Cause-effect sediment-quality benchmarks for the protection of benthic invertebrates are needed for polychlorinated biphenyls (PCBs) to support predictive risk assessments and retrospective evaluations of the causes of observed sediment toxicity. An in-depth evaluation of PCB aquatic toxicity and organic carbon partitioning was conducted to predict sediment effect concentrations using the equilibrium partitioning (EqP) approach. This evaluation was limited to invertebrate toxicity data, because PCBs may exert toxicity to invertebrates and fish via different toxicological mechanisms. As a result of differences in organic carbon partitioning among PCBs of differing levels of chlorination, the estimated EqP benchmarks increase with increasing degree of chlorination for various commercial and environmental PCB mixtures. Studies of spiked sediment toxicity using PCBs were reviewed, and their results generally were consistent with EqP predictions. Additionally, toxicity and benthic community data were reviewed for eight PCB-contaminated sites; these data also showed agreement with EqP predictions. None of these lines of evidence supports previously proposed, empirical sediment-quality guidelines for PCBs. Reasons for the lack of agreement between cause-effect and association-based benchmarks are discussed, and areas of future research to further refine EqP predictions for PCBs are identified.

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