Methyl mercury exposure in populations at risk: Analysis of NHANES 2011-2012

•Asian women of childbearing age are at increased risk of elevated MeHg.•Asian adults ≥50 years of age are at increased risk of elevated MeHg.•Over 75,000 infants born in the US annually may be at risk of health outcomes from MeHg exposure.•Sequential screening with a fish consumption history question followed by TBHg testing shows high validity.•Screening for prenatal mercury exposure should be considered among high risk groups.

BackgroundIngestion of fish contaminated with methyl mercury can lead to adverse health outcomes, particularly when exposure occurs in utero. NHANES 2011-2012 includes total blood mercury (TBHg) and methyl mercury (MeHg) measurements as well as a unique race/ethnicity category for Asians, allowing for improved analysis of determinants of risk.ObjectiveOur objective was to characterize the current burden of MeHg exposure in the US among subgroups who are at risk of health effects due to their physiologic vulnerability to MeHg's effects and/or due to frequent fish consumption, specifically women of childbearing age (WCBA) and adults ≥50 years of age.MethodsWe calculated 90th and 95th percentile estimates as well as geometric means of MeHg for predictive variables. We used multivariable linear regression analyses to estimate the proportional change in mean MeHg associated with each category of all predictive variables. We calculated the validity of screening procedures using fish consumption questions and TBHg testing to predict elevated MeHg.ResultsThe geometric mean MeHg levels were highest among Asian WCBA (1.17 µg/L) and Asians ≥50 years old (2.49 µg/L). Over 23% of Asian WCBA had levels ≥3.5 µg/L and 25% of Asians ≥50 years old had levels ≥5.8 µg/L. Frequency of fish consumption explained 21-23% of the variation in MeHg. Twenty-five percent of women eating fish≥twice per week had MeHg ≥3.5 µg/L. TBHg showed high validity for MeHg ≥5.8 µg/L, and two-step screening using ≥2 fish meals/month followed by TBHg also showed high validity.ConclusionAsian WCBA continue to have increased MeHg exposure from fish consumption, putting their offspring at risk. Screening for MeHg among high-risk groups should be considered.