Quick Chemical Screening

Hundreds of pesticides that have already undergone traditional toxicity studies will be among the first chemicals run through rapid computer tests, EPA announced on Aug. 2. The program is a prelude to a much wider effort by the agency to use computer-assisted toxicity testing.

The widely used herbicide atrazine and the insecticide permethrin are among more than 300 chemicals EPA selected to analyze in its first round of rapid computerized toxicity tests known as high-throughput screening bioassays. These range from biochemical studies to ascertain whether a chemical interferes with the function of a critical enzyme to tests on cells to determine whether exposure to the substance triggers reactions similar to an immune system response.

The effort will include a handful of chemicals that aren't pesticides. They are several phthalates, which are additives in some plastics; perfluorooctanoic acid, used to make coatings for nonstick cookware, such as DuPont's Teflon; and perfluorooctane sulfonic acid, a chemical that was formerly the basis for 3M's Scotchgard products.

As part of a new program called ToxCast, EPA will link the results of the new computer studies to any adverse effects found through traditional toxicity testing of the 300-plus substances on laboratory animals (C&EN, Aug. 6, page 34). Those effects include cancer, birth defects, reproductive problems, or nervous system dysfunction.

The agency intends to integrate information from the new studies with existing toxicity data to create a computer model for screening thousands of substances that have never undergone traditional toxicity testing. EPA plans to use the computer model to pinpoint which untested chemicals are most likely to cause adverse effects. Those substances will become leading candidates for traditional toxicity testing.

Once the model is completed, EPA regulators want to screen untested industrial chemicals, inert ingredients in pesticides, and contaminants in drinking water for potential health effects, according to the agency.

Robert J. Kavlock, director of EPA's National Center for Computational Toxicology, tells C&EN that the agency is seeking partners within academe, industry, and other organizations to collaborate with the agency on evaluating the information generated by the first round of ToxCast computer tests.

"Analyzing the data is going to be a challenge," Kavlock says. "No one's tried to do this many chemicals across this many assays."

More information on ToxCast, including an EPA announcement on a Cooperative Research & Development Agreement on data analysis, is available at www.epa.gov/ncct/toxcast/news.html.