Fish consumption, mercury exposure, and their associations with scholastic achievement in the Seychelles Child Development Study

Abstract

Studies of neurodevelopmental outcomes in offspring exposed to MeHg from maternal consumption of fish have primarily measured cognitive abilities. Reported associations have been subtle and in both adverse and beneficial directions. Changes in functional outcomes such as school achievement and behavior in exposed children and adolescents have not been examined. We undertook an assessment of school success of children in the Seychelles Child Development Study (SCDS) main cohort to determine if there were any associations with either prenatal or recent postnatal MeHg exposure. The primary endpoints were Seychelles nationally standardized end-of-year examinations given when the cohort children were 9 and 17 years of age. A subgroup (n=215) from the main cohort was also examined at 9 years of age using a regional achievement test called SACMEQ. Prenatal MeHg exposure was 6.8 ppm in maternal hair; recent postnatal exposure was 6.09 ppm at 9 years and 8.0 ppm at 17 years, measured in child hair. Multiple linear regression analyses showed no pattern of associations between prenatal or postnatal exposure, and either the 9- or 17-year end-of-year examination scores. For the subgroup of 215 subjects who participated in the SACMEQ test, there were significant adverse associations between examination scores and postnatal exposure, but only for males. The average postnatal exposure level in child hair for this subgroup was significantly higher than for the overall cohort. These results are consistent with our earlier studies and support the interpretation that prenatal MeHg exposure at dosages achieved by mothers consuming a diet high in fish are not associated with adverse educational measures of scholastic achievement. The adverse association of educational measures with postnatal exposure in males is intriguing, but will need to be confirmed by further studies examining factors that influence scholastic achievement.

Figure 1

Partial residuals plots from the linear regression models for Primary 6 and Secondary 3 Math and French scores, with a linear trend of postnatal THg hair level for Secondary 3 and linear trends for female and male for Primary 6 adjusted for covariates. The dashed lines in plot are the lines when fitting excluding outliers.

Figure 2

Partial residuals plot from the linear regression models for SACMEQ Cohort boys and girls. The left panel shows regression results for SACMEQ tests for Mathematics (upper graph) and Reading Comprehension (lower graph). The right panel shows the Primary 6 End-of-Year Examination Mathematics (upper graph) and Reading Comprehension (lower panel) results for the SACMEQ subjects. All analysis results are plotted with a linear trend of postnatal THg hair level adjusted for covariates.