PCB CONCENTRATIONS OF LAKE-MICHIGAN INVERTEBRATES - RECONSTRUCTION BASED ON PCB CONCENTRATIONS OF ALEWIVES (ALOSA-PSEUDOHARENGUS) AND THEIRBIOENERGETICS

Invertebrate PCB concentrations are a poorly quantified but crucial st ep in the trophic transfer of organochlorine contaminants to fishes. I n fact, current attempts to quantify PCB fluxes in the Lake Michigan p elagic food web are hampered by poor knowledge of invertebrate PCB con centrations. Models exist that estimate PCB concentrations in fish bas ed upon PCB concentrations in their food. We have used a complementary approach and estimated invertebrate PCB concentrations based upon his torical records of alewife PCB concentrations in Lake Michigan. We fir st developed a model of total PCB accumulation in alewife (Alosa pseud oharengus) using a bioenergetics-based approach to growth. The PCB ass imilation efficiency between invertebrate prey and alewife predators w as estimated to be about 0.40. We then used the model to hindcast PCB concentrations in the invertebrates that comprised alewife prey. We es timated that median PCB concentrations of Lake Michigan invertebrates have dropped roughly 10-fold from 1976 to 1990; for example, the estim ated Diporeia hoyi PCB concentration has dropped from ca. 0.48 mg.kg(- 1) wet weight to 0.04 mg.kg(-1) wet weight over this time period. The biomagnification ratio (alewife PCB/zooplankton PCB) is about 16-fold (Diporeia hoyi) to 40-fold (copepods/cladocerans). The PCB concentrati ons in Lake Michigan invertebrates and alewife that we have estimated for 1993 and 1994 should be viewed as predictions, testable as data be come available. Because historic data on invertebrate PCB concentratio ns in Lake Michigan are exceedingly scarce, our estimates should be us eful for studies that attempt to quantify the Lake Michigan PCB fluxes or future modeling efforts that attempt to incorporate multiple level s of the Lake Michigan food web.