Chlorination by-products and Bladder Cancer

Now that we've considered well water contamination, let's turn our attention to water supplied by public or private water suppliers. All of the same contaminants that can be found in well water, can also be found in "city water". The EPA (Environmental Protection Agency) in the US regulates the maximum allowable levels of some contaminants in water and states regulate other pollutants.

In order to cleanse the water supplied to households of bacteria, water suppliers use chlorine treatment. Chlorine reacts with naturally occuring organic compounds in water and leaves behind trihalomethane [THM]. THM has been linked to cancer since the 1960 and more recent studies are still confirming the link between cancer and chlorination of water.

Here is a study, conducted in Canada, that considered the link between bladder cancer and THM's.

SpringerLink - Article: "Case-control study of bladder cancer and chlorination by-products in treated water (Ontario, Canada)
Will D. King and Loraine D. Marrett

Chlorine is by far the most commonly used chemical for the disinfection of water supplies in North America. However, chlorine reacts with organic material in the raw water producing a number of halogenated hydrocarbon by-products. This population-based case-control study in Ontario, Canada examined the relationship between bladder cancer and exposure to chlorination by-products in public water supplies. Residence and water source histories and data from municipal water supplies were used to estimate individual exposure according to water source, chlorination status, and by-product levels (represented by trihalomethane [THM] concentration). Exposures were estimated for the 40-year period prior to the interview, using 696 cases diagnosed with bladder cancer between 1 September 1992 and 1 May 1994 and 1,545 controls with at least 30 years of exposure information. Odds ratios (OR) adjusted for potential confounders were used to estimate relative risk. Those exposed to chlorinated surface water for 35 or more years had an increased risk of bladder cancer compared with those exposed for less than 10 years (OR=1.41, 95 percent confidence interval [CI]=1.10�1.81). Those exposed to an estimated THM level 50 g/liter for 35 or more years had 1.63 times the risk of those exposed for less than 10 years (CI=1.08�2.46). These results indicate that the risk of bladder cancer increases with both duration and concentration of exposure to chlorination by-products, with population attributable risks of about 14 to 16 percent. Chlorination by-products represent a potentially important risk factor for bladder cancer.

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