Water treatment by-products linked with cancer

Source : http://www.eht-forum.org/news.html?fileId=news100210074010&from=home&id=0
Increased risk of colon cancer possible for people drinking chlorine-treated water, suggests meta-analysis
Source: SXC/fragallo	Disinfecting drinking water keeps people safe from pathogens but evidence suggests that exposure to the by-products of chemicals used to treat water could increase the risk of colon and rectal cancer, according to public health researchers writing this month online in the International Journal of Epidemiology. But they caution the findings are based on “limited evidence”.   “This meta-analysis points to an association between exposure to disinfection by-products and an increase in the risk of colorectal cancer,” write Bayzidur Rahman, from The University of Sydney, Australia, and colleagues.   Water is usually treated with chlorine, a cheap and easy-to-use disinfectant, to remove pathogens before it becomes suitable for drinking. During the process several by-products are produced as the chlorine breaks down and reacts with organic matter in the water. These chemicals, the most common of which is trihalomethane, have been shown to cause liver, kidney and intestinal tumours in mice.   Several studies have also looked at the risk of cancer in humans exposed to chlorinated water. A previous meta-analysis, which considered the evidence published up to 1992, suggested the risk of developing bladder, colon or rectal cancer was 10–40% higher for people exposed to disinfection by-products in their drinking water compared with those that were not. More research has been published since then, but with inconsistent findings.   To get a clearer picture of any risk of colorectal cancer, Rahman and colleagues analysed the results of 13 studies published up to 2009, including some of the research included in the previous analysis. They looked for research that gave an indication of quantified cancer risks associated with treated water, and ones that gave specific details of the exposure levels that people experienced. Pulling together all the data from these pieces of research, and taking into consideration the quality of each study, they used statistical tests to analyse the findings.   They found that the odds of getting colon cancer were slightly but significantly  higher for people exposed to chlorination by-products in their water than those who were not. The same was true for rectal cancer, but this result was less reliable and may have been swayed by poor-quality research, according to the authors.   They explain that although the possible increased risk of colon cancer is small, it could lead to huge numbers of cancer cases because a large number of people drink water containing disinfection by-products. “Therefore, the association requires further investigation.”   The evidence used to come to this conclusion is “limited”, as the researchers followed strict criteria when selecting the research included in the analysis. By doing this they hoped to weed out poor-quality studies, making their results more precise.
Reference and link
1. Rahman M B, Driscoll T, Cowie C, Armstrong BK. Disinfection by-products in drinking water and colorectal cancer: a meta-analysis. Int J Epidemiol 2010. doi: 10.1093/ije/dyp371 US Centers for Disease Control and Prevention information about disinfection by-products