Assessing the ecological risk of toxic chemicals on coastal and estuarine ecosystems

Assessing ecological risk requires knowledge of chemical exposure, biological effects caused by chemical exposure, and the ecological context for interpreting chemical effects. Ecological risks to the Piscataqua River and Great Bay Estuary in New Hampshire and Maine, USA were characterized by weighing the evidence of chemical exposure in water, sediment, and tissue and the evidence of biological effects to representative pelagic, epibenthic, benthic, eelgrass, salt marsh, and avian species. Individual measures of exposure or effects were weighted based on the quality and adequacy of the data to infer harm to ecological receptors. Risk was estimated based on the preponderance, magnitude, extent, and strength of causal relationships between the exposure and effects data. There was high confidence of intermediate to low levels of risk from sediment exposure, moderate confidence of low risk from water exposure, and high confidence of negligible exposure to avian species. Using exposure concentrations measured for areas of concern and reference areas (ambient), the probability of an effect or the probability of exceeding a benchmark, criterion, or standard was calculated. Contaminants that had a greater probability (p \u3e 0.05) of exceeding effect levels in the areas of concern than for reference conditions were identified as risk drivers. The approach can be used to characterize the level of risk, communicate the confidence associated with the conclusions, and identify chemicals most likely responsible for risk. The fraction of chemical that is biologically available is determined by the amount of chemical that is unbound and uncomplexed. Therefore, the sorption capacity of various substrates (geosorbents) was determined by measuring the concentration of phenanthrene that could be sorbed without exceeding toxic levels in the aqueous solution. Regression analysis between the sorption parameters and the composition of the sorbent material showed that the fraction of organic carbon (foc ) and soot carbon were most important in explaining total sorption. The kinetic mass transfer rates were inversely proportional to the distribution coefficient suggesting nonequilibrium sorption. Direct measurements of sorption capacity could improve estimates of ecological risk and determine safe exposure levels in sediment