The anti-estrogenic activity of sediments from agriculturally intense watersheds: assessment using in vivo and in vitro assays

The goal of the current study was to determine whether sediments from agriculturally intense watersheds can act as a potential source of anti-estrogenic endocrine-disrupting compounds. The specific objectives of the current study were to determine (1) whether female fathead minnows (Pimephales promelas) experience alterations in endocrine function when exposed to sediments collected from agriculturally intense watersheds and (2) if these sediments display anti-estrogenic activity in an in vitro assay. In addition, sediment samples were analyzed for the presence of steroid hormones and pesticides associated with local agricultural practices. To accomplish this, sediments and water were collected from three sites within two agriculturally intense Nebraska watersheds (Bow Creek and the Elkhorn River). In 2009, minnows were exposed to sediment and/or water collected from the two Bow Creek sites (East Bow Creek and the Confluence) in the laboratory, while in 2010, minnows were exposed to sediment and/or water from East Bow Creek, the Confluence and the Elkhorn River. Following the 7-day exposure period, the hepatic mRNA expression of two-estrogen responsive genes, estrogen receptor α (ERα) and vitellogenin (Vtg) was determined. In 2009, females exposed to Confluence sediments, in the presence of laboratory water or Confluence water, experienced significant reductions in ERα expression relative to unexposed and Confluence water-exposed females. The defeminization of these females suggests the presence of a biologically available anti-estrogenic compound in sediments collected from this site. In 2010, sediments were assessed for anti-estrogenic activity on days 0 and 7 of the exposure period using a 4-h yeast estrogen screen. Lipophilic extracts (LEs) of day 0 sediments collected from the Confluence and the Elkhorn River induced significant reductions in the estrogenic reporter activity of treated yeast cultures suggesting the presence of a lipophilic anti-estrogenic compound in these extracts. Chemical analysis revealed the presence of a variety of steroid hormones, including those associated with the production of beef cattle (i.e. β-trenbolone, α-zearalanol and α-zearalenol), in sediments indicating that compounds utilized by local beef cattle operations are capable of entering nearby watersheds. Overall, the results of this study indicate that an environmentally relevant anti-estrogenic compound is present in sediments from agriculturally intense watersheds and that this compound is bioavailable to fish. Furthermore, the presence of steroid hormones in sediments from these watersheds provides evidence indicating that steroids are capable of sorbing to sediments.     

Effects of food ration on survival and sublethal responses of lake chubsuckers (Erimyzon sucetta) exposed to coal combustion wastes

Study organisms in chronic toxicological bioassays are often provided with excessive resources to remove food limitations as a confounding experimental variable. Under more ecologically realistic situations, resources are often less abundant and such restrictions may alter the responses of organisms to environmental contaminants. Here, we investigated the interaction between resource level and sediment toxicity in the lake chubsucker, Erimyzon sucetta. For 78 days we fed fish one of three ration levels (1X, 2X, 4X; uncontaminated food) that was grazed directly from either clean sand or coal ash-contaminated sediments. Despite provision of uncontaminated food, fish exposed to the contaminated sediments accumulated significant whole body concentrations of As, Se, Sr, and V. Food ration affected the pattern of Se accumulation, with lowest concentrations accumulated by fish supplied with the lowest rations (1X). Paradoxically, fish in the 1X-ash treatment were most adversely effected by ash-exposure, despite having Se burdens much lower than fish in the 2X- and 4X-ash treatments. Fish in the 1X-ash treatment exhibited higher mortality, lower proportional growth, and increased incidence of fin erosion compared to fish provided with higher rations. Such results may, in part, be explained by the apparent inability of fish with reduced rations to maintain positive energy balance, as evidenced by their higher standard metabolic rates compared to control fish fed similar rations. Our results underscore the importance of considering resource quantity and nutritional factors in chronic bioassays in order to draw more ecologically realistic conclusions about contaminant effects.     

