Interstitial Water Concentrations Research Articles

Toxicity of copper in an oxic stream sediment receiving aquaculture effluent

Sediments were collected from a stream (upstream, outfall and downstream) receiving copper laden catfish pond effluent to assess toxicity to non-target biota. No significant reduction in Hyalella azteca survival or growth (10 d), or Typha latifolia germination and root and shoot growth (7 d) were observed after exposure to upstream and outfall sediments. A significant reduction in H. azteca survival was observed after exposure to the downstream sediment sample; however, no reduction in T. latifolia germination or seedling growth was detected. Bulk sediment copper concentrations in the upstream, outfall and downstream samples were 29, 31, and 25 mg Cu/kg dry weight, respectively. Interstitial water (IW) concentrations ranged from 0.053 to 0.14 mg Cu/l with 10 d IW toxicity units ⩾0.7. Outfall samples were amended with additional concentrations of copper sulfate so that bulk sediment measured concentrations in the amended samples were 172, 663, 1245, and 1515 mg Cu/kg dry weight. Survival was the most sensitive endpoint examined with respect to H. azteca with a no observed effects concentration (NOEC) and lowest observed effects concentration (LOEC) of 1245 and 1515 mg Cu/kg, respectively. NOEC and LOEC for T. latifolia root growth were 663 and 1245 mg Cu/kg, respectively. IW copper concentrations were ⩾0.86 mg Cu/l with H. azteca intersitial water toxicity unit (IWTU) concentrations ⩾1.2. Sequential extraction qualitatively revealed the carbonate and iron oxide fractions which accounted for a majority of the copper binding. In this instance, the copper which was applied to catfish ponds does not appear to be adversely impacting the receiving stream system.

Toxicity and bioaccumulation of ddt in freshwater amphipods in exposures to spiked sediments

AbstractThe amphipods Hyalella azteca and Diporeia spp. were exposed to sediments dosed with dichlorodiphenyltrichloroethane (DDT), and the toxicity and toxicokinetics were determined. The toxicity was evaluated with the equilibrium partitioning (EqP) and critical body residue approaches. The DDT in the sediments degraded during the equilibration period prior to organism exposure. Thus, the toxicity using EqP pore‐water toxic units (TUs) was evaluated for DDT and its degradation product, dichlorodiphenyld‐ichloroethane (DDD), as the ratio of the predicted interstitial water concentration divided by the water‐only LC50 values. The sum of TUs (ΣTU) was assumed to best represent the toxicity of the mixture. For H. azteca, the 10‐d LC50 was 0.98 and 0.33 ΣTU for two experiments. For Diporeia spp., no toxicity was found in the first experiment with up to 3 ΣTU predicted in the interstitial water. However, in the second experiment, the 28‐d LC50 was 0.67 ΣTU. These data suggest that the EqP approach approximately predicts the toxicity for the combination of DDT and DDD in sediment, provided a toxic unit approach is employed. The critical body residue approach also used TUs because DDT is biotransformed by H. azteca and because of the dual exposure to DDT and DDD. Because biotransformation was only determined in the second experiment, the critical body residue approach could only be evaluated for that case. The TUs were calculated as the ratio of the concentration in the live amphipods divided by the respective LR50 (residue concentration required to produce 50% mortality) values. The LR50 was 1.1 ΣTU for H. azteca for the 10‐d exposure and 0.53 for Diporeia spp. after a 28‐d exposure. Thus, this approach was also quite successful in predicting the toxicity. The accumulation and loss rates for H. azteca were much greater than for Diporeia spp. Thus, 10‐d exposures represent steady‐state conditions for H. azteca, while even at 28‐d, the Diporeia spp. are not at steady state.

