Prenatal exposures to environmental chemicals and birth order as risk factors for child behavior problems

Objectives: To assess whether polychlorinated biphenyls (PCBs), methylmercury, lead, or parental child-rearing attitudes was most crucial for maladaptive behavior problems, we examined Japanese 30-month-old children followed up from pregnancy. Methods: The Child Behavior Checklist (CBCL) was used to assess the behavior problems in 306 children. The associations of cord-blood total PCBs (σPCB), total mercury (THg), and lead with each CBCL subscale were examined by multivariate analyses. Results: The median values in cord blood of the 306 children were 48.3 (5 and 95 percentiles, 18.6-116.3) ng/g-lipid for σPCB, 10.2 (4.1-24.5). ng/g for THg, and 1.0 (0.5-1.7) μg/dl for lead. The internalizing score of the CBCL was significantly correlated with σPCB (r=0.113) in the children, though no significant correlation was seen between any CBCL score and either THg or lead. The significant correlation disappeared when conducting multiple regression analysis with possible confounders; at that time, the birth order, home environment, and maternal intelligence quotient were significantly related to the internalizing score. Three CBCL scores and σPCB levels were significantly higher in the first-born children than in the second-born or following children, and the partial correlation coefficient with the adjustment for all confounders except birth order was significant between the internalizing score and σPCB in the latter children (r=0.175). Conclusions: Internalizing behavior appears to be affected by prenatal exposure to PCBs at low levels. Under lower-level exposures, however, behavior problems may be more strongly associated with parental child-rearing attitudes involved in birth order, than with such hazardous chemicals.