A site-specific evaluation of mercury toxicity was conducted for sediments of the Calcasieu River estuary (Louisiana, USA). Ten-day whole-sediment toxicity tests assessed survival and growth (dry weight) of the amphipods Hyalella azteca and Leptocheirus plumulosus under estuarine conditions (10 ppt salinity). A total of 32 sediment samples were tested for toxicity, including 14 undiluted site sediment samples and 6 sediment dilution series. All sediment samples were analyzed for total mercury and numerous other chemical parameters, including acid volatile sulfide (AVS) and simultaneously extracted metals (SEM). No toxicity attributable to mercury was observed, indicating that a site-specific threshold for total mercury toxicity to amphipods exceeds 4.1 mg/kg dry weight. Site-specific factors that may limit mercury bioavailability and toxicity include relatively high sulfide levels. Additionally, the chemical extractability of mercury in site sediments is low, as indicated by SEM mercury analyses for three sediment samples containing a range of total mercury concentrations.http://link. springer-ny.com/link/service/journals/00244/bibs/37n4p488.++ +html
Abstract-Fourteen-day, whole-sediment toxicity tests using the amphipod Hyalella azteca and the midge Chironomus tentans were conducted on spiked sediment samples representing a range of hexachlorobenzene (HCB) concentrations. High rates of survival and growth relative to controls were observed in both test species. No observed effects concentrations (NOECs) were equal to the highest HCB concentration tested (42 mg/kg, normalized to 1% total organic carbon). Available literature on the aquatic toxicity of this hydrophobic chemical shows an absence of lethal and sublethal effects from exposure to HCB at or below water solubility concentrations, and toxicity from exposure to dissolved HCB in sediment porewater therefore would not be expected. Because whole-sediment toxicity tests integrate exposure to HCB dissolved in porewater and adsorbed to particles, it was considered possible that exposure via sediment ingestion could cause toxicity; however, no such effect was observed in this study.
Three approaches were used in a site‐specific sediment toxicity evaluation for hexachlorobutadiene (HCBD), a chemical not previously tested for toxicity in sediment. The results of a sediment dilution study, spiked sediment toxicity tests, and a probabilistic model based on equilibrium partitioning theory were used to estimate ecological effects thresholds for HCBD in sediments of a Gulf Coast estuary. Twenty‐nine sediment samples, including 11 undiluted samples and six dilution series, were tested for toxicity under estuarine conditions (10%0 salinity) using Hyalella azteca and Leptocheirus plumulosus. Site sediment was used as diluent, and all samples were assayed for a range of organic and inorganic chemicals. A logistic relationship was observed between HCBD concentrations and organism response, and nonlinear regression explained approximately 90% of the observed variation in amphipod survival as a function of HCBD. Spiked sediment toxicity test results generally agreed with the results of the dilution study, demonstrating the causality of the observed concentration–response relationship. Effects thresholds were estimated as HCBD concentrations corresponding to 80% amphipod survival. The most conservative effects thresholds from the spiked sediment and dilution studies were 0.63 mg/kg normalized to 1% total organic carbon (mg/kg1%OC) for H. azteca and 1.4 mg/kg1%OC for L. plumulosus. Aquatic LC50s for 10 species and a measured acute–chronic ratio from the published literature were used to predict a distribution of sediment effects thresholds for HCBD, with 10th and 90th percentile values of 2.6 and 45 mg/kg1%OC, respectively. The predicted and observed sediment effects thresholds thus agreed relatively well, although the H. azteca and L. plumulosus test results from this study seem to be somewhat more conservative than the majority of published aquatic toxicity test results.
Fourteen‐day, whole‐sediment toxicity tests using the amphipod Hyalella azteca and the midge Chironomus tentans were conducted on spiked sediment samples representing a range of hexachlorobenzene (HCB) concentrations. High rates of survival and growth relative to controls were observed in both test species. No observed effects concentrations (NOECs) were equal to the highest HCB concentration tested (42 mg/kg, normalized to 1% total organic carbon). Available literature on the aquatic toxicity of this hydrophobic chemical shows an absence of lethal and sublethal effects from exposure to HCB at or below water solubility concentrations, and toxicity from exposure to dissolved HCB in sediment porewater therefore would not be expected. Because whole‐sediment toxicity tests integrate exposure to HCB dissolved in porewater and adsorbed to particles, it was considered possible that exposure via sediment ingestion could cause toxicity; however, no such effect was observed in this study.
Abstract-Three approaches were used in a site-specific sediment toxicity evaluation for hexachlorobutadiene (HCBD), a chemical not previously tested for toxicity in sediment. The results of a sediment dilution study, spiked sediment toxicity tests, and a probabilistic model based on equilibrium partitioning theory were used to estimate ecological effects thresholds for HCBD in sediments of a Gulf Coast estuary. Twenty-nine sediment samples, including 11 undiluted samples and six dilution series, were tested for toxicity under estuarine conditions (10‰ salinity) using Hyalella azteca and Leptocheirus plumulosus. Site sediment was used as diluent, and all samples were assayed for a range of organic and inorganic chemicals. A logistic relationship was observed between HCBD concentrations and organism response, and nonlinear regression explained approximately 90% of the observed variation in amphipod survival as a function of HCBD. Spiked sediment toxicity test results generally agreed with the results of the dilution study, demonstrating the causality of the observed concentration-response relationship. Effects thresholds were estimated as HCBD concentrations corresponding to 80% amphipod survival. The most conservative effects thresholds from the spiked sediment and dilution studies were 0.63 mg/kg normalized to 1% total organic carbon (mg/kg 1%OC ) for H. azteca and 1.4 mg/kg 1%OC for L. plumulosus. Aquatic LC50s for 10 species and a measured acute-chronic ratio from the published literature were used to predict a distribution of sediment effects thresholds for HCBD, with 10th and 90th percentile values of 2.6 and 45 mg/kg 1%OC , respectively. The predicted and observed sediment effects thresholds thus agreed relatively well, although the H. azteca and L. plumulosus test results from this study seem to be somewhat more conservative than the majority of published aquatic toxicity test results.
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