Prenatal exposure to organophosphate pesticides — those commonly used on food crops — is associated with a child having a lower intelligence score at age 7, according to researchers at the University of California, Berkeley’s School of Public Health.
Organophosphates (OP) are a group of pesticides that are well-known neurotoxicants. Indoor use of two common OPs — chlorpyrifos and diazinon — has been phased out over the past decade, mostly because of health risks to children.
The study confirmed that for every tenfold increase in OP levels detected in the mother during pregnancy, there was an overall 5.5 point drop in her child’s IQ at age 7. Furthermore, children with the highest prenatal exposure levels scored seven points lower on a standardized measure of intelligence compared with children who had the least exposure.
“These associations are substantial, especially when viewing this at a population-wide level,” said study principal investigator Brenda Eskenazi, Ph.D., UC Berkeley professor of epidemiology and of maternal and child health.
“That difference could mean, on average, more kids being shifted into the lower end of the spectrum of learning, and more kids needing special services in school.”
The UC Berkeley research is one of three studies published April 21st in the journal Environmental Health Perspectives that shows a link between pesticide exposure and childhood IQ. The other two studies — from Mount Sinai Medical Center and Columbia University — examined urban populations in New York City; the UC Berkeley study focused on children living in Salinas, an agricultural area in Monterey County, California.
“It is very unusual to see this much consistency across populations in studies, so that speaks to the significance of the findings,” said lead author Maryse Bouchard, Ph.D., who was working as a UC Berkeley post-doctoral researcher with Eskenazi during the study.
“The children are now at a stage where they are going to school, so it’s easier to get good, valid assessments of cognitive function.”
The study followed 329 children as part of the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS), an ongoing longitudinal study led by Eskenazi. In 1999, researchers began enrolling pregnant women into the study who came in for regular visits in which they answered questionnaires; once the children were born, their health and development were measured periodically.
Participants gave urine samples twice during pregnancy to check for dialkyl phosphate (DAP) metabolites, the breakdown product of about 75 percent of the organophosphorus insecticides in use in the United States. The two urine results were averaged together; the children were also tested at regular intervals between ages 6 months and 5 years.
Once the children reached age 7, they were given the Wechsler Intelligence Scale for Children – Fourth Edition (WISC-IV) to assess their cognitive abilities, including verbal comprehension, perceptual reasoning, working memory and processing speed.
Not only did higher DAP levels during pregnancy affect the children’s overall IQ scores, but it also caused lower scores in each of the four cognitive development subcategories. The findings were consistent even after researchers factored in maternal education, family income and exposure to other environmental contaminants, including DDT, lead and flame retardants.
“There are limitations to every study; we used metabolites to assess exposure, so we cannot isolate the exposure to a specific pesticide chemical, for instance,” said Eskenazi. “But the way this and the New York studies were designed — starting with pregnant women and then following their children — is one of the strongest methods available to study how environmental factors affect children’s health.”
Although prenatal OP pesticide exposure was strongly correlated with childhood IQ, exposure to pesticides after birth was not. This suggests that exposure during fetal brain development was more critical than childhood exposure.
Maternal DAP levels in the UC Berkeley study were somewhat higher than average compared with the general population, but they were not out of the range of measurements found among women in a national study.
“These findings are likely applicable to the general population,” said Bouchard, who is currently a researcher at the University of Montreal’s Department of Environmental and Occupational Health. “In addition, the other two studies being published were done in New York City, so the connection between pesticide exposure and IQ is not limited to people living in an agricultural community.”
People are exposed to OP pesticides by eating foods that come from chemically treated crops. Farm workers, gardeners, florists, pesticide applicators and manufacturers of these insecticides may be at greater risk than the average person.
“Many people are also exposed when pesticides are used around homes, schools or other buildings,” said study co-author Asa Bradman, Ph.D., associate director of the Center for Environmental Research in Children’s Health at UC Berkeley.
The researchers recommend that consumers thoroughly wash fruits and vegetables—to go beyond a quick rinse and use a soft brush when practical. Consumers should also consider buying organic produce as a way to reduce pesticide exposure from food, they said.
“I’m concerned about people not eating right based on the results of this study,” said Eskenazi. “Most people already are not getting enough fruits and vegetables in their diet, which is linked to serious health problems in the United States. People, especially those who are pregnant, need to eat a diet rich in fruits and vegetables.”
The new IQ findings come less than a year after another CHAMACOS study discovered a link between prenatal pesticide exposure and attention problems in 5-year-old children.
Source: University of California