The Chlorine Dilemma

Chlorination of drinking water and municipal wastewater can create toxic chemical by-products, but alternatives pose their own set of hazards. Chlorine disinfection has been instrumental in the provision of safe drinking water, but the use of chlorine has a dark side: In addition to inactivating water-borne pathogens, chlorine reacts with natural organic matter to produce a variety of toxic disinfection by-products (DBPs). Regulatory guidelines were established in the United States for DBPs, such as chloroform, shortly after they were discovered in chlorinated drinking water in the mid-1970s, and the discovery of a potential link between DBPs and increased rates of miscarriages and bladder cancer led to more stringent regulations and substantial changes in the operation of water treatment systems during the past decade ( 1 ). These concerns and the risks associated with storing chlorine gas have recently led many drinking-water and wastewater treatment plants to discontinue the use of chlorine disinfection (see the figure). A series of recent studies suggest that some of these changes have had unintended consequences that pose risks to public health and the environment.