Wednesday, September 4, 1991 - Page updated at 12:00 AM

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Lawn Herbicides Increase The Cancer Risk For Dogs, Study Says -- Research Urged To Determine Effect On Humans


WASHINGTON - Homeowners who spray with weed-killing herbicides may get good-looking lawns, but they could give their dogs cancer, a study says.

National Cancer Institute (NCI) researchers reported yesterday that dogs whose owners use a herbicide containing 2,4-D have up to twice the risk of developing lymphatic cancer. The study said research is needed to determine whether household use of the plant-killing chemical could also pose a risk to humans.

The study, published in the Journal of the National Cancer Institute, said that when homeowners sprinkled or sprayed their lawns with 2,4-D herbicide four or more times a year, dogs that played on the lawns were twice as likely to develop a cancer called malignant lymphoma.

If the chemical was used less frequently, the lymphoma risk dropped, but even with just one herbicide application a season the cancer risk was one-third higher than among dogs whose owners did not use the chemical.

Earlier studies on farms in Nebraska showed that agricultural workers who mixed and sprayed the herbicide more than 20 days per year were up to three times more likely to develop lymphoma.

Dr. Robert Hoover of NCI said such farm studies have led researchers to become concerned about the risk of cancer among the general population from widespread use of the herbicide on lawns, parklands and golf courses.

Although no studies have been conducted on the human effects of herbicide use around non-farm homes, Hoover said "there may be, in fact, a risk related to the levels of exposure."

Howard Hayes, primary author of the study, said the research "supports the idea that exposure to 2,4-D, as used for lawn care, plays a role in causing lymphomas in dogs. The study also suggests that the potential health hazards of human exposure to 2,4-D at home warrant further study."

Malignant lymphoma in dogs is similar to non-Hodgkin's lymphoma in humans. It is a cancer that strikes the lymphatic, or immune, system.

The incidence of lymphoma among Americans has increased about 50 percent since 1973 - one of the largest increases of any cancer. The NCI estimates that about 37,000 new cases will be diagnosed in the U.S. this year.

The conclusion was based on a study of the chemical exposures of 491 dogs with lymphoma, compared with 466 dogs of similar age and background that did not have lymphoma. For comparison, the researchers studied 479 dogs that had other types of cancer.

Dogs with lymphoma were found to be 1.3 to 2 times more likely to have been exposed to 2,4-D herbicide in their yards than the other groups of dogs.

The risk of lymphoma was highest for dogs whose owners applied the chemical more than four times annually. The cancer risk dropped slightly if the chemical was applied only by professional lawn companies.

Copyright (c) 1991 Seattle Times Company, All Rights Reserved.


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