Environmental Factor, April 2010, National Institute of Environmental Health Sciences
Pesticide Exposure and Child Development
By Thaddeus Schug
On March 16, epidemiologist and NIEHS grantee Brenda Eskenazi, Ph.D., visited NIEHS to discuss her research with farm workers in California, which involves determining how pesticide exposure impacts child development and reproductive health and field testing interventions as primary prevention measures to protect workers and their families from harmful exposures.
Eskenazi, who is the Jennifer and Brian Maxwell Professor of Maternal and Child Health and Epidemiology at the University of California, Berkeley (UCB), presented a Distinguished Lecture seminar titled "Organophosphate Pesticide Exposure and the Development of Children Living in an Agricultural Community: Results of the CHAMACOS Study." The lecture was hosted by NIEHS Principal Investigator Matthew Longnecker, M.D., Sc.D.
Eskenazi directs the NIEHS/EPA-funded CHAMACOS Center (http://cerch.berkeley.edu/research-programs/chamacos-study), named after the word for "small child" in Mexican Spanish (see text box). The project is a longitudinal birth cohort study that has followed a population of children from before birth through age 9. Data was gathered on 536 infants, born in 2000-2001, whose mothers were enrolled during pregnancy. As Eskenazi explained, "The goal of this ongoing study is to assess the health effects of low-level, chronic pesticide exposure and other exposures in children living in an agricultural community based in the Salinas Valley of California. We also hope to reduce exposures to children by intervention and community outreach programs."
Pesticide exposure in children living in an agricultural community
The Salinas Valley, considered the "Salad Bowl of the World," is one of the world's richest agricultural areas. Eskanazi noted that "take-home" pesticide exposure - on clothing and skin - was extremely high for the workers and their families whose homes, schools, and playgrounds were located very close to cultivated fields. Eskanazi's team measured exposure by analyzing blood, urine, skin, teeth, clothing, soil samples, and data collected from California state agriculture records.
Eskanazi said that pregnant women in the study showed higher organophosphate (OP) urinary metabolite levels than did women of child-bearing age who participated in the National Health and Nutrition Examination Survey (NHANES). Levels in samples collected in the postpartum period were about twice as high as levels during pregnancy. Higher levels of OP pesticide metabolites in maternal urine during pregnancy were associated with shorter gestational duration. A ten-fold increase in average dimethyl, but not diethyl, phosphate metabolites was associated with a decrease of three days in gestational duration.
Lower levels of acetyl cholinesterase - suggesting higher OP exposure - in umbilical cord blood were also associated with significantly shorter length of gestation. No adverse associations were found between OP exposure and infant birth weight, length, or head circumference. However, neonates whose mothers had higher OP pesticide metabolite levels during pregnancy were more likely to have abnormal reflexes in the neonatal period as assessed by the Brazelton Neonatal Behavioral Assessment Scale. OP exposure was associated with both an increase in the number of abnormal reflexes and with the proportion of infants with more than three abnormal reflexes.
PON1 as a Predictor of Pesticide Susceptibility
"Given the same level of pesticide exposure, some individuals may be more susceptible to the potential adverse effects of pesticides depending on their genetic makeup and expression of genes encoding key metabolic enzymes," Eskanazi observed. "For example, the human enzyme paraoxonase (PON1) detoxifies various organophosphate pesticides with different efficiency, depending on the main single nucleotide polymorphism (SNP) at position 192 and other SNPs along promoter and coding regions."
The pesticide susceptibility project is determining PON1 genotype for two polymorphisms, 192 and 108, and measuring enzyme activity levels - paraoxonase, diazoxonase, chlorpyrifos oxonase, and arylesterase - in maternal and child blood from the CHAMACOS cohort. "We will also examine whether PON1 status modifies the association of pesticides and neurodevelopment," said Eskanazi.
(Thaddeus Schug, Ph.D., is a postdoctoral research fellow in the NIEHS Laboratory of Signal Transduction.)
Center for the Health Assessment of Mothers and Children of Salinas
The CHAMACOS Center works with families in a farm worker community to learn how pesticides and other environmental exposures affect the health of mothers and children. The center is comprised of several research projects investigating the environment and children's health in the Salinas Valley, Monterey County, Calif.
CHAMACOS is a project of the UCB Center for Children's Environmental Health Research, in partnership with Natividad Medical Center, Clinica de Salud del Valle de Salinas, and other community organizations. The center has a strong community base, with an Advisory Board and Farm Worker Council, which earned it a Chancellor's Community-University Partnership Award in 2002.
The goals of the UC Berkeley Children's Center and CHAMACOS study are:
- To assess pesticide and other environmental exposures in pregnant women and young children;
- To examine the potential health effects of these exposures on childhood growth, neurodevelopment, and respiratory disease;
- To learn more about the mechanisms of pesticide immunotoxicity and neurotoxicity;
- To develop community-based outreach and interventions that reduce take-home pesticide exposure among children of farm workers.