Prenatal Exposure to Organophosphate Pesticides May Play a Role in Children's Attention Problems

Spraying pesticide in California (USDA Photo by Charles O'Rear)

Scientists at UC Berkeley have found that women exposed to organophosphate pesticides while pregnant are more likely to have children with attention problems at age five. In a separate study, they reveal that some children may be genetically more susceptible to organophosphates than others.

The two studies published in the October issue of Environmental Heath Perspectives are part of a longitudinal investigation by the Center for the Health Assessment of Mothers and Children in Salinas (CHAMACOS) led by director Brenda Eskenazi, Maxwell Professor of Maternal and Child Health and Epidemiology in the School of Public Health and a member of COEH. The study enrolled over 600 predominantly Mexican-American pregnant women living in the Salinas Valley, an agricultural region in North Central California, starting in 1999. Eskenazi and her research team have been working with families in the community for more than a decade to learn how pesticides and other environmental exposures affect the health of mothers and children.1

Organophosphate (OP) pesticides are potent toxins widely used in agriculture to protect fruits and vegetables from insects and pests. "We know these chemicals are neurotoxins at very high doses," said Eskenazi. "The question was whether we would find any associations when the exposures were considerably lower, but perhaps more constant, and whether some populations are more vulnerable than others."

As a marker of prenatal OP exposure, researchers measured six dialkyl phosphate (DAP) metabolities in maternal urine twice during pregnancy. The DAPs represent 80% of the total OP pesticides used in the Salinas Valley. They found every 10-fold increase in maternal DAP concentration was associated with a five times greater odds of attention-deficit hyperactivity disorder (ADHD) assessment at age 5. The association was strongest among boys.2

Eskenazi said the OP levels measured in pregnant women in Salinas Valley were somewhat higher than the general U.S. population of women of reproductive age, but not out of range. "If you look at the levels of metabolites of the women during pregnancy compared to women of reproductive age in the National Health and Nutrition Examination Survey of the U.S. population, there is a great deal of overlap in the distributions, which means that there are many people in the United States who have similar levels of pesticide metabolites."

"We took a sample of urine and looked to see the metabolites in that urine, but those metabolites could come from eating or from exposure to the metabolites themselves in the environment," reports Eskenazi. "We don't know enough about it yet." Nonetheless, she recommends washing fruits and vegetables and soaking berries and rinsing them several times, especially while pregnant.

A second study by Eskenazi and COEH co-authors Nina Holland, Karen Huen, Asa Bradman and Kim Harley suggests how one's genotype may influence susceptibility to OPs. "If you and I are exposed to the same level of a chemical," questions Eskenazi, "but I have one genotype and you have another, am I more likely to have associations with adverse neurodevelopment than you are, given the same exposure?"

Scientists analyzed blood samples from over 350 children from the CHAMACOS study, and they found those with certain paraoxonase 1 (PON1) genotypes, which determine levels and efficiency of enzymes that break down the toxic metabolites of OPs, had more neurodevelopmental delays than those with other genotypes.3 PON1 measurements have been associated with diseases of the nervous system including Alzheimer's, ischemic stroke and Parkinson's, and with childhood autism, according to the authors.

"Our study was too small to say anything definitely," said Eskenazi. "But a trend was suggestive that there may be an increased susceptibility." To confirm their findings, the authors recommend a follow-up study that pools information from other research centers with similar data.

CHAMACOS Awarded $7.5 Million over 5 Years

The National Institute of Environmental Health Sciences and the U.S. Environmental Protection Agency recently granted CHAMACOS, led by principal investigator Eskenazi, $7.5 million over 5 years to study the children from the Salinas Valley into puberty.

The grant will help support graduate and post-doctoral students pursuing research into the health impacts of exposures to chemicals including agricultural pesticides, flame retardants and dichlorodiphenyltrichloroethane, or DDT.

 

1 CHAMACOS project website: http://ehs.sph.berkeley.edu/chamacos
2 Marks AR, Harley K, Bradman A, Kogut K, Barr DB, Johnson C, Calderon N, Eskenazi B. Organophosphate pesticide exposure and attention in young Mexican-American children: the CHAMACOS study. Environ Health Perspect. 2010 Dec;118(12):1768-74.
3 Press release by Sarah Yang, Media Relations at UC Berkeley.
4 Eskenazi B, Huen K, Marks A, Harley KG, Bradman A, Barr DB, Holland N. Organophosphate pesticide exposure and attention in young Mexican-American children: the CHAMACOS study. Environ Health Perspect. 2010 Dec;118(12):1768-74.

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