Person:

Li, Miling

Seafood consumption is the primary route of methylmercury (MeHg) exposure for most populations. Inherent uncertainties in dietary survey data point to the need for an empirical tool to confirm exposure sources. We therefore explore the utility of Hg stable isotope ratios in human hair as a new method for discerning MeHg exposure sources. We characterized Hg isotope fractionation between humans and their diets using hair samples from Faroese whalers exposed to MeHg predominantly from pilot whales. We observed an increase of 1.75‰ in δ202Hg values between pilot whale muscle tissue and Faroese whalers’ hair but no mass-independent fractionation. We found a similar offset in δ202Hg between consumed seafood and hair samples from Gulf of Mexico recreational anglers who are exposed to lower levels of MeHg from a variety of seafood sources. An isotope mixing model was used to estimate individual MeHg exposure sources and confirmed that both Δ199Hg and δ202Hg values in human hair can help identify dietary MeHg sources. Variability in isotopic signatures among coastal fish consumers in the Gulf of Mexico likely reflects both differences in environmental sources of MeHg to coastal fish and uncertainty in dietary recall data. Additional data are needed to fully refine this approach for individuals with complex seafood consumption patterns.

Background: Methylmercury (MeHg) exposure is associated with adverse effects on neurodevelopment and cardiovascular health. Previous work indicates most MeHg is from marine fish sold in the commercial market, but does not fully resolve supply regions globally. This information is critical for linking changes in environmental MeHg levels to human exposure in the U.S. population. Objectives: We used available data to estimate the geographic origins of seafood consumed in the United States (major ocean basins, coastal fisheries, aquaculture, freshwater) and how shifts in edible supply affected MeHg exposures between 2000–2002 and 2010–2012. Methods: Source regions for edible seafood and MeHg exposure in the United States were characterized from national and international landing, export and import data from the Food and Agricultural Organization of the United Nations and the U.S. National Marine Fisheries Service. Results: Our analysis suggests 37% of U.S. population-wide MeHg exposure is from mainly domestic coastal systems and 45% from open ocean ecosystems. We estimate that the Pacific Ocean alone supplies more than half of total MeHg exposure. Aquaculture and freshwater fisheries together account for an estimated 18% of total MeHg intake. Shifts in seafood types and supply regions between 2000–2002 and 2010–2012 reflect changes in consumer preferences (e.g., away from canned light meat tuna), global ecosystem shifts (e.g., northern migration of cod stocks), and increasing supply from aquaculture (e.g., shrimp and salmon). Conclusion: Our findings indicate global actions that reduce anthropogenic Hg emissions will be beneficial for U.S. seafood consumers because open ocean ecosystems supply a large fraction of their MeHg exposure. However, our estimates suggest that domestic actions can provide the greatest benefit for coastal seafood consumers. https://doi.org/10.1289/EHP2644