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Stanford Report, July 24, 2002

Research to estimate pesticides' effects on children


Give an infant a stuffed teddy bear and before long she'll be nibbling on its ears, nose and feet. After all, biting, tasting and touching are all part of the normal growing up process.

But as children begin to explore their surroundings, they inevitably come in contact with a wide array of potentially harmful substances -- from paints to pesticides -- that can be swallowed, inhaled and even absorbed through the skin. Although the accumulation of hazardous chemicals in the body can have harmful effects on development and behavior, determining the amount of toxic exposure in a child is still largely a matter of guesswork.

Professor James O. Leckie has received an EPA grant to study the effects of pesticide exposure in children, especially the sons and daughters of farmworkers. As part of the research, Leckie and his team videotape children at home to document and quantify their exposure to pesticide residues. Photo: L.A. Cicero

To address this problem, the Environmental Protection Agency (EPA) has awarded Professor James O. Leckie a three-year, $541,000 grant to develop a scientific way to accurately estimate pesticide exposure among children -- especially the sons and daughters of California farmworkers.

The grant is a direct result of the 1996 Food Quality Protection Act, which required the EPA to re-evaluate the health effects of commercial and household pesticides on children. Of particular concern to EPA regulators is determining how pesticide exposure affects agricultural households, where children often live in proximity to poisonous agrochemicals.

"We've been working in the area of exposure analysis for about 10 years," said Leckie, the C. L. Peck, Class of 1906, Professor in the School of Engineering. "The new EPA grant builds on mathematical models that we developed using methodologies that are, in a sense, revolutionary."

Reality TV

One novel technique developed by Leckie and his research team is to videotape individual children at home -- a method designed to document and quantify a child's real-life exposure to pesticide residues.

"We videotape kids for periods of up to eight hours to see what they touch and to determine their hand-to-mouth and object-to-mouth activity," he said. "By applying software we have developed, we quantify each child's dermal contact behavior on a second by second basis. Using this information allows us to estimate the amount of chemicals that are transferred to their skin or their mouth."

Leckie pointed out that children come in frequent contact with harmful particles while crawling and playing in household dust or tracked-in soil. He said that, unlike adults, children are far more sensitive to low concentrations of toxic chemicals because of their developing organs, high metabolism and high skin-surface-area-to-body-weight ratio.

"In a growing body, cellular membranes are expanding. As a result, toxic chemicals readily pass through those membranes," Leckie observed. "Also, biochemical pathways in children are not complete yet and can be easily damaged. This damage is often manifested in slow learning and slow development."

So far, Leckie and his students have videotaped 80 children, many in the Salinas Valley of Monterey County -- one of California's biggest agricultural regions. The tapes have revealed that, in one hour, a typical child might have as many as 60 hand-to-mouth contacts with pesticide-contaminated surfaces -- or roughly one per minute.

"Kids under the age of 1 are mouthing all of the time. They're very curious, and their sensory response is to taste and feel," he explained.

Hispanic workforce

The EPA study will use data from farmworker children between the ages of 1 and 6 -- the most tactile age group, according to Leckie.

"We can take a subset of 20 or 30 children and, using statistical resampling methods, project the results to a large population," he noted. "Our goal is to develop a mathematical model that will allow researchers to quantify cumulative and aggregate exposure to various agricultural pesticides over weeks, months and years -- and across all nondietary routes: dermal, inhalation and ingestion."

California, with the largest agricultural output of all 50 states, used more than 188 million pounds of pesticides in 2000. The state's agricultural workforce is estimated at 1 million, the vast majority of which are Hispanic farmworkers.

"Because they are among the most poorly paid and least protected in the United States workforce today, many farmworkers and their families live in conditions which expose them chronically to toxic agrochemicals," Leckie said. "But virtually all regulations for controlling chemicals in the U.S. have used adult white males as the control target. We're now realizing that was the worst possible choice. You really want the most vulnerable populations: children and pregnant women."

Exposure analysis is a relatively young science, he concluded.

"We still have a lot to learn at the molecular and behavioral level -- especially when it comes to children."