Job Exposure to Pesticide May Raise Cancer Risk

NEW YORK (Reuters Health) - Daily on-the-job exposure to the pesticide diazinon appears to increase the risk of lung cancer and possibly other cancers, according to new findings from the US government-sponsored Agricultural Health Study, a project begun in 1993 to investigate the health effects of pesticides on farm families in Iowa and North Carolina.

By December 2002, 301 of 4,961 men with occupational exposure to diazinon had developed lung cancer compared with 968 of 18,145 with no occupational exposure to diazinon.

"We found evidence of an association of lung cancer and leukemia risk with increasing lifetime exposure days to diazinon," Dr. Michael C. R. Alavanja from the National Cancer Institute in Rockville, Maryland and colleagues report in the American Journal of Epidemiology.

The results were unchanged after adjusting for cigarette smoking, "suggesting that confounding due to smoking probably does not explain the elevated risks of lung cancer," the authors write.

They also point out an association between diazinon use and lung cancer was reported in an earlier analysis of the Agricultural Health Study, with fewer years of follow-up.

Diazinon is an organophosphate -- a chemical derived from nerve gas agents developed during World War II. Studies linking organophosphates to neurological disorders and other largely noncancer health risks prompted the US Environmental Protection Agency in 2000 to start phasing out residential use of diazinon in home, garden and lawn products. By 2004, the phase out was complete.

The EPA has also proposed new restrictions on agricultural use of diazinon. Nonetheless, in 2004, approximately 4 million pounds of the pesticide were applied in agricultural settings in the US.

In a 1997 review of the cancer-causing potential of diazinon, the EPA classified the chemical as "not likely a human carcinogen" based on studies in rodents. However, some laboratory and epidemiologic data, including the latest findings from the Agricultural Health Study, paint a different picture.

Alavanja and colleagues add that as more cancer cases accrue in the study, they will be in a better position to "clarify whether diazinon is associated with cancer risk in humans."

SOURCE: American Journal of Epidemiology, December 1, 2005.