Abstract
Many studies evaluating methylmercury (MeHg) toxicity rely on whole blood total mercury (THg) measurements to estimate MeHg exposure. However, whole blood THg includes other forms of mercury (Hg), such as inorganic Hg, which have different exposure sources and toxicological effects than MeHg. Therefore, estimating the whole blood MeHg/THg ratio is critical to predicting MeHg exposure and, subsequently, efforts to establish an exposure–response relationship for use in risk assessment. A large, representative dataset (National Health and Nutrition Examination Survey (NHANES) 2011–2016) was used to determine the whole blood MeHg/THg ratio among (a) self-reported fish and shellfish consumers, ≥ 15 years of age (the “full adult” population (N = 5268 training dataset; N = 2336 test dataset)) and (b) female fish and shellfish consumers, 15–44 years of age (the “women of reproductive age” population (N = 1285 training dataset; N = 560 test dataset)). Unadjusted and adjusted linear and spline models with direct measurements for both THg and MeHg were evaluated. The mean whole blood MeHg/THg ratio was 0.75 (95% confidence interval (CI): 0.74, 0.75). This ratio was significantly higher among those with higher THg concentrations. All models exhibited excellent fit (adjusted R2 from 0.957 to 0.982). Performance was slightly improved in spline versus linear models. For the full adult population and women of reproductive age, the unadjusted spline model predicted whole blood MeHg concentrations of 5.65 µg/L and 5.55 µg/L, respectively, when the THg concentration was 5.80 µg/L. These results suggest that whole blood THg is a good predictor of whole blood MeHg among fish and shellfish consumers.
Highlights
Mercury (Hg) is a naturally occurring heavy metal of great concern to public health
Health concerns have been associated with exposure to elemental Hg (Hg vapor) [5, 12], inorganic Hg [10, 13], and methylmercury (MeHg) [14, 15]
We used data from National Health and Nutrition Examination Survey (NHANES), a cross-sectional survey conducted by the US Centers for Disease Control (CDC) of the non-institutionalized civilian US population in the 50 states and the District of Columbia
Summary
Ample research has demonstrated that exposure to various forms of Hg is associated with impaired neurodevelopment [1,2,3], nervous system effects in adults [4,5,6], cardiovascular diseases [7, 8], and renal toxicity [9, 10]. The chemical form of Hg affects its environmental fate and transport, sources of exposure, and toxicity. Health concerns have been associated with exposure to elemental Hg (Hg vapor) [5, 12], inorganic Hg [10, 13], and methylmercury (MeHg) [14, 15]. Exposure to MeHg is a particular public health concern due to its well-documented neurotoxicity, among children [14, 15]. MeHg is the most common form of Hg to which humans are exposed [16], and a substantial proportion of the US population is likely exposed to MeHg at concentrations above recommended limits [17]
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