EVIDENCE THAT PCBS ARE APPROACHING STABLE CONCENTRATIONS IN LAKE-MICHIGAN FISHES

We examined PCB concentration data for seven species of Lake Michigan fishes to determine what trends were apparent approximate to 20 yr aft er PCB restrictions became effective. Total PCB concentrations in all seven species, lake trout (Salvelinus namaycush), rainbow trout (Oncor hynchus mykiss), brown trout (Salmo trutta), chinook salmon (Oncorhync hus tshawytscha), coho salmon (Oncorhynchus kisutch), alewife (Alosa p seudoharengus), and bloater chub (Coregonus hoyi) declined and appeare d to stabilize in the mid-to-late 1980s. Concentrations in two species , chinook and coho salmon, appear to have increased slightly since the late 1980s. All species are currently well below the high PCB levels that existed when PCB use was curtailed in the 1970s. We believe stabi lizing concentrations are the result of large pools of PCBs that are b eing recycled in the environment. Atmospheric and sediment PCB inputs to the lake probably constitute current PCB sources. Increasing concen trations in chinook and coho salmon are likely the result of changing growth dynamics caused by alterations in the mid-trophic levels of the food web. Median stable PCB concentrations estimated in this analysis are below the current FDA action level of 2 mg/kg, but not appreciabl y below this threshold. Improvements beyond these levels may result if management practices that maximize fish growth rates are implemented. Detection of future improvements in PCB levels may require samples in the range of 1000-2000 fish because of the high variability in PCB co ncentrations among individuals.