Assessing Sources of Human Methylmercury Exposure Using Stable Mercury Isotopes

Abstract

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.

Tracing mercury pathways in Augusta Bay (southern Italy) by total concentration and isotope determination

“…(offset ¼ 1.9‰) and the Faroese whalers (offset 1.7‰) (Li et al, 2014). Hence, our results would seem to imply that consumption of seafood from AB represents the primary Hg exposure pathway for local population.…”

“…Hence, our results would seem to imply that consumption of seafood from AB represents the primary Hg exposure pathway for local population. In addition, results encourage the application of a þ2.0 ± 0.2‰ correction to human hair d 202 Hg values to find the average dietary mercury isotopic signature in future studies of human exposure to MeHg, since MDF offset variations in hair likely depend only on the efficiencies of demethylation pathways in the human body (Li et al, 2014). Furthermore human hair samples from AB area exhibited high positive MIF values (mean D 199 Hg 1.20 ± 0.19‰ [1SD; n ¼ 21]; median 1.17‰) (Fig.…”

Isotopic study of mercury sources and transfer between a freshwater lake and adjacent forest food web

“…Based on this, we propose that the anomalously high δ 202 Hg value in the bat hair is caused by an internal metabolic fractionation of δ 202 Hg upon bioaccumulation of MMHg from the aquatic ecosystem. Previous studies have documented 1-2‰ higher δ 202 Hg values, but identical Δ 199 Hg values, in birds and in mammals including seals, whales, and human hair compared to their respective diets, and have attributed this to δ 202 Hg fractionation associated with internal demethylation of MMHg (Day et al, 2012;Kwon et al, 2014;Laffont et al, 2011;Li et al, 2014;Perrot et al, 2012;. In contrast, the bat excrement samples, composed mainly of IHg, displayed similar Hg isotope values as the bulk sediment but much lower Δ 199 Hg values compared to bat hair, which is composed mainly of MMHg.…”

Quantifying mercury isotope dynamics in captive Pacific bluefin tuna (Thunnus orientalis)

“…Hg values observed in mammals, birds, and human hair (Laffont et al, 2011;Day et al, 2012;Perrot et al, 2012;Kwon et al, 2014Kwon et al, , 2015Li et al, 2014 (Wiederhold et al, 2010). Given that MMHg in muscle tissues is most often associated with thiol-ligands (Olson et al, 1978;Schultz and Newman, 1997), we presume that MMHg with higher d…”