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The ΣPAH model estimates the probability of toxicity of PAH‐contaminated sediments using a combination of equilibrium partitioning, QSAR, toxic unit, additivity, and concentration‐response models. The sediment concentration of organic carbon and 13 PAH (polynuclear aromatic hydrocarbon) compounds were measured. Interstitial water concentrations (PAH1W) of the 13 compounds were predicted by equilibrium partitioning. The 10‐d LC50 of each compound in interstitial water (10‐d LC501W) was predicted by a QSAR regression of 10‐d LC501W (from spiked sediment tests) to Kow. Toxic unit concentrations of individual compounds (TU1) were predicted as PAH1w/10‐d LC501w. The total number of toxic units of the 13 compounds (ΣTU1) was calculated assuming the additivity of toxic effects of PAHs. ΣTU1 was used to predict the probability of toxicity to marine and estuarine amphipods using a concentration‐response model derived from spiked sediment toxicity tests. The ΣPAH model was verified by comparing predicted and observed toxicity in field‐collected sediment samples. There was 86.6% correspondence and no significant difference between predicted and observed toxicity at PAH‐contaminated sites. Ecological‐effect levels predicted by theΣPAH model correspond with several sediment‐quality guidelines.

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Sediment toxicity to the amphipod Eohaustonus estuanus, sediment contamination, and the abundance of amphipods were examined along a contamination gradient in the Launtzen Channel and adjacent parts of Richmond Harbor, Call forma Dieldnn and DDT were formulated and ground at this site from 1945 to 1966 Sediment contamination by both dieldrin and the sum of DDT and its metabolites (EDDT) was positively correlated with sediment toxicity and negatively correlated with the abundance of amphipods excluding Grandidierella japonica The maximum dieldnn and ΣDDT concentrations in toxic units were 0 018 and 9 43, respectively, indicating that ΣDDT was the dominant ecotoxicological factor Concentrations of PAHs, PCBs, and metals were not sufficient to cause appreciable toxicity, except at one PAH contaminated station Relations between ΣDDT, sediment toxicity, and amphipod abundance are similar at three ΣDDT contaminated sites The 10 d LC50 for ΣDDT in field‐collected sediment was 2,500 μg/g organic carbon (OC) for Eohaustonus estuanus in this study, 1,040 μg/g OC for Rhepoxymus abromus exposed to Palos Verdes Shelf, California, sediment, and 2,580 μg/g OC for Hyalella azteca exposed to sediment from a freshwater stream system near Huntsville, Alabama The threshold for 10 d sediment toxicity occurred at about 300 μg ΣDDT/g OC The abundance of amphipods (except Grandidierella japonica) was reduced at EDDT concentrations > 100 μg/g OC Correlations between toxicity, contamination, and biology indicate that acute sediment toxicity to Eohaustonus estuanus, Rhepoxymus abromus, or Hyalella azteca in lab tests provides reliable evidence of biologically adverse sediment contamination in the field

The toxicity of fluoranthene in sediment to the marine benthic amphipods, Rhepoxynius abronius (Barnard) and Corophium spinicorne (Stimpson) was determined in relation to the equilibrium partitioning approach to the development of sediment quality criteria. Toxicity tests were conducted with well‐sorted fine sands at three levels of organic carbon (OC), 0.18, 0.31 and 0.48%. Measured interstitial water concentrations of fluoranthene less than 50 μg/L were highly correlated with predictions based on the equilibrium partitioning model. LC50s based on bulk (total) fluoranthene concentrations increased significantly with increasing sediment OC. LC50s based on fluoranthene concentrations in interstitial water were not significantly different between 0.18 and 0.48% OC or between 0.31 and 0.48% OC, but the LC50 at 0.31% OC was significantly higher than that at 0.18% OC. The regression of sediment OC on bulk fluoranthene LC50 was linear, indicating that the concentration of fluoranthene in interstitial water was constant at equitoxic conditions, as predicted by the equilibrium partitioning model. The 10‐d LC50 of fluoranthene in interstitial water (23.8 μg/L) was intermediate between the U.S. Environmental Protection Agency's (U.S. EPA) acute (40 μg/L) and chronic (16 μg/L) water quality values for fluoranthene. Within the limitations of these experiments (i.e., one chemical, two species, sandy sediment with low carbon content), the results indicate that sediment quality criteria derived from the equilibrium partitioning model and water quality criteria would protect sensitive benthic invertebrates. The epibenthic, tube‐dwelling Corophium was less sensitive to test sediments than the infaunal, free‐burrowing Rhepoxynius, possibly because of different routes of exposure to fluoranthene. There was a close correspondence between estimates of sediment quality for fluoranthene based on distinctly different methodologies including equilibrium partitioning, apparent effects threshold, toxicity tests applied to experimentally spiked sediment and toxicity tests applied to field‐collected sediment.