Cancer In Dogs Exposed To Lawn Chemicals,
American Veterinary Medical Association Warns Veterinarians
(Beyond Pesticides, May 3, 2004) Exposure to herbicide-treated lawns and gardens increases the risk of bladder cancer by four to seven times in Scottish Terriers, according to a study by Purdue University veterinary researchers published in the April 15, 2004 issue of the Journal of the American Veterinary Medicine Association (J Am Vet Med Assoc 2004; 24:1290-1297). The study adds to earlier research conducted by the National Institutes of Health that found elevated rates of canine lymphoma in dogs exposed to lawn pesticides (1991). (See Beyond Pesticides factsheet) Meanwhile the American Veterinary Medical Association issued a release, "Herbicide Exposure May Increase Cancer Risk in Dogs," with the study authors' recommendations that owners of Scottish Terriers "should decrease their dogs' exposure to lawns or gardens treated with common herbicides, particularly phenoxy herbicides and possibly nonphenoxy herbicides" and "veterinarians should perform routine (every six months) cytologic urine exams in Scottish Terriers and other 'genetically high risk' breeds over six years old."
As these warnings about lawn pesticides are hitting the news wires, EPA and the chemical industry, hoping for support from the environmental community, are planning to issue guidelines and/or tips that urge people to "use pesticides safely" or "read the pesticide label." The group putting the documents together has refused to (i) disclose the Purdue study and other studies alerting the public to the link between lawn pesticides and adverse health and environmental effects, and (ii) support the public's right-to-know when pesticides are going to be used through neighborhood notification, so that people can take precautionary action by vacating the area and staying off treated lawns and landscapes. Local environmental and public health advocates have been successful in recent years in moving schools, parks, and town and city governments to adopt alternative practices that do not use toxic lawn pesticides. (See Daily News, February 19, 2004) [Join the Pesticide-Free Zone Campaign and national network]
A team of veterinary researchers including Lawrence T. Glickman, VMD, Dr.PH, has found an association between risk of transitional cell carcinoma of the urinary bladder in Scottish terriers and the dogs' exposure to chemicals found in lawn treatments. The study, based on a survey of dog owners whose pets had recently contracted the disease, may be useful not only for its revelation of potentially carcinogenic substances in our environment, but also because studying the breed may help physicians pinpoint genes in humans that signal susceptibility to bladder cancer.
"The risk of transitional cell carcinoma (TCC) was found to be between four and seven times more likely in exposed animals," said Dr. Glickman, a professor of epidemiology and environmental medicine in Purdue's School of Veterinary Medicine. "While we hope to determine which of the many chemicals in lawn treatments are responsible, we also hope the similarity between human and dog genomes will allow us to find the genetic predisposition toward this form of cancer found in both Scotties and certain people."
The research, which
Dr. Glickman conducted the research with Malathi Raghavan, Deborah W.
Knapp, Patty L. Bonney and Marcia H. Dawson, all of Purdue's School
of Veterinary Medicine, and Indianapolis veterinarian Marcia Dawson.
According to the National Cancer Institute, about 38,000 men and 15,000 women are diagnosed with bladder cancer each year. Only about 30 percent of human bladder cancers develop from known causes. As Scottish terriers - often called Scotties - have a history of developing bladder cancer far more frequently than other breeds, Dr. Glickman and his team decided to examine the dogs' diet, lifestyle and environmental exposures for a possible link to bladder cancer.
In an earlier study, Dr. Glickman and his colleagues found Scotties are already about 20 times more likely to develop bladder cancer as other breeds. "These dogs are more sensitive to some factors in their environment," Dr. Glickman said. "As pets tend to spend a fair amount of time in contact with plants treated with herbicides and insecticides, we decided to find out whether lawn chemicals were having any effect on cancer frequency."
Dr. Glickman's group obtained their results by surveying the owners of 83 Scottish terriers. All of the animals had bladder cancer and were of approximately the same age. Based on an 18-page questionnaire, owners documented their dogs' housing, duration of exposure to the lawn or garden and information on the particular lawn treatment used (dog owners provided either the label from the treatment bottle or, if a company sprayed the lawns directly from a truck, the name of the lawn service). The results were then compared with a control group of 83 unexposed Scottish terriers of similar age that were undergoing treatment for unrelated ailments.
"We found that the occurrence of bladder cancer was between four and seven times higher in the group exposed to herbicides," Dr. Glickman said. "The level of risk corresponded directly with exposure to these chemicals: The greater the exposure, the higher the risk."