Sediment quality assessment survey and toxicity identification evaluation studies in Lavaca Bay, Texas, a marine Superfund site

A sediment quality assessment survey was conducted in Lavaca Bay, Texas, in proximity to a marine Superfund National Priority List (NPL) site. Previous studies at this site had focused primarily on the degree and extent of mercury contamination. The purpose of this survey was to determine the potential ecotoxicological impacts of contaminants, using sensitive sediment toxicity tests in conjunction with a comprehensive chemical analysis of the sediments. In addition, phase I toxicity identification evaluation (TIE) studies were conducted at several of the more toxic sites. Sea urchin (Arbacia punctulata) fertilization and embryological development tests with sediment pore water were employed to assess the toxicity of the sediments. Elevated levels of mercury were found in a number of samples as much as 10-20 times that of background. Six stations had total polycyclic aromatic hydrocarbon (PAH) concentration above the probable effect level (PEL) guideline value, and some stations had concentrations as much as 1000 times above background levels. Eighteen of the 24 stations exhibited toxicity in one of the toxicity tests, while 14 stations were toxic in both tests. A number of stations within the fish closure area exceeded 8-16 of the PEl guidelines. Both aeration and the C18 column treatments were effective in reducing toxicity from the pore water of the two stations included in the TIE. This information, in conjunction with the fact that two of the four stations with the highest mercury concentrations were not toxic, suggests that the toxicity observed in this study is primarily due to organics, probably PAHs, and not mercury. We recommend that these other contaminants of concern be considered in any remedial actions that are planned for this NPL site and that impacts on the ecosystem, as well as human health issues, also be considered.     

Toxicity assessment of urban marine sediments from Western Norway using a battery of stress-activated receptors and cell-based bioassays from fish

A luciferase reporter gene-based bioassay battery consisting of stress-activated receptors from fish, complemented with traditional fish cell-based bioassays, were used to assess the toxicity of marine sediment samples from the Byfjorden area around the city of Bergen (Norway). The reporter assays covered a wide range of cellular signalling and metabolic pathways, representing different molecular initiating events in the adverse outcome pathway framework. Cytotoxicity, generation of reactive oxygen-species, and induction of 7-ethoxyresorufin-O-deethylase activity were analysed using fish liver and gill cell lines. Chemical analyses of the sediment extracts revealed complex contamination profiles, especially at the innermost stations, which contained a wide array of persistent organic pollutants, polycyclic aromatic hydrocarbons, and metals. Sediment extracts from these sites were more potent in activating the stress-activated receptors than the other extracts, reflecting their toxicant profiles. Importantly, receptor- and cell-based bioassays complemented the chemical analyses and provided important data for future environmental risk assessments of urban marine sediments.     

Status and trend of butyltin contamination in Masan Bay, Korea

The current status and historical trend of butyltin contamination in Masan Bay was evaluated using water, sewage effluents, surface sediments and sediment cores. Samples were taken during 2004–2005, after the introduction of TBT regulation in Korea. The levels were at nd-2.4 ng Sn/L for TBT and nd-6.4 ng Sn/L for ΣBT in seawater, and 6–165 ng Sn/g dw (TBT) and 11–329 ng Sn/g dw (ΣBT) in surface sediments from Masan Bay. Three butyltins were detected in STP effluent which acts like an additional source of butyltin to the bay. Butyltin contamination in sediment has apparently increased in the inner part of the bay in the past two decades. Regulation was effective in reducing TBT pollution in seawater, but not effective enough for sediments. Hence, it is important to monitor TBT in sediments.     

