In addition, Scottish terriers exposed to certain herbicides, including the common weed killer 2,4-D, were more than four times likely to develop bladder cancer than those whose yards were untreated, according to a 2004 study by Purdue University veterinarians.
Results of other studies have been mixed, with some showing an increased lymphoma risk in pets exposed to lawn chemicals and others finding no link.
Malignant lymphoma in dogs closely resembles non-Hodgkin’s lymphoma. More than 60,000 Americans a year are diagnosed with the disease, making it the sixth most common cancer in the United States.
“The close interaction and shared household environments of dogs and their human owners provides a unique opportunity for evaluating how herbicide and pesticide exposure may contribute to human non-Hodgkin’s lymphoma,” the study authors wrote.
Pesticides may increase the risk of the disease in people, too. Last year, Danish researchers found that people with high levels of DDT and other organochlorine pesticides were more likely to develop non-Hodgkin’s lymphoma years later.
“Clearly dogs are not humans, but physiologically speaking, they are very similar,” said Lisa Barber, a veterinary oncologist at Tufts University and study author.
“The most heartbreaking thing is their short lifespan. It’s also what makes them useful models for human disease,” she said. Because dogs live accelerated lives compared with humans, researchers can gather information on a lifetime of exposure much more quickly than in people.
Using animals as sentinels for human health is not a new concept. More than 100 years ago, miners took caged canaries into coal mines to warn them of toxic gases.
In the 1950s, thousands of people in Japan died or suffered serious effects from eating mercury-poisoned fish from Minamata Bay. Locals had first noticed strange neurological symptoms in cats, which they described as dancing in the streets before collapsing and dying.
Pets also played an important role in drawing a link between asbestos and mesothelioma. In the 1980s, researchers found high levels of asbestos fibers in the lungs of pet dogs diagnosed with the lung disease. The finding helped increase understanding of the threats that asbestos posed to people, said Reif from Colorado State.
More recently, researchers have found that ozone, the main ingredient of smog, may contribute to asthma in cats, and household tobacco smoke may be a risk factor for nose, throat and lung cancers in dogs.
A rise in hyperthyroidism in cats also has been linked to brominated flame retardants, which are used in upholstery and electronics and contaminate dust and canned cat foods. Cats with overactive thyroids – which can lead to weight loss, increased appetite, hyperactivity and death – had higher blood levels of the chemicals, according to one small study led by Environmental Protection Agency scientists.
Because of their meticulous grooming habits, cats may ingest a lot of dust. The link to hyperthyroidism in felines “should be alarming to parents of crawling toddlers who explore their environments by putting everything in their mouths,” said Donna Mensching, veterinary medical director of the Washington Poison Center in Seattle.
Toddlers with high exposure to the flame retardants have lower IQs, according to one study. The chemicals also have been linked to altered thyroid hormones in pregnant women, which might harm a baby’s brain development.
Looking at the way environmental pollutants might interact with genetics in animal breeds susceptible to certain diseases may benefit human health as well.
“We know something about their breed history and susceptibility to certain diseases, which may make it easier to tease out gene-environment interactions,” said Dr. Robert A. Hiatt, an epidemiologist at the University of San Francisco and a former family physician.