Abstract
Total mercury content (THg) in hair is an accepted biomarker for chronic dietary methylmercury (MeHg) exposure. In artisanal and small-scale gold mining (ASGM) communities, the validity of this biomarker is questioned because of the potential for contamination from inorganic mercury. As mining communities may have both inorganic and organic mercury exposures, the efficacy of the hair-THg biomarker needs to be evaluated, particularly as nations begin population exposure assessments under their commitments to the Minamata Convention. We sought to validate the efficacy of hair THg for public health monitoring of MeHg exposures for populations living in ASGM communities. We quantified both THg and MeHg contents in hair from a representative subset of participants (N = 287) in a large, population-level mercury exposure assessment in the ASGM region in Madre de Dios (MDD), Peru. We compared population MeHg-THg correlations and %MeHg values with demographic variables including community location, sex, occupation, and nativity. We observed that hair MeHg-THg correlations were high (r > 0.7) for all communities, regardless of location or nativity. Specifically, for individuals within ASGM communities, 81% (121 of 150 total) had hair THg predominantly in the form of MeHg (i.e., >66% of THg) and reflective of dietary exposure to mercury. Furthermore, for individuals with hair THg exceeding the U.S. EPA threshold (1.0 μg/g), 88 out of 106 (83%) had MeHg as the predominant form. As a result, had urine THg solely been used for mercury exposure monitoring, approximately 59% of the ASGM population would have been misclassified as having low mercury exposure. Our results support the use of hair THg for monitoring of MeHg exposure of populations in ASGM settings where alternative biomarkers of MeHg exposure are not feasible.
Highlights
IntroductionThe Minamata Convention on Mercury is an international effort to reduce the negative impacts of anthropogenic mercury pollution
For the subsample selected for this study, the median THg value in the proximal 2-cm hair segments was 1.51 μg/g and 2.55 μg/g for residents living within (N = 150) and outside (N = 137) of mining communities, respectively (Table 1, Figure 2B).These THg values correspond to 71% and 80% of the residents living within and outside of mining surpassing the US Environmental Protection Agency (EPA) threshold value of 1.0 μg/g hair THg, respectively
While total hair mercury alone is not sufficient to capture all forms of mercury exposure, this research shows that excluding hair THg assessments without an alternative biomarker for MeHg exposure could lead to significant underestimation of population exposure risks
Summary
The Minamata Convention on Mercury is an international effort to reduce the negative impacts of anthropogenic mercury pollution. The extent and rates of endogenous iHg accumulation processes are generally low relative to MeHg uptake in hair [13,17,42] While these prior studies in ASGM areas suggest that hair THg levels could overestimate dietary MeHg exposure in the community [43], these studies are not designed to inform population monitoring practices as they used non-random selection of small, convenience samples with limited spatial variability, or they directly targeted individuals involved in gold refining [29]. Regardless, national biomonitoring programs such as Peru, Colombia, and Uganda exclude hair THg in their population surveillance plans for communities near ASGM due to uncertainties raised in reports that directly studied individuals engaged in amalgam burning Instead, these programs recommend urine, an accepted biomarker for iHg exposure, and possibly THg in blood—a biomarker for recent MeHg and iHg exposure and not necessarily long-term exposure.
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