Development of a toxicity identification evaluation procedure for characterizing metal toxicity in marine sediments

AbstractA multiagency effort is underway to develop whole sediment toxicity identification evaluation (TIE) methods. Whole sediment TIE methods will be critical tools for characterizing toxicity at hazardous waste sites (e.g., Superfund sites) and in the conduct of environmental risk assessments. The research approach is based on the predominance of three classes of toxicants in sediments: ammonia, nonpolar organic chemicals, and metals. Here we describe a procedure for characterizing acute toxicity caused by metals in whole marine sediments. The procedure involves adding a chelating resin to sediments, resulting in the sequestration of bioavailable metal while not stressing testing organisms. Within the testing chambers, the presence of resin resulted in statistically significant reductions in the overlying and interstitial water concentrations of five metals (cadmium, copper, nickel, lead, and zinc) generally by factors of 40 and 200. Toxicity to both the amphipod Ampelisca abdita and mysid Americamysis bahia (formerly Mysidopsis bahia) of sediments spiked with the five metals was decreased by approximately a factor of four when resin was present. While very effective at reducing the concentrations and toxicity of metals, the resin has only minor ameliorative effects on the toxicity of ammonia and a representative nonpolar toxicant (Endosulfan). Resin and accumulated metal were easily isolated from the testing system following exposures allowing for the initiation of phase II TIE (identification) procedures. This procedure using the addition of a chelating resin provides an approach for determining the importance of metals to the toxicity of marine sediments. Work is continuing to validate the method with environmentally contaminated sediments.

Influence of anthropogenic activity on the vertical distribution of Zn, Cd, Pb and Cu in interstitial water and coastal marine sediments (Cádiz bay, SW Spain)

The vertical profiles of Zn, Cd, Pb and Cu were determined for sediment and interstitial water from three stations in Cádiz Bay. The concentrations of the different metals measured in the surface sediments depend on the distance from the waste water discharge points existing in this zone and on their nature (urban or industrial). The highest levels of Pb and Cd (70 and 0.31 µg g–1, respectively) were found near urban effluents, and the highest levels of Zn and Cu (230 and 106 µg g–1, respectively) near industries related to the construction of ships. The vertical profiles of Zn, Cd, Pb and Cu in both sediment and interstitial water show an important increase in concentrations in the surface layers and are relatively constant from 20 cm. The interstitial water concentrations are lower than the sediment concentrations, ranging from 13 to 57 µg L–1 for Zn, from 3 to 11 µg L–1 for Pb, from 9 to 320 µg L–1 for Cu and from 0.07 to 2.4 µg L–1 for Cd. The values obtained for the geoaccumulation index reported by Müller (1979) classify the study area as intermediate, between an uncontaminated and moderately contaminated ecosystem. The surface enrichment factor values calculated for the four metals from the different stations suggest a unique origin of metal contamination in this zone.

Copper bioavailability in Steilacoom Lake sediments.

Sediments were collected from Steilacoom Lake, Pierce County, in Washington State, and amended with copper sulfate (nominal concentrations of 800, 1,000, 1,500, and 2,000 mg Cu/kg dry weight) to assess copper bioavailability to Hyalella azteca, Chironomus tentans, or Ceriodaphnia dubia. H. azteca survival and C. tentans survival and growth were not significantly affected, with 10-day no observed effects concentrations (NOEC) and lowest observed effects concentrations (LOEC) of 2,010 and >2,010 mg Cu/kg, respectively. C. dubia was the most sensitive organism tested with 10-day NOEC and LOECs for survival and reproduction of 906 and 1,469 mg Cu/kg, respectively. Sediment AVS concentrations were <0.15 micromol/g, while simultaneously extracted metal (SEM) concentrations were >/=5. 71 micromol Cu/g. Dissolved interstitial water concentrations ranged from below detection (0.010 mg/L) to 0.24 mg Cu/L, with interstitial water toxicity units as high as 3.4. Based on this study, effects to C. dubia may occur at bulk sediment concentrations >906 mg Cu/kg. Further, AVS and interstitial water concentrations are not accurate predictors of copper bioavailability in Steilacoom Lake.

