TRIHALOMETHANES

        Trihalomethanes. What are Trihalomethanes? Trihalomethanes (THMs) are small organic compounds similar in structure to methane, but also containing chlorine and/or bromine. The compounds are the major by-products of disinfection of water supplies. They are formed when naturally occurring organic substances react with chlorine used to disinfect drinking water. The trihalomethanes of significance in disinfected water are chloroform, dichlorobromomethane, chlorodibromomethane, and bromoform.

        What are the Health Effects of THMs? The health effects of THMs are unclear. Studies of human populations have indicated a slightly higher incidence of bladder and colon cancer in areas where the drinking water has been chlorinated. Other studies, however, have not shown an increased risk of cancer. While animal studies have shown mutagenic and carcinogenic potential of THMs, it has been suggested that these results are unreliable since the animals are exposed to THM levels 10,000 times greater than humans are exposed to.

        How may I be Exposed to THMs? THMs are found in disinfected drinking water supplies. The levels of THMs are dependent on the amount of naturally occurring organic material found in the source water and the amount of chlorine used in disinfection.

        Are the Levels of Trihalomethanes in Drinking Water Dangerous to my Health? The data from animal studies show that the risk of getting cancer from THMs is extremely low. It is estimated that the risk of getting cancer from the consumption of 1 mg/L of chloroform in water is 1 chance in 10 million. 20 mg/L chlorodibromomethane results in a cancer risk of 1 in a million, whil 81 mg/L of bromoform produces a similar risk. Currently the limit for THMs in drinking water is 100 mg/L, however, as the combined toxicity of the THMs is unknown, the limit is being reduced further to 80 mg/L.




Source: http://www.ci.sf.ca.us/puc/wqfs/tocsec4.htm