Shellfish, Not Tap Water, Emerges as the Biggest PFAS Source for Americans

For years, the public conversation about PFAS—the notoriously persistent “forever chemicals” that have contaminated water supplies across the United States—has centered on the tap. Municipal water systems, private wells, and military fire-training grounds have dominated headlines, and for good reason: these compounds are found in a large fraction of American drinking water sources. But a new analysis of national survey and biomonitoring data suggests that when it comes to the average American’s actual dose of legacy PFAS, the seafood on the plate matters far more than the water in the glass. The study, published in Environmental Science and Pollution Research, estimates that shellfish and finfish together account for more than half of the dietary and drinking water intake of seven legacy PFAS compounds in the U.S. population, while drinking water contributes a comparatively modest share.

The research, conducted by Hongbing Sun of Rider University, took an unusually rigorous dual approach to a question that has long been difficult to answer. Rather than relying on a single modeling strategy, the study combined two complementary methods: an intake-based model that multiplies measured PFAS concentrations in foods and water by national consumption data, and a regression-based analysis that links what people report eating and drinking to the PFAS levels actually measured in their blood. The data backbone for both approaches was the National Health and Nutrition Examination Survey, or NHANES, the Centers for Disease Control and Prevention’s ongoing program that collects detailed dietary recall information and blood serum samples from a representative cross-section of the U.S. population. Because NHANES has consistently measured the same seven legacy PFAS compounds across survey cycles, it allowed the researcher to track exposure pathways over the 2015 to 2020 period.

The headline number from the intake-based model is a population-average total PFAS intake of approximately 17.4 nanograms per day from 2015 to 2020. That figure may sound small—nanograms are billionths of a gram—but PFAS compounds are defined by their extraordinary persistence. Their carbon-fluorine bonds, among the strongest in organic chemistry, resist degradation in the body and the environment alike, so compounds like perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) accumulate over years and decades. The serum half-life of PFOS in humans has been estimated at several years, meaning that even small daily doses compound into measurable body burdens. This toxicokinetic reality is precisely why identifying the dominant intake pathways matters: cutting off the largest source, even a modest one in absolute mass terms, can bend the curve of long-term accumulation.

When the researcher broke down that 17.4 nanograms per day by source, the results were striking. Shellfish alone accounted for 43.2 percent of estimated intake, with finfish contributing another 9.2 percent—meaning aquatic foods supplied more than half of the total. Drinking water, despite its cultural prominence as the symbol of PFAS contamination, contributed 15.5 percent. Dairy products came in at 14.4 percent, meat at 10.4 percent, and plant foods at 7.4 percent. The explanation for shellfish’s dominance lies in the biology of the animals themselves. Bivalves such as clams, oysters, and mussels are filter feeders that pump enormous volumes of water through their bodies, concentrating dissolved contaminants including PFAS. Because these compounds bind readily to proteins in animal tissue, filter-feeding organisms effectively act as biological concentrators, accumulating PFAS at levels that can far exceed those in the surrounding water.

Crucially, the regression-based analysis—grounded in actual biomonitoring rather than modeled intake—told the same story. Using survey-weighted standardized regression coefficients, the study examined how self-reported consumption of different food categories and drinking water related to interindividual variability in serum PFAS concentrations across the population. Shellfish consumption again emerged as the largest contributor to variability in blood PFAS levels across survey periods, while drinking water consumption contributed relatively little at the national level between 2015 and 2020. This convergence of two methodologically independent approaches is what gives the finding its weight. Intake models can be criticized for depending on uncertain concentration data, and regression analyses for confounding, but when both point to the same conclusion, the signal becomes difficult to dismiss.

The finding does not mean drinking water is unimportant, and the study’s national averages deserve careful interpretation. PFAS contamination of water is intensely local. Communities near industrial sites, airports, and military installations where aqueous film-forming foam has been used can face drinking water concentrations orders of magnitude above the national norm, and for those residents, water may well be the dominant exposure route. Earlier research, including a 2016 analysis in Environmental Science & Technology Letters, linked PFAS detections in U.S. drinking water supplies to proximity to industrial facilities, military fire-training areas, and wastewater treatment plants. More recent surveys by the U.S. Geological Survey have detected PFAS in tap water across the country, with private wells often facing distinct exposure profiles from public supplies. What the new study establishes is that at the population scale, after averaging across contaminated hotspots and clean supplies alike, the food supply—seafood above all—carries the larger share of legacy PFAS exposure.

