 μg L–1 of 65Cu, which is about 2.8 times higher than the background Cu concentration of unexposed snails.(26)
To determine if pre-exposure to 65Cu induced physiological and/or biochemical changes that would subsequently affect Cu uptake by snails, we conducted a companion experiment to evaluate the growth of snails chronically exposed to 10 μg L–1 of 65Cu. The estimated growth rate constants (kg ± 95% CI, in day–1) for the control and treated (65Cu-exposed) snails were 0.034 ± 0.002 and 0.039 ± 0.003, respectively. The log-transformed dry weights of control and treated snails were not different (ANCOVA, F(1,91) = 2.08, p = 0.15), suggesting that 65Cu exposure did not affect growth.
Modification of Cu Isotopic Ratios upon Exposure to Natural Inorganic Particles
The extent of 63Cu enrichment in snails was greatest between the controls and the first exposure concentration. Figure 1 shows a nonlinear shift in the 65/63Cu of snails exposed to increasing dietary concentrations of Cu-bearing ARPs collected downstream of an acid mine drainage inflow to the Animas River, Colorado (ARP). Specifically, snail’s 65/63Cu decreased from 4.88 ± 0.74 to 2.95 ± 0.17 when the dietary Cu concentration increased from 14 to 542 μg g–1 (Table S2, Supporting Information). Further increases in the dietary Cu exposure only marginally reduced the snail’s 65/63Cu. The shift in the isotopic Cu ratio of the exposed snails indicates that the Cu from the natural particles mixed with diatoms was accumulated and thus bioavailable. Uptake of Cu by native snails (e.g., field-collected or laboratory-reared snails) would not have been detected under similar exposure conditions (eq S2, Supporting Information).
figure

Figure 1. 65/63Cu (±SD) in L. stagnalis soft tissue after exposure to increasing concentrations of ARP mixed with diatoms. Each symbol represents 65/63Cu for six to seven individuals and three diatom samples (μg g–1 ± SD). The dotted line represents the 65/63Cu of native snails.

When the snails were exposed to diatoms amended with increasing concentration of Cu-bearing Fe–Al particles, both 63Cu and 65Cu were accumulated, but for every 2 atoms of 63Cu taken up, only 1 atom of 65Cu was accumulated (i.e., the 65/63Cu ratio of natural materials is roughly 0.5).(26) Because the Cu isotopic ratio of the experimental snails had been manipulated to favor 65Cu (65/63Cu ratio of 4.88), the uptake of Cu from the natural particles reduced the 65/63Cu ratio in the snail tissues (Figure 1). More than 98% of the 63Cu in the exposure originated from the ARP, that is, the 63Cu concentration in the diatoms mixed with the ARP was 9 μg g–1.
Calculation of Background 63Cu Concentrations
To independently follow the accumulation of 63Cu that originated from the exposure to the natural particles (ARP), it was necessary to calculate the concentration of 63Cu that occurred in each sample prior to the exposure (i.e., the background 63Cu concentration). For this, we used the snail background 65Cu concentration ([65Cu]snail0 in μg g–1) and the relative abundance of 65Cu in the isotopically enriched snails (psnail65).
Specifically, we first quantified the snail 65Cu accumulation (μg g–1) during the exposure to the ARP. For this, we used the first terms of the integrated form of a kinetic biodynamic model (eq 2)(27) in which kuf (g g–1 day–1) is the rate constant of Cu uptake from diatoms mixed with the ARP (i.e., kuf is assumed to be similar for both Cu isotopes), [65Cu]food (μg g–1) is the 65Cu concentration in the diatoms mixed with the ARP, ke (day–1) is the rate constant of Cu loss, and T1 is the exposure duration (days) (Table 1). Loss of background 65Cu by the snails is assumed to be negligible during the short uptake phase (i.e., 6 h), whereas loss of newly accumulated 65Cu is assumed to be negligible compare to that of [65Cu]snail0 during depuration.(2)
Table 1. Values Used for Calculating Cu Background Concentrations, Cu Uptake from ARP, and the Relative Abundance of 65Cu in L. stagnalis
parameter/variablesymbolunitvalue
rate constant of uptake from foodkufg g–1 day–10.14
rate constant of lossakeday–10.026
exposure durationT1day0.25
depuration durationT2day2
dietary Cu concentration during exposure to ARPb[Cu]foodμg g–114–953c
dietary Cu concentration during depuration and during the enrichment phase to 65Cub[Cu]foodμg g–17–9c
a

From Croteau and Luoma.(47)

b

Total Cu concentration.

c

Range.

The background 65Cu concentration in each experimental snail ([65Cu]0snail) was then determined by solving eq 2 for [65Cu]0snail using the depuration period T2 (days), the snail 65Cu concentration measured at the end of the depuration period ([65Cu]snail), and the accumulated 65Cu concentration, as determined above. Because snails were fed lettuce that had a 65Cu concentration of ∼2.6 μg g–1, the 65Cu accumulated during the depuration phase (0.7 μg g–1) was also subtracted from the observed snail 65Cu concentration.
The pre-existing concentrations of 63Cu in each experimental snail ([63Cu]0snail in μg g–1) was then determined using the calculated background 65Cu concentration (as described above) and the relative abundance of 65Cu in the control snails (psnail65, eq 1):(3)
63Cu Accumulation from Exposure to Natural Particles
Figure 2 shows that accumulation of <25 ng of 63Cu was sufficient to induce a significant change in the snail’s 65/63Cu. For example, snails exposed to the lowest Cu concentration in their diet (542 μg g–1) accumulated 23.6 ng of 63Cu after 6 h of exposure, which increased their 63Cu burden from 37.3 to 61.0 ng. Correspondingly, snails accumulated roughly half that amount of 65Cu, but 65Cu accumulation was not detectable (P = 0.2) because of the large 65Cu background concentration. Assuming no preferential assimilation of Cu isotopes by the snails and no transfer of Cu from ARP to diatoms,(8) the decrease in the snail’s 65/63Cu was thus due exclusively to 63Cu accumulation from the ARP. As a result, significant Cu accumulation in L. stagnalis for the lowest amount of ARP mixed with food was detected only when both the accumulated Cu concentration and the Cu exposure concentrations were expressed in terms of 63Cu, not in terms of the total Cu concentration (as commonly used) nor in terms of 65Cu concentration (Figure S2, Supporting Information). The dose response nature of the 63Cu uptake demonstrated that the 63Cu was bioavailable from the ARP.
figure

Figure 2. Snail Cu accumulation (ng ± SD) as a function of the dietary Cu concentration. The solid and open bars represent 63Cu and 65Cu accumulation, respectively.

Normalization of the accumulated 63Cu concentrations to account for the exposure duration reveals that 63Cu influx rates into L. stagnalis (μg g–1 day–1) increased linearly with 63Cu exposure concentration ranging from 9 to 587 μg g–1 (Figure 3). The Cu uptake rate constant from food (kuf) for the ARP was 0.14 ± 0.03 g g–1 day–1 (±95 CI). kuf was determined from the slope of the regression between 63Cu uptake rate into L. stagnalis soft tissue after a short exposure time (to minimize the influence of efflux)(28) and the dietborne exposure concentrations (data from the linear portion of the curve). The rate constant of metal uptake represents first-order accumulation processes (i.e., metal influx solely depends on the exposure concentration). kuf is expressed as μg of metal (g of tissue)−1 day–1 per μg metal (g of food)−1, or g of food per g of tissue per day.
figure

Figure 3. 63Cu uptake rates (μg g–1 day–1 ± SD) in L. stagnalis soft tissue after dietborne exposures. Each symbol represents Cu influxes for six to seven individuals and three diatom samples (μg g–1 ± SD). The solid line represents the statistically significant linear regression relationship.

The Cu uptake rate constant from food (kuf) for the ARP was nearly 5 times lower than the kuf for Cu bound to synthetic hydrous ferric oxide, but similar to the kuf for CuO nanoparticles mixed with diatoms (Table 2). As shown in Figure 3, 63Cu influxes into L. stagnalis deviated from linearity to level off around 145 μg of 63Cu g–1 day–1 when 63Cu exposure concentrations exceeded 587 μg g–1. The relationship between Cu influx and dietborne Cu concentrations has also been reported to deviate from linearity when snails were offered diatoms labeled with high concentrations of Cu.(29) Experiments conducted with Zn, Ag, Ni, and Cd also showed that dietary Zn and Ag can suppress influxes in L. stagnalis.(24, 29, 30) The elevated concentrations of Fe, Al, and Zn in the ARP might have acted synergistically with Cu to suppress Cu influxes (Table S2, Supporting Information).
Table 2. Rate Constants of Dietary Cu Uptake (kuf ± 95% CI) and Cu Assimilation Efficiency (AE ± SD) in L. stagnalis Determined for Different Food Sources and/or Cu Forms
dietary exposure tokuf (g g–1 day–1)AE (%)ref
lettuce pre-exposed to CuNO30.16 ± 0.0486 ± 247
diatoms pre-exposed to CuNO30.06 ± 0.005[72–82]29
diatoms mixed with CuO nanoparticles0.13 ± 0.0241 ± 4Croteau et al., unpublished data
diatoms mixed with synthetic Cu-HFO0.69 ± 0.20[71–93]8
diatoms mixed with ARP0.14 ± 0.0344 ± 11this study
Cu Assimilation Efficiency and Food Ingestion Rates
The reverse labeling approach allows determination of important digestive processes such as food ingestion rates (IR) and assimilation efficiency (AE). Food ingestion rates (IR) during the feeding phase (g of ingested food per g of body tissue per day) were determined by mass-balance calculations using the total amount of 63Cu retained in the snails after depuration (63Cusnail in ng), the amount of 63Cu egested in the feces during depuration (63Cufeces in ng), the 63Cu concentration in the diatoms mixed with the ARP ([63Cu]diatoms in ng g–1), the snail’s dry weight (wtsnail in g), and the exposure duration (T1):(4)
For example, IR for snails exposed to diatoms mixed with ARP did not vary significantly among exposure concentrations; that is, IR averaged 0.26 ± 0.04 g g–1 day–1. Food IR was, however, 5 times higher for the controls, suggesting that feeding was inhibited whenever ARP were mixed with the diatoms. Specifically, food IR averaged 1.4 ± 0.7 g g–1 day–1 for the control snails and decreased to 0.26 ± 0.04 g g–1 day–1 when the 63Cu exposure concentration increased from 9 to 754 μg g–1 (Figure 4A). Concentration-dependent feeding inhibition has been observed in L. stagnalis exposed to diatoms labeled with high levels of Cu.(29)
figure

Figure 4. (A) Food ingestion rate (g g–1 day–1 ± SD) and (B) Cu assimilation efficiencies (% ± SD) in snails exposed for 6 h to diatoms mixed with increasing amounts of ARP. The solid line represents the statistically significant linear regression relationship.

Cu AE (%) for each experimental organism was calculated using mass-balance calculations and averaged by treatment (eq 5). AE represents the proportion of ingested Cu that is transported across the gut membrane and retained in soft tissue.(31)(5)
Cu assimilation efficiency steadily declined with increasing exposure concentrations (p = 0.02, Figure 4B). Specifically, Cu AE decreased from 72 ± 0.1 to 37 ± 5% when dietary 63Cu exposure concentration increased from 9 to 754 μg g–1. Overall, Cu AE was 44 ± 11%, which is lower than the Cu AE reported for Cu sorbed to synthetic hydrous ferric oxide (80–90%)(8) and for Cu associated with a natural food source (e.g., 72–82% in diatoms)(29) (Table 2). The Cu AE reported for the ARP is, however, comparable to that found for Cu from CuO nanoparticles (Table 2). Mass transfer of Cu from the ARP to the diatoms prior to ingestion likely was small and, therefore, contributed little to the observed uptake and Cu AE, as shown by Cain et al.(8) for Cu sorbed to colloidal hydrous ferric oxide. The reduction of Cu influx at the highest exposure concentrations (Figure 3) could thus be explained, in part, by the decline in AE. This suggests that the snail’s physiological processes controlling the assimilation of Cu were impaired at the highest exposure concentrations. It remains unclear which constituent of the food (i.e., trace metal or major element or both) was responsible for the impairment.

