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Understanding the Dangers of Disinfection Byproducts

Updated: Oct 25, 2021

Why are chlorine chemicals added to my drinking water?

Chlorine disinfection is a chemical process used in municipal water systems, private wells, schools and businesses where chlorinated chemicals are added to inactivate or kill disease causing organisms (pathogens) found in the water source. Common water sources include lakes, rivers, reservoirs, wells or ground water from which water is drawn and treated. Disinfection typically involves the use of disinfectants such as chlorine, chlorine dioxide and a combination of chlorine and ammonia (chloramines) to render disease organisms harmless. These disinfection methods can kill pathogens, but can also create disinfection byproducts (DPBs) that may be harmful to human health. Ozone is also used as a disinfectant by some water purification systems.

What are disinfection byproducts? Trihalomethanes (THMs) are a group of four chemicals that form when chlorine reacts with naturally occurring organic matter in the water. The trihalomethanes include chloroform, bromodichloromethane, dibromochloromethane, and bromoform. Haloacetic Acids (HAA5) are a group of five chemicals that are formed along with other disinfection byproducts when chlorine or other disinfectants used to control microbial contaminants in drinking water react with naturally occurring organic matter. These include monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid. Bromate is a chemical that is formed when the ozone used to disinfect drinking water reacts with naturally occurring bromide found in the source water. Chlorite is a byproduct formed when chlorine dioxide is used to disinfect water.

What are the health effects of disinfection byproducts? Since the discovery of these chemical byproducts in drinking water in 1974, many toxicological studies on the health effects from exposure to DBPs have been conducted. The studies have shown that disinfection byproducts are carcinogenic in laboratory animals. The DPBs include bromate, certain trihalomethanes and haloacetic acids. Chlorite and certain trihalomethanes and haloacetic acids have also been shown to cause adverse reproductive or developmental effects in laboratory animals. A number of epidemiology studies have investigated the relationship between exposure to chlorinated water and cancer. Some have suggested an increased cancer risk to those exposed to chlorinated waters while others have demonstrated none. The US EPA stated that while the agency cannot conclude there is a link between exposure to chlorinated water and cancer, the studies have suggested an association between bladder, rectal, and colon cancer and exposure to chlorinated surface water.


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