Pesticides May Wipe Out More Than Bugs

Mounting Evidence Supports Link Between Pesticides and Lower IQ

Fran Lowry

April 26, 2011

April 26, 2011 — Prenatal exposure to organophosphate (OP) pesticides that are widely used on fruit and vegetable crops throughout the United States has been linked to IQ deficits in school-age children, according to 3 new studies published online April 21 in Environmental Health Perspectives.

The studies add to the growing body of literature linking exposure to pesticides and insecticides to adverse neurologic and cognitive outcomes in children.

In February, a study in Pediatrics and reported by Medscape Medical News at that time showed that prenatal exposure to piperonyl butoxide, a chemical added to pyrethroid insecticides used in the home, was associated with delayed neurodevelopment in young children.

"The fact that 3 research groups reached such similar conclusions independently adds considerable support to the validity of the findings," Hugh A. Tilson, PhD, editor-in-chief of Environmental Health Perspectives, said in a statement.

In the first study, Stephanie M. Engel, PhD, from University of North Carolina, Chapel Hill, and colleagues analyzed third trimester maternal urines for OP metabolites and prenatal maternal blood for paraoxonase 1 (PON1) activity and genotype in 360 multiethnic pregnant women living in New York City between 1998 and 2002. PON1 is a key enzyme in the metabolism of OPs.

Genotype May Increase Risk

The investigators found that prenatal total dialkylphosphate metabolite level was associated with a decrement in mental development at 12 months among blacks and Hispanics and that the association was more marked in children of mothers who carried the PON1Q192R QQ genotype.

Among older children, increasing prenatal total dialkyl- and dimethylphosphate metabolites were associated with decrements in perceptual reasoning in the maternal PON1 Q192R QQ genotype. Greater decrements were associated with increasing prenatal exposure.

In the second study, researchers from the University of California (UC), Berkeley, School of Public Health found that prenatal exposure to OP pesticides was related to lower intelligence scores at the age of 7 years.

The UC Berkeley study focused on predominantly Latino children of farmworkers living in Salinas, an agricultural area in Monterey County, California.

The researchers, led by Maryse F. Bouchard, PhD, assessed exposure to OP pesticides by measuring dialkyl phosphate metabolites in urine collected during pregnancy and also in the offspring at the age of 6 months and 1, 2, 3½, and 5 years. They also administered the Wechsler Intelligence Scale for Children IV to 329 7-year-old children.

These researchers found that prenatal but not postnatal urinary dialkylphosphate concentrations were associated with poorer intellectual development in 7-year-old children. Compared with children in the lowest quintile of maternal dialkylphosphate concentrations, those in the highest quintile had an average deficit of 7.0 IQ points.

The findings held after the investigators controlled for maternal education, family income, and exposure to other environmental contaminants, including DDT, lead, and flame retardants.

"These associations are substantial, especially when viewing this at a population-wide level," Brenda Eskenazi, PhD, senior author of the UC Berkeley study, said in a press release issued by her institution. "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."

Widespread Use Continues

The third study, by Virginia Rauh, ScD, MSW, from Columbia University, New York City, and colleagues, showed children exposed to prenatal chlorpyrifos (CPF), a pesticide used to kill roaches and other pests, had declining IQ and memory. It is now banned for use in the home but is still commonly used to spray food crops.

In the study, Dr. Rauh and her team measured prenatal CPF exposure using umbilical cord blood plasma and then assessed neurodevelopment among 7-year-old children using the Wechsler Intelligence Scales for Children IV.

They found that, for each standard deviation increase in exposure (4.61 pg/g), IQ levels declined by 1.4%, and working memory declined by 2.8%.

"These findings are important in light of continued widespread use of CPF in agricultural settings and possible longer-term educational implications of early cognitive deficits," the investigators write.

"Since agricultural use of CPF is still permitted in the US, it is important that we continue to monitor the levels of exposure in potentially vulnerable populations, including pregnant women in agricultural communities, and evaluate the long-term neurodevelopmental implications of exposure to CPF and other organophosphate insecticides," they conclude.

"It is well known that findings from individual epidemiologic studies may be influenced by chance and other sources of error. This is why researchers often recommend their results be interpreted with caution until they are supported by similar findings in other study populations," Dr. Tilson commented.

"As a group, these papers add substantial weight to the evidence linking OP pesticides with adverse effects on cognitive development by simultaneously reporting consistent findings for 3 different groups of children."

Dr. Tilson, Dr. Engel, Dr. Bouchard, Dr. Eskenazi, and Dr. Rauh have disclosed no relevant financial relationships. Environmental Health Perspectives is published by the National Institute of Environmental Health Sciences, National Institutes of Health, Public Health Service, US Department of Health and Human Services. It is available online.

Environ Health Perspect. Published online April 21, 2011.

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