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

Abstract

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 mu g/L. In adjusted models, a doubling of blood mercury levels at late pregnancy (beta= 1.84, 95% confidence interval [CI]: 0.39, 3.29), in cord blood (beta = 2.24, 95% CI: 0.22, 4.27), and at 2 years (beta = 2.12, 95% CI: 0.54, 3.70) and 3 years (beta = 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.