Background

Organophosphate pesticides are widely used in agriculture and for other purposes, leading to ubiquitous exposure in human populations. Some studies reported cognitive deficits in children exposed prenatally to organophosphate pesticides, but findings from recent studies were inconsistent. Furthermore, recent biomonitoring studies suggest exposure levels have decreased. Hence, the risks from current prenatal exposure to organophosphate pesticides for child neurodevelopment are uncertain. Furthermore, sex-differences also remain to be better documented in relation to potential neurodevelopmental effects.

Objective

To examine the association between prenatal exposure to organophosphate pesticides and IQ scores among boys and girls living in several major Canadian cities.

Methods

We used data from the MIREC cohort (Maternal-Infant Research on Environmental Chemicals). Women were recruited in 2008–2011 from 10 Canadian cities during their first trimester of pregnancy, and urine spot samples were collected for measurement of three dimethyl alkyl phosphate (DMAP) and three diethyl alkyl phosphate (DEAP) metabolites. When children were 3–4 years of age, we used the Wechsler Preschool and Primary Scales of Intelligence-III (WPPSI-III) to assess cognitive ability of children from 6 out of the 10 cities (Halifax, Hamilton, Kingston, Montreal, Toronto, and Vancouver). We analysed the association between maternal exposure to organophosphate pesticides (DMAP and DEAP urinary metabolites) and children’s IQ scores with generalized estimating equations (GEEs) to take into account the clustered-data resulting from the six study sites. All analyses were sex-stratified (n = 296 boys and 311 girls).

Results

The participants were predominantly well-educated, white women, with a relatively high household income. Children had a mean age of 3.4 years at the moment of IQ assessment (range, 3.0–4.1 years). In girls, there was no association between IQ scores and DEAPs or DMAPs. Higher concentrations of DEAPs were significantly associated with poorer Verbal IQ scores (for a 10-fold increase in concentrations, −6.28; 95% CIs, −12.13, −0.43) in boys. The association for Performance IQ in boys also indicated poorer scores with higher DEAP concentrations, but the confidence intervals included the null value (−4.05; 95% CIs, −10.19, 2.10). The relation between DMAPs and IQ scores in boys was also negative, but association estimates were small and not significant.

Conclusion

Urinary metabolites of organophosphate pesticides were not associated with IQ in girls, but we observed that higher maternal urinary DEAPs were associated with poorer Verbal IQ in boys. However, exposure misclassification may be an issue as only one urine sample per woman was analysed. The present study contributes to the accumulating evidence linking exposure to organophosphate pesticides during fetal development with poorer cognitive function in children, bringing data on the risks in a context of low exposure levels encountered in primarily urban populations from Canada.