The Seychelles Child Development Study of methyl mercury from fish consumption: analysis of subscales from the Child Behaviour Checklist at age 107 months in the main cohort

Methyl mercury (MeHg) is neurotoxic and all fish contain at least trace amounts. Consequently, prenatal or fetal exposure occurs when pregnant women consume fish and children are exposed postnatally when they breastfeed or consume fish. However, the level of exposure at which toxicity occurs is presently unknown. Since behavioural endpoints can be sensitive indicators of toxic exposure, we administered the Child Behaviour Checklist (CBCL) to measure behaviour as part of a prospective, longitudinal, double blind study (n = 779) of prenatal MeHg exposure, the Seychelles Child Development Study (SCDS). The CBCL Total T score was a primary endpoint at 66 and 107 month evaluations of the cohort and showed no association with prenatal or postnatal MeHg exposure. This paper reports the results of a secondary analysis of the CBCL subscales to see if specific aspects of behaviour might show associations. The SCDS main cohort was enrolled in 1989-90 and evaluated on five occasions through 107 months of age. The child's primary caregiver completed the CBCL at the 107 month evaluation. Prenatal exposure was determined by measuring total mercury (THg) in maternal hair growing during pregnancy and recent postnatal exposure by analysing the child's hair taken at the 107 month evaluation. Analysis included linear and nonlinear multiple regression models. For prenatal MeHg exposure, the Social Problems subscale was significantly associated and the Somatic Complaints subscale was marginally associated. Both were beneficial associations. For postnatal exposure the Thought Problems subscale was associated in an adverse direction. This secondary analysis identified a small number of subtle beneficial and adverse associations with prenatal and postnatal MeHg exposure for specific CBCL subscales. These analyses provide no evidence for an adverse effect of prenatal exposure. The adverse postnatal association is difficult to interpret because we measured only recent (about one month) exposure and no adjustment was made for the multiplicity of endpoints.