Discussion

Applications of tracer techniques have been invaluable to the study of processes that influence the fate of minerals and trace elements in various biological systems.(2, 6-9, 32) However, typical tracing requires labeling the source of contamination, which does not necessarily represent the speciation of the native metals, and may affect many kinds of assessments. For example, the physical location of metals within a particle can vary greatly, but systematically labeling each geochemical phase is impossible, yet each phase can influence metal bioavailability. The “reverse labeling” approach described herein is advantageous because it allows measurements of AE to be made on particles in their native state (i.e., no manipulation or labeling). It involves enriching test organisms in a low abundance isotope (of the metal of interest) prior to exposure to naturally contaminated particles. Our results showed that 8 weeks of exposure to 10 μg L–1 of 65Cu increases the relative abundance of 65Cu in the soft tissues of freshwater snails from ∼32% to >80%, which was sufficient to detect uptake.
The use of snails isotopically enriched in 65Cu allowed detecting accumulation of 24 ng of Cu after a short dietary exposure (e.g., 6 h) to natural Cu-bearing Fe–Al particles. Greater sensitivity could be gained with a greater enrichment of the organisms with 65Cu. In this study, uptake of 63Cu from the lettuce probably capped the enrichment factor of 65Cu. That is, we estimated that psnail65 in this experiment could not have exceeded 90% because snails consumed food containing 63Cu during the 65Cu enrichment phase (Table 1). Specifically, there was approximately 5 μg g–1 of 63Cu in the lettuce offered as food to the snails during the 65Cu enrichment phase, which yielded an uptake of 13 μg g–1 of 63Cu over the pre-exposure period (eq 2, first term). This uptake was, however, offset by a loss of 22 μg g–1 of 63Cu (eq 2, second term). Thus, exposed snails became progressively depleted in 63Cu as they were becoming enriched in 65Cu. Rearing young snails in an environment that is completely free of 63Cu would increase the 65/63Cu ratio. However, the experimental pre-exposure would be more demanding. For example, the isotopic composition of the food would need to be manipulated to reduce the isotopic signature of 63Cu. The increased effort would likely yield only a marginal improvement in sensitivity. Finding the experimental setup that is practical and will achieve a satisfactory level of sensitivity is key to the reverse labeling approach.
Greater sensitivity could also be gained with longer pre-exposures to waterborne 65Cu, higher pre-exposure concentrations, or both. However, further gain in sensitivity would be offset by the risks of eliciting toxicity because of a greater Cu accumulation by the test organisms. Greater Cu bioaccumulation could induce physiological and biochemical changes that could subsequently affect uptake, as described above. Pre-exposure conditions thus need to also take into account the test organism’s “health”. Importantly, our results demonstrated that pre-exposure to 65Cu had no effect on the snail’s growth rate, indicating a lack of sublethal effects.(33) Past exposure to metals, especially acute metal pre-exposure, can induce physiological or biochemical changes that can later affect metal uptake.(34-37) Although there is no clear consistent effect of metal pre-exposure on metal uptake, we cannot rule out the possibility that Cu uptake from the ARP in L. stagnalis had been somewhat influenced by the pre-exposure to 65Cu. The use of low pre-exposure concentrations can minimize this confounding influence, although comparisons of bioaccumulation kinetics between native and isotopically enriched snails are needed to fully assess the effects of pre-exposure.
Geochemical and Biological Influences on Copper Bioavailability
Differences in kuf among studies suggest that Cu bioavailability to L. stagnalis is 4 times higher for Cu bound to synthetic hydrous ferric oxide (HFO) than for Cu associated with the ARP (Table 2). In contrast, Cu bioavailability from the ARP is similar to that of CuO nanoparticles mixed with diatoms, suggesting that the geochemical nature of the particles influences the extent of Cu bioavailability. Metals sorbed to particle surfaces such as Cu on hydrous ferric oxides appear to be highly bioavailable,(8) in contrast to metals occluded in particles such as synthetic CuO nanoparticles.(26) The precise geochemical composition of the ARP is unknown, however. From the study of Schemel et al.,(22) one can hypothesize the complex nature of the ARP on the basis of the sequence leading to colloidal particle formation. That is, about half of the Fe was particulate (<10 kDa) upstream of the confluence of the acid Cement Creek (source) with the Animas River (Table S1, Supporting Information). Upon mixing, Al precipitated rapidly between pH 4 and 6.5, with the remaining Fe precipitating by the downstream end of the mixing zone where the colloid particles were harvested (see Materials and Methods). Cu sorption increased from 0 in Cement Creek to about 50% after mixing and transport to the collection site. Thus, one hypothesis is that Al is precipitated onto iron oxide that had already sorbed Cu, as some fraction of Fe is already precipitated in Cement Creek, with further sorption of Cu and precipitation of Al occurring upon neutralization. Another hypothesis is that Cu adsorbed to aluminum oxides or to a mixed aluminum–iron oxide. In either scenario, Cu may be less available because of stronger binding and/or occlusion by precipitation of Al and Fe onto existing surfaces. In laboratory studies, Al was incorporated into the iron oxide at levels of up to 30 mol % (defined as Al/Fe + Al) when present during Fe precipitation.(38) At higher Al concentrations, aluminum hydroxide phases also formed. An Al mole percent of about 70% is estimated for the Animas River assuming that half the Fe had precipitated prior to mixing of Cement Creek water into the river. Thus, the ARP likely is composed of both aluminum-substituted iron oxides and aluminum oxides, in addition to iron oxides formed in Cement Creek. Cu surface complexation equilibria and desorption kinetics for this complex mixture have not been evaluated.
In addition to geochemical factors, biological factors play a crucial role in determining metal bioavailability to a species. For example, digestive processes(39) and gut conditions such pH, Eh, and enzyme activity(40) can affect the release of ingested metals in the gut, thereby influencing their uptake. Our studied species, L. stagnalis, has a complex digestive system that utilizes extra- and intracellular digestive pathways,(41) although the acidity of the gut lumen is reported to be circum neutral.(42) High concentrations of pollutants in the diet can also disrupt gut function and feeding activity,(24, 29, 43) both of which are of significance to higher level processes such as growth and reproduction.(44) Our results show that the presence of ARP in the diet of L. stagnalis induced a dietary metal stress captured by a steady decline of Cu AE with increasing exposure concentrations and by the suppression of their feeding rates, which suggests that starvation might be a mode of stress for benthic feeders.
Our results show that the reverse labeling approach offers a unique tool to unify both biological and geochemical influences when the bioavailability of metals associated with complex geochemical phases is evaluated. The approach offers the potential to systematically investigate the bioavailability of a wide variety of geochemical phases and metals, which would provide crucial insights to advance the current understanding of the influence of solid-phase geochemical speciation on metal bioavailability. For example, our study provides not only evidence that Cu associated with natural Fe–Al particles is bioavailable but also a method to explain the potential direct uptake of metals from colloids, which addresses a long-standing uncertainty in the literature (e.g., Newman and McIntosh(45) and Farag et al.(46)). Most important, the reverse labeling approach shows great potential for addressing questions involving uptake of an element that naturally has multiple isotopes in various scientific areas such as environmental contamination and nutrition.

Supporting Information

Metal concentrations in particles and water collected in the Animas River; concentrations of Fe, Cu, Al, Zn, and Pb in diatoms mixed with ARP; ICP-MS analysis; growth rate experiment, prediction of Cu accumulation in native snails after exposure to ARP, and Cu concentrations in snails after exposure to diatoms mixed with ARP. This material is available free of charge via the Internet at http://pubs.acs.org.

The authors declare no competing financial interest.

Acknowledgment

We are grateful to Samuel Luoma and Aı̈da Farag for reviewing the manuscript, as well as three anonymous reviewers whose comments improved the manuscript. Support for this research was provided by the Toxics Substance Hydrology Program of the U.S. Geological Survey. We thank Briant Kimball for his assistance and guidance in collecting the ARP. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. government.