Use of Ulva Lactuca to distinguish pH‐dependent toxicants in marine waters and sediments

AbstractUlva lactuca (sea lettuce) is a cosmopolitan marine attached green seaweed capable of sequestering high environmental levels of ammonia. Ammonia can be acutely toxic to marine organisms and is often found in dredged sediments from highly industrial areas or from areas with high carbon inputs. For the purposes of dredged sediment disposal as well as in determining causes of toxicity in complex mixtures, it is important to distinguish ammonia toxicity from the toxicity of other compounds. The use of U. lactuca to selectively remove ammonia from waters and sediments as part of a toxicity identification and evaluation (TIE) procedure was evaluated. Ulva lactuca lowered concentrations of total ammonia from 75 to 17 mg/L in &lt;8 h in water‐only exposures. This treatment also reduced 48‐h amphipod mortality from 75 to 20%. In whole sediments, U. lactuca lowered interstitial water concentrations of ammonia from 60 to 20 mg/L, while keeping overlying water concentrations below detectable limits (&lt;1 mg/L). To determine the limitations of the U. lactuca method to selectively remove ammonia from solution, metal and organic accumulation experiments were performed. Ulva lactuca generally took up &lt;15% of metals present, with most of the exposures resulting in less than a 10% uptake. In contrast, U. lactuca removed 77% of lindane and 95% of fluoranthene. Results of a TIE conducted on sediments from an industrial marine harbor indicated U. lactuca was useful, in conjunction with other procedures, in categorizing ammonia as a sediment toxicant.

Sediment toxicity evaluation for hexachlorobenzene: spiked sediment tests with Leptocheirus plumulosus, Hyalella azteca, and Chironomus tentans.

Hexachlorobenzene (HCB) is a hydrophobic organic chemical that has shown a lack of toxicity in aquatic tests at concentrations up to and exceeding the solubility limit. The equilibrium partitioning approach to deriving sediment quality benchmarks, which assumes that toxicity can be predicted based on contaminant concentrations in interstitial water, predicts that HCB will not produce direct toxicity to benthic invertebrates as a sediment contaminant. However, the potential for toxicity due to direct exposure to sediment-adsorbed HCB has not been thoroughly established. This study evaluated the survival and growth of the estuarine amphipod Leptocheirus plumulosus, the freshwater amphipod Hyalella azteca, and the midge Chironomus tentans (freshwater) following 10-day exposure to sediment spiked with a range of HCB concentrations. H. azteca was tested under both freshwater and estuarine (10 ppt salinity) conditions. No significant toxicity was observed for any test species at the highest test concentration (60 mg/kg normalized to 1% organic carbon). Minimum detectable differences were less than or equal to 20% for three of eight test endpoints. The observed results add to the available weight of evidence indicating a limited potential for HCB-related sediment toxicity to benthic invertebrates.

Toxicokinetics of fluoranthene to the amphipod, Leptocheirus plumulosus, in water-only and sediment exposures

The ability of the equilibrium partitioning (EqP) and critical body residue (CBR) approaches to predict the toxicity of the polycyclic aromatic hydrocarbon, fluoranthene, to a standard sediment toxicity test organism, the amphipod Leptocheirus plumulosus was examined in a series of water-only and sediment exposures. Concentrations of fluoranthene in water that resulted in 50% mortality (10-d LC 50) were 39.2 (35.1–43.8, 95% C.I.) and 39.2 (34.1-– 45.1, 95% C.I.) μg / liter in replicate tests. CBR or tissue concentrations that produced 50% mortality after replicate 8-d water-only exposures (LD 50) were 0.694 (0.596–0.876, 95% C.I.) and 2.44 (1.83–3.68, 95% C.I.) mmol total fluoranthene-equivalents/kg wet wt tissue, values somewhat lower than the range of CBR established for nonpolar narcotics in other organisms ( 2–8 mmol kg ). No significant mortality of L. plumulosus was observed over 26-d sediment toxicity tests, even though estimated interstitial water concentrations (up to 212 μg/liter) exceeded the average water-only LC 50 (39.2 μg/liter) by more than a factor of five, suggesting that the EqP approach over-estimated toxicity to this species. Average tissue concentrations attained in sediment tests ( 0.30 mmol kg ) were substantially lower than the CBR for nonpolar narcotics in other organisms, and in the water-only tests. Thus, lack of mortality in sediment exposures agrees with CBR predictions. The CBR approach appears to be a useful complement to the EqP approach for predicting the toxicity of sediment-associated contaminants.

