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Do Environmental Pollutants Cause Cancer in Dogs?

Risks Not Limited to Chemicals
Clearly, another reason why just banning all carcinogens known to man would not solve the problem is that environmental risks of cancer are not limited to chemicals. A 1995 study in the American Journal of Epidemiology found that dogs living in houses with high magnetic fields, as measured by the current configuration wire code, were nearly seven times more likely to develop lymphosarcoma. This included both cables above and below ground. Interestingly, Moore states that these findings have never been shown in humans. Another non-chemical risk factor for cancer in dogs is the failure of the owner to have the dog spayed. This is one of the most common and well-documented risk factors for cancer in female dogs. Says Moore, “Female dogs who are intact are much more likely to develop mammary cancer than those who are spayed. Spaying before the first heat cycle reduces the risk to almost zero.” This risk steadily increases with each heat, up to about 6 to 8 percent risk of mammary cancer after the dog has gone through two to three cycles. Once the dog hits about two and a half years of age, 40 percent will develop mammary cancer. Says Moore, “This is a disease we can practically eliminate by spaying dogs early.”

Additionally, diet can further reduce the risk of mammary cancer. One research study looked at the diet of dogs the year before they had surgery for mammary cancer. For dogs on a low-fat diet, the level of protein (measured on a dry-matter basis, not based on the crude analysis number reported on the bag) was strongly predictive for how long they would live. Protein greater than 27 percent on a dry-matter basis correlated with survival past three years of age. Those dogs on a low-fat diet with less than 23 percent protein survived less than six months. Protein levels made no difference or had no effect if the dog was on a high-fat diet. In addition to diet composition, the researchers also found those dogs that were overweight at one year of age were three times as likely to develop mammary cancer.

More Studies May Provide Better Answers
So should you just avoid all possible carcinogens?

“That’s fine if you don’t drink or eat,” says Glickman, “but they are everywhere.” Even environmental factors as ubiquitous as sunlight can increase risk of cancer, especially in light-skinned pets. It’s a matter of exposure levels combined with genetics.

How high does the risk have to be to be important? Glickman recommends that we consider how likely the animal is to be exposed. A 20 percent increased risk may be important for dogs who are exposed a lot, whereas a twofold increased risk is less worrisome if the animal will not receive much exposure. Thus, for Scottish Terriers, a breed in which it is calculated that 75 percent of bladder cancers are related to chemical exposure, it is best to avoid phenoxyherbicides and insecticides, whereas a moderate exposure is much less likely to cause a problem for other dogs.

In defining “a lot” and “not much,” Glickman notes that “this speaks to the concept of attributable risk, which is the proportion of a specific type of cancer that can be attributed to a specific exposure such as insecticides. Attributable risk is a function of how many individuals in a population are exposed to insecticides plus the risk of cancer associated with insecticides. Thus, a chemical associated with a small increased risk of bladder cancer is important if a high proportion of dogs are exposed. In contrast, a chemical like asbestos is associated with a very high risk of mesothelioma, but very few dogs are exposed, and the attributable risk is thought to be low in people (about 5 percent of all lung cancers). In contrast, the attributable risk for lung cancer (90 percent) associated with smoking is very high even though the risk of lung cancer associated with smoking is relatively low, since so many people smoke.”

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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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