Historical PFAS trends in the Great Lakes using four decades of archived fish

Per- and polyfluoroalkyl substances (PFASs) have been manufactured since the 1940s, but environmental monitoring of these chemicals did not begin until the early 2000s, making historical trends of PFAS concentrations difficult to determine. This study uses archived whole lake trout ( Salvelinus namaycush ) and walleye ( Sander vitreus ) from the United States Environmental Protection Agency’s Great Lakes Fish Monitoring and Surveillance Program to quantify PFAS bioaccumulation from 1975 to 2020. Analysis of the fish archive revealed that total bioaccumulative PFASs in predator fish peaked around 2008 and have since been decreasing. While PFAS trends in fish tissue are somewhat consistent across lakes, there are differences in fractional contributions of PFASs. For example, the decreasing trends in fish from Lakes Ontario, Erie, Michigan, and Huron are strongly driven by perfluorooctane sulfonate (PFOS), which manufacturers within the United States began phasing out in 2002. In contrast, fish from Lake Superior have relatively stable PFOS concentrations, and the decreasing trend is primarily driven by reduction in long-chain carboxylates. Shifts in manufacturing chemistry are further demonstrated by changes in isomer fingerprints, indicating a shift away from electrofluorination and toward fluorotelomerization. Transition from long- to short-chain sulfonamides is visible in the data, reflecting the phaseout of long-chain PFASs. Reconstructing historical trends can help elucidate how previous PFAS reductions have impacted ecosystems.