Predicting stress in benthic communities of southeastern US estuaries in relation to chemical contamination of sediments

Matching data on sediment contaminants and macroinfaunal community structur e from 231 subtidal stations in southeastern U.S. estuaries were used to de velop a framework for evaluating risks of benthic impacts from multiple-con taminant exposure. Sediment contamination was expressed as the mean ratio o f individual contaminant concentrations relative to corresponding sediment quality guidelines, that is, to effects range-median (ERM) values, probable effects level (PEL) values, or an aggregate of the two. The probability of a degraded benthos was relatively low in samples with mean ERM quotients l ess than or equal to 0.020, PEL quotients less than or equal to 0.035, or c ombined ERM/PEL quotients less than or equal to 0.024. Only 5% of stations within these ranges had degraded benthic assemblages, while 95% had healthy assemblages. A higher probability of benthic impacts was observed in sampl es with mean ERM quotients >0.058, PEL quotients >0.096, or ERM/PEL quotien ts >0.077. Seventy-three to 78% of stations with values in these upper rang es had degraded benthic assemblages, while 22 to 27% had healthy assemblage s. Only four stations (three with degraded, one with healthy assemblages) h ad mean ERM or PEL quotients >1.0, which is the beginning of the range asso ciated with a high probability of mortality in short-term laboratory toxici ty tests using amphipods.