Metals, acid-volatile sulfides, organics, and particle distributions of contaminated sediments

An overview of key physical/chemical parameters for contaminated sediments is presented. While sediment cores from remote lakes show little or no enrichment with heavy metals (Pb, Hg, Cd, Zn, Cu) and PAHs in top layers, the contamination near industrial areas is more significant. Cd in more bioavailable geochemical phases can occur in response to Cu inputs to sediments, and aeration during dredging operations of anaerobic sediments can reduce the pH causing release of heavy metals. The toxicity of anaerobic sediments to benthos can be effectively predicted based on interstitial water concentrations and the molar ratio between simultaneously extracted metals and acid-volatile sulfides (SEM/AVS). The toxicity of PAHs and other organics can be predicted based on equilibrium partitioning. Principal component analysis indicates that PAHs are associated with organic carbon and silt, and PCBs with inorganic clay. Finally, formulated reference sediments appear to be useful in toxicity testing by creating uniform parameters matching field conditions, and by isolating the effects of specific contaminants.

A comparison of interstitial water isolation methods demonstrates centrifugation with aspiration yields reduced losses of organic constituents

Spiked sediment and seawater were used to evaluate the recoveries of neutral organic compounds in interstitial water (IW) separated by centrifugation and sampled using a unique aspiration system. An average recovery of 94%±0.8% (SE, n=116) of ten polynuclear aromatic hydrocarbons and four chlorinated hydrocarbons was obtained from spiked estuarine IW using the aspiration system. Centrifugation of spiked sediment using the aspiration system recovered significantly higher IW concentrations of acenaphthene, phenanthrene, fluoranthene and DOC than did IW filtration, or in situ IW collection by fritted glass, or membrane covered, vessels.

Metals, acid-volatile sulfides, organics, and particle distributions of contaminated sediments

An overview of key physical/chemical parameters for contaminated sediments is presented. While sediment cores from remote lakes show little or no enrichment with heavy metals (Pb, Hg, Cd, Zn, Cu) and PAHs in top layers, the contamination near industrial areas is more significant. Cd in more bioavailable geochemical phases can occur in response to Cu inputs to sediments, and aeration during dredging operations of anaerobic sediments can reduce the pH causing release of heavy metals. The toxicity of anaerobic sediments to benthos can be effectively predicted based on interstitial water concentrations and the molar ratio between simultaneously extracted metals and acid-volatile sulfides (SEM/AVS). The toxicity of PAHs and other organics can be predicted based on equilibrium partitioning. Principal component analysis indicates that PAHs are associated with organic carbon and silt, and PCBs with inorganic clay. Finally, formulated reference sediments appear to be useful in toxicity testing by creating uniform parameters matching field conditions, and by isolating the effects of specific contaminants.

A comparison of equilibrium partitioning and critical body residue approaches for predicting toxicity of sediment-associated fluoranthene to freshwater amphipods

