In the study, the researchers calculated the potential contribution of Perfluorooctanesulfonic acid (PFOS), a type of PFAS, from the consumption of locally caught freshwater fish to human blood serum levels of the chemicals. Data was analyzed from over 500 composite samples of fish fillets, collected across the U.S. from 2013–2015 under the U.S. Environmental Protection Agency’s (EPA's) monitoring programs—the National Rivers and Streams Assessment and the Great Lakes Human Health Fish Fillet Tissue Study.

Analysis of the data revealed that the median level of total targeted PFAS in fish fillets from rivers and streams across the U.S. was 9,500 nanograms per kilogram (ng/kg), with a median level of 11,800 ng/kg in the Great Lakes. Additionally, none of the 349 samples analyzed in the National Rivers and Streams Assessment contained no detectable PFAS.

Overall, PFOS was found to be the largest contributor to total PFAS levels, averaging 74 percent of the total. The median levels of total detected PFAS in freshwater fish across the U.S. were 278 times higher than levels in commercially relevant retail fish tested by the U.S. Food and Drug Administration (FDA).

Furthermore, exposure assessment based on the data suggests that a single serving of freshwater fish per year (with the median level of PFAS as detected by the U.S. EPA monitoring programs) translates into a significant increase of PFOS levels in human blood serum. Consuming a single serving of fish can be equivalent to drinking a month’s worth of water at 48 parts per trillion (ppt) of PFOS, reflected in human blood serum PFOS levels.

Researchers hypothesize that PFAS levels in fish as determined by the present study is lower than levels found by FDA due to the fact that some commercially caught fish are grown in controlled aquaculture environments, or far offshore in the ocean where pollution is more diluted. Furthermore, with industry phasing out the commercial use of PFAS, pollution levels in freshwater may be decreasing. Still, contamination levels are currently high enough that any freshwater fish consumption likely impacts PFAS levels in human blood serum.

Finally, the researchers underline the lack of guidance in the U.S. regarding safe fish consumption, with only 14 out of 50 states having issued a fish consumption advisory specific to PFAS. The study’s authors also call for future research on the contribution of different PFAS exposure routes to blood serum levels, as well as PFAS levels in food and locally caught fish. A national food exposure guideline does not exist for PFAS.