Pollutants Found in House Dust Increase Pesticide's Toxicity

Four pollutants found in house dust add to the ability of a common household insecticide to inhibit an enzyme important in neurologic function in humans. Building on substantial evidence that the insecticide chlorpyrifos inhibits cholinesterase, a biochemical critical for nerve cell transmission, researchers at the Johns Hopkins School of Public Health found that pollutants in house dust increase this adverse effect in studies with purified enzyme. The four pollutants, polycyclic aromatic hydrocarbons (PAHs) that are among the most abundant components of house dust, are pyrene, benzo(a)pyrene, fluoranthene, and anthracene. The study appeared in the April 1999 issue of Toxicology Letters.

Lead author David A. Jett, PhD, assistant professor, Environmental Health Sciences, Johns Hopkins School of Public Health, said, "When acetylcholinesterase was incubated with chlorpyrifos-oxon together with the PAHs, the inhibitory effect on acetylcholinesterase was additive. These data suggest that some PAHs have anticholinesterase activity, and contribute in an additive manner to the inhibitory effect of chlorpyrifos-oxon on acetylcholinesterase in the test tube. Further research is needed to determine the toxicologic relevance of these findings."

To study whether the PAHs increased chlorpyrifos's inhibition of cholinesterase, the researchers added specific concentrations of pyrene, benzo(a)pyrene, fluoranthene, and anthracene to an incubation mixture containing chlorpyrifos and purified cholinesterase. They then measured cholinesterase inhibition in the presence or absence of several different concentrations of the four PAHs, noting the concentrations that caused cholinesterase to be inhibited by 50 percent, as well as the maximal activity of the enzyme.

The data suggested that the combined effects of the PAHs were additive but not synergistic with the effects of low concentrations of chlorpyrifos. Although all four PAHs inhibited cholinesterase activity by themselves, their potencies differed, with benzo(a)pyrene having the greatest relative effect on cholinesterase in combination with chlorpyrifos, and fluoranthene having the least. Perhaps most important, the combined effects appeared to be greatest at low-level concentrations of chlorpyrifos commonly encountered in environmental exposures.

A 1981 report indicates that 90 percent of all homes in the United States use pesticides, and usage is likely to be even higher today. The primary source of exposure to pesticides for the general U.S. population is in the indoor environment of the home.

Support for this study was provided by a Johns Hopkins University faculty development award.