Equilibrium partitioning (EqP) theory, which has been used to develop sediment quality criteria, predicts that the effects of organic compounds in sediments can be assessed by comparison of organic carbon-normalized sediment concentrations and estimated pore-water concentrations to effects determined in water-only exposures. A complementary approach, the critical body residue (CBR) theory, examines actual body burdens in relation to toxic effects. Critical body residue theory predicts that the narcotic effects of nonpolar compounds should be essentially constant for similar organisms, and narcosis should be observed at body burdens of 2 to 8 μmol/g tissue. This study compares these two approaches for predicting toxicity of the polycyclic aromatic hydrocarbon (PAH) fluoranthene. The freshwater amphipods Hyalella azteca and Diporeia spp. were exposed for up to 30 d to sediment spiked with radiolabeled fluoranthene at concentrations of 0.1 (trace) to 3,940 nmol/g dry weight (=346 μmol/g organic carbon). Mean survival of Diporeia was generally high (>70%) and not significantly different from that of control animals. This result agrees with EqP predictions, because little mortality was observed for Diporeia in 10-d water-only exposures to fluoranthene in previous studies. After 10-d exposures, mortality of H. azteca was not significantly different from that of controls, even though measured interstitial water concentrations exceeded the previously determined 10-d water-only median lethal concentration (LC50). Equilibrium partitioning overpredicted fluoranthene sediment toxicity in this species. More mortality was observed for H. azteca at later time points, and a 16-d LC50 of 3,550 nmol/g dry weight sediment (291 μmol/g organic carbon) was determined. A body burden of 1.10 μmol fluoranthene-equivalents/g wet weight in H. azteca was associated with 50% mortality after 16-d exposures. Body burdens as high as 5.9 μmol/g wet weight resulted in little mortality in Diporeia. Diporeia, which has limited ability to metabolize fluoranthene and a higher lipid content, appears to be less sensitive than H. azteca, which does metabolize fluoranthene. These results demonstrate that the CBR approach is a useful complement to the EqP approach for the prediction and assessment of toxicity associated with contaminated sediments.

Laboratory effects of microcosm size and the pesticide chlorpyrifos on benthic macroinvertebrate colonization of soft estuarine sediments

A 42-d flow-through experiment was conducted to evaluate the effects of the organo-phosphate pesticide, chlorpyrifos, and microcosm size (small: 144 cm 2; large: 400 cm 2) on benthic estuarine macroinvertebrate colonization. Nested central and perimeter (outside margin) cores were used to assess animal distribution within microcosms. Fine-grained, organically-rich (approximately 4.0% organic carbon and 20% dry wt) sediments were nominally fortified with chlorpyrifos controls, low (1.0) and high treatments (10.0 μg −1 wet sediment). Large microcosms contained a significantly (p < 0.05) higher average taxa richness (10.9) than small microcosms (8.6) but small microcosms contained a significantly greater average animal density (295.8; numerical abundance adjusted to unit area) than large microcosms (120.5). Density of the polychaete, Neanthes succinea, the amphipod, Corophium acherusicum, and the barnacle, Balanus sp., was significantly greater in small microcosms but density of Ensis minor was significantly greater in large microcosms. In small and large microcosms, respectively, densities averaged significantly greater numbers in perimeter cores (e.g. 203.1 and 75.1) vs central cores (71.9 and 45.4). Average density decreased significantly with increasing chlorpyrifos concentration from controls (326.8), to low (123.8) and high (78.8) treatments. The density decrease was significantly related only to C. acherusicum whose densities decreased from controls (285.8) to low (88.5) and high (43.9) dosed microcosms. Application of an equilibrium partitioning model indicated that density of C. acherusicum was sensitive to an estimated interstitial water concentration of approximately 0.48 μg liter −1. Non-metric multidimensional scaling ordination analyses provided important insights into response patterns not available through ANOVA procedures. A permutation procedure (ANOSIM) detected a significant size effect ( p < 0.0001) and a significant effect between controls and low ( p < 0.042) and high doses ( p < 0.013) but not between low and high chlorpyrifos treatments ( p < 0.465). A single species, C. ascherusicum, as in the ANOVA analyses, dominated contributions to community average percent dissimilarity in most combinations of microcosm size and chlorpyrifos treatment effects (range: 8.4–21.9%). Community structure differed significantly in several combinations of microcosm size, core position and chlorpyrifos treatment. Results confirm earlier work that intrinsic design factors influence benthic macroinvertebrate community structure and determine taxa available to pesticide exposure in microcosms.

