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Do Environmental Pollutants Cause Cancer in Dogs?

According to Glickman, “No one chemical type of flea and tick dip accounted for the increased risk; however, the active ingredients generally account for less than 5 percent of the total product. The remaining ingredients were labeled as ‘inert” and consisted of solvents such as benzene, toluene, xylene and petroleum distillates, many of which are themselves known carcinogens [in people and lab animals].” A second study in 2004 by Glickman also looked at the spot-on flea and tick products such as Advantage® and Frontline® but found no increase in cancer. These products are minimally absorbed into the dog’s bloodstream and consequently are not excreted via the bladder. [Ed. Note: For more about over-the-counter spot-on products, see our blog on the current  (2009) EPA investigation into their toxicity.]

Research also suggests a link between 2,4-D (marketed under many names, including Ded-Weed, Lawn-Keep, Weedone, Plantgard, Miracle and Demise), a phenoxyherbicide commonly used on lawns, and cancer. The findings, however, conflict. A 1991 study published in the Journal of the National Cancer Institute reported that pet dogs in homes where 2,4-D was applied to the lawn at least four times per year had twice the risk of developing lymphoma, compared to dogs who lived where lawns were not treated. These findings were challenged by the Chemical Industry Task Force, and the ensuing reanalysis of the original data found no significant relationship between the herbicide and lymphoma in dogs. (Kaneene, John B. and Miller, RoseAnn. “Re-analysis of 2,4-D use and the occurrence of canine malignant lymphoma.” Veterinary and Human Toxicology, 41, No. 3: 164–170. June 1999).
A subsequent 1994 study in the scientific journal Cancer, Epidemiology, Biomarkers and Prevention did, however, show that dogs living around residences recently treated with 2,4-D absorbed measurable amounts of the herbicide for several days after application. Dogs exposed to lawns within seven days of treatment were 50 times more likely to have high levels of the herbicide than those exposed to lawns treated more than seven days previously. The highest concentration of 2,4-D was found in dogs walking on lawns within two days after the lawn had been treated. Despite these higher herbicide concentrations, Dr. Antony Moore, veterinary oncologist at Veterinary Oncology Consultants in New South Wales, Australia, states, “This is not sufficient to say that use of the herbicides causes a high risk for cancer. However, if you’re an owner and have a dog, why use 2,4-D when there are other equally good herbicides available?”

The link between herbicides and cancer in the general dog population may be debatable, but when one considers a specific breed, the Scottish Terrier, the link is clear. Overall, Scottish Terriers are at 18 times increased risk of transitional cell carcinoma (bladder cancer) when compared to mixed-breed dogs. When exposed to lawns treated with phenoxyherbicides four or more times a year, Scottish Terriers had a four times higher risk of developing bladder cancer than those who were not exposed to herbicide. That risk increased to seven times if they were exposed to both herbicides and insecticides.

This suggests a question: If these chemicals are carcinogenic, why are they still around? Well, says Dr. Moore, “It’s very hard to show that a factor causes cancer. We can only show that it increases the risk of getting cancer. For example, a study out of Italy showed that dogs who lived with people who used paints and solvents were at 4.6 [percent] higher risk of developing lymphoma. This finding does not tell you that because you spill solvent on the ground and a dog walks through it one time, the individual dog’s risk is higher.”

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Submitted by Dwight | January 31 2010 |

I'm a graduate of Ashland University with degrees in science and secondary education. One of my former professors, Dr. Weidenhamer, has made national news due to his research of childrens' toys and jewelry and presence of high levels of lead and cadmium contained within them. The biggest dangers occurs when the children have prolonged exposure to the lead and smaller children putting the toys in their mouth. Many of the toys that have shown extremely high levels of lead are ones made overseas (mostly China). Here's a link that about this: (http://personal.ashland.edu/~jweiden/lead.htm) and (http://blogs.consumerreports.org/safety/2009/09/lead-levels-in-childrens...).

My wife and I rescued a black lab mix dog. He goes through a lot of chew toys. While at the store, I noticed many of the toys we get for our dog also comes from overseas (ie. China). I've even come across some toys that are exactly the same as what's found at children's toy stores.

This got me to thinking. Should pet owners also be concerned of the possibility of lead in their pet toys? Has there been any research of the effects of lead in pets (dogs)? Since dogs tend to do a lot more of putting things in their mouth, chewing, and swallowing small amounts of chewed up plastic, what are the dangers of lead poisoning of our pets?

I've emailed my professor, Dr. Weidenhamer, regarding the testing of pet toys. He stated that some of the soft plastics used in pet toys are also used in physical therapy for people. Due to the large number of children's toys and general public's concern of their children, he doesn't have the time to test the pet toys.

We love our dog. He's an important part of our family. I know many others feel the same way about their dog(s). From going to the store the other day and seeing bottled water for dogs (which personally, I think is over the top), I know many people want the best for their dog...to be happy, healthy, loved, and well cared for. I feel that this is something that should also be looked into. Out of our love, I don't want to be an irresponsible pet owner and get something that could potentially be harmful for our dog. There are days that I believe our dog doesn't have too many IQ points to spare...he can't afford to lose anymore. (just kidding, he is pretty smart) Seriously, I think as a responsible pet owner, we need to speak on their behalf as to the hidden potential dangers of lead contained within pet toys.

So now, whenever we do get him some toys, I check the labels as to where they were made. It's not a guarantee, but hopefully it's a step in the right direction of keeping our beloved dog healthy.

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