Chlorination By-Products

Drinking water comes from natural sources in the environment, with naturally occurring disease-causing microorganisms. Because of this, water must be disinfected in order to be [Page 104]potable and safe for human consumption. However, common disinfectants may also react with naturally occurring components of the water to create by-products that can have cancerous or other health effects.

Drinking water sources typically derive from either surface or ground waters. Surface water has naturally occurring pathogens, which are biological agents, such as bacteria, that cause human diseases. Some of the most dangerous of these pathogens originate from the gastrointestinal (GI) tracts of mammals. When animals or humans defecate near surface water, the water may become contaminated with these pathogens, which causes illness when humans drink the water. In countries with adequate drinking water treatment, waterborne illnesses have become a rare event. But in the developing world, unsafe water is still a major cause of illness.

According to Water for People, a charity dedicated to providing adequate drinking water and wastewater sanitation throughout the world, globally 884 million people lack safe drinking water and 2.5 billion people lack adequate sanitation, resulting in the deaths of approximately 6,000 people daily, mostly children. Many common illnesses in the developing world have been almost eradicated in societies with adequate water disinfection, for example, cholera, dysentery, Legionnaires’ disease, Pontiac fever, typhoid fever, and polio.

Within the United States, one of the most famous outbreaks of waterborne illness was the 1993 Cryptosporidium outbreak in Milwaukee, Wisconsin, causing illness in over 400,000 people, resulting in over 100 deaths, and creating an estimated $96.2 million in costs associated with illness. Although the cause of this outbreak was believed to be an ineffective filtration process, publicly supplied drinking water is meant to have an adequate chlorine residual remaining in the water when it leaves the plant to ensure adequate disinfection when it arrives at a consumer's tap.

Although chlorine is used in drinking water treatment to disinfect and protect humans, it also reacts with organics and inorganics in the water to form chlorination by-products, many of which have been shown to cause cancer or to cause adverse reproductive or developmental effects (such as certain trihalomethanes and certain haloacetic acids) in laboratory animals. Other methods of disinfection exist, which also have disinfection by-products such as chlorine dioxide and ozone. Chlorine dioxide is chlorine containing a compound used to disinfect water. It reacts in water to form chlorite, which has been shown to cause adverse effects in laboratory animals.

The U.S. Environmental Protection Agency (EPA) does not regulate chlorination by-products alone, but regulates all disinfection by-products, including trihalomethanes, halo-acetic acids, chlorite, and bromate through the stage 1 Disinfectants/Disinfection Byproducts Rule, as follows:

• Trihalomethanes (THMs) include chloroform, bromodichloromethane, dibromochloromethane, and bromoform. THMs form when chlorine and other disinfectants react with organic and inorganic matter in water. The maximum allowable annual average of THMs is 80 parts per billion (µg/l).
• Haloacetic acids (HAA5) include monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid. HAA5s form when chlorine and other disinfectants react with organic and inorganic matter in water. The maximum allowable annual average of HAA5 is 60 parts per billion (µg/l).
• Chlorite is formed when chlorine dioxide is used to disinfect water. The maximum allowable annual average of chlorite is 1 part per million (mg/l).
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• Bromate forms when ozone used for disinfection reacts with bromide present in water. The maximum allowable annual average of bromate is 10 parts per billion (µg/l).

Another form of chlorine may also be used for disinfection of drinking water. Chlorine can be combined with ammonia to form chloramines. Chloramines, on the whole, are more stable than chlorine. Because of this, they are less likely to react with organic matter, reducing the formation of THMs and HAA5s. This characteristic also makes chloramines more stable in the distribution system and weaker as disinfectants when compared to chlorine. Because of the lower production of by-products and greater stability in the distribution system, chloramines are gaining in popularity as disinfectants within the United States. Within humans, chloramines are neutralized within the digestive system, but chloramines can be toxic to fish. Tap water treated with chloramines should be treated prior to use in aquariums.

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