Fetuses that are exposed to organophosphate pesticides are more likely to have lower-than-average IQs at the age of 7 years than other children, according to an article published in Environmental Health Perspectives.

Any organic compound that contains phosphorous is an organophosphate – they are commonly used as fertilizers and pesticides in agriculture. Acetylcholinesterase, an essential enzyme for good nerve function in animals, insects, and humans is irreversibly inactivated by organophosphates. Put simply, organophosphates impair the good functioning of our nervous system – the human brain is part of our nervous system. The following organophosphates are commonly used – diazinon, malathion, phosmet, azinphos methyl, methyl parathion, chlorpyrifos, tetrachlorvinphos, and parathion.

A group of researchers led by Maryse Bouchard wanted to find out whether prenatal and postnatal exposure to organophosphate (OP) pesticides might have an impact on schoolchildren’s IQs.

They performed a study on agricultural working families in California – most of them Latinos. They took urine samples and measured levels of DAP (dialkyl phosphate) metabolites; they were collected during pregnancy and when the children were aged 6 months, and 1, 2, 3.5 and 5 years old.

When the 329 children were seven years old, the investigators used the Wechsler Intelligence Scale for Children. They made allowances for factors which might affect a child’s IQ for other reasons, such as the mothers academic level and intelligence, the HOME score, and language of cognitive assessment.

Their findings showed that pregnant mothers with the highest DAP metabolite levels in their urine were much more likely to have 7-year-old children with lower-than-average IQs. In this study, an average IQ score was 100. Pregnant mothers with the highest DAP urine levels (top quintile) had 7-year-old children with IQ scores seven points lower than the pregnant mothers with the lowest DAP urine levels (bottom quintile).

Brenda Eskenazi, Ph.D., of the University of Berkeley, California, said:

“That’s not unlike the decreases we see in children with high lead exposure.”

Only DAP urine levels during pregnancy appear to have an impact on subsequent IQ when the fetus becomes a 7-year-old child, the researchers stressed. DAP urine levels in babies and children after birth had no impact.

The authors concluded:

“Prenatal but not postnatal urinary DAP concentrations were associated with poorer intellectual development in 7-year-old children. Maternal urinary DAP concentrations in the present study were higher, but nonetheless within the range of levels measured in the general U.S. population.”

Environmental Health Perspectives
doi:10.1289/ehp.1003185
“Prenatal Exposure to Organophosphate Pesticides and IQ in 7-Year Old Children”
Maryse F. Bouchard, Jonathan Chevrier, Kim G. Harley, Katherine Kogut, Michelle Vedar, Norma Calderon, Celina Trujillo, Caroline Johnson, Asa Bradman, Dana Boyd Barr, Brenda Eskenazi

Written by Christian Nordqvist