Maternal Methylmercury Exposure through Rice Ingestion and Offspring Neurodevelopment in Rural China: A Prospective Cohort Study

Abstract

Background: Dietary methylmercury intake can occur not only through fish ingestion but also through rice ingestion; however, rice does not contain the same beneficial nutrients as fish. In rural China, where rice is a staple food, associations between prenatal methylmercury exposure and offspring neurodevelopment were investigated.Methods: 398 mothers living in Daxin, China were recruited at parturition, and had a hair sample collected. Hair total mercury concentrations were measured as a proxy for methylmercury exposure. Mothers completed a semi-quantitative food frequency questionnaire, including rice and fish ingestion. Children were assessed at 12 months (n=270, 68%) and 36 months (n=197, 49%) using the Bayley Scales of Infant Development-II, yielding age-adjusted scores for the Mental Developmental Index (MDI) and Psychomotor Developmental Index (PDI). Multivariable regression was used to model log-transformed hair mercury with outcomes, adjusting for potential confounders, including fish and rice intake. Results: Among 398 mothers, 86% ingested rice daily, 43% never ate fish, and 11% ingested fish >twice/week. Maternal hair mercury averaged 0.48 mcg/g (median: 0.40 mcg/g). At 12 months, in adjusted models, a doubling in hair mercury corresponded to a 1.5-point decrease in the MDI (95% CI: -2.9, -0.03), while a doubling in hair mercury was associated with a 0.82-point decrease in the PDI (95% CI: -2.5, 0.86). At 36 months, in adjusted models, confidence intervals were wide for both MDI and PDI. A doubling in hair mercury corresponded to a 0.32-point decrease in the MDI (95% CI: -2.1, 1.5), and a 1.0-point decrease in the PDI (95% CI: -3.3, 1.3). Conclusions: For 12-month old children from rural China, prenatal methylmercury exposure was associated with statistically significant decrements in cognition; however, this association attenuated over time and was diminished and no longer statistically significant at 36 months. Funding: NIEHS R15ES022409 R21ES026412