Abstract

 As part of a comprehensive ecological risk assessment, risks to benthic invertebrates were assessed for a small, channelized stream in southwestern Ohio. Based on comparisons with screening-level sediment quality benchmarks, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and metals were identified for further evaluation. First, sediment chemistry data were evaluated using the equilibrium partitioning (EqP) approach, to predict causal relationships between chemistry and toxicity. Application of the EqP approach for PCBs involved calculating an aquatic toxicity benchmark for invertebrates and estimating a partition coefficient for total PCBs, based on the site-specific composition of PCB mixtures. Second, chemical concentrations in invertebrate tissue were compared to literature-based effects concentrations. Third, benthic invertebrate community quality was directly assessed by comparing site-specific Invertebrate Community Index (ICI) values to ICI values for regional reference sites of similar physical habitat quality. Fourth, in situ and laboratory toxicity studies conducted by other researchers were evaluated. These lines of evidence led to conclusions that differ dramatically from those inferred from screening-level sediment quality guidelines. Potential toxicity to benthic invertebrates is limited to a few hot spots and does not appear to be affecting the benthic community. Physical habitat quality, rather than chemical toxicity, is the most important factor affecting benthic invertebrates in the creek.