Comparing the genotoxicity of a potentially carcinogenic and a noncarcinogenic PAH,singly, and in binary combination,on peripheral blood cells of the European sea bass

Research on the toxicological mechanisms of polycyclic aromatic hydrocarbons (PAHs) deemed carcinogenic and noncarcinogenic has mostly been developed for individual compounds even though, in the environment, PAHs invariably occur in mixtures. The present work aimed at understanding the interaction effects of two model PAHs, the potentially carcinogenic benzo[b]fluoranthene (B[b]F) and the noncarcinogenic phenanthrene (Phe) to a marine fish (the sea bass Dicentrarchus labrax). The study endeavoured an ecologically‐relevant scenario with respect to concentrations and contaminant matrix, sediments, which are the main reservoirs of these substances in the environment, due to their hydrophobic nature. For the purpose, 28‐day laboratorial bioassays with spiked sediments (with individual and combined PAHs at equitoxic concentrations) were conducted. Genotoxicity was determined in peripheral blood through the “Comet” assay and by scoring erythrocytic nuclear abnormalities (ENA). The results showed that exposure to either PAHs induced similar levels of DNA strand breaks, although without a clear dose‐ or time‐response, likely due to the low concentrations of exposure and potential shits in PAH bioavailability during the assays. However, clastogenic/aneugenic lesions were only observed in fish exposed to B[b]F‐spiked sediments. Conversely, the combination assays revealed a supra‐additive effect especially at chromosome level, linked to concentrations of PAHs in water. A decrease in DNA‐strand breakage was observed over time during all assays, revealing some ability of fish to cope with this DNA lesion. Overall, the findings show that low‐moderate concentrations of sediment‐bound mixed PAHs may significantly increase the hazard of mutagenesis even when the individual concentrations indicate low risk, especially considering that chromosome‐level damage is unlikely to be repaired, leading to the fixation of DNA lesions upon prolonged exposures. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1307–1318, 2016.     

Sediment contamination and biological effects in a Chesapeake Bay marina

Complementary measures of sediment toxicity, sediment chemistry and benthic community structure were evaluated at stations within and on the outside perimeter of an enclosed marina on the Bohemia River, a northeastern tributary to Chesapeake Bay. Sediment concentrations of polynuclear aromatic hydrocarbons, copper and tributyltin (TBT) were elevated at stations inside the marina basin. A 28 day partial life-cycle test with the amphipod Hyalella azteca indicated no significant lethal effects associated with test sediments. However, amphipods exposed to sediments collected from three stations inside the marina basin were significantly larger than amphipods from control sediments, possibly as the result of hormesis. Sediment pore water from two out of the three stations eliciting enhanced amphipod growth caused a reduction in light emission by luminescent bacteria in the Microtox^® assay. Furthermore, sediments from these two stations contained the greatest measured concentrations of copper and TBT. Benthic infaunal communities that typically reflect environmental degradation were found exclusively at stations within the marina basin. The area of environmental impact appears to be localized to the enclosed basin, as the marina design limits flushing and, hence, contaminant export.     

Expression of P-glycoprotein in killifish (Fundulus heteroclitus) exposed to environmental xenobiotics

P-glycoproteins (P-gp) are transmembrane efflux flippases that prevent the cellular accumulation of moderately hydrophobic compounds and are responsible for certain multidrug resistance phenotypes in tumor cell lines and human patients. We investigated whether P-gps could be involved in a contaminant resistant phenotype observed in a population of fish exposed over generations to high levels of planar halogenated aromatic hydrocarbons (PHAHs). Hepatic and intestinal epithelial P-gp expression was examined by immunoblot and immunohistochemistry in killifish (Fundulus heteroclitus) from New Bedford Harbor, MA (NBH), a Superfund site highly contaminated with PHAHs, and from Scorton Creek on Cape Cod, MA (SC), a relatively unpolluted site. The NBH population has developed resistance to the toxicity of PHAHs. Hepatic P-gp levels were more than 40% greater in fish freshly collected from SC than in fish freshly collected from NBH. When killifish from either site were maintained in clean water for up to 78 days to permit depuration of bioaccumulated contaminants, hepatic P-gp levels decreased approximately 50% by day 8. P-glycoprotein expression was detected in the intestinal epithelium in 55% of freshly collected NBH fish. However, depurated NBH fish and freshly caught and depurated SC fish rarely expressed P-gp in the intestine. In an effort to determine whether environmental chemicals at the two sites might contribute to altered P-gp expression, depurated fish were exposed either to sediment collected from SC or 2,3,7,8-tetrachlorodibenzofuran, a contaminant found at the NBH site and a model aryl hydrocarbon receptor agonist. Neither exposure affected hepatic P-gp levels in killifish. Elevated intestinal P-gp in NBH fish might counter the absorption of P-gp substrates/inducers and thus limit the amount of these compounds reaching the liver, which might account for the lower hepatic P-gp levels in NBH fish compared to SC fish. The differences in hepatic P-gp levels (SC>NBH) and intestinal P-gp (NBH>SC) in freshly collected fish also might reflect environmental exposure to different anthropogenic contaminants or microbial, algal, plant or other natural products via the water column, sediment, or diet at each site.     

