Postnatal exposure to methyl mercury and neuropsychological development in 7-year-old urban inner-city children exposed to lead in the United States

Abstract

Background The most common route for general population exposure to methyl mercury (MeHg) is fish consumption. Recommendations to pregnant women about consuming fish contaminated with MeHg are also applied to children, but there are few studies available about the effects of low level postnatal MeHg exposure in them. Objectives To investigate the association between postnatal methyl mercury exposure and neuropsychological development in a study of children also exposed to lead, both measured at 7 years. Methods We measured MeHg concentrations in blood samples from the Treatment of Lead-exposed Children (TLC) trial in which 780 children with elevated concentrations of lead in blood were followed with neuropsychological tests from ages 12–33 months through 7 years. Here we examine blood MeHg concentration and neuropsychological test scores, both measured at age 7 years. We used a maximum likelihood method to estimate geometric mean MeHg concentration and generalized linear regression models to analyze MeHg and neuropsychological test scores. Results Geometric mean MeHg concentration was 0.56 (95% confidence interval: 0.52, 0.59) μg/L. A 1 μg/L increase in MeHg was associated with a 2.1 (95% confidence interval: 0.4, 3.8) point increase in Full Scale IQ and 0.2 (95% confidence interval: 0.02, 0.4) point increase in Learning Slope index T score on a test of verbal memory. Conclusions Our results suggest that the relatively low MeHg exposure in US school-aged children from this population has no detectable adverse effect on neuropsychological development. The positive associations observed between MeHg and neurodevelopment may indirectly reflect consumption of beneficial polyunsaturated fatty acids from seafood.

Biomonitoring of mercury, cadmium, and lead exposure in Japanese children: a cross-sectional study

“…Mean hair Hg level in that study was 6.09 lg/g at 9 years and 8.0 lg/g at 17 years. The benefit of n3-PUFA content of the fish is hypothesized to outweigh the risk of MeHg exposure from fish intake [30]. Our findings of median hair Hg 1.40 (range: 0.31-3.96) lg/g are slightly lower than that of previous Japanese study, and mean hair Hg in our study (1.49 lg/g) is much lower than that of Seychelles cohort.…”

Impairment in Working Memory and Executive Function Associated with Mercury Exposure in Indigenous Populations in Upper Amazonian Peru

“…These dose-related effects have also been reported outside of Amazonia regions, such as the Faroe Islands where longitudinal work has found that every 10-ppm increase in Hg is associated with a 1.8 to 2.2-point mean decrease in IQ score [ 20 ]. The findings are consistent with other studies conducted across the globe [ 21 , 22 , 23 ] and provide strong evidence (with exceptions reported from studies in the Seychelle Islands [ 23 , 24 ] and the United States [ 25 ] that exposure to MeHg negatively impacts the general intelligence of humans.…”

Neuropsychological effects and cognitive deficits associated with exposure to mercury and arsenic in children and adolescents of the Mojana region, Colombia

“…In contrast, while it is true that evidence from associated studies has reported its neurotoxic impact, it is important to outline that there are also other longitudinal studies that differ not only among these, but also among themselves. Some studies have found that there are no patterns of alteration in the development of cognitive and/or neuropsychological skills (Boucher et al, 2010;Forns et al, 2014;, Lee et al, 2017;Wang et al, 2014). As for evidence of impairment, similar results to those cited above have also been found, which indicated impairment or diminution of neurocognitive functions in accordance with the final longitudinal analyses (Kim et al, 2018;Valeri et al, 2017;van Wijngaarden et al, 2017;Debes et al, 2016).…”