Total Blood Mercury Predicts Methylmercury Exposure in Fish and Shellfish Consumers
Total mercury (THg) has been used as a proxy for methylmercury (MeHg) in whole blood; however, it is unclear if this results in exposure misclassification. We estimated blood MeHg from blood THg measurements using a representative sample of the United States population. National Health and Nutrition Examination Survey (NHANES) 2011-2016 data were randomized into training and test datasets. Analysis included a) self-reported fish and shellfish consumers, ≥ 15 years (N=5268 training; N=2336 test), “full” and b) women fish and shellfish consumers, 15 to 44 years (N=1285 training; N=560 test), “reproductive”. Unadjusted and adjusted (age, sex, race/ethnicity, income, body mass index) linear and spline models were evaluated. Among the full population in the training dataset, geometric mean THg was 0.99 µg/L (95% confidence interval (CI): 0.97, 1.02), geometric mean MeHg was 0.74 µg/L(95% CI: 0.71, 0.76). The mean ratio of MeHg to THg (MeHg/THg) was 0.75 (95% CI: 0.74, 0.75). MeHg/THg was significantly higher among those with higher THg concentrations. All models exhibited excellent fit (adjusted R2 from 0.957 to 0.982). Small improvements in performance were observed in spline versus linear models. The unadjusted spline model is recommended. Among women of reproductive age, this model predicts MeHg=5.55 µg/L when THg=5.80 µg/L. THg is not identical to MeHg in whole blood, but may be used to predict MeHg among fish and shellfish consumers.