Bioavailability of sediment-associated Cu and Zn to Daphnia magna

Exposures to mining-impacted, field-collected sediment (Clear Creek, CO, USA) contaminated with Cu (2.4 mg/g) and Zn (5.2 mg/g) were acutely toxic to juvenile Daphnia magna. Dissolved Cu and Zn in the overlying water (sediment+reference water) were at levels that could cause acute toxicity. To reduce dissolved metals below toxic levels, the sediment was repeatedly rinsed to remove any easily mobilized metals. Washing the sediment reduced dissolved Cu by 60% and Zn by 80%. D. magna exposed to washed sediment experienced higher survival (95%) compared to those exposed to the original sediment (<50%). Cu and Zn that remained associated with suspended sediment after washing were not bioavailable, since survival and tissue metal concentrations in D. magna exposed to both filtered (>0.45 microm) and unfiltered overlying water were statistically similar. Multiple regression analysis indicated that only dissolved Cu significantly contributed to mortality of D. magna whereas particulate Cu, particulate Zn, and dissolved Zn did not. Regression analysis on a combined dataset from all Clear Creek exposures (washed and unwashed), revealed a significant (p < 0.0001, r(2) = 0.76) relationship between the concentration of dissolved copper in the overlying water and the mortality of exposed Daphnia, yielding an estimated LC50 of 26 microg/L dissolved copper (hardness approximately 140 mg/L). The results of this study indicate that if the sediment of Clear Creek was subjected to a resuspension event that there would be a significant efflux of metals from the sediment into the water column, resulting in potentially toxic levels in the water column.     

Estrogenic activity of surface waters using zebrafish- and human-based in vitro assays: The Danube as a case-study

Most in vitro reporter gene assays used to assess estrogenic contamination are based on human estrogen receptor α (hERα) activation. However, fish bioassays can have distinct response to estrogenic chemicals and mixtures, questioning the relevance of human-based bioassays for assessing risk to this species. In this study, zebrafish liver cells stably expressing zebrafish ERβ2 (ZELHβ2) and human breast cancer cells expressing hERα (MELN) were used to quantify the estrogenic activity of 25 surface water samples of the Danube River, for which chemicals have been previously quantified. Most samples had a low estrogenic activity below 0.1 ng/L 17β-estradiol-equivalents that was more often detected by MELN cells, while ZELHβ2 response tend to be lower than predicted based on the chemicals identified. Nevertheless, both bioassays quantified well a higher estrogenic activity at two sites, which was confirmed in vivo using a transgenic zebrafish assay. The results are discussed considering the effect-based trigger values proposed for water quality monitoring.     

Integrated ecotoxicological assessment of marine sediments affected by land-based marine fish farm effluents: physicochemical, acute toxicity and benthic community analyses

