Known colloquially as "forever chemicals," per- and polyfluoroalkyl substances (PFAS) are highly persistent chemicals that have been used extensively by industry and in consumer products (1). Epidemiological studies show that exposure to some PFAS can contribute to health problems such as cancers and metabolic changes in humans (2). Many PFAS used on land end up in the marine environment, where they can accumulate in aquatic food webs (3). However, the importance of marine seafood for human exposures remains unclear. On page 1305 of this issue, Qiu et al. (4) present a global modeling assessment of legacy PFAS exposure risks from marine fish consumption. The results suggest that human exposures to legacy PFAS from marine fish are generally low and have been reduced by the phasing out of legacy PFAS production.
Qiu et al. focused on so-called "long-chained legacy PFAS" that were predominantly produced in Europe and North America. Long-chained PFAS include the "C8 PFAS," which contain eight total carbons, as well as longer-chained PFAS with more than eight carbons (>C8 PFAS). Major Western manufacturers phased out production of these PFAS in the early to mid-2000s, although formal regulation took additional decades, and many alternative PFAS are now being produced (3). Legacy PFAS concentrations in marine wildlife in many regions have decreased in response to these production shifts, although the timing of these responses has varied regionally (5, 6), and limited data has made it difficult to conduct such an analysis at a global scale.
Qiu et al. modeled human exposures to legacy PFAS based on estimated marine seafood consumption in 44 countries between 2002 and 2021. Their analysis used spatially interpolated global seawater concentrations as an input to a bioaccumulation model for 212 marine fish species and combined this with international seafood trade flows to map the redistribution of PFAS exposures worldwide. They subsequently analyzed whether exposure levels from marine seafood were a concern by comparing them with available toxicity thresholds for individual PFAS and reported the result as a Hazard Index. When the Hazard Index is <1, there is generally low health concern. Qiu et al. found that the Hazard Index for exposures to legacy PFAS from marine fish were <1 for most of the countries they evaluated. Only Greenland and Denmark, where marine fish consumption is high, had Hazard Indexes >1. The authors' findings indicate that the countries with the greatest marine fish PFAS exposures predominantly have high frequencies of fish consumption and are located within the historically high-PFAS production regions of North America and Europe. Even after accounting for trade, PFAS contamination in consumed marine fish remains notably regional: Qiu et al. identified Europe as the primary center of PFAS transport through marine fish trade, whereas intercontinental distribution remains limited. This highlights the management of contamination from PFAS sources as critical to reducing exposures in the most affected countries.
The relatively low marine fish exposures calculated by Qiu et al. for most countries are consistent with prior understanding that legacy PFAS exposures are mainly from drinking water and/or freshwater fish consumption, particularly near contaminated sites (2, 5). For example, inmeasured PFAS concentrations in freshwater fish in the United States are typically one to two orders of magnitude higher than those of commercial marine fish (7), a pattern that is also observed in Europe. This is attributed to a stronger influence of PFAS sources on freshwater systems owing to closer source proximity and less dilution. Similarly, higher concentrations of PFAS have been observed in coastal ecosystems strongly influenced by direct industrial inputs. This occurs, for example, in Qiu et al.'s estimates of concentrations in large semienclosed seas, such as the Bohai Sea, and in samples from smaller bays and estuaries, which may be difficult to study in a global modeling analysis (7). Qiu et al.'s modeled marine fish PFAS exposures are lower than previous estimates of total fish exposures in Europe (8), suggesting that consumption of freshwater and near-source marine fish not captured in this study may be responsible for a large fraction of PFAS exposure from fish and shellfish. Site-specific monitoring and management, including fish consumption advisories, are therefore likely to continue playing a notable role in reducing exposures from PFAS in fish.
Qiu et al. report that modeled global exposures to C8 PFAS decreased by 40 to 72% across compounds when comparing the periods 2002 to 2009 and 2010 to 2021. Although data were not available on temporal trends in exposure to >C8 PFAS, similar observations might be expected owing to similar phase-out timelines by major Western manufacturers and observations in other studies (9, 6). Although phase-out timelines varied regionally, the findings of Qiu et al. suggest that the global fish trade has not markedly altered the effect of production phase-outs on marine fish exposures (2, 5).
The findings of Qiu et al. present a promising picture of legacy PFAS exposures from marine fish: Production phase-outs have been globally effective, and existing management structures can play a leading role in mitigating ongoing exposures. However, the analysis also shows that it can take decades for measurement capabilities and toxicity evaluations to enable global-scale assessments of exposure risks. Legacy PFAS are being rapidly replaced by a variety of "alternative" PFAS structures (1, 10), many of which have been detected in marine ecosystems (6, 11). These range from short-chained PFAS to structures such as sulfonamides, perfluoroalkylethers and chlorinated PFAS. Many alternative PFAS cannot be quantified using available methods, but some have already been found to be as toxic as legacy compounds (6, 11, 12). The rapid proliferation of new PFAS compounds suggests that more proactive management approaches are needed (13, 14). For example, the European Union is moving towards implementing a class-based PFAS management strategy, supported by a scientific consensus about the extreme persistence and hazard potential of PFAS as a class (13). This strategy enables regulation of new, nonessential PFAS based on an extrapolation of risk from well-studied PFAS with similar structures (14, 15). International collaboration on such management approaches can help to prevent the story of legacy PFAS from repeating.