Associations of prenatal and early childhood mercury exposure with autistic behaviors at 5 years of age: The Mothers and Children's Environmental Health (MOCEH) study

Background Although mercury is an established neurotoxin, only few longitudinal studies have investigated the association between prenatal and early childhood mercury exposure and autistic behaviors. Methods We conducted a longitudinal cohort study using an ongoing prospective birth cohort initiated in 2006, wherein blood mercury levels were measured at early and late pregnancy; in cord blood; and at 2 and 3 years of age. We analyzed 458 mother-child pairs. Autistic behaviors were assessed using the Social Responsiveness Scale (SRS) at 5 years of age. Both continuous SRS T-scores and T-scores dichotomized by a score of ≥ 60 or < 60 were used as outcomes. Results The geometric mean of mercury concentrations in cord blood was 5.52 μg/L. In adjusted models, a doubling of blood mercury levels at late pregnancy (β = 1.84, 95% confidence interval [CI]: 0.39, 3.29), in cord blood (β = 2.24, 95% CI: 0.22, 4.27), and at 2 years (β = 2.12, 95% CI: 0.54, 3.70) and 3 years (β = 2.80, 95% CI: 0.89, 4.72) of age was positively associated with the SRS T-scores. When the SRS T-scores were dichotomized, we observed positive associations with mercury levels at late pregnancy (relative risk [RR] = 1.31, 95% CI: 1.08, 1.60) and in cord blood (RR = 1.28, 95% CI: 1.01, 1.63). Conclusion We found that blood mercury levels at late pregnancy and early childhood were associated with more autistic behaviors in children at 5 years of age. Further study on the long-term effects of mercury exposure is recommended.