References

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    Au, Angela P.; Reddy, Manju B.
    Journal of Nutrition (2000), 130 (5), 1329-1334 CODEN: JONUAI; ISSN:0022-3166. (American Society for Nutritional Sciences)
    Caco-2 cells and radioactive iron (59Fe) were used to evaluate the effects of dietary factors on nonheme iron bioavailability from semipurified meals. Study 1 was conducted to evaluate the effect of enhancers (ascorbic acid) and inhibitors (bran, phytate, tea) on iron bioavailability when added to semipurified meal contg. egg albumen, bovine serum albumin (BSA), casein, beef, and soybean as protein sources. Protein solubilization following in vitro digestion of individual test meals was not much different from control. The nonheme iron solubilization (0.8±0.0 to 5.9±0.3 vs. 4.9±0.8 mg/L) varied significantly among the meals. The total iron uptake for each meal was calcd. based on the % of radioiron taken up and transported by Caco-2 cells and the amt. of nonheme iron present in the solns. The iron uptake ratios were calcd. as test/control values. With the exception of BSA and ascorbic acid, the effects of dietary factors were similar to those seen in humans. A correlation (r = 0.97) was found between the published human absorption data and the iron uptake by the Caco-2 cells. Thus, the Caco-2 cells can be used in assessing human iron absorption and the feasibility of this cell model in studying iron bioavailability from various food combinations, otherwise not easily performed in humans.
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    Characterization of uptake and loss dynamics is crit. to understanding risks assocd. with contaminant exposure in aquatic animals. Dynamics are esp. important in addressing questions such as why coexisting species in nature accumulate different levels of a contaminant. Here the authors manipulated copper (Cu) stable isotopic ratios (as an alternative to radioisotopes) to describe for the first time Cu dynamics in a freshwater invertebrate, the bivalve Corbicula fluminea. In the lab., Corbicula uptake and loss rate consts. were detd. from an environmentally realistic waterborne exposure to 65Cu (5.7 μg L-1). That is, the authors spiked deionized water with Cu that was 99.4% 65Cu. Net tracer uptake was detectable after 1 day and strongly evident after 4 days. Thus, short-term exposures necessary to det. uptake dynamics are feasible with stable isotopes of Cu. In Corbicula, 65Cu depuration was biphasic. An unusually low rate const. of loss (0.0038 d-1) characterized the slow component of efflux, explaining why Corbicula strongly accumulates copper in nature. The authors incorporated the authors' ests. of rate consts. for dissolved 65Cu uptake and physiol. efflux into a bioaccumulation model and showed that dietary exposure to Cu is likely an important bioaccumulation pathway for Corbicula.
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    OpenURL UNIV OF NORTH TEXAS
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    Harvey, L. J.; Dainty, J. R.; Beattie, J. H.; Majsak-Newman, G.; Wharf, S. G.; Reid, M. D.; Fairweather-Tait, S. J.
    European Journal of Clinical Nutrition (2005), 59 (3), 363-368 CODEN: EJCNEQ; ISSN:0954-3007. (Nature Publishing Group)
    To det. copper absorption from copper contg. foods labeled either intrinsically or extrinsically with a highly enriched Cu-65 stable isotope label. A longitudinal cross-over study. The study was conducted at the Institute of Food Research, Human Nutrition Unit, Norwich, UK. Subjects were recruited locally via advertisements placed around the Norwich Research Park. A total of 10 volunteers (nine female, one male) took part in the study, but not all volunteers completed each of the test meals. A highly enriched Cu-65 stable isotope label was administered to volunteers in the form of a ref. dose or in breakfast test meals consisting of red wine, soya beans, mushrooms or sunflower seeds. Fecal monitoring and mass spectrometry techniques were used to est. the relative quantities of copper absorbed from the different test meals. True copper absorption from the ref. dose (54%) was similar to extrinsically labeled red wine (49%) and intrinsically labeled sunflower seeds (52%), but significantly higher than extrinsically labeled mushrooms (35%), intrinsically (29%) and extrinsically (15%) labeled soya beans and extrinsically labeled sunflower seed (32%) test meals. The use of Cu-65 extrinsic labels in copper absorption studies requires validation according to the food being examd.; intrinsic and extrinsic labeling produced significantly different results for sunflower seeds.
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    OpenURL UNIV OF NORTH TEXAS
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    Science of the Total Environment (2005), 339 (1-3), 89-101 CODEN: STENDL; ISSN:0048-9697. (Elsevier Ltd.)
    There is a well documented accumulation of Hg in fish to concns. of concern for human consumption. Variation in fish Hg burden between lakes is often high and may result from differences in Hg transfer through lower levels of the food web where mercury is bioconcd. to phytoplankton and transferred to herbivorous zooplankton. Prior research derived patterns of Hg accumulation in freshwater invertebrates from field collected animals. This study provides results from controlled mesocosm expts. comparing the effects of zooplankton compn., algal abundance, and the chem. speciation of Hg on the ability of zooplankton to accumulate Hg from phytoplankton and transfer that Hg to planktivores. Expts. were conducted in 550-L mesocosms across a gradient of algal densities manipulated by inorg. nutrient addns. Enriched, stable isotopes of org. (CH3200HgCl) and inorg. (201HgCl2) Hg were added to mesocosms and their concns. measured in water, seston, and 3 common zooplankton species. After 2 wk, monomethylmercury (MMHg) concns. were 2-3 times lower in the 2 copepod species, Leptodiaptomus minutus and Mesocyclops edax than in the cladoceran, Daphnia mendotae. All 3 zooplankton species had higher MMHg concns. in mesocosms with low vs. high initial algal abundance. However, despite higher concns. of inorg. Hg (HgI) in seston from low nutrient mesocosms, there were no significant differences in the HgI accumulated by zooplankton across nutrient treatments. Bioaccumulation factors for MMHg in the plankton were similar to those calcd. for plankton in natural lakes and a 4-compartment (aq., seston, macrozooplankton, and periphyton/sediments) mass balance model after 21 days accounted for ∼18% of the CH3200Hg and ∼33% of the 201Hg added. Results from our expts. corroborate results from field studies and suggest the importance of particular zooplankton herbivores (e.g., Daphnia) in the transfer of Hg to higher trophic levels in aquatic food webs.
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    OpenURL UNIV OF NORTH TEXAS
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    Science (Washington, DC, United States) (1991), 251 (4995), 794-6 CODEN: SCIEAS; ISSN:0036-8075.
    The efficiency with which a variety of ingested elements (Ag, Am, C, Cd, P, S, Se, and Zn) were assimilated in marine calanoid copepods fed uniformly radiolabeled diatoms ranged from 0.9% for Am to 97.1% for Se. Assimilation efficiencies were directly related to the cytoplasmic content of the diatoms. This relation indicates that the animals obtained nearly all their nutrition from this source. The results suggest that these zooplankton, which have short gut resisence times, have developed a gut lining and digestive strategy that provides for assimilation of only sol. material. Because of fraction of total cellular protein in the cytoplasm of the diatoms increased markedly with culture age, copepods feeding on senescent cells should obtain more protein than those feeding on rapidly dividing cells. Elements that are appreciably incorporated into algal cytoplasm and assimilated in zooplankton should be recycled in surface waters and have longer oceanic residence times than elements bound to cell surfaces.
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    Cain, D. J.; Croteau, M. N.; Luoma, S. N.Bioaccumulation dynamics and exposure routes of Cd and Cu among species of aquatic mayflies Environ. Toxicol. Chem. 2011, 30, 2532– 2541
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    Bioaccumulation dynamics and exposure routes of Cd and Cu among species of aquatic mayflies
    Cain, Daniel; Croteau, Marie-Noele; Luoma, Samuel
    Environmental Toxicology and Chemistry (2011), 30 (11), 2532-2541 CODEN: ETOCDK; ISSN:0730-7268. (Wiley-Blackwell)
    Consumption of periphyton is a potentially important route of metal exposure to benthic invertebrate grazers. The present study examd. the bioaccumulation kinetics of dissolved and dietary Cd and Cu in five species of mayflies (class Insecta). Artificial stream water and benthic diatoms were sep. labeled with enriched stable metal isotopes to det. physiol. rate consts. used by a biokinetic bioaccumulation model. The model was employed to simulate the effects of metal partitioning between water and food, expressed as the bioconcn. factor (BCF), as well as ingestion rate (IR) and metal assimilation efficiency of food (AE), on the relative importance of water and food to metal bioaccumulation. For all test species, the contribution of dietary uptake of Cd and Cu increased with BCF. For a given BCF, the contribution of food to the body burden increased with kuf, the metal uptake rate const. from food that combined variation in IR and AE. To explore the relative importance of water and diet exposure routes under field conditions, we used estd. site-specific aq. free-ion concns. to model Cd and Cu accumulation from aq. exposure, exclusively. The predicted concns. accounted for less than 5% of the obsd. concns., implying that most bioaccumulated metal was acquired from food. At least for the taxa considered in this study, we conclude that consumption of metal-contaminated periphyton can result in elevated metal body burdens and potentially increase the risk of metal toxicity.
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    OpenURL UNIV OF NORTH TEXAS
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    Cain, D. J.; Croteau, M. N.; Fuller, C. C.Dietary bioavailability of Cu adsorbed to colloidal hydrous ferric oxide to freshwater benthic grazers Environ. Sci. Technol. 2013, , DOI: 10.1021/es3044856
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    Buchwalter, D. B.; Luoma, S. N.Differences in dissolved cadmium and zinc uptake among stream insects: mechanistic explanations Environ. Sci. Technol. 2005, 39, 498– 504
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    9.
    Differences in Dissolved Cadmium and Zinc Uptake among Stream Insects: Mechanistic Explanations
    Buchwalter, David B.; Luoma, Samuel N.
    Environmental Science and Technology (2005), 39 (2), 498-504 CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    This work examd. the extent to which dissolved Cd and Zn uptake rates varied in several aquatic insect taxa commonly used as ecol. health indicators. The authors attempted to explain mechanisms underlying obsd. differences. By comparing dissolved Cd and Zn uptake rates in several aquatic insect species, it was demonstrated that species vary widely in these processes. Dissolved uptake rates were not related to gross morphol. features, e.g., body size or gill size (features affecting water permeability and thus having iono-regulatory importance); however, finer morphol. features, specifically the relative no. of iono-regulatory cells (chloride cells), appeared to be related to dissolved metal uptake rates. This observation was supported by Michaelis-Menten type kinetics expts. which showed dissolved Cd uptake rates were driven by the no. of Cd transporters and not by the affinity of those transporters to Cd. Ca concns. in exposure media similarly affected Cd and Zn uptake rates in the caddisfly, Hydropsyche californica. Dissolved Cd and Zn uptake rates strongly co-varied among species, suggesting these metals are transported by similar mechanisms.
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    OpenURL UNIV OF NORTH TEXAS
  10. 10.
    Hintelmann, H.; Evans, R. D.; Villeneuve, J. Y.Measurement of mercury methylation in sediments by using enriched stable mercury isotopes combined with methylmercury determination by gas chromatography–inductively coupled plasma mass spectrometry J. Anal. At. Spectrom. 1995, 10, 619– 624
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    10.