Toxicity of sediment-associated tributyltin to infaunal invertebrates: Species comparison and the role of organic carbon

Experiments with three species of infaunal invertebrates (a polychaete, Armandia brevis and amphipods, Rhepoxynius abronius and Eohaustorius washingtonianus) with different modes of feeding gave a wide range in toxic response to sediment associated tributyltin (TBT), while exhibiting consistent lethal tissue residues. These studies showed that bioaccumulation and toxicity of sediment-associated TBT were strongly controlled by the organic carbon content of the sediment, which we concluded was primarily due to its influence on interstitial water (IW) concentrations of TBT. Major differences in the response to sediment-associated TBT were found between species, which was attributed to differences in their rates of uptake and elimination of this compound. Predictions for bioaccumulation and toxicity for each species based on these toxicokinetic rates were matched closely by observed values. Based on comparisons of water-only and IW exposures (when water and sediment concentrations of TBT were in equilibrium) and predictions made with toxicokinetic rates, the major route of uptake for each of the species tested appeared to be from dissolved TBT. We determined the mean (sd) organic-carbon normalized sediment-water partition coefficient (K oc) to be approximately 25 100 (5500) for TOC values ranging from 0.3 to 1.0%, which was five times higher than the reported K ow. Additionally, we determined the dissolved organic carbon—water partition coefficient (K doc) to be 1652, which was three fold lower than the K ow. The results also showed that the K oc could be influenced by infaunal organisms, presumably by reducing IW concentrations below predicted values, which raises questions about the environmental relevance of sediment bioassays using these organisms and the expected IW concentrations present in field sediments.

Predicting the toxicity of metal‐spiked laboratory sediments using acid‐volatile sulfide and interstitial water normalizations

AbstractNumerous studies have shown that dry weight concentrations of metals in sediments cannot be used to predict toxicity across sediments. However, several studies using sediments from both freshwater and saltwater have shown that interstitial water concentration or normalizations involving acid‐volatile sulfide (AVS) can be used to predict toxicity in sediments contaminated with cadmium, copper, nickel, lead, or zinc across a wide range of sediment types. Six separate experiments were conducted in which two or three sediments of varying AVS concentration were spiked with a series of concentrations of cadmium, copper, lead, nickel, or zinc or a mixture of four of these metals. The amphipod Ampelisca abdita was then exposed to the sediments in 10‐d toxicity tests. Amphipod mortality was sediment dependent when plotted against dry weight metals concentration but was not sediment dependent when plotted against simultaneously extracted metal (SEM)/AVS or interstitial water toxic units (IWTUs). Sediments with SEM/AVS ratios &lt;1.0 were seldom (2.3%) toxic (i.e., caused &lt;24% mortality), while sediments with SEM/AVS ratios &gt;1.0 were frequently (80%) toxic. Similarly, sediments with &lt;0.5 IWTU were seldom toxic (3.0%), while sediments with &gt;0.5 IWTU were toxic 94.4% of the time. These results, coupled with results from related studies, demonstrate that an understanding of the fundamental chemical reactions which control the availability of cadmium, copper, lead, nickel, and zinc in sediments can be used to explain observed biological responses. We believe that using SEM/AVS ratios and IWTUs allows for more accurate predictions of acute mortality, with better causal linkage to metal concentration, than is possible with sediment evaluation tools which rely on dry weight metal concentrations.

