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Common herbicide linked to cancer.

Common herbicide linked to cancer

Exposure to a common herbicide significantly increases the risk of non-Hodgkin's lymphoma (NHL), according to a National Cancer Institute report. The broadleaf plant killer, a phenoxyherbicide called 2,4-dichlorophenoxyacetic acid (2,4-D), is one of the active ingredients in Agent Orange, used during the Vietnam war.

Swedish researchers reported in 1979 and 1981 associations between phenoxyherbicide use and not only NHL but also two other cancers, soft-tissue sarcoma and Hodgkin's disease. In the current study, headed by Shelia K. Hoar and reported in the Sept. 5 JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION, only the NHL connection was found.

Hoar and her colleagues tracked down all cases of the three cancers diagnosed between 1976 and 1982 in white Kansas men, and questioned the patients or their survivors about occupation and exposure to herbicides. To further check the herbicide information, the researchers interviewed local pesticide suppliers.

When the researchers compared the herbicide exposure among the cancer patients and among age-matched white men from the general Kansas population, they found that the incidence of NHL, but not of the other two cancers, increased with increased exposure to 2,4-D.

The more exposure to that particular herbicide, they found, the greater the risk -- the incidence of NHL among farmers exposed 20 days or more per year was six times that of the general population, while those who used it six to 10 days per year were at 1.6 times the risk. The greatest danger was to people who had handled the chemical extensively -- people who mixed or applied it were at eight times the risk.

The study did not show any increased risk among backyard gardeners. "We can't say they're at risk," notes Hoar," but there's reason for caution and concern. I think when we know anything is carcinogenic we have to consider that even a low dose may be hazardous."

The report has sparked concern in the federal government. Lois Rossi of the Environmental Protection Agency, who monitors the agency's 2,4-D program, says, "We're going to review the entire study. We feel that the conclusions in the report are well-founded. It's of obvious concern." In the meantime, she recommends that farmers and backyard gardeners follow label instructions carefully, wear protective clothing and handle 2,4-D with caution.

The report is evidently being taken seriously by the pesticide industry as well. Representatives of a 13-company task force of 2,4-D producers met with the researchers late last week to discuss the study; David Dietz, a spokesperson for the task force, says, "We're going to clearly pay attention to the finding."

Because of questions regarding exposure levels and other aspects of the previous study by Swedish researchers, the task force disputed those findings. But the current study, says Dietz, is more credible. The news isn't all bad, according to Dietz -- the overall incidence of NHL among farmers who wore protective equipment was not as greatly elevated. "That for us is interesting and probably good," he says. But further analysis of the amount of 2,4-D use by the protective equipment wearers could show an exposure-related risk, Hoar says.

The study is also of relevance to people exposed to Agent Orange, an herbicide sprayed during the Vietnam war in what was then South Vietnam. 2,4-D was one of the two active ingredients used in the herbicide; the other was 2,4,5-trichlorophenol (2,4,5-T). Operation Ranch Hand, a study of 1,200 Vietnam veterans conducted by the U.S. Air Force, did not show any excess of NHL, but there weren't enough people in the study to reveal the increased risk, says Hoar. According to a Veterans Administration spokesperson, the VA plans on reviewing the current study to determine if Vietnam veterans exposed to the herbicide in the course of duty and who develop NHL are due service-related disability benefits.

Animal studies have shown that chemical contaminants called dioxins, produced during the manufacture of 2,4,5-T, are toxic as well as carcinogenic. Research on the health effects on Agent Orange has focused on one particular 2,4,5-T contaminant, with relatively little attention paid to 2,4-D and its contaminants.

Arnold Schecter, whose studies have shown measurable levels of dioxins in the fat tissue of people in industrialized countries (SN:7/13/85,p.26), says that the new study ought to focus attention on what component in the 2,4-D herbicide is causing problems. "We've written off, perhaps erroneously, 2,4-D," he says.

"The key question," says Schecter, a professor of preventive medicine at the State University of New York in Binghamton, "is: Is the problem in 2,4-D or in a contaminant? 2,4-D has other dioxins that have been considered less toxic than the 2,4,5-T contaminants. These other dioxins have been found in smoke and ash from municipal and industrial incinerators; if they are what's causing the cancer in Kansas farmers, then we must give much more serious consideration to their toxic health effects."
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Author:Silberner, Joanne
Publication:Science News
Date:Sep 13, 1986
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