    Measurement of mercury methylation in sediments by using enriched stable mercury isotopes combined with methylmercury determination by gas chromatography-inductively coupled plasma mass spectrometry
    Hintelmann, Holger; Evans, R. Douglas; Villeneuve, Janice Y.
    Journal of Analytical Atomic Spectrometry (1995), 10 (9), 619-24 CODEN: JASPE2; ISSN:0267-9477. (Royal Society of Chemistry)
    A novel technique for the calcn. of Hg methylation rates in sediments by using enriched stable Hg isotopes is described. The method takes advantages of the ability of an inductively coupled plasma mass spectrometry (ICP-MS) instrument to measure individual isotopes. An ICP-MS instrument was used as a detector for the detn. of methylmercury compds. after sepn. by gas chromatog. (GC). MeHg+ was isolated from sediments by distn., converted to methylethylmercury by Na tetraethylborate and analyzed after purge-and-trap precollection on a Tenax adsorber and thermodesorption onto the GC column. Detection limits are ≈1 pg (as Hg) abs. or 0.02 ng g-1 dry sediment. The precision was ≈4% relative std. deviation when 250 pg of methylmercury were processed. The accuracy of the GC-ICP-MS technique was demonstrated by anal. of an International At. Energy Agency certified ref. material (IAEA CRM 356) Harbor Sediment, giving a concn. of 5.40 ± 0.40 ng g-1, compared with the certified value of 5.47 ± 0.38 ng g-1. Hg methylation was studied by spiking sediments with stable enriched Hg isotopes at in situ Hg concns. not perturbing the system. More than 3% of the Hg added to a lake sediment was methylated during a 21 d incubation period. Isotope ratios of total Hg differed significantly from isotope ratios of methylmercury at the end of the expt., suggesting that the system was still not in equil. after 21 d.
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    OpenURL UNIV OF NORTH TEXAS
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    A review, with 33 refs. Calcium is important for bone health. Calcium absorption consists of an active vitamin D-mediated component and a passive diffusional component. At present, the calcium absorption tests using calcium isotopes (radioactive or stable) appear to be the most reproducible way of detg. calcium absorption. The major nutrient sources for calcium are milk and milk products, whereas some of the green vegetables have a low bioavailability of calcium. The calcium supplement might be taken as milk (or milk products) or, in patients with lactose intolerance, as calcium supplements. Quite a no. of calcium supplements are available on the market, and many of them are marketed without proper knowledge of the bioavailability of the actual prepn.
    >> More from SciFinder ®
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    OpenURL UNIV OF NORTH TEXAS
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    Use of calcium tracers and biomarkers to determine calcium kinetics and bone turnover
    Weaver, C. M.
    Bone (New York) (1998), 22 (5, Suppl.), 103S-104S CODEN: BONEDL; ISSN:8756-3282. (Elsevier Science Inc.)
    A review with 16 refs. The purpose of this article is to review approaches to measuring calcium metab. and bone turnover, which can be used to assess bone loss during spaceflight and to evaluate the effectiveness of interventions aimed at reducing bone loss. Isotopic tracers of calcium can be used to det. absorption, excretion, retention, body pool sizes, and turnover rates. Because 99% of the body's calcium is in the bone, calcium tracer kinetics can provide an accurate assessment of bone turnover rates. Biomarkers can be used to assess qual. changes in bone formation and bone resorption, but they do not predict bone d. or quantitate net calcium retention. The usefulness of biomarkers has been validated against calcium tracer kinetics and bone histomorphometry. Calcium kinetics and biomarkers of bone turnover can assess changes in calcium metab. and bone turnover long before changes in bone d. can be detected.
    >> More from SciFinder ®
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    OpenURL UNIV OF NORTH TEXAS
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    Van den Heuvel, E. G. H. M.; Muys, T.; Pellegrom, H.; Bruyntjes, J. P.; van Dokkun, W.; Spanhaak, S.; Schaafsma, G.A new method to measure iron absorption from the enrichment of 57Fe and 58Fe in young erythroid cells Clin. Chem. 1998, 44, 649– 654
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    A new method to measure iron absorption from the enrichment of 57Fe and 58Fe in young erythroid cells
    Van Den Heuvel, Ellen G. H. M.; Muys, Theo; Pellegrom, Hillie; Bruyntjes, Joost P.; Van Dokkum, Wim; Spanhaak, Steven; Schaafsma, Gertijan
    Clinical Chemistry (Washington, D. C.) (1998), 44 (3), 649-654 CODEN: CLCHAU; ISSN:0009-9147. (American Association for Clinical Chemistry)
    Iron absorption can be measured by the incorporation of stable iron isotopes into erythrocytes, 14 days after isotope administration. The disadvantage of this method is the high dose of isotopes needed to obtain a sufficient enrichment. Therefore, in this study cell fractions rich in young erythroid cells were prepd. by using a d. sepn. method. From 10 women blood was taken 4, 5, and 7 days after oral and i.v. administration of 57Fe and 58Fe. In these cell fractions and in whole blood taken 14 days after isotope administration, isotope enrichment was measured and absorption calcd. Absorption calcd. from the isotope enrichment in the reticulocyte-rich cell fractions (12.2 ± SEM 3.7%) was not significantly different from absorption based on whole-blood values (13.0±3.3%). Because a threefold higher isotope enrichment was found in the cell fractions, the required dose of stable isotopes can be reduced to one-third of the dose used in the traditional method without loss of sensitivity.
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    OpenURL UNIV OF NORTH TEXAS
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    Cornelis, R.Use of radiochemical methods as tools for speciation purposes in environmental and biological sciences Analyst 1992, 117, 583– 588
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    14.
    Use of radiochemical methods as tools for speciation purposes in environmental and biological sciences
    Cornelis, Rita
    Analyst (Cambridge, United Kingdom) (1992), 117 (3), 583-8 CODEN: ANALAO; ISSN:0003-2654.
    A review with 29 refs. Chem. speciation for a few elements can be facilitated to a great extent by incorporating a suitable radioisotope into the system and measuring the radiation of the isolated species. This radio-spiking can be applied to in vitro and in vivo labeled expts. Radionuclides are, however, also present as an anthropogenic contaminant from various nuclear fission activities. The radiotracer should be added under such conditions that it behaves in exactly the same way as the isotopes it represents. It should possess an adequate radioactive half-life, and preferably be a γ-emitter because of the ease of detection. Radiotracer labeling is now widely used to study speciation problems of many essential and toxic elements in body fluids and tissues. It can be used to trace the different locations where the element is metabolized and stored, and subsequently to detect the element in the isolated biocomponents. The detn. of the location of a radiotracer in a cell by autoradiog. proved to be impractical because of the lack of resoln. Radiochem. is similarly very useful for investigating particular aspects of the speciation of heavy metals as they occur in the ecosystem, and to follow the fate and effects of fission nuclides in the environment as they are carried around by the water and air masses. However, in certain circumstances the behavior of fission products appears to be different from that of their stable analogs. For the actinides they simply do not exist. Radiochem. methods are a major tool for identifying and quantifying the nuclides in the different species.
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    OpenURL UNIV OF NORTH TEXAS
  15. 15.
    Stürup, S.; Hansen, H. R.; Gammelgarrd, B.Application of enriched stable isotopes as tracers in biological systems: a critical review Anal. Bioanal. Chem. 2008, 390, 541– 554
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    15.
    Application of enriched stable isotopes as tracers in biological systems: a critical review
    Sturup Stefan; Hansen Helle Rusz; Gammelgaard Bente
    Analytical and bioanalytical chemistry (2008), 390 (2), 541-54 ISSN:.
    The application of enriched stable isotopes of minerals and trace elements as tracers in biological systems is a rapidly growing research field that benefits from the many new developments in inorganic mass spectrometric instrumentation, primarily within inductively coupled plasma mass spectrometry (ICP-MS) instrumentation, such as reaction/collision cell ICP-MS and multicollector ICP-MS with improved isotope ratio measurement and interference removal capabilities. Adaptation and refinement of radioisotope tracer experiment methodologies for enriched stable isotope experiments, and the development of new methodologies coupled with more advanced compartmental and mathematical models for the distribution of elements in living organisms has enabled a broader use of enriched stable isotope experiments in the biological sciences. This review discusses the current and future uses of enriched stable isotope experiments in biological systems.
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    OpenURL UNIV OF NORTH TEXAS
  16. 16.
    Jannasch, H. W.; Honeyman, B. D.; Balistrieri, L. S.; Murray, J. W.Kinetics of trace element uptake by marine particles Geochim. Cosmochim. Acta 1988, 52, 567– 577
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    16.
    Kinetics of trace element uptake by marine particles
    Jannasch, Hans W.; Honeyman, Bruce D.; Balistrieri, Laurie S.; Murray, James W.
    Geochimica et Cosmochimica Acta (1988), 52 (2), 567-77 CODEN: GCACAK; ISSN:0016-7037.
    Removal of 46Sc, 65Zn, and 230Th by natural particulates in Puget Sound seawater was studied under lab. conditions. Overall metal sorption rates for the faster uptake reactions are proportional to their final distribution coeff., Kdα. Time to reach 90% of final fraction sorption is <1 min for Sn to ∼6 days for Zn. Sorption rate variations for the different metals indicate particle residence time as a master variable in scavenging, and the rate vs. Kdα relationship allows Th to be used as an analog for other scavenged metals. Linearizing the sorption data to an overall 1st-order reaction model suggests that for these expts. 4 distinct processes exist with characteristic time periods of <1 min, ∼20 min, ∼4 h, and several days. The results suggest that scavenging is affected by both surface chem. properties and biol. activity. In general, stronger binding metals sorb rapidly via chem. and phys. processes, while metals with weaker particle assocns. are taken up more slowly and may be controlled biol. Two uptake models and the theor. limits of rate controlling processes such as surface reactions, diffusion, and mass transfer are discussed.
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    OpenURL UNIV OF NORTH TEXAS
  17. 17.
    Griscom, S. B.; Fisher, N. S.; Luoma, S. N.Geochemical influences on assimilation of sediment-bound metals in clams and mussels Environ. Sci. Technol. 2000, 34, 91– 99
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    17.
    Geochemical influences on assimilation of sediment-bound metals in clams and mussels
    Griscom, Sarah B.; Fisher, Nicholas S.; Luoma, Samuel N.
    Environmental Science and Technology (2000), 34 (1), 91-99 CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    A series of expts. was performed to evaluate the extent to which Cd, Co, Ag, Se, Cr, and Zn bound to sediments with different geochem. properties could be assimilated by the mussel Mytilus edulis and the clam Macoma balthica. Oxidized and reduced radio-labeled sediments were fed to suspension-feeding animals, the depuration patterns of the individuals were followed by γ-spectrometry, and the assimilation efficiencies (AEs) of ingested metals were detd. AEs from geochem. diverse sediments typically varied less than 2-fold and ranged from 1% for Cr to 42% for Zn. Metals were assimilated from anoxic sediment by both animals; Ag, Cd, and Co AEs in M. balthica were 9-16%, 2-fold lower than from oxic sediment, but in M. edulis AEs were about two times greater from anoxic sediment for all metals but Ag. For oxic sediment, Cd and Co AEs in M. edulis decreased 3-4-fold with increased sediment exposure time to the metals with smaller but significant effects also noted for Zn and Se but not Ag. A less pronounced decrease in AE for M. balthica was evident only after 6 mo exposure time. Sequential extns. of the oxidized sediments showed a transfer of metals into more resistant sediment components over time, but the rate did not correlate with a decrease in metal AEs. Comparing the two bivalves, TOC concns. had an inconsistent effect on metal AEs. AEs of metals from bacteria-coated glass beads were slightly higher than from humic acid-coated beads, which were comparable with whole-sediment AEs. There was correspondence of AE with desorption of Ag, Cd, Co, and Se (but not Zn) from sediments into pH 5 seawater, measured to simulate the gut pH of these bivalves. The results imply that metals assocd. with sulfides and anoxic sediments are bioavailable, that the bioavailability of metals from sediments decreases over exposure time, that org. carbon content generally has a small effect on AEs, and that AEs of sediment-bound metals differ among species.
