A new study shows that high levels of exposure to the pesticide chlorpyrifos (search) may raise the risk of lung cancer. The findings are published in the Dec. 1 issue of the Journal of the National Cancer Institute.

Chlorpyrifos is one of the most widely used insecticides in the U.S., with about 8-10 million pounds of it used in the agricultural industry in 1999. It’s in about 800 products including food crop pest control, indoor pest control, and pet collars.

But you probably won’t find chlorpyrifos in your home. Not any more, that is. It was widely used in U.S. homes until 2000, when the Environmental Protection Agency phased it out or limited its residential use.

The new findings come from Michael Alavanja, DrPH, of the National Cancer Institute, and colleagues. Alavanja’s team reviewed data from more than 54,000 pesticide applicators in Iowa and North Carolina. Just under half had been exposed to chlorpyrifos.

Those with the most chlorpyrifos exposure had about twice the lung cancer risk as unexposed pest control professionals. The link held after factoring in other possible influences, including smoking, other occupational exposures, and previous lung diseases. The authors note that there weren’t enough smokers in the study who were exposed to the chemical for a complete analysis.

Still, the chemical isn’t a smoking gun for lung cancer, and it also wasn’t linked to most other cancers studied.

“Our findings suggest an association between chlorpyrifos use and incidence of lung cancer that deserves further evaluation,” write the researchers.

By Miranda Hitti, reviewed by Charlotte E. Grayson MD

SOURCES: Lee, W. Journal of the National Cancer Institute, Dec. 1, 2004; vol 96: pp 1781-1789. News release, Journal of the National Cancer Institute.