The results also align with a growing body of international evidence. The European Food Safety Authority concluded in 2020 that food is the primary exposure route for PFAS among Europeans, with fish and seafood prominent among the contributing categories. Swedish market-basket analyses published in 2025 reached similar conclusions, and the Danish Veterinary and Food Administration has implemented some of the world’s strictest PFAS limits in foods, targeting exactly the animal-derived products that bioaccumulate these compounds. In the United States, the Food and Drug Administration has been testing seafood, dairy, and produce for PFAS, and Consumer Reports reported in 2024 on PFAS detections in some milk samples, including organic varieties. The new NHANES-based analysis stitches these fragmented observations into a coherent national picture, quantifying each pathway’s relative contribution with survey-weighted statistics.

There are important caveats and open questions. The study focused on seven legacy PFAS compounds consistently measured in NHANES—chemicals like PFOA, PFOS, PFHxS, and PFNA that have been phased out of major industrial uses in the United States but persist in the environment and in human blood. The replacement chemistry now flooding the market, including short-chain and fluorotelomer compounds, is largely invisible to standard biomonitoring panels, and their dietary accumulation patterns remain poorly characterized. The author explicitly calls for continued monitoring of both legacy and emerging replacement PFAS in foods and drinking water to improve exposure assessment. Moreover, intake estimates depend on PFAS concentration data drawn from published monitoring studies of varying scope and vintage, and dietary recall instruments capture consumption patterns imperfectly. Concentrations in specific seafood items vary widely by species, harvest location, and whether the product is farmed or wild-caught, so the population-average figures conceal substantial heterogeneity among individual consumers.

For public health policy, the implications are significant. Regulatory attention in the United States has concentrated heavily on drinking water—the Environmental Protection Agency’s health advisories for PFOA and PFOS and its Fifth Unregulated Contaminant Monitoring Rule have driven billions of dollars in anticipated water-treatment investment. Those efforts remain essential, particularly for overburdened communities that bear disproportionate contamination burdens, as studies of New Jersey water systems have documented. But the new findings suggest that a comprehensive exposure-reduction strategy must also encompass the food supply: surveillance of PFAS in retail seafood, guidance for high-consuming populations, and consideration of how contaminated water used in aquaculture and food processing propagates the chemicals into the diet. They also complicate a common public health dilemma, since seafood offers well-established nutritional benefits, including omega-3 fatty acids, and blanket avoidance advice could cause harm of its own.

What makes this study resonate beyond the technical literature is how it upends intuition. The invisible threat, it turns out, may arrive not through the faucet we scrutinize but through the oyster platter and the salmon fillet we consume without a second thought. As PFAS regulation matures and water treatment strips the compounds from municipal supplies, the relative importance of dietary pathways will only grow, making food-based exposure assessment an increasingly urgent frontier. The 17.4 nanograms per day flowing into the average American body is a small number with large consequences—and more than half of it, this analysis shows, comes from the sea.

Subject of Research: Relative contributions of dietary and drinking water pathways to PFAS exposure in the U.S. population

Article Title: Relative contributions of dietary and drinking water pathways to PFAS exposure in the U.S. population: intake-based and biomonitoring analyses

Article References: Sun, H. (2026). Relative contributions of dietary and drinking water pathways to PFAS exposure in the U.S. population: intake-based and biomonitoring analyses. Environmental Science and Pollution Research, 33(30), 15638-15648. https://doi.org/10.1007/s11356-026-38233-6

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38233-6

Keywords: PFAS, forever chemicals, shellfish, seafood, drinking water, NHANES, biomonitoring, dietary exposure, PFOA, PFOS, food contamination, exposure assessment