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    OpenURL UNIV OF NORTH TEXAS
  18. 18.
    Fuller, C. C.; Davis, J. A.; Waychunas, G. A.Surface chemistry of ferrihydrite: part 2. Kinetics of arsenate adsorption and coprecipitation Geochim. Cosmochim. Acta 1993, 57, 2271– 2282
    [CrossRef], [CAS]
    18.
    Surface chemistry of ferrihydrite: Part 2. Kinetics of arsenate adsorption and coprecipitation
    Fuller, Christopher C.; Davis, James A.; Waychunas, Glenn A.
    Geochimica et Cosmochimica Acta (1993), 57 (10), 2271-82 CODEN: GCACAK; ISSN:0016-7037.
    The kinetics of As(V) adsorption by ferrihydrite was investigated in copptn. and post-synthesis adsorption expts. conducted in pH 7.5-9.0. In copptn. expts., As(V) was present in soln. during the hydrolysis and pptn. of iron. In adsorption expts., a period of rapid (<5 min) As(V) uptake from soln. was followed by continued uptake for at least eight days, as As(V) diffused to adsorption sites on ferrihydrite surfaces within aggregates of colloidal particles. The time dependence of As(V) adsorption is well described by a general model for diffusion into a sphere if a subset of surface sites located near the exterior of aggregates is assumed to attain adsorptive equil. rapidly. The kinetics of As(V) desorption after an increase in pH were also consistent with diffusion as a rate-limiting process. Aging of pure ferrihydrite prior to As(V) adsorption caused a decrease in adsorption sites on the ppt. owing to crystallite growth. In copptn. expts., the initial As(V) uptake was significantly greater than in post-synthesis adsorption expts., and the rate of uptake was not diffusion limited because As(V) was coordinated by surface sites before crystallite growth and coagulation processes could proceed. After the initial adsorption, As(V) was slowly released from coppts. for at least one month, as crystallite growth caused desorption of As(V). Adsorption densities as high as 0.7 mol As(V) per mol of Fe were measured in coppts., in comparison to 0.25 mol As(V) per mol of Fe in post-synthesis adsorption expts. Despite the high concn. of As(V) in the ppts., EXAFS spectroscopy (Waychunas et al., 1993) showed that neither ferric arsenate nor any other As-bearing surface ppt. or solid soln. was formed. The high adsorption densities are possible because the ferrihydrite particles are extremely small, approaching the size of small dioctahedral chains at the highest As(V) adsorption d. The results suggest that the solid soln. model proposed by L. E. Fox (1989, 1992) for control of arsenate and phosphate concns. in natural waters may be invalid.
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    OpenURL UNIV OF NORTH TEXAS
  19. 19.
    Lee, J. S.; Lee, B. G.; Luoma, S. N.; Yoo, H.Importance of equilibration time in the partitioning and toxicity of zinc in spiked sediment bioassays Environ. Toxicol. Chem. 2004, 23, 65– 71
    [CrossRef], [PubMed], [CAS]
    19.
    Importance of equilibration time in the partitioning and toxicity of zinc in spiked sediment bioassays
    Lee, Jung-suk; Lee, Byeong-gweon; Luoma, Samuel N.; Yoo, Hoon
    Environmental Toxicology and Chemistry (2004), 23 (1), 65-71 CODEN: ETOCDK; ISSN:0730-7268. (SETAC Press)
    The influences of spiked Zn concns. (1-40 μmol/g) and equilibration time (∼95 days) on the partitioning of Zn between pore water (PW) and sediment were evaluated with estuarine sediments contg. 2 levels (5 and 15 μmol/g) of acid volatile sulfides (AVS). Their influence on Zn bioavailability was also evaluated by a parallel, 10-day amphipod (Leptocheirus plumulosus) mortality test at 5, 20, and 85 days of equilibration. During the equilibration, AVS increased (≤2-fold) with spiked Zn concn. ([Zn]), whereas Zn-simultaneously extd. metals ([SEM]; Zn with AVS) remained relatively const. Concns. of Zn in PW decreased most rapidly during the initial 30 days and by 11- to 23-fold during the whole 95-day equilibration period. The apparent partitioning coeff. (Kpw, ratio of [Zn] in SEM to PW) increased by 10- to 20-fold with time and decreased with spiked [Zn] in sediments. The decrease of PW [Zn] could be explained by a combination of changes in AVS and redistribution of Zn into more insol. phases as the sediment aged. Amphipod mortality decreased significantly with the equilibration time, consistent with decrease in dissolved [Zn]. The median lethal concn. (LC50) value (33μM) in the 2nd bioassay, conducted after 20 days of equilibration, was 2-fold the LC50 in the initial bioassay at 5 days of equilibration, probably because of the change of dissolved Zn speciation. Sediment bioassay protocols using a short equilibration time and high spiked metal concns. could accentuate partitioning of metals to the dissolved phase and shift the pathway for metal exposure toward the dissolved phase.
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    OpenURL UNIV OF NORTH TEXAS
  20. 20.
    Böhlke, J. K.; de Laeter, J. R.; De Bièvre, P.; Hidaka, H.; Peiser, H. S.; Rosman, K. J. R.; Taylor, P. D. P.Isotopic composition of the elements, 2001 J. Phys. Chem. Ref. Data 2005, 34, 57– 67
    [CrossRef], [CAS]
    20.
    Isotopic Compositions of the Elements, 2001
    Bohlke, J. K.; de Laeter, J. R.; De Bievre, P.; Hidaka, H.; Peiser, H. S.; Rosman, K. J. R.; Taylor, P. D. P.
    Journal of Physical and Chemical Reference Data (2005), 34 (1), 57-67 CODEN: JPCRBU; ISSN:0047-2689. (American Institute of Physics)
    A review. The Commission on At. Wts. and Isotopic Abundances of the International Union of Pure and Applied Chem. completed its last review of the isotopic compns. of the elements as detd. by isotope-ratio mass spectrometry in 2001. That review involved a crit. evaluation of the published literature, element by element, and forms the basis of the table of the isotopic compns. of the elements (TICE) presented here. For each element, TICE includes evaluated data from the "best measurement" of the isotope abundances in a single sample, along with a set of representative isotope abundances and uncertainties that accommodate known variations in normal terrestrial materials. The representative isotope abundances and uncertainties generally are consistent with the std. at. wt. of the element Ar(E) and its uncertainty U[Ar(E)] recommended by CAWIA in 2001.
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    OpenURL UNIV OF NORTH TEXAS
  21. 21.
    U.S. Environmental Protection Agency. Methods for Measuring the Acute Toxicity of Effluents and Receiving Waters to Freshwater and Marine Organisms; U.S. EPA: Washington, DC, 2002; EPA-821-R-02-012.
    There is no corresponding record for this reference.
    OpenURL UNIV OF NORTH TEXAS
  22. 22.
    Schemel, L. E.; Kimball, B. A.; Runkel, R. L.; Cox, M. H.Formation of mixed Al-Fe colloidal sorbent and dissolved-colloidal partitioning of Cu and Zn in the Cement Creek – Animas River confluence, Silverton, Colorado Appl. Geochem. 2007, 22, 1467– 1484
    [CrossRef], [CAS]
    22.
    Formation of mixed Al-Fe colloidal sorbent and dissolved-colloidal partitioning of Cu and Zn in the Cement Creek - Animas River Confluence, Silverton, Colorado
    Schemel, Laurence E.; Kimball, Briant A.; Runkel, Robert L.; Cox, Marisa H.
    Applied Geochemistry (2007), 22 (7), 1467-1484 CODEN: APPGEY; ISSN:0883-2927. (Elsevier Ltd.)
    Transport and chem. transformations of dissolved and colloidal Al, Fe, Cu and Zn were studied by detailed sampling in the mixing zone downstream from the confluence of Cement Creek (pH 4.1) with the Animas River (pH 7.6). Complete mixing resulted in circumneutral pH in the downstream reach of the 1300 m study area. All four metals were transported through this mixing zone without significant losses to the streambed, and they exhibited transformations from dissolved to colloidal forms to varying degrees during the mixing process. Nearly all of the Al formed colloidal hydrous Al oxides (HAO) as pH increased (4.8-6.5), whereas colloidal hydrous Fe oxides (HFO) were supplied by Cement Creek as well as formed in the mixing zone primarily at higher pH (>6.5). The short travel time through the mixing zone (approx. 40 min) and pH limited the formation of HFO from dissolved Fe2+ supplied by Cement Creek. Although the proportions of HAO and HFO varied as the streams mixed, the colloidal sorbent typically was enriched in HAO relative to HFO by a factor of 1.5-2.1 (by mole) in the pH range where dissolved-to-colloidal partitioning of Cu and Zn was obsd. Model simulations of sorption by HFO (alone) greatly underestimated the dissolved-to-colloidal partitioning of Zn. Previous studies have shown that HAO-HFO mixts. can sorb greater amts. of Zn than HFO alone, but the high Zn-to-sorbent ratio in this mixing zone could also account for greater partitioning. In contrast to Zn, comparisons with model simulations did not show that Cu sorption was greater than that for HFO alone, and also indicated that sorption was possibly less than what would be expected for a non-interactive mixt. of these two sorbents. These field results for Cu, however, might be influenced by (org.) complexation or other factors in this natural system. Lab. mixing expts. using natural source waters (upstream of the confluence) showed that the presence of HFO in the mixed sorbent resulted in greater Cu partitioning than for HAO alone, and that the effect was greater with increasing (mole fraction) HFO. This was consistent with field results that showed greater Cu sorption when addnl. HFO was formed in the downstream reach of the mixing zone. Further research is needed to identify the significance of surface-related mechanisms specific to HAO-HFO mixts. that could affect the partitioning of Cu in natural systems.
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    OpenURL UNIV OF NORTH TEXAS
  23. 23.
    Irving, E. C.; Baird, D. J.; Culp, J. M.Ecotoxicological responses of the mayfly Baetis tricaudatus to dietary and waterborne cadmium: implications for toxicity testing Environ. Toxicol. Chem. 2003, 22, 1058– 1064
    [CrossRef], [PubMed], [CAS]
    23.
    Ecotoxicological responses of the mayfly Baetis tricaudatus to dietary and waterborne cadmium: Implications for toxicity testing
    Irving, Elaine C.; Baird, Donald J.; Culp, Joseph M.
    Environmental Toxicology and Chemistry (2003), 22 (5), 1058-1064 CODEN: ETOCDK; ISSN:0730-7268. (SETAC Press)
    Trace metals readily accumulated by stream periphyton may enter aquatic food chains through grazer ingestion. Hence, expts. were conducted to det. the ecotoxicol. responses of the grazing mayfly B. tricaudatus to dietary cadmium. Short-term feeding expts. indicated that B. tricaudatus nymphs did not initially avoid grazing on cadmium-contaminated diatom mats. During a partial life-cycle expt., 4 and 10 μg/g of dietary cadmium significantly inhibited grazing whereas 10 μg/g significantly inhibited growth. Feeding inhibition was the likely mechanism that inhibited growth (i.e., through reduced energy intake). Conversely, when exposed to waterborne cadmium using lethal toxicity test procedures, B. tricaudatus nymphs were relatively tolerant (96-h median lethal concn., 1.611 μg/L). Thus, sublethal responses to dietary exposure appeared to be more sensitive than lethal responses to waterborne exposure. Because adult mayfly fecundity is a function of nymph size at emergence, dietary cadmium exposure could increase the extinction probability within mayfly populations. The present study highlights the importance of dietary exposure routes in detg. the ecotoxicol. responses of an organism to a contaminant. Furthermore, the findings emphasize the advantage of evaluating a combination of ecol. relevant, lethal, and sublethal endpoints in lab. methods used to generate data for ecol. risk assessment and regulation.
