Exploratory Use of Stable Mercury Isotopes to Distinguish Dietary Sources of Methylmercury and Their Relation to Neurodevelopment - Project Summary For most populations, fish consumption is considered the main dietary source for methylmercury, a potent neurotoxin. Fish tissue is also a rich source for beneficial nutrients. Rice is a staple food for more than three billion people. Where rice is a dietary staple, it can also be an important dietary source of methylmercury, without the same beneficial nutrients as fish. There is evidence that methylmercury toxicity is modified by diet (rice versus fish). As diet is the primary pathway for methylmercury exposure, analyses of mercury in hair and blood reflect dietary methylmercury exposure, however, these biomarkers do not differentiate between methylmercury sources. Rice and fish consumption are usually estimated using self-reported food frequency questionnaires; however food frequencies are often inaccurate due to recall bias. To characterize the relationship between methylmercury and neurodevelopment (independent of modification by nutrition), it is critical to characterize the dietary source of methylmercury, with less measurement error. Stable mercury isotopes have been used to track dietary methylmercury sources in food webs, and may be used to distinguish between rice and fish methylmercury intake in human populations. Briefly, mercury is comprised of seven isotopes; all seven isotopes are subject to mass dependent fractionation (MDF), while mass independent fractionation (MIF) occurs mainly for the two odd-isotopes. Unlike MDF, MIF is conserved during trophic transfer and metabolism. We measured stable mercury isotopes in a subset of 21 maternal hair samples from our birth cohort in rural China, where most mothers ingested rice daily, and more than 40% of the mothers rarely or never ingested fish. Our findings indicated that MIF in human hair can be used to distinguish methylmercury intake from rice versus fish in our cohort. Thus hair MIF is a promising novel biomarker, which should be further validated. We propose to analyze mercury isotopes in banked third trimester maternal hair samples for those participants, whose offspring completed the 12-month neurodevelopmental assessment (n=264 hair samples). We propose the following aims: Aim 1. Determine how the isotopic composition of mercury in maternal hair varies depending on diet, among pregnant mothers in rural China, after controlling for potential confounders (e.g., maternal education, etc.). Aim 2. In models investigating prenatal methylmercury exposure and children's neurodevelopment, we will explore whether the source of methylmercury exposure, determined from maternal hair MIF, modifies its effect on children's neurodevelopmental outcomes. In summary, use of hair MIF will improve our understanding of methylmercury toxicity by accounting for modifying effects of diet with better sensitivity and precision than has been possible previously.