An integrated ecotoxicological assessment of marine sediments affected by land-based marine fish farm effluents was developed using physicochemical and benthic community structure analyses and standardised laboratory bioassays with bacteria (Vibrio fischeri), amphipods (Ampelisca brevicornis) and sea urchin larvae (Paracentrotus lividus). Intertidal sediment samples were collected at five sites of the Rio San Pedro (RSP) creek, from the aquaculture effluent to a clean site. The effective concentration (EC₅₀) from bacterial bioluminescence and A. brevicornis survival on whole sediments and P. lividus larval developmental success on sediment elutriates were assessed. Numbers of species, abundance and Shannon diversity were the biodiversity indicators measured in benthic fauna of sediment samples. In parallel, redox potential, pH, organic matter and metal levels (Cd, Cu, Ni, Pb and Zn) in the sediment and dissolved oxygen in the interstitial water were measured in situ. Water and sediment physicochemical analysis revealed the exhibition of a spatial gradient in the RSP, evidenced by hypoxia/anoxia, reduced and acidic conditions, high organic enrichment and metal concentrations at the most contaminated sites. Whereas, the benthic fauna biodiversity decreased the bioassays depicted decreases in EC₅₀, A. brevicornis survival, P. lividus larval success at sampling sites closer to the studied fish farms. This study demonstrates that the sediments polluted by fish farm effluents may lead to alterations of the biodiversity of the exposed organisms.     

Toxicity assessment of wastewaters, river waters, and sediments in Austria using cost-effective microbiotests

The toxicity and chemical quality of surface water and sediment in the River Traun in Austria were studied because of recurrent fish mortality in some alpine rivers over the last few years. The analyses were carried out on samples collected during winter and summer upstream and downstream of two municipal wastewater treatment plants (WWTPs) and on effluents taken at the points of discharge of these two plants. Toxicity tests were performed on 20 samples of surface water, effluent, and sediment pore water. The test battery was composed of microbiotests with protozoans (Protoxkit F), microalgae (Algaltoxkit F), crustaceans (Daphtoxkit F magna and Thamnotoxkit F), and a higher plant (seed germination and root elongation assay on cress). Direct contact tests were performed on whole sediment with crustaceans (Ostracodtoxkit F). The physical-chemical characteristics of the surface water, effluent, and sediment pore water samples analyzed were conductivity, total hardness, pH, O(2), BOD(5), TOC, DOC, AOX, NH(4), NH(3), NO(2), PO(4)--P, Cd, Pb, Cu, and Zn. The toxicity data were expressed as percentage mortality or percentage inhibition, depending on the effect criterion of the respective assay. None of the water samples collected upstream and downstream of the WWTPs showed any significant (short-term) toxicity in either winter or in summer, but the effluents of the first municipal wastewater treatment plant were toxic to some of the test biota. All the sediment pore water samples induced serious inhibition of root growth of cress, and several pore waters were toxic to other test biota as well, particularly at the outlets of the WWTPs. The toxic character of some sediments was confirmed by direct contact tests with the ostracod crustacean. The chemical analyses did not reveal particularly high concentrations of any chemical that is very toxic. As a result no direct causal relationship could be established between the detected toxic effects and the chemical composition of the surface waters or sediment pore waters. The outcome of this preliminary study again highlights the need to complement chemical analyses with toxicity tests to determine the toxic hazard to aquatic environments that may be threatened by contamination. Furthermore, the investigations also confirmed the need to apply a battery of tests for an ecologically meaningful evaluation of the hazards of waters, sediments, and wastewaters. Finally, the results of the 360 bioassays performed show that culture-independent microbiotests are practical and reliable tools for low-cost toxicity monitoring of aquatic environments.     

Ecotoxicological evaluation for the screening of areas polluted by mining activities

The aim of this study was to evaluate the applicability of three bioassays representing multiple trophic levels, for the preliminary ecotoxicological screening of sediments from sites contaminated by mining activities. Of the bioassays used in this study, the ostracod test was the most responsive. Vibrio fischeri luminiscence inhibition assay was less sensitive to the toxicants in the sediments than the phytotoxicity assays. The general trend observed was an increase in toxicity values measured by the bioassays with increasing metal mobilization in sediment samples. Therefore, the test battery can be used as a rapid and sensitive tool to evaluate the heavy metal contamination in sediments.     

