The objective of this study was to describe the postnatal exposure to Hg and to evaluate its association with neuropsychological
development among preschool children. The study population are 4–5 years old children (n = 1252) participant in
the Spanish INMA Project. Total Hg was measured in cord blood and in hair samples taken at 4 years of age (2008–2012).
Neuropsychological development was assessed using the McCarthy Scales of Children’s Abilities (MSCA). Information on
covariates and possible confounders was obtained by questionnaires during pregnancy and childhood. Generalized additive
and linear regression models were built in order to assess the relationship between MSCA scores and Hg exposure. We also
evaluated the magnitude of the possible bias generated from measurement error in seafood intake estimate from questionnaire
and Hg determination. The geometric mean of hair Hg was 0.98 μg/g [95% confidence interval (CI) 0.94, 1.03]. In the regression
analysis, the association between Hg and the MSCA scores was positive for all the scales and statistically significant for
the verbal (β = 0.89; 95%CI 0.38, 1.39), memory (β = 0.42; 95%CI 0.09, 0.76) and general cognitive scales (β = 1.35; 95%CI
0.45, 2.25). However, these associations were clearly attenuated when we adjusted by the children’s fish intake variables or
when took into account theoretical scenarios of low precision in fish intake and Hg measurements. Hg levels in this Spanish
population were high in comparison with other European countries; however, we did not observe adverse effects on child
neuropsychological development associated with this postnatal exposure to Hg