Pesticides Hit Home: Rating the Risks for Kids in California. (Science Selections)
Tenenbaum, David J., Environmental Health Perspectives
Pesticides have long been suspected of causing childhood cancer, but establishing a cause-and-effect relationship is difficult. Children are exposed to unknown varieties and quantities of pesticides. Parents seldom know which compounds are being used in nearby agricultural fields. Epidemiologic studies often suffer from case-response bias: parents of sick children are more likely to remember using pesticides. And when cancer clusters are investigated, the cases are often too few to prove an association with pesticides.
Robert Gunier and colleagues at the California Department of Health Services describe a methodology to address these limitations [EHP 109:1071-1078]. The methodology compares pesticide use to location, and weights both hazard and usage to give an effective measure of the actual danger of the chemicals. Using data from California's Pesticide Use Report, a mandatory statewide pesticide-application reporting system begun in 1990, they determined which census block groups (subdivisions of census tracts) had received which pesticides from 1991 to 1994. To increase statistical power, they focused on the 38 most used insecticides, fungicides, and herbicides in the state and grouped the pesticides in four categories: genotoxicants, reproductive and developmental toxicants, probable carcinogens, and possible carcinogens (California has banned known human carcinogens from agricultural use). More than 36 million pounds of genotoxic active ingredients were used in California during the average year.
Pesticides were assigned a numerical hazard factor, based on toxicity and exposure factors:
* cancer class (probable or possible human carcinogen), determined by the U.S. Environmental Protection Agency;
* cancer potency, or how much the incidence of cancer increases with dose (usually determined by laboratory animal studies);
* volatilization flux rate, or how rapidly the compound enters the atmosphere (important because inhalation is a major exposure route); and
* field half-life, or how long the compound lingers in the field. …