Technical basis and proposal for deriving sediment quality criteria for metals

AbstractIn developing sediment quality criteria (SQC) for metals, it is essential that bioavailability be a prime consideration. Different studies have shown that while dry weight metal concentrations in sediments are not predictive of bioavailability, metal concentrations in interstitial (pore) water are correlated with observed biological effects. A key partitioning phase controlling cationic metal activity and toxicity in the sediment‐interstitial water system is acid‐volatile sulfide (AVS). Acid‐volatile sulfide binds, on a mole‐to‐mole basis, a number of cationic metals of environmental concern (cadmium, copper, nickel, lead, zinc) forming insoluble sulfide complexes with minimal biological availability. Short‐term (10‐d) laboratory studies with a variety of marine and freshwater benthic organisms have demonstrated that when AVS concentrations in spiked or field‐collected sediments exceed those of metals simultaneously extracted with the AVS, interstitial water metal concentrations remain below those predicted to cause effects, and toxicity does not occur. Similar observations have been made in life‐cycle laboratory toxicity tests with amphipods and chironomids in marine and freshwater sediments spiked with cadmium and zinc, respectively. In addition, field colonization experiments, varying in length from several months to more than 1 year, with cadmium‐ or zinc‐spiked freshwater and marine sediments, have demonstrated a lack of biological effects when there is sufficient AVS to limit interstitial water metal concentrations. These studies on metal bioavailability and toxicity in sediments serve as the basis for proposed SQC for the metals cadmium, copper, nickel, lead, and zinc. Specifically, four approaches for deriving criteria are described: (a) comparison of molar AVS concentrations to the summed molar concentration of the five metals simultaneously extracted with the AVS; (b) measurement of interstitial water metal concentrations and calculation of summed interstitial water criteria toxic units (IWCTU) for the five metals, based upon final chronic values from water quality criteria documents; (c) calculation of summed IWCTU based upon sediment AVS concentrations and metal‐specific partitioning of the metals to organic carbon; and (d) calculation of summed IWCTU based upon partitioning of the metals to a minimum binding phase sorbent (chromatographic sand). For a number of reasons, SQC derived using these approaches generally should be considered “no effect” values, i.e., with these techniques it is possible to predict when sediment metals will not be toxic, but not necessarily when metal toxicity will be manifested. Currently, approaches (a) and (b) are the most useful in terms of predicting metal bioavailability and deriving SQC. Further research is required, however, to fully implement approaches (c) and (d). Additional research also is required to thoroughly understand processes controlling bioaccumulation of metals from sediments by benthic organisms, as well as accumulation of metals by pelagic species that ingest metal‐contaminated benthos.

Evaluation of metals in marine and freshwater surficial sediments from the environmental monitoring and assessment program relative to proposed sediment quality criteria for metals

AbstractSurficial sediments collected from Lake Michigan (N = 46) and the Virginian Province of the east coast of the U.S. (N = 131) by the Environmental Monitoring and Assessment Program (EMAP) of the U.S. Environmental Protection Agency (EPA) were evaluated relative to a proposed approach to sediment quality criteria (SQC) for five metals (copper, cadmium, zinc, nickel, and lead). Concentrations of acid‒volatile sulfide (AVS), simultaneously extracted metals (SEM) from the AVS extraction, total metals, and total organic carbon were measured in the sediments. Interstitial pore‒water concentrations of the five metals also were measured in the freshwater sediment samples. Overall, 91% of 131 surficial marine sediments and 50% of 46 surficial freshwater sediments contained detectable AVS. In 93 of the marine sediments the concentrations of AVS were greater than total SEM (molar sum of copper, cadmium, zinc, nickel, and lead) indicating a low probability of bioavailable metal. In contrast, 91% of the surficial freshwater samples contained greater concentrations of total SEM than AVS. However, pore‒water concentrations of the five metals in the freshwater samples were uniformly low and never exceeded 0.3 toxic units based on an additive toxicity model that utilized final chronic values from EPA water quality criteria documents for the five metals. These predictions of minimal metal bioavailability in the EMAP samples were consistent with a general lack of toxicity in laboratory assays with the sediments and with the fact that they had been collected predominantly from ostensibly uncontaminated sites.

Effect of bioturbation on metal‐sulfide oxidation in surficial freshwater sediments

AbstractRecent studies have demonstrated the role of acid‐volatile sulfide (AVS) in controlling the bioavailability of several cationic metals in anoxic sediments. However, metal‐sulfide complexes can be relatively labile with respect to oxidation associated with factors such as seasonal changes in rates of oxidation/production of AVS. Another potentially important mechanism of AVS oxidation in surficial sediments is bioturbation. We used different densities of the burrowing oligochaete Lumbriculus variegatus in a series of laboratory experiments to evaluate the effect of bioturbation on oxidation of AVS and subsequent bioavailability of cadmium and zinc spiked into freshwater sediments. Metal bioavailability was determined directly by bioaccumulation in the test organisms and indirectly through analysis of interstitial (pore) water metal concentrations. In our studies, horizon‐specific sediment analyses were conducted to assess spatial differences in AVS and pore‐water metal concentrations specifically related to organism activity. Burrowing activity of the oligochaete significantly reduced AVS concentrations in surficial sediments in a density‐dependent manner and resulted in elevated interstitial water concentrations of cadmium but not zinc. Concentrations of cadmium in pore water from deeper horizons (below the zone of active burrowing) were consistently lower than those in the surficial sediments. The bioaccumulation of cadmium and zinc by L. variegatus was reflective of pore‐water concentrations of the two metals, i.e., there was significant accumulation of cadmium, but not zinc, by the oligochaetes. Overall, our results indicate that bioturbation can enhance the bioavailability of some cationic metals in surficial sediments, via oxidation of AVS, and demonstrate the importance of analyzing surficial sediments when assessing bioavailability of metals in sediments.