Dr. Glickman said it is possible the active ingredient in most lawn and garden sprays - a compound known by its chemical name of 2,4-D - was to blame, although EPA has not classified it as a carcinogen despite other epidemiological studies linking it to cancer in dogs and people. However, he said, it also is possible that one of the so-called inert ingredients in the mixture - ingredients which often make up nearly two-thirds of a treatment's volume - could be responsible for the increased risk.
"These other ingredients are thought to be inert and, therefore, are not tested or even listed on the product label," Dr. Glickman said. "But 4 billion pounds of these other untested chemicals reach our lawns and gardens every year, and we theorize they are triggering cancer in these animals, which are already at risk because of a peculiarity in their genome."
Scottish terriers' genetic predisposition toward developing bladder cancer makes them ideal as "sentinel animals" for researchers like Dr. Glickman because they require far less exposure to a carcinogen than other breeds before contracting the disease.
"You might compare them to the canaries used in coal mines a century ago," he said. "The difference is that we don't deliberately place our research animals in harm's way. We study animals that have already contracted diseases, bring them to the hospital and then try to find out what combination of genetic predisposition and environmental influence added up to make them ill." Dr. Glickman said the similarity between dog and human genomes could lead researchers to find the gene in humans that makes them susceptible to developing bladder cancer.
While environmental and public health advocates have pointed to studies like these and called for the banning of aesthetic lawn pesticides, especially in view of documented off-target drift of the chemicals and widespread and uncontrolled involuntary exposure in the outdoor and indoor environment, Dr. Glickman said that, "Finding the dog gene could save years in the search for it in humans and could also help us determine which kids need to stay away from lawn chemicals." "If such a gene exists in dogs, it's likely that it exists in a similar location in the human genome," Dr. Glickman said. But Dr. Glickman emphasized that because the effect was a combination of chemical and genetic predisposition, the results do not suggest that everyone should avoid treated lawns.
With an implied departure from environmental and public health policy to protect the most vulnerable, which in this case could be millions of people, Dr. Glickman said, "We don't want to indicate that every person is susceptible." "Because this study shows that exposure to the chemicals exacerbates a genetic predisposition in Scotties towards developing TCC, it's likely that only a segment of the human population would be in similar danger. "But we still need to find out who those individuals with the same predisposition are. Until we do, we won't know who's safe and who isn't."
As a next step, Dr. Glickman will survey children, as well as dogs, in households that have treated lawns and compare the chemicals in their urine samples with those from households where lawns have not been treated.
"It's important to find out which lawn chemicals are being taken up by both children and animals," he said. "We hope to start this spring."
Funding for this research was provided in part by the Scottish Terrier Club of America and the American Kennel Club's Canine Health Foundation.
T. (Larry) Glickman, (765) 494-6301, [email protected]
Purdue News Service: (765) 494-2096; [email protected]
Herbicide Exposure and the Risk of Transitional Cell Carcinoma of the Urinary Bladder
in Scottish Terrier Dogs
Lawrence T. Glickman, Malathi Raghavan,
Deborah W. Knapp, Patty L. Bonney
and Marcia H. Dawson
Objective: To determine whether exposure to lawn or garden chemicals was associated with an increased risk of transitional cell carcinoma (TCC) of the urinary bladder in Scottish terriers. Design: Case-control study. Animals: 83 Scottish terriers with TCC (cases) and 83 Scottish terriers with other health-related conditions (controls). Procedure: Owners of study dogs completed a written questionnaire pertaining to exposure to lawn or garden chemicals during the year prior to diagnosis of TCC for case dogs and during a comparable period for control dogs. Results: The risk of TCC was significantly increased among dogs exposed to lawns or gardens treated with both herbicides and insecticides (odds ratio [OR], 7.19) or with herbicides alone (OR, 3.62), but not among dogs exposed to lawns or gardens treated with insecticides alone (OR, 1.62), compared with dogs exposed to untreated lawns. Exposure to lawns or gardens treated with phenoxy herbicides (OR, 4.42) was associated with an increased risk of TCC, compared with exposure to untreated lawns or gardens, but exposure to lawns or gardens treated with nonphenoxy herbicides (OR, 3.49) was not significantly associated with risk of TCC. Conclusions and Clinical Relevance: Results suggest that exposure to lawns or gardens treated with herbicides was associated with an increased risk of TCC in Scottish terriers. Until additional studies are performed to prove or disprove a cause-and-effect relationship, owners of Scottish terriers should minimize their dogs' access to lawns or gardens treated with phenoxy herbicides. (J Am Vet Med Assoc 2004;24:1290-1297)