81. Organophosphate pesticides exposure during fetal development and IQ scores in 3 and 4-year old Canadian children (lay summary)

Nkinsa PN, Muckle G, Ayotte P, Lanphear BP, Arbuckle TE, Fraser WD, Bouchard MF. Environmental Research 2020 Aug 7:110023. doi: 10.1016/j.envres.2020.110023

Organophosphate pesticides are widely used in agriculture leading to exposure to these chemicals in the general population.  Fruits and vegetables are common sources of exposure for pregnant women and children.  Though there is some evidence that higher exposure to these chemicals may be associated with adverse effects on childhood neurodevelopment, the studies are inconsistent.  Also, few studies have examined boys and girls separately.

The goal of this study was to examine associations between prenatal exposure to organophosphate pesticides and child IQ at around age 3 in the MIREC study.  This research was led by a graduate student at the University of Montreal.  Prenatal exposure to organophosphate pesticides was measured in urine samples collected from mothers during their first trimester.  Specifically, six different pesticide metabolites were measured and were summed into dimethyl alkyl phosphates (DMAP) and diethyl organophosphates (DEAP) metabolites. Children’s IQ was measured using a test of cognitive ability called the Wechsler Preschool and Primary Scale of Intelligence-III.  This test measures Verbal, Performance, and Full scale IQ scores based on an assessment of, for example, vocabulary and information processing.   Using statistical models, researcher examined the association between prenatal exposure to these pesticide metabolites and children’s IQ.

No association was observed between any of the pesticide metabolites and IQ scores in girls. In boys, higher concentrations of the DEAP metabolites was associated with poorer verbal and performance IQ.  A 10-fold increase in maternal urinary DEAP concentrations was associated with a 6 point lower verbal IQ score in boys.

These results suggest that boys may be more susceptible to the potential adverse effects of exposure to organophosphate pesticides than girls.  One of the challenges of this type of research is that these pesticides are rapidly eliminated from the body and one urine measurement per woman may not be a good indicator of exposure during early pregnancy.  Future studies should measure pesticides multiple times per woman throughout pregnancy and examine whether associations with child IQ consistently differ between boys and girls.