Association between prenatal mercury exposure and pediatric neurodevelopment: The Japan environment and children's...

Mercury pollution, including from its use during gold mining and refining, remains an important problem worldwide. In particular, methylmercury, a microbial alteration of mercury released into the environment, is a major environmental neurotoxicant. Although there has been growing concern about the health hazards of exposure to low levels of mercury, the effects of prenatal mercury exposure on neurodevelopmental outcomes in children have remained controversial. In the Japan Environment and Children's Study, a large-scale nationwide birth cohort study, we measured methylmercury and inorganic mercury concentrations in cord blood and conducted developmental scoring tests at ages 2 and 4 years. We then analyzed the associations between mercury levels in cord blood and neurodevelopmental outcomes. Measurements of cord blood obtained from 3822 participants revealed median values of 7.39 ng/ml (5th percentile: 2.95, 95th percentile: 18.1) and 0.25 ng/ml (5th percentile: 0.10, 95th percentile: 0.58) for methylmercury and inorganic mercury, respectively. Analyzing the association with fish consumption, bonito-tuna was most strongly correlated with both methylmercury and inorganic mercury in cord blood. Although the association between cord blood mercury and neurodevelopmental scores was subsequently examined in 3083 individuals, we found no significant association with either methylmercury or inorganic mercury. Further quartile group analysis based on methylmercury concentrations in cord blood revealed no concentration-dependent association between a prenatal mercury exposure and neurodevelopment in children. However, various factors influence neurodevelopment, and long-term observational studies that consider those covariates are necessary for a more definitive conclusion. Although the findings of our study provide important insights into the association between prenatal mercury exposure and neurodevelopment, further research is needed to make recommendations for safe mercury intake thresholds during pregnancy.