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    OpenURL UNIV OF NORTH TEXAS
  24. 24.
    Croteau, M. N.; Dybowska, A. D.; Luoma, S. N.; Valsami-Jones, E.A novel approach reveals that ZnO nanoparticles are bioavailable and toxic after dietary exposure Nanotoxicology 2011, 5, 79– 90
    [CrossRef], [CAS]
    24.
    A novel approach reveals that zinc oxide nanoparticles are bioavailable and toxic after dietary exposures
    Croteau, Marie-Noele; Dybowska, Agnieszka D.; Luoma, Samuel N.; Valsami-Jones, Eugenia
    Nanotoxicology (2011), 5 (1), 79-90 CODEN: NANOGK; ISSN:1743-5404. (Informa Healthcare)
    If engineered nanomaterials are released into the environment, some are likely to end up assocd. with the food of animals due to aggregation and sorption processes. However, few studies have considered dietary exposure of nanomaterials. Here we show that zinc (Zn) from isotopically modified 67ZnO particles is efficiently assimilated by freshwater snails when ingested with food. The 67Zn from nano-sized 67ZnO appears as bioavailable as 67Zn internalized by diatoms. Apparent agglomeration of the zinc oxide (ZnO) particles did not reduce bioavailability, nor preclude toxicity. In the diet, ZnO nanoparticles damage digestion: snails ate less, defecated less and inefficiently processed the ingested food when exposed to high concns. of ZnO. It was not clear whether the toxicity was due to the high Zn dose achieved with nanoparticles or to the ZnO nanoparticles themselves. Further study of exposure from nanoparticles in food would greatly benefit assessment of ecol. and human health risks.
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    OpenURL UNIV OF NORTH TEXAS
  25. 25.
    Croteau, M. N.; Luoma, S. N.; Pellet, B.Determining metal assimilation efficiency in aquatic invertebrates using enriched stable metal isotope tracers Aquat. Toxicol. 2007, 83, 116– 125
    [CrossRef], [PubMed], [CAS]
    25.
    Determining metal assimilation efficiency in aquatic invertebrates using enriched stable metal isotope tracers
    Croteau, Marie-Noele; Luoma, Samuel N.; Pellet, Bastien
    Aquatic Toxicology (2007), 83 (2), 116-125 CODEN: AQTODG; ISSN:0166-445X. (Elsevier B.V.)
    We employ a novel approach that combines pulse-chase feeding and multi-labeled stable isotopes to det. gut passage time (GPT), gut retention time (GRT), food ingestion rate (IR) and assimilation efficiency (AE) of three trace elements for a freshwater gastropod. Lettuce isotopically enriched in 53Cr, 65Cu and 106Cd was fed for 2 h to Lymnaea stagnalis. The release of tracers in feces and water was monitored for 48 h, during which unlabeled lettuce was provided ad libidum. The first defecation of 53Cr occurred after 5 h of depuration (GPT), whereas 90% of the ingested 53Cr was recovered in the feces after 22.5 h of depuration (GRT). 53Chromium was not significantly accumulated in the soft tissues upon exposure. In contrast, 65Cu and 106Cd assimilation was detectable for most exptl. snails, i.e., 65/63Cu and 106/114Cd ratios in exposed snails were higher than those for controls. Food IR during the labeled feeding phase was 0.16±0.07 g g-1 d-1. IR was inferred from the amt. of 53Cr egested in the feces during depuration and the concn. of 53Cr in the labeled lettuce. Assimilation efficiencies (±95% CI) detd. using mass balance calcns. were 84±4% for Cu and 85±3% for Cd. The ratio method yields similar AE ests. Expanding the application of this novel stable isotope tracer technique to other metals in a wide variety of species will provide unique opportunities to evaluate the interplay between digestive processes and dietary influx of metals. Understanding the biol. processes that modulate diet-borne metal uptake is crucial to assess the toxicity of diet-borne metals.
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    OpenURL UNIV OF NORTH TEXAS
  26. 26.
    Misra, S. K.; Dybowska, A.; Berhanu, D.; Croteau, M. N.; Luoma, S. N.; Boccaccini, A. R.; Valsami-Jones, E.Traceable nanoparticles: isotopically modified 65CuO nanoparticles Environ. Sci. Technol. 2012, 46, 1216– 1222
    [ACS Full Text ACS Full Text], [CAS]
    26.
    Isotopically Modified Nanoparticles for Enhanced Detection in Bioaccumulation Studies
    Misra, Superb K.; Dybowska, Agnieszka; Berhanu, Deborah; Croteau, Marie Noele; Luoma, Samuel N.; Boccaccini, Aldo R.; Valsami-Jones, Eugenia
    Environmental Science & Technology (2012), 46 (2), 1216-1222 CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    This work presents results on synthesis of isotopically enriched (99% 65Cu) Cu oxide nanoparticles and its application in ecotoxicol. studies. 65CuO nanoparticles were synthesized as spheres (7 nm) and rods (7 × 40 nm). Significant differences were obsd. between the reactivity and dissoln. of spherical and rod shaped nanoparticles. The extreme sensitivity of the stable isotope tracing technique developed here allowed detg. Cu uptake at exposure concns. equiv. to background Cu concns. in freshwater systems (0.2-30 μg/L). Without a tracer, detection of newly accumulated Cu was impossible, even at exposure concns. surpassing some of the most contaminated water systems (>1 mg/L).
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    OpenURL UNIV OF NORTH TEXAS
  27. 27.
    Luoma, S. N.; Rainbow, P. S.Why is metal bioaccumulation so variable? Biodynamics as a unifying concept Environ. Sci. Technol. 2005, 39, 1921– 1931
    [ACS Full Text ACS Full Text], [CAS]
    27.
    Why Is Metal Bioaccumulation So Variable? Biodynamics as a Unifying Concept
    Luoma, Samuel N.; Rainbow, Philip S.
    Environmental Science and Technology (2005), 39 (7), 1921-1931 CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Ecol. risks from metal contaminants are difficult to document because responses differ among species, threats differ among metals, and environmental influences are complex. Unifying concepts are needed to better tie together such complexities. Here we suggest that a biol. based conceptualization, the biodynamic model, provides the necessary unification for a key aspect in risk: metal bioaccumulation (internal exposure). The model is mechanistically based, but empirically considers geochem. influences, biol. differences, and differences among metals. Forecasts from the model agree closely with observations from nature, validating its basic assumptions. The biodynamic metal bioaccumulation model combines targeted, high-quality geochem. analyses from a site of interest with parametrization of key physiol. consts. for a species from that site. The physiol. parameters include metal influx rates from water, influx rates from food, rate consts. of loss, and growth rates (when high). We compiled results from 15 publications that forecast species-specific bioaccumulation, and compare the forecasts to bioaccumulation data from the field. These data consider concns. that cover 7 orders of magnitude. They include 7 metals and 14 species of animals from 3 phyla and 11 marine, estuarine, and freshwater environments. The coeff. of detn. (R2) between forecasts and independently obsd. bioaccumulation from the field was 0.98. Most forecasts agreed with observations within 2-fold. The agreement suggests that the basic assumptions of the biodynamic model are tenable. A unified explanation of metal bioaccumulation sets the stage for a realistic understanding of toxicity and ecol. effects of metals in nature.
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    OpenURL UNIV OF NORTH TEXAS
  28. 28.
    Luoma, S. N.; Fisher, N. S.Uncertainties in assessing contaminant exposure from sediments. In Ecological Risk Assessment of Contaminated Sediments; Ingersoll, C. G.; Dillon, T.; Biddinger, G. R., Eds.; SETAC Special Publication Series: Pensacola, FL, 1997.
    There is no corresponding record for this reference.
    OpenURL UNIV OF NORTH TEXAS
  29. 29.
    Croteau, M. N.; Luoma, S. N.Predicting dietborne metal toxicity from metal influxes Environ. Sci. Technol. 2009, 43, 4915– 4921
    [ACS Full Text ACS Full Text], [CAS]
    29.
    Predicting Dietborne Metal Toxicity from Metal Influxes
    Croteau, Marie-Noele; Luoma, Samuel N.
    Environmental Science & Technology (2009), 43 (13), 4915-4921 CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Dietborne metal uptake prevails for many species in nature. However, the links between dietary metal exposure and toxicity are not well understood. Sources of uncertainty include the lack of suitable tracers to quantify exposure for metals such as copper, the difficulty to assess dietary processes such as food ingestion rate, and the complexity to link metal bioaccumulation and effects. The authors characterized dietborne copper, nickel, and cadmium influxes in a freshwater gastropod exposed to diatoms labeled with enriched stable metal isotopes. Metal influxes in Lymnaea stagnalis correlated linearly with dietborne metal concns. over a range encompassing most environmental exposures. Dietary Cd and Ni uptake rate consts. (kuf) were, resp., 3.3 and 2.3 times higher than that for Cu. Detoxification rate consts. (kdetox) were similar among metals and appeared 100 times higher than efflux rate consts. (ke). Extremely high Cu concns. reduced feeding rates, causing the relationship between exposure and influx to deviate from linearity; i.e., Cu uptake rates leveled off between 1500 and 1800 nmol g-1 day-1. L. stagnalis rapidly takes up Cu, Cd, and Ni from food but detoxifies the accumulated metals, instead of reducing uptake or intensifying excretion. Above a threshold uptake rate, however, the detoxification capabilities of L. stagnalis are overwhelmed.
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    OpenURL UNIV OF NORTH TEXAS
  30. 30.
    Croteau, M. N.; Misra, S. K.; Luoma, S. N.; Valsami-Jones, E.Silver bioaccumulation dynamics in a freshwater invertebrate after aqueous and dietary exposure to nanosized and ionic Ag Environ. Sci. Technol. 2011, 45, 6600– 6607
    [ACS Full Text ACS Full Text], [CAS]
    30.
    Silver Bioaccumulation Dynamics in a Freshwater Invertebrate after Aqueous and Dietary Exposures to Nanosized and Ionic Ag
    Croteau, Marie-Noele; Misra, Superb K.; Luoma, Samuel N.; Valsami-Jones, Eugenia
    Environmental Science & Technology (2011), 45 (15), 6600-6607 CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    The authors compared silver (Ag) bioavailability and toxicity to a freshwater gastropod after exposure to ionic silver (Ag+) and to Ag nanoparticles (Ag NPs) capped with citrate or with humic acid. Silver form, exposure route, and capping agent influence Ag bioaccumulation dynamics in Lymnaea stagnalis. Snails efficiently accumulated Ag from all forms after either aq. or dietary exposure. For both exposure routes, uptake rates were faster for Ag+ than for Ag NPs. Snails efficiently assimilated Ag from Ag NPs mixed with diatoms (assimilation efficiency (AE) ranged from 49 to 58%) and from diatoms pre-exposed to Ag+ (AE of 73%). In the diet, Ag NPs damaged digestion. Snails ate less and inefficiently processed the ingested food, which adversely impacted their growth. Loss rates of Ag were faster after waterborne exposure to Ag NPs than after exposure to dissolved Ag+. Once Ag was taken up from diet, whether from Ag+ or Ag NPs, Ag was lost extremely slowly. Large Ag body concns. are thus expected in L. stagnalis after diet-borne exposures, esp. to citrate-capped Ag NPs. Ingestion of Ag assocd. with particulate materials appears as the most important vector of uptake. Nanosilver exposure from food might trigger important environmental risks.
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    OpenURL UNIV OF NORTH TEXAS
  31. 31.
    Wang, W. X.; Fisher, N. S.Delineating metal accumulation pathways for marine invertebrates Sci. Total Environ. 1999, 237–238, 459– 472
    [CrossRef], [CAS]
    31.
    Delineating metal accumulation pathways for marine invertebrates
    Wang, W.-X.; Fisher, N. S.
    Science of the Total Environment (1999), 237/238 (), 459-472 CODEN: STENDL; ISSN:0048-9697. (Elsevier Science Ireland Ltd.)
    A review with 80 refs. concerning metal accumulation pathways in marine invertebrates, emphasizing studies using both exptl. and modeling approaches, is given. Topics discussed include: sepn. of uptake pathways using a kinetic modeling approach; and significance of exposure pathways.
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    OpenURL UNIV OF NORTH TEXAS
  32. 32.
    Wang, W. X.; Fisher, N. S.; Luoma, S. N.Kinetic determinations of trace element bioaccumulation in the mussel Mytilus edulis Mar. Ecol.: Prog. Ser. 1996, 140, 91– 113
