hedistributionpatternsofpolycyclicaromatichydrocarbons(PAH)andpolychlorinatedbiphenyls(PCBs) were determined in four benthic invertebrate species of western Lake Erie, USA, to assess and compare the processes governing the exposure dynamics of these two classes of contaminants. Significant differences in the sum of 17 PAH compounds were observed among the four species, with mayflies containing the highest PAH body burden, followed by dreissenid mussels, amphipods, and crayfish. For PCBs, mayflies contained significantly higher concentrations of the sum of 39 PCB congeners than the other organisms, and dreissenids had higher levels than crayfish. No significant differences were found in the SPCB levels between dreissenids and amphipods or between amphipods and crayfish. For PCBs, the relationship between biota-sediment accumulation factors (BSAFs) and log Kow followed a parabolic pattern indicative of selective bioaccumulation. In contrast, BSAFs for PAHs were inversely related to log Kow, suggesting that metabolism of the higher Kowcompounds was occurring. These results support the conclusion that mayflies and dreissenids play major roles in the transfer of PAHs and PCBs to upper trophic levels, and they demonstrate that the exposure dynamics of PAHs and PCBs are different in the benthic components of aquatic food webs.