Great Lakes Fishery Commission

Updated 2023-09-18 20:28:32

Lake Michigan -> 7.0 Habitat -> Contaminants in Fish Fillets

7.2.1 Declining concentrations of toxic chemicals in Lake Michigan fish

Legacy contaminants such as polychlorinated biphenyls (PCBs), organochlorine pesticides, and mercury have been routinely monitored in whole lake trout over long periods of time. Recent reporting shows declining concentrations of PCBs in whole lake trout at EPA’s Sturgeon Bay long-term sampling site in Lake Michigan (USEPA 2021a).  While contaminant concentrations in whole fish are not necessarily comparable to concentrations in fish fillets, it does show overall burdens of these contaminants present in fish.  The level of contaminants in sport fish fillets is important when assessing the risk of toxic chemical exposure to humans and considering the LMC’s goal of promoting human consumption of safe fish.  

PCBs and mercury in fish fillets drive most fish consumption advisories for lake trout and other species across Lake Michigan states (see Other Resources below for fish consumption advisories for each state).  Levels of PCBs and mercury in fish fillets have declined substantially since the 1970s; however, recent data show a possible leveling off or increase in concentrations of these contaminants in fillets of some measured species during the past decade (ECCC and USEPA 2022). Specifically, coho salmon were reported to have lower PCB levels, whereas levels in Chinook salmon, lake trout, lake whitefish and walleye increased.  Levels of mercury declined in lake trout, remained stable in coho salmon and lake whitefish and increased in Chinook salmon and walleye.  Prior to the reporting period (2015), EPA collected nearshore fish fillet samples as part of the Great Lakes Human Health Fish Fillet Tissue Study (GLHHFFTS).  Species-specific composite samples (about 30 samples per lake) were analyzed for PCBs, mercury and per- and polyfluoroalkyl substances (PFAS), dioxins and furans (USEPA 2021b). The percentage of sampled nearshore fish populations with fish fillet concentrations above the EPA Human Health Fish Tissue Benchmark was highest for PCBs (53%) and lower for mercury (13%) and perfluorooctane sulfonic acid (PFOS; 5%), a common PFAS compound found in fish.

In recent years, PFAS have emerged as important chemicals of concern in Lake Michigan and the other Great Lakes.  Continued assessments of the levels of these contaminants in fish fillets should remain a priority for fish-consumption advisory programs around the lake.