    [CrossRef], [CAS]
    32.
    Kinetic determinations of trace element bioaccumulation in the mussel Mytilus edulis
    Wang, Wen-Xiong; Fisher, Nicholas S.; Luoma, Samuel N.
    Marine Ecology: Progress Series (1996), 140 (1 to 3), 91-113 CODEN: MESEDT; ISSN:0171-8630. (Inter-Research)
    Lab. expts. employing radiotracer methodol. were conducted to det. the assimilation efficiencies from ingested natural seston, the influx rates from the dissolved phase and the efflux rates of 6 trace elements (Ag, Am, Cd, Co, Se and Zn) in the mussel Mytilus edulis. A kinetic model was then employed to predict trace element concn. in mussel tissues in 2 locations for which mussel and environmental data are well described: South San Francisco Bay (California, USA) and Long Island Sound (New York, USA). Assimilation efficiencies from natural seston ranged from 5 to 18% for Ag 0.6 to 1% for Am, 8 to 20% for Cd 12 to 16% for Co, 28 to 34% for Se, and 32 to 41% for Zn. Differences in chlorophyll a concn. in ingested natural seston did not have significant impact on the assimilation of Am, Co, Se and Zn. The influx rate of elements from the dissolved phase increased with the dissolved concn., conforming to Freundlich adsorption isotherms. The calcd. dissolved uptake rate const. was greatest for Ag, followed by Zn > Am = Cd > Co > Se. The estd. adsorption efficiency from the dissolved phase was 1.53% for Ag, 0.34% for Am, 0.31% for Cd, 0.11% for Co, 0.03% for Se and 0.89% for Zn. Salinity had an inverse effect on the influx rate from the dissolved phase and dissolved phase and dissolved org. carbon concn. had no significant effect on trace element uptake. The calcd. efflux rate consts. for all elements ranged from 1.0 to 3.0% d-1. The route of trace element uptake (food vs dissolved) and the duration of exposure to dissolved trace elements (12 h vs 6 d) did not significantly influence trace element efflux rates. A model which used the exptl. detd. influx and efflux rates for each of the trace elements, following exposure from ingested food and from water, predicted concns. of Ag, Cd, Se and Zn in mussels that were directly comparable to actual tissue concns. independently measured in the 2 ref. sites in national monitoring programs. Sensitivity anal. indicated that the total suspended solids load, which can affect mussel feeding activity, assimilation, and trace element concn. in the dissolved and particulate phases, can significantly influence metal bioaccumulation for particle-reactive elements such as Ag and Am. For all metals, concns. in mussels are proportionately related to total metal load in the water column and their assimilation efficiency from ingested food, under conditions typical of coastal waters. For Ag, Am, Cd, Co and Zn, the relative contribution from the dissolved phase decreases significantly with increasing trace element partition coeffs. for suspended particles and the assimilation efficiency in mussels of ingested trace elements; values range between 33 and 67% for Ag 5 and 17% for Am, 47 and 82% for Cd, 4 and 30% for Co, and 17 and 51% for Zn.
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    OpenURL UNIV OF NORTH TEXAS
  33. 33.
    Newman, M. C.; Unger, M. A.Sublethal effects to individuals. In Fundamentals of Ecotoxicology; CRC Press: New York, 2003.
    There is no corresponding record for this reference.
    OpenURL UNIV OF NORTH TEXAS
  34. 34.
    Boisson, F.; Hartl, M. G. J.; Fowler, S. W.; Amiard-Triquet, C.Influence of chronic exposure to silver and mercury in the field on the bioaccumulation potential of the bivalve Macoma balthica J. Exp. Mar. Biol. Ecol. 1998, 311, 315– 337
    There is no corresponding record for this reference.
    OpenURL UNIV OF NORTH TEXAS
  35. 35.
    Blackmore, G.; Wang, W. X.Uptake and efflux of Cd and Zn by the green mussel Perna viridis after metal preexposure Environ. Sci. Technol. 2002, 36, 989– 995
    [ACS Full Text ACS Full Text], [CAS]
    35.
    Uptake and Efflux of Cd and Zn by the Green Mussel Perna viridis after Metal Preexposure
    Blackmore, Graham; Wang, Wen-Xiong
    Environmental Science and Technology (2002), 36 (5), 989-995 CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Cadmium and zinc uptake from the dissolved phase, assimilation efficiency from the dietary phase, efflux rate consts., and body burden as well as clearance rate were measured in the green mussel Perna viridis with or without lab. preexposure to Cd or Zn. Efflux rate consts. and clearance rates were little affected by preexposure to either Cd or Zn. In contrast, the assimilation of Cd increased by 1.2-1.6× in mussels preexposed to Cd (subsequent Cd concns. 10.2-25.9 μg g-1) as compared to controls (0.19-0.39 μg g-1). This increase corresponded to an elevation in the proportion of Cd assocd. with the metallothionein-like proteins (MTLPs) in the mussels, suggesting that exposure to Cd and subsequent induction of MTLPs affected Cd accumulation. Exposure to Zn only resulted in elevated body concns. following 7-d exposure to 250 μg L-1, although Zn and Cd uptake from the dissolved phase were reduced by 24-47% by exposure to a lower concn. (100 μg L-1) for 7 and 21 d. Despite the lack of an increase in body Zn concn., the subcellular distribution was altered such that the proportion of Zn assocd. with the metal-rich granules increased. This study indicates the importance of the subcellular distribution of metals in affecting the biokinetics and thus the toxic effects of metals on aquatic animals. Cd preexposure has potential effects on its influx from the dietary phase, e.g., increasing the importance of dietary uptake and further increasing the body burdens. In contrast, preexposure to Zn has a neg. effect on Cd and Zn influx from the dissolved phase, suggesting the mechanism of Zn regulation but also potentially reducing Cd uptake and body concns. over the long-term exposure. Such effects may have implications for biomonitoring studies involving a single species that modifies physiol. processes affecting metal uptake (and hence bioavailability). Caution is needed in extrapolating data to species not capable of making such changes, particularly for Cd, which is not regulated and for which the effects of an elevated body burden are most obvious.
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    OpenURL UNIV OF NORTH TEXAS
  36. 36.
    Shi, D. S.; Blackmore, G.; Wang, W. X.Effects of aqueous and dietary preexposure and resulting body burden on silver biokinetics in the green mussel Perna viridis Environ. Sci. Technol. 2003, 37, 936– 943
    [ACS Full Text ACS Full Text], [CAS]
    36.
    Effects of Aqueous and Dietary Preexposure and Resulting Body Burden on Silver Biokinetics in the Green Mussel Perna viridis
    Shi, Dalin; Blackmore, Graham; Wang, Wen-Xiong
    Environmental Science and Technology (2003), 37 (5), 936-943 CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    To det. whether preexposure of green mussel Perna viridis to Ag influenced metal uptake kinetics the authors compared various physiol. indicators of metal uptake kinetics between the control mussels and mussels preexposed to Ag in both diet and water at different levels (up to 5 wk). In all preexposed mussels, the assimilation of Ag increased by 1.1-3.0 times with increasing Ag body concn. (0.651-19.3 μg g-1) as compared with the controls (Ag body concn. of 0.311-0.479 μg g-1), whereas the efflux rate consts. decreased by 45-88%. There was no significant increase in Ag assocd. with the metallothionein-like protein (MTLP) fraction following exposure of the mussels to Ag through either the dissolved or food phase. The clearance rates were little affected or depressed by Ag preexposure, and the relationship between the Ag influx rate from the dissolved phase and the Ag preexposure was somewhat complicated. The influx rate decreased with increasing Ag body burden at <2.5 μg g-1, above which it increased with increasing Ag body burden. These results indicate that the mussels may modify physiol. processes to ambient chronic Ag exposure, consequently accumulating more Ag. Ag body concn. in these mussels may therefore increase disproportionally in response to increasing Ag concn. in the ambient environments. Ag preexposure and resulting body burden should be considered carefully when interpreting the obsd. Ag concn. in biomonitoring animals to evaluate the Ag pollution in seawater.
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    OpenURL UNIV OF NORTH TEXAS
  37. 37.
    Rainbow, P. S.; Ng, T. Y. T.; Shi, D.; Wang, W. X.Acute dietary pre-exposure and trace metal bioavailability to the barnacle Balanus amphitrite J. Exp. Mar. Biol. Ecol. 2004, 311, 315– 337
    [CrossRef], [CAS]
    37.
    Acute dietary pre-exposure and trace metal bioavailability to the barnacle Balanus amphitrite
    Rainbow, Philip S.; Ng, Tania Y.-T.; Shi, Dalin; Wang, Wen-Xiong
    Journal of Experimental Marine Biology and Ecology (2004), 311 (2), 315-337 CODEN: JEMBAM; ISSN:0022-0981. (Elsevier B.V.)
    Rates of uptake from soln. and assimilation efficiencies of the trace metals Ag, Cd and Zn were investigated in the barnacle Balanus amphitrite after exposure in the lab. for 19 days to low and high doses of added Ag and Cd in a diatom (Thalassiosira weissflogii) diet, the major route of metal uptake in barnacles. The hypothesis under test was that acute metal pre-exposure would affect the assimilation efficiency (AE) of that and other metals and their rate of uptake from soln. It was found that pre-exposure of the barnacles to atypically high dietary challenges of Cd and Ag did not cause changes in the rates of uptake of Cd, Ag or Zn from soln. Similarly, there was no clear consistent effect of dietary pre-exposure to Cd or Ag on the assimilation efficiency of Cd, Ag or Zn. The efflux rates of the metals were also comparable following the acute dietary exposure. Subcellular fractionation data indicated that the majority of the three metals were partitioned in the insol. fraction, with very little in the sol. fraction consisting of metallothionein-like proteins and other (heat-sensitive) proteins. The lack of induction of increased Cd or Ag AE after pre-exposure in barnacles contrasts with results for mussels; this inconsistency is interpreted to result from differences in physiol. accumulation patterns, the barnacles relying to an extreme extent on insol. detoxification.
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    OpenURL UNIV OF NORTH TEXAS
  38. 38.
    Cismasu, A. C.; Michel, F. M.; Stebbins, J. F.; Levard, C.; Brown, G. E.Properties of impurity-bearing ferrihydrite I. Effects of Al content and precipitation rate on the structure of 2-line ferrihydrite Geochim. Cosmochim. Acta 2012, 92, 275– 291
    [CrossRef], [CAS]
    38.
    Properties of impurity-bearing ferrihydrite I. Effects of Al content and precipitation rate on the structure of 2-line ferrihydrite
    Cismasu, A. Cristina; Michel, F. Marc; Stebbins, Jonathan F.; Levard, Clement; Brown, Gordon E., Jr.
    Geochimica et Cosmochimica Acta (2012), 92 (), 275-291 CODEN: GCACAK; ISSN:0016-7037. (Elsevier Ltd.)
    The assocn. of Al with ferrihydrite (Fh) may have a considerable effect on the compn., structure, and surface properties of Fh nanoparticles, and thus impact its reactivity and interaction with pollutant species. Aluminous Fh is abundant in natural environments, but the mode of assocn. of Al with this nanomineral is not yet fully understood. Al3+ speciation may vary from true chem. substitution for Fe3+, to adsorption or surface pptn., and/or to formation of a mixt. of two (or more) individual nanoscale phases. The conditions of formation (i.e. slow vs. rapid pptn.) may also affect the nature of Fh nanoparticles in terms of their crystallinity, phase purity, and Al speciation. A variety of lab. (TEM, NMR, ICP-AES) and synchrotron-based techniques (X-ray total scattering and PDF anal., scanning transmission X-ray microscopy, Al K-edge XANES spectroscopy) were used to characterize two synthetic Al-bearing Fh series formed at different pptn. rates in the presence of 5-40 mol% Al. We find that Al is dominantly octahedrally coordinated in the synthetic Fh samples and that up to 20-30 mol% Al substitutes for Fe in the Fh structure, regardless of the synthesis method we used. Formation of sep. aluminous phases (e.g., gibbsite) was most significant at Al concns. above 30 mol% Al in slowly pptd. samples. However, small amts. (<6% of total Al) of Al-hydroxide phases were also detected by NMR spectroscopy in samples with lower Al content (as low as 15 mol% Al), particularly in the Fh series that was pptd. slowly. Furthermore, it appears that the amt. of Al incorporated in Fh is not affected by the synthesis methods we used and is more likely controlled by the accumulated strain caused by Al substitution in the Fh lattice. Given the prevalence of naturally occurring aluminous ferrihydrite, assumptions about ferrihydrite reactivity in natural environments should consider the impact of Al substitution on redn. potential, Fe bioavailability, as well as sorption reactions.