Evaluation of seven sediment toxicity tests and their relationships to stream parameters

A survey of sediment microbial activity and toxicity to Daphnia magna, Ceriodaphnia dubia, and Selenastrum capricornutum was conducted on two streams receiving numerous effluents in Ohio—the Little Scioto River and Dick's Creek. Microbial activity assays included alkaline phosphatase, dehydrogenase, β-galactosidase, β-glucosidase. Activity was compared to overlying water chemistry and revealed several statistically significant correlations. No macrofaunal assay toxicity was observed in Dick's Creek. Sediment toxicity was found at two stations in the Little Scioto River, and varied in degree and organism sensitivity with time of sampling. These results support earlier studies suggesting the need for multiple trophic-level assays in aquatic ecosystem evaluations of toxicant impacts.     

Using an Integrated Approach to Assess the Sediment Quality of an Mediterranean Lagoon,the Bizerte Lagoon (Tunisia)

The present study investigates the quality of surface sediments from the Bizerte lagoon (North Tunisia) using an integrated approach including chemical contaminant analysis, bioassays and sediment quality guidelines (SQGs). Sediment samples were collected at 9 sites and analyzed for eight heavy metals (Hg, Cd, Cr, Cu, Pb, Zn, Ni, Fe and Mn). PAHs, PCBs, OCPs were measured previously in the same sediment samples. Our results indicated that the highest concentrations of metals were found near urban areas due to the municipial and industrial wastewater discharges. Sediment pollution assessment was carried out using geoaccumulation index and enrichment factor, which indicate a widespread pollution by Cd, Pb, Ni and Zn in the studied sediments. For bioassays, aqueous and organic extracts were used to assess toxicity and genotoxicity in sediments by using Microtox^® and SOS Chromotest, respectively. Toxicity levels were compared to metallic and organic pollutants contents. Our results highlight differences in the pattern of responses between the different assays and show no correlation with all the studied contaminants, emphasizing the influence of other contaminants not analyzed in the present study. Based on SQGs, the results of toxicity assessment indicated that adverse effects caused by Ni and Zn would be expected frequently. Nickel was found to have the highest predicted acute toxicity, followed by Zn, Pb, Cd, Cu and Cr. There was no significant relationship between sediment toxicity calculated from heavy metal concentrations (SQG approach) and those measured with bioassays. These findings support the use of integrated approachs for evaluating the environmental risks of sediments.     

Toxicity assessment of reference and natural freshwater sediments with the LuminoTox assay

We examined the possibility of adapting the LuminoTox, a recently-commercialized bioanalytical testing procedure initially developed for aqueous samples, to assess the toxic potential of sediments. This portable fluorescent biosensor uses photosynthetic enzyme complexes (PECs) to rapidly measure photosynthetic efficiency. LuminoTox testing of 14 CRM (Certified Reference Material) sediments was first undertaken with (1) a "solid phase assay" (Lum-SPA) in which PECs are in intimate contact with sediment slurries for a 15 min exposure period and (2) an elutriate assay (Lum-ELU) in which PECs are exposed for 15 min to sediment water elutriates. CRM sediment toxicity data were then compared with those generated with the Microtox Solid Phase Assay (Mic-SPA). A significant correlation (P < 0.05) was shown to exist between Lum-SPA and Mic-SPA, indicating that both tests display a similar toxicity response pattern for CRM sediments having differing contaminant profiles. The sediment elutriate Lum-ELU assay displayed toxicity responses (i.e. measurable IC20s) for eight of the 14 CRM sediments, suggesting that it is capable of determining the presence of sediment contaminants that are readily soluble in an aqueous elutriate. Lum-SPA and Mic-SPA bioassays were further conducted on 12 natural freshwater sediments and their toxicity responses were more weakly, yet significantly, correlated. Finally, Lum-SPA testing undertaken with increasing mixtures of kaolin clay confirmed that its toxicity responses, in a manner similar to those reported for the Mic-SPA assay, are also subject to the influence of grain size. While further studies will be required to more fully understand the relationship between Lum-SPA assay responses and the physicochemical makeup of sediments (e.g., grain size, combined presence of natural and anthropogenic contaminants), these preliminary results suggest that LuminoTox testing could be a useful screen to assess the toxic potential of solid media.     

