Study blames chlorine for colon, bladder tumors
By Jean Sonmor
Toronto Sun
12/06/95

It's just as the old guy with the whiskey habit said all along; "Drinking water can kill you."
A study released yesterday concludes long term drinking and bathing in chlorinated water likely causes a 34% increase in the incidence of bladder and colon cancer.
Across the province chlorinated water may account for 180 deaths a year from the two types of cancer.

Researchers from the Ontario Cancer Treatment and Research Foundation also investigated rectal cancer but found no statistically significant link.

The risk increases with the length of exposure and the concentration of chlorinated byproducts in the water. In Brantford and Peterboro, for example, where the byproducts of chlorination have traditionally been high, the increased incidence could b e higher than 60% for people who have used the water for more than 35 years.

In Metro the byproduct levels are much lower and so is the risk. The study found no evidence of the so-called Great Lakes effect; water originating from the Great Lakes was found to be slightly safer.

Potential lifesaver

"Eliminating the chlorination of water would reduce the number of bladder and colon cancer cases by 10% to 13%," said Will King of Queen's University, the lead researcher in the study.
The study is being described by experts as "important" and the findings "very significant."
"I did not anticipate the risk being this high," said Dr. Barry Thomas, head of the criteria section of Health Canada, which sets national guidelines for drinking water "This is one of the most extensive studies ever done. I'm not aware of another study of this size and complexity. About 5,000 residents participated in the case controlled study, which covered an area containing 93% of Ontario's population.

The links between chlorinated water and colon and bladder cancer have been investigated since the early 1980's but this is the most conclusive proof yet that there is a positive link. "There's still some doubt but it's getting increasingly smaller," Thomas said. Chlorine, which is used as a disinfectant to control bacteria in 73% of this province (and all of Metro), is not itself considered the culprit in cancer. Rather, the byproducts that are formed when the chlorine reacts with organic matter.

Metro risk low

In Metro the levels of chlorination byproducts are very low- between 12 and 14 parts per billion. In Peterboro the average for the same year was 91ppb. In Brantford 82 ppb. In some prairie towns, levels shoot up to nearly 1,000 ppb.

"The study found a statistically significant increase in the two cancers over 25 ppb and higher again over 50 ppb. "I don't want to say it's a small risk, "said King, who with Dr. Loraine Marrett designed and conducted the study. "Above 50 ppb we began to see increasing risk. In 1990, 38% of the province's population had a water source with that level. "In view of the study we'll be re-examining our guidelines," said Thomas, whose department two years ago reduced the national guideline from 350 ppb to 100 ppb. It took us eight years to do that. We have to get the provinces' approval."

Ontario has yet to adopt it, although 99% of the municipal drinking water in Ontario now meets the new guideline, said Jim Smith of the Ontario ministry of the environment. "This is not good news," said Jim bishop of MDS Environmental and former Ontario water chief.

Cancer Risk

Some facts from a study one on cancer risks in chlorinated water by the Ontario Cancer Treatment and Research Foundation and University of Toronto.

• THMs- trihalomathanes- are byproducts of chlorination that form when water containing organic matter (decay of leaves; human/animal waste, etc.) is chlorinated. The maximum limit for THMs in water is 100 parts per billion.
• The study found long-term consumption of chlorinated water increases the risk of bladder and colon cancer. Between 10-13% of all bladder and colon cancers in Ontario may be attributable to chlorinated water. An estimated 1,400 Ontarians will be diagnosed with bladder cancer this year, while 3,800 people will be diagnosed with colon cancer.
• People using treated water with low chlorination byproducts (ie. ground water), or water with high levels for a shorter time period (less than 35 years), do not appear to be at increased risk for bladder and colon cancer
• There's a 60% increase in the risk of bladder cancer for people exposed to high levels of chlorinated byproducts for more than 35 years compared to people with little or no exposure. The figure is slightly lower for colon cancer.

Tips on reducing exposure to THMs and some other chlorination byproducts in treated water used for drinking.

• Aerate tap water in a blender.
• Store water in the refrigerator for 24 hours.
• Use water treatment devices containing activated carbon. Follow all filter flushing and replacement instructions to avoid risk of bacterial contamination.

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