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    OpenURL UNIV OF NORTH TEXAS
  39. 39.
    Decho, A. W.; Luoma, S. N.Time-courses in the retention of food material in the bivalves Potamocorbula amurensis and Macoma balthica: significance to the absorption of carbon and chromium Mar. Ecol. Prog. Ser. 1996, 78, 303– 314
    [CrossRef]
    There is no corresponding record for this reference.
    OpenURL UNIV OF NORTH TEXAS
  40. 40.
    Mayer, L. M.; Schick, L. L.; Self, R. F. L.; Jumars, P. A.; Findlay, R. H.; Chen, Z.; Sampson, S.Digestive environments of benthic macroinvertebrate guts: enzymes, surfactants and dissolved organic matter J. Mar. Res. 1997, 55, 785– 812
    [CrossRef], [CAS]
    40.
    Digestive environments of benthic macroinvertebrate guts: enzymes, surfactants and dissolved organic matter
    Mayer, Lawrence M.; Schick, Linda L.; Self, Robert F. L.; Jumars, Peter A.; Findlay, Robert H.; Chen, Zhen; Sampson, Stephen
    Journal of Marine Research (1997), 55 (4), 785-812 CODEN: JMMRAO; ISSN:0022-2402. (Sears Foundation for Marine Research)
    Hydrolytic enzyme activity, surfactancy, and dissolved org. matter in the digestive lumens of 19 benthic echinoderm and polychaete species were examd., using consistent and quantifiable methods. Enzyme activities were compared with those of extracellular enzymes from ambient sediments. Enzyme activities ranged over five orders of magnitude, with avs. decreasing in the order polychaetes > echinoderms > sediment. Highest activities in animals were usually assocd. with fluid phase in midgut sections, with posterior-ward decreased indicating little export to the external environment. At some phyletic levels, activity correlated inversely with animal size. Hydrolase patterns reflected food type; for example, high lipase:protease rations in carnivores reflected esterified lipids in their diets. High surfactant activity was found in gut sections having high enzyme activity. Deposit feeders had the most intense surfactancy, including evidence for micelles. While enzymes reflected the biochem. nature of the digestive food substrate regardless of feeding mode (e.g., deposit vs. suspension feeder), surfactants reflected diln. of this digestible substrate with mineral grains. Dissolved org. matter levels were high, with amino acids reaching levels >1M and lipids commonly 1 g L-1. Among polychaete deposit-feeders, low mol. wt. amino acids reflected the compn. of the food substrate, but were present at much higher concns. than could be explained by sediment present in the gut-suggesting longer residence times for fluid than for transiting sediment particles. Deposit feeder digestive fluids are better able to solubilize sedimentary food substrates than are sedimentary extracellular enzymes, owing to either more powerful solubilizing agents of to their deployment in freely diffusing, dissolved form. Gut environments may lead to chem. condensation as well as solubilization reactions.
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    OpenURL UNIV OF NORTH TEXAS
  41. 41.
    Boer, H. H.; Kits, K. S.Histochemical and ultrastructural study of the alimentary tract of the freshwater snail Lymnaea stagnalis J. Morphol. 1990, 205, 97– 111
    [CrossRef]
    There is no corresponding record for this reference.
    OpenURL UNIV OF NORTH TEXAS
  42. 42.
    Carriker, M. R.Observations on the functioning of the alimentary system of the snail Lymnaea stagnalis appressa Say Biol. Bull. 1946, 91, 88– 111
    [CrossRef], [PubMed], [CAS]
    42.
    Observations on the functioning of the alimentary system of the snail Lymnaea stagnalis appressa Say
    CARRIKER M R
    The Biological bulletin (1946), 91 (1), 88-111 ISSN:0006-3185.
    There is no expanded citation for this reference.
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    OpenURL UNIV OF NORTH TEXAS
  43. 43.
    Farag, A. M.; Woodward, D. F.; Brumbaugh, W.; Goldstein, J. N.; MacConnell, E.; Hogstrand, C.; Barrows, F. T.Dietary effects of metals-contaminated invertebrates from the Coeur d’Alene River, Idaho, on cutthroat trout Trans. Am. Fish. Soc. 1999, 128, 578– 592
    [CrossRef], [CAS]
    43.
    Dietary effects of metals-contaminated invertebrates from the Coeur d'Alene River, Idaho, on cutthroat trout
    Farag, A. M.; Woodward, D. F.; Brumbaugh, W.; Goldstein, J. N.; MacConnell, E.; Hogstrand, C.; Barrows, F. T.
    Transactions of the American Fisheries Society (1999), 128 (4), 578-592 CODEN: TAFSAI; ISSN:0002-8487. (American Fisheries Society)
    Benthic macroinvertebrates with elevated concns. of metals were collected from the Coeur d'Alene (CDA) River, Idaho, pasteurized, and fed to cutthroat trout Oncorhynchus clarki in the lab. from start of feeding until 90 d posthatch. Invertebrates were collected from two sites known to contain elevated concns. of metals: near Pinehurst in the South Fork of the CDA River and at Cataldo, approx. 5 km below the confluence of the South Fork and the North Fork. Invertebrates collected from a relatively clean site in the North Fork were used as a ref. diet. The authors performed measurements of fish health that indicate reduced fitness of fish fed the South Fork and Cataldo diets. Effects measured were reduced feeding activity, increased no. of macrophage aggregates and hyperplasia of cells in the kidney, degeneration of mucosal epithelium in the pyloric caecae, and metallothionein induction. These effects would likely reduce growth and survival of fish in the wild. Vacuolization of glial cells were also obsd. in fish fed the Cataldo diet. Metals in the water often exacerbated the histol. effects obsd. Although the invertebrates collected near Cataldo had lower concns. of arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) than the invertebrates from the South Fork, fish fed the Cataldo diet had equally high or higher concns. of all metals except As by day 44. The Cataldo diet also caused the most deleterious effects on survival and growth. These findings are esp. important for early life stage fish, whose diet consists wholly of benthic macroinvertebrates. Therefore, fish feeding on invertebrates in the CDA River below the Bunker Hill smelting complex are at risk of reduced fitness.
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    OpenURL UNIV OF NORTH TEXAS
  44. 44.
    Maltby, L.; Kedwards, T. J.; Forbes, V. E.; Grasman, K.; Kammenga, J. E.; Munns, W. R.; Ringwood, A. H.; Weis, J. S.; Wood, S. N.Linking individual-level responses and population-level consequences. In Ecological Variability: Separating Natural from Anthropogenic Causes of Ecosystems Impairment; Baird, D. J.; Burton, G. A., Eds.; SETAC Press: Pensacola, FL, 2001.
    There is no corresponding record for this reference.
    OpenURL UNIV OF NORTH TEXAS
  45. 45.
    Newman, M. C.; McIntosh, A. W.Appropriateness of Aufwuchs as a monitor of bioaccumulation Environ. Pollut. 1989, 60, 83– 100
    [CrossRef], [PubMed], [CAS]
    45.
    Appropriateness of aufwuchs as a monitor of bioaccumulation
    Newman, Michael C.; McIntosh, Alan W.
    Environmental Pollution (Oxford, United Kingdom) (1989), 60 (1-2), 83-100 CODEN: ENPOEK; ISSN:0269-7491.
    A review with many refs. on the rapidly growing use of aufwuchs in the monitoring of trace element bioaccumulation.
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    OpenURL UNIV OF NORTH TEXAS
  46. 46.
    Farag, A. M.; Nimick, D. A.; Kimball, B. A.; Church, S. E.; Harper, D. D.; Brumbaugh, W. G.Concentrations of metals in water, sediment, biofilm, benthic macroinvertebrates, and fish in the Boulder River watershed, Montana, and the role of colloids in metal uptake Arch. Environ. Contam. Toxicol. 2007, 52, 397– 409
    [CrossRef], [PubMed], [CAS]
    46.
    Concentrations of Metals in Water, Sediment, Biofilm, Benthic Macroinvertebrates, and Fish in the Boulder River Watershed, Montana, and the Role of Colloids in Metal Uptake
    Farag, Aida M.; Nimick, David A.; Kimball, Briant A.; Church, Stanley E.; Harper, David D.; Brumbaugh, William G.
    Archives of Environmental Contamination and Toxicology (2007), 52 (3), 397-409 CODEN: AECTCV; ISSN:0090-4341. (Springer)
    To characterize the partitioning of metals in a stream ecosystem, concns. of trace metals including As, Cd, Cu, Pb, and Zn were measured in water, colloids, sediment, biofilm (also referred to as aufwuchs), macroinvertebrates, and fish collected from the Boulder River watershed, Montana. Median concns. of Cd, Cu, and Zn in water throughout the watershed exceeded the US EPA acute and chronic criteria for protection of aquatic life. Concns. of As, Cd, Cu, Pb, and Zn in sediment were sufficient in the tributaries to cause invertebrate toxicity. The concns. of As, Cu, Cd, Pb, and Zn in invertebrates from lower Cataract Creek (63, 339, 59, 34, and 2,410 μg/g dry wt., resp.) were greater than the concns. in invertebrates from the Clark Fork River watershed, Montana (19, 174, 2.3, 15, and 648 μg/g, resp.), that were assocd. with reduced survival, growth, and health of cutthroat trout fed diets composed of those invertebrates. Colloids and biofilm seem to play a crit. role in the pathway of metals into the food chain and concns. of As, Cu, Pb, and Zn in these 2 components are significantly correlated. We suggest that transfer of metals assocd. with Fe colloids to biol. components of biofilm is an important pathway where metals assocd. with abiotic components are 1st available to biotic components. The significant correlations suggest that Cd, Cu, and Zn may move independently to biota (biofilm, invertebrates, or fish tissues) from water and sediment. The possibility exists that Cd, Cu, and Zn concns. increase in fish tissues as a result of direct contact with water and sediment and indirect exposure through the food chain. However, uptake through the food chain to fish may be more important for As. Although As concns. in colloids and biofilm were significantly correlated with As water concns., As concns. in fish tissues were not correlated with water. The pathway for Pb into biol. components seems to begin with sediment because concns. of Pb in water were not significantly correlated with any other component and because concns. of Pb in the water were often below detection limits.
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    OpenURL UNIV OF NORTH TEXAS
  47. 47.
    Croteau, M. N.; Luoma, S. N.A biodynamic understanding of dietborne metal uptake by a freshwater invertebrate Environ. Sci. Technol. 2008, 42, 1801– 1806
    [ACS Full Text ACS Full Text], [CAS]
    47.
    A Biodynamic Understanding of Dietborne Metal Uptake by a Freshwater Invertebrate
    Croteau, Marie-Noele; Luoma, Samuel N.
    Environmental Science & Technology (2008), 42 (5), 1801-1806 CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Aquatic organisms accumulate metals from dissolved and particulate phases. Diet-borne metal uptake likely prevails in nature, but the physiol. processes governing metal bioaccumulation from diet are not fully understood. We characterize diet-borne Cu, Cd, and Ni uptake by a freshwater gastropod (Lymnaea stagnalis) both in terms of biodynamics and membrane transport characteristics. We use enriched stable isotopes to trace newly accumulated metals from diet, det. food ingestion rate (IR) and est. metal assimilation efficiency (AE). Upon 18-h exposure, diet-borne metal influx was linear over a range encompassing most environmental concns. Dietary metal uptake rate consts. (kuf) ranged from 0.104 to 0.162 g g-1 day-1, and appeared to be an expression of transmembrane transport characteristics. Although kuf values were 1000-times lower than uptake rate consts. from soln., biodynamic modeling showed that diet is the major Cd, Cu, and Ni source in nature. AE varied slightly among metals and exposure concns. (84-95%). Suppression of Cd and Cu influxes upon exposure to extreme concns. coincided with a 10-fold decrease in food IR, suggesting that feeding inhibition could act as an end point for dietary metal toxicity in L. stagnalis.
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    OpenURL UNIV OF NORTH TEXAS

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Received 11 January 2013
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