Abstract
Invertebrate PCB concentrations are a poorly quantified but crucial step in the trophic transfer of organochlorine contaminants to fishes. In fact, current attempts to quantify PCB fluxes in the Lake Michigan pelagic food web are hampered by poor knowledge of invertebrate PCB concentrations. Models exist that estimate PCB concentrations in fish based upon PCB concentrations in their food. We have used a complementary approach and estimated invertebrate PCB concentrations based upon historical records of alewife PCB concentrations in Lake Michigan. We first developed a model of total PCB accumulation in alewife ( Alosa pseudoharengus) using a bioenergetics-based approach to growth. The PCB assimilation efficiency between invertebrate prey and alewife predators was estimated to be about 0.40. We then used the model to hindcast PCB concentrations in the invertebrates that comprised alewife prey. We estimated that median PCB concentrations of Lake Michigan invertebrates have dropped roughly 10-fold from 1976 to 1990; for example, the estimated Diporeia hoyi PCB concentration has dropped from ca. 0.48 mgkg -1 wet weight to 0.04 mgkg -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 concentrations in Lake Michigan invertebrates and alewife that we have estimated for 1993 and 1994 should be viewed as predictions, testable as data become available. Because historic data on invertebrate PCB concentrations in Lake Michigan are exceedingly scarce, our estimates should be useful for studies that attempt to quantify the Lake Michigan PCB fluxes or future modeling efforts that attempt to incorporate multiple levels of the Lake Michigan food web.
Published Version
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