National Drinking Water Database

Chloramines (as Cl₂)

Monochloramine, a combination of chlorine and ammonia, is added by many water utilities to drinking water as a disinfectant against microorganisms. Monochloramine and related chloramines, dichloramine and trichloramine, also form in water following treatment with chlorine (Lee 2009). Unlike chlorine, chloramines do not dissipate from tap water either on standing or by boiling (USEPA 2009a).

As summarized by Health Canada in its review of chloramine, inhalation of chloramine fumes may lead to burning in eyes and throat, transient cough, shortness of breath, nausea and vomiting (Health Canada 1995). In sensitive mucous membrane areas such as the respiratory tract, chloramines decompose to ammonia and hypochlorous acid, which can combine with moisture to form hydrochloric acid, producing respiratory tract damage (Health Canada 1995). Chloramine exposure is also a likely contributor to eye irritation observed in swimming pools, according to research by the Centers for Disease Control and Prevention, the West Virginia Bureau for Public Health and the University of Sheffield (Bowen 2007; Goyder 2000; Kaydos-Daniels 2008). Concerns over skin, digestive system and lung toxicity have been reported following exposure to chloramine in drinking water (Weintraub 2006). In people, short-term exposure to monochloramine, at a level approximately four times the maximum allowed residual disinfectant level, increased plasma apolipoprotein, a risk factor for coronary heart disease (WHO 2004b; Wones 1993).

As an additional health hazard, the use of chloramine as a tap water disinfectant causes leaching of lead from pipes and plumbing fixtures (Maas 2007), leading to significant elevation of blood lead levels in exposed populations, especially infants and children (Edwards 2009; Miranda 2007). Chloramines are also associated with excessive nitrification in tap water (Zhang 2009), a microbiological process during which ammonia is oxidized to nitrite, a water contaminant associated with the life-threatening blood disorder methemoglobinemia (blue baby syndrome) (Health Canada 1995).

Both chloraminated and chlorinated water have more mutagenic potency than raw or ozonated water (Richardson 2007; WHO 2004a). Chloramines have less potential than chlorine to produce cancer-causing disinfection byproducts called trihalogenated methanes (THMs). However, chloramines can produce other toxic byproducts including a potent animal carcinogen called N-nitrosodimethylamine (NDMA) (Choi 2002; World Health Organization (WHO) 2008a). NDMA causes tumors of the liver, lung and kidney in rats. The International Agency for Research on Cancer (IARC) classifies NDMA as probably carcinogenic to humans (IARC 2008a). NDMA is a mutagen, which means it directly damages the structure of DNA. In mice, NDMA is also a transplacental carcinogen, meaning that exposure during fetal life can result in liver tumors during adult life (Anderson 1989).

A 2005 survey by the American Water Works Association found that 29 percent of all utilities now use chloramines for secondary disinfection; other utilities use chlorine (Seidel 2005). Additionally, due to reaction of free chlorine with organic matter in source water, three quarters of water utilities have levels of chloramine residuals of one to three mg/L (parts per million or ppm) in finished water that enters distribution systems (WHO 2004b).

Chlorine (as Cl₂) and chlorination byproducts (bromodichloromethane, dibromochloromethane, bromoform, monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid and dibromoacetic acid).

Chlorine is a highly reactive, toxic gas added as a disinfectant in drinking water to kill microbes such as E. coli. Chlorine and chlorine breakdown products [elemental chlorine (Cl₂), chloride ion (Cl^-) and hypochlorous acid (HOCl)] combine with the organic matter that contaminates source waters to produce harmful byproducts, collectively referred to as chlorination byproducts (CBPs). In spite of the diligent efforts of the water utilities to filter and clean water before they chlorinate, levels of chlorination byproducts remain high in the water consumed by millions of people each day.

Disinfection of tap water is a critical public health measure that saves thousands of lives each year by reducing the incidence of waterborne disease. But the use of toxic disinfectants such as chlorine is no substitute for cleaning up America's waters now polluted with industrial, agricultural and urban runoff. When water utilities chlorinate source water contaminated with animal waste, sewage, fertilizer, algae and sediment in order to provide water free of disease-causing microorganisms, high levels of chlorination byproducts are formed (EWG 2002).

Disinfection byproducts (DBPs) are a complex mixture of hundreds of potentially toxic compounds (Richardson 2007). Only trihalomethanes (