A model of the oxidation of iron and cadmium sulfide in sediments

AbstractA model is presented for the temporal and vertical variation of acid‐volatile sulfide (AVS), simultaneously extracted cadmium (SEMcd), and cadmium interstitial water concentration in sediments. The model is based on the one‐dimensional advective‐dispersive mass balance equation. Transport by particle and pore‐water mixing is considered. The state variables include the components of AVS and SEMcd, namely iron sulfide (FeS) and cadmium sulfide (CdS), and sorbed + pore‐water cadmium (CdT). In addition, particulate organic carbon (POC), iron oxyhydroxide, and dissolved oxygen are explicitly modeled. The oxidation, displacement, and partitioning reactions that are sources and sinks of the state variables are included. The model is applied to three experimental data sets. Two of these employed marine sediments with typical organic carbon and AVS concentrations. The third employed a freshwater sediment with a high POC and low AVS. The calibration produced similar partitioning parameters on an organic carbon basis for both sediments. However, the oxidation and partitioning behavior of the FeS in the low AVS freshwater sediment was distinctly different from the high AVS cases. The model successfully reproduces the major features of the experimental data: the progressive decrease in AVS and SEMcd, and an increase in the SEMcd to AVS ratio in the surface layers. It is less successful in reproducing the pore‐water cadmium concentrations.

Predicting the toxicity of metal‐contaminated field sediments using interstitial concentration of metals and acid‐volatile sulfide normalizations

AbstractWe investigated the utility of interstitial water concentrations of metals and simultaneously extracted metal/acid‐volatile sulfide (SEM/AVS) ratios to explain the biological availability of sediment‐associated divalent metals to benthic organisms exposed in the laboratory to sediments from five saltwater and four freshwater locations in the United States, Canada, and China. The amphipod Ampelisca abdita or the polychaete Neanthes arenaceodentata were exposed to 70 sediments from the five saltwater locations, and the amphipod Hyalella azteca or the oligochaete Lumbriculus variegatus were exposed to 55 sediments from four freshwater locations in 10‐d lethality tests. Sediment toxicity was not related to dry weight metals concentrations. Almost complete absence of toxicity in spiked sediments and field sediments where metals were the only known source of contamination and where interstitial water toxic units (IWTUs) were &lt;0.5 indicates that toxicity associated with sediments having SEM/AVS ratios &lt;1.0 from two saltwater locations in industrial harbors was not metals‐related as these sediments contained &lt;0.5 IWTU. Metals‐associated toxicity was absent in 100% of sediments from the remaining three saltwater field locations, where metals were the only known source of contamination and SEM/AVS ratios were ≤1.0. Two‐thirds of 45 sediments from seven saltwater and freshwater field locations having both IWTUs &gt;0.5 and SEM/AVS ratios &lt;1.0 were toxic. Toxicity was observed less often when SEM/AVS ratios &gt;1.0 (39%) or IWTUs &gt;0.5 (55%) were used alone. The difference between the molar concentrations of SEM and AVS (SEM – AVS) can provide important insight into the extent of additional available binding capacity, the magnitude by which AVS binding has been exceeded, and, when organism response is considered, the potential magnitude of importance of other metal binding phases. For these reasons, SEM – AVS should be used instead of SEM/AVS ratios as a measure of metals availability. Over all published experiments with both metal‐spiked and field sediments, SEM – AVS and IWTUs accurately (99.2%) identified absence of sediment toxicity and with less accuracy (79.1%) identified the presence of toxicity.