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Adding Up the Risks
In toxicology, the dose makes the poison, meaning that it takes a certain level of a chemical to cause an adverse health effect. In some cases, however, it may be several small doses that make the poison when a mixture of chemicals works together to have a toxic effect.
Researchers from EPA's Human Health Research Program in the Office of Research and Development are studying the risk to human health from exposure to a variety of pyrethroid pesticides, including mixtures. Pyrethroids are insecticides that are derived from pyrethrins, which are a natural product of the Chrysanthemum genus. They act by attacking the nervous system of insects and animals. In the United States, there are nearly two dozen registered pyrethroids. In 2000, they comprised about 25 percent of the world insecticide market.
The overall goal of the pyrethroids cumulative risk project is to develop models that will allow researchers to provide accurate estimates of human exposure. These exposure-dose-response models will serve to help meet EPA's assessment needs to evaluate cumulative risks to pesticides under the Food Quality Protection Act.
“This research is exciting and important because we're taking the lessons learned from research on other pesticides, and expanding it to better characterize the potential risks from pyrethroids,” said Kevin Crofton, Ph.D., an EPA scientist conducting pyrethroid research in Research Triangle Park, N.C.
Crofton and his colleagues study and chart the relationship between exposure rates and various adverse outcomes in laboratory rats. They use the animal data and extrapolate those relationships to humans. This results in specific information that estimates the exposure levels at which human health is at risk.
Researchers are looking at these types of exposure-response patterns for a number of individual pyrethroids, and studying the responses that result from exposure to a mixture of pyrethroids. This is particularly important since a person's exposure to any one pyrethroid is likely to be too low to cause an effect. It is possible, however, that a combination of exposures, all added together, could lead to some undesirable effect.
In the end, EPA's cumulative risk assessment of pyrethroids will help to protect human health by providing better guidance regarding the possible dangers from exposure to a variety of common pesticides.
For more information, visit: www.epa.gov/pesticides/cumulative/