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LAWN CHEMICALS
INCREASE CANCER RISK IN DOGS
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.
Source:
Lawrence T. (Larry) Glickman, (765) 494-6301,
ltg@purdue.edu
Purdue News Service: (765) 494-2096;
purduenews@purdue.edu
ABSTRACT
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)
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(Beyond Pesticides, May 3, 2004) | .gif)
