As opposition grows against Fraser Health's proposed chlorination of Chilliwack's water another C word is making the rounds: cancer.

In an interview with CBC Tuesday, mayor Sharon Gaetz said chlorine was linked to bladder and colon cancer. A website hosting one of two anti-chlorine petitions being circulated also cites bladder cancer as a risk.

However, the science behind the claims is a little more ambiguous.

According to the World Health Organization (WHO): "In a study on the effects of progressively increasing chlorine doses . . . on healthy male volunteers (10 per dose), there was an absence of adverse, physiologically significant toxicological effects in all of the study groups."

But another study, cited by the WHO, suggested "An increased risk of bladder cancer appeared to be associated with the consumption of chlorinated tapwater in a population-based, case-control study of adults consuming chlorinated or non-chlorinated water for half of their lifetimes."

It's vital to note, however, that chlorine itself may not be to blame. The United States' Environmental Protection Agency explains:

"Several human studies have investigated the relationship between exposure to chlorinated drinking water and cancer. These studies were not designed to assess whether chlorine itself causes cancer, but whether trihalomethanes or other organic compounds occurring in drinking water as a result of chlorination are associated with an increased risk of cancer. These studies show an association between bladder and rectal cancer and chlorination byproducts in drinking water."

At his presentation to council last week, Fraser Health environmental health officer Binnie Silva acknowledged public concerns about those potentially cancerous chlorine byproducts (along with potential changes to the way the water tastes).

But he said that Chilliwack's groundwater system is ideally suited to chlorination and would minimize the development of such byproducts.

"Those sources of water have high organic loads, which leads to production of chloramines, which cause the taste and odour issues, as well as the disinfection byproducts."

He also said systems that rely on lakes or streams require heavier chlorination to disinfect the water.

"The city source, being such a good source, we don't think those would be of any particular concern."

tolsen@chilliwacktimes.com