Impact of selenium and other trace elements on the endangered adult razorback sucker

A study was conducted with endangered the razorback sucker (Xyrauchen texanus) to determine if environmental exposure to selenium in flooded bottomland sites affected survival, growth, and egg-hatching success. Adults were stocked at three sites adjacent to the Colorado River near Grand Junction, Colorado, in July 1996: hatchery ponds at Horsethief Canyon State Wildlife Area (referred to here as Horsethief; the reference site), a diked tertiary channel at Adobe Creek, and North Pond at Walter Walker State Wildlife Area (WWSWA). Fish were collected in April 1997 and spawned. After two spawnings adults from the three sites were held at Horsethief for an 86-day selenium depuration period. Selenium concentrations at Horsethief were 1.4-3.0 microg/L in water, 0.8-0.9 microg/g in sediment, 4.5 microg/g in muscle plug, and 6.0 microg/g in eggs; at Adobe Creek, <0.7-4.5 microg/L in water, 1.2-2.5 microg/g in sediment, 16-20 microg/g in zooplankton, 9.6 microg/g in muscle plug, and 40 microg/g in eggs; and at North Pond, 3.2-17 microg/L in water, 16-94 microg/g in sediment, 32-48 microg/g in zooplankton, 14 microg/g in muscle plug, and 55 microg/g in eggs. During the depuration period, when adults from Adobe Creek and North Pond were held at Horsethief, the fish lost 7%-13% of their selenium burden in 59 days and 14%-21% in 86 days. Larvae from North Pond adults had the most deformities, followed by Adobe Creek adults, with the fewest deformities found in the Horsethief adults.     

Influence of Taxonomy, Ecology, and Seasonality in River Stage on Fish Contamination Risks in Floodplain Swamps of the Lower Mississippi River

We compared contamination levels in fish from contaminated and uncontaminated floodplain swamps of the lower Mississippi River to assess differences in contamination risks between swamps, across different taxonomic and ecological groupings of fishes within and between swamps, and with seasonality in river stage. Fish tissue levels of inorganic contaminants were substantially lower than environmental levels in both swamps, suggesting either that fish were not uptaking these contaminants, or they were effectively eliminating the contaminants from their bodies. Tissue levels of organic contaminants were high relative to environmental levels, suggesting that these contaminants were bioaccumulating. Organic contaminants were significantly higher in fish from the contaminated swamp (Devil's Swamp) than in fish from a reference swamp up river (Tunica Swamp). Because the organic contaminants were largely confined to sediments, we expected bottom-oriented fishes to have higher concentrations than pelagic fishes. Assuming that uptake was primarily through the food chain, we expected top predators to exhibit higher concentrations than low-level consumers. We also expected year- round swamp residents to exhibit higher accumulations than more transitory users of backswamp habitat. However, organic contaminant levels did not differ in the directions expected for any of these groupings. We did observe differences in organic contaminant levels within and between swamps for different taxonomic groupings of fishes (species and genera). Some taxa occupying low to middle positions in the food web (e.g., gizzard shad, Lepomis spp.) exhibited higher concentrations than taxa near the top of the food web. Within Devil's Swamp, organic contaminant levels were significantly higher at low river stage, when fish were confined to the swamp, than at high river stage, when fish were free to move between the river and the swamp. We caught more species and more fish per unit effort in Devil's Swamp than in Tunica Swamp, contrary to expectations if contaminants in the former were negatively impacting population and community structure. Species richness differences between swamps were a consequence of catch differences, with higher catch corresponding to inclusion of more rare species. The lower catch in Tunica Swamp may have resulted from physical modifications of its waterways to support agriculture and hunting. The results of this study underscore the importance in factoring information on the taxonomy and ecology of organisms, and seasonal changes in environmental conditions, into assessments of contamination risks.