Ripples in the Water - Chlorination and Cancer Risk in Dogs

Author: Sharon M. Albright, DVM, CCRT

Bladder cancer affects tens of thousands of dogs in the United States each year, with certain breeds like the Scottish Terrier, West Highland White Terrier, and Shetland Sheepdog being particularly susceptible. This suggests a genetic influence on cancer risk, but environmental factors also play a large role in triggering this type of cancer. We already know that human bladder cancer is linked to environmental chemical exposure. People exposed to herbicides, cigarette smoke, inorganic arsenic in groundwater, chlorination byproducts in tap water, and acrolein (a chemical found in indoor air pollution and some heat-treated foods) have a higher risk of developing bladder cancer. Since dogs share our homes and water sources, do they also share this increased cancer risk?

Bladder cancer: The most common form of bladder cancer in dogs and humans is urothelial cell carcinoma (UCC), also known as transitional cell carcinoma (TCC). It is a cancer that originates from the cells lining the inside of the bladder. Common clinical signs include bloody urine and straining to urinate or inability to urinate. In dogs, this cancer often recurs following treatment and unfortunately leads to the death of many affected dogs.

Thanks to AKC Canine Health Foundation (CHF) funding, scientists at the University of Wisconsin-Madison College of Veterinary Medicine have been exploring the link between environmental chemical exposure and cancer in dogs to provide veterinarians and dog owners with proven and practical cancer prevention strategies (CHF Grant: 02780: Bladder Carcinogen Exposures in Pet Dogs). Zeroing in on bladder cancer, they examined exposure to and urinary concentrations of four cancer-causing chemicals: chlorination byproducts, inorganic arsenic, acrolein, and the herbicide 2,4-D. While they found no differences in exposure to arsenic, acrolein, or the herbicide, they did find significant differences in chlorination byproduct exposure between healthy and affected dogs.

Owners of dog breeds at high risk for bladder cancer should limit their dog’s access to chlorinated swimming pools and install water filtration units to remove chlorination byproducts from the dog’s drinking water.

Chlorinated water contains breakdown products that can cause genetic mutation. We know there is a link between bladder cancer in people and chlorination byproduct exposure through swimming, bathing, and showering. Similarly, in this study, dogs with bladder cancer were more likely to swim in a chlorinated pool than healthy dogs. In addition, the concentration of chlorination byproducts reported in municipal tap water was four times higher in the zip codes where dogs with bladder cancer lived compared to those where healthy dogs lived. All of this evidence supports the idea that chlorination byproduct exposure may contribute to the risk of developing bladder cancer in dogs. Therefore, owners of high-risk dog breeds can minimize their dog’s exposure by limiting access to swimming pools and installing water filtration units to remove chlorination byproducts from the dog’s drinking water.

What about environmental chemical exposure and other dog cancers? The research team is also studying chemical exposures and the risk of lymphoma, a cancer of the immune system, in the Boxer Dog breed (CHF Grant: 02885: Exposure to Environmental Chemicals in Boxers with Lymphoma). Preliminary results suggest that certain chemicals are associated with an increased risk of lymphoma in this breed. CHF will share the final results of this important research to provide veterinarians and dog owners with even more information to help prevent and treat canine cancer. Visit for more information on CHF’s commitment to fight canine cancer.

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