Assessment of Potential Cancer Risk from Consumption of PCBs Bioaccumulated in Fish and Shellfish.

We evaluated the potential cancer risk to adults from ingesting polychlorinated biphenyls (PCBs) in fish and shellfish using an equilibrium partitioning model of PCB bioaccumulation in the aquatic animal. Estimated potential cancer risk to humans increased exponentially with increasing hydrophobicity of the PCB. However, the addition of food-chain sources of PCBs was necessary to cause potential cancer risk to exceed 10(-6). Environmental degradation of the PCB reduced cancer risk by reducing the exposure concentration; 3.3 degradation half-lives were required to reduce cancer risk estimates by one order of magnitude. PCB biotransformation to nongenotoxic metabolites (no increase in the cancer slope factor) by the aquatic animal reduced cancer risk by reducing the steady-state concentration of PCBs in the edible tissue. Even relatively slow biotransformation (e.g., metabolic half-life of 100 days) reduced cancer risk estimates under the default model conditions. Nonequilibrium conditions, such as limited exposure time, reduced potential cancer risk by reducing contaminant concentrations in the aquatic animal. Risk assessment using toxic equivalency factors predicted substantially greater potential risk for specific congeners than for PCB mixtures. Our evaluation demonstrates that deviation from conventional assumptions used in risk assessment (e.g., negligible biotransformation and degradation; steady-state equilibrium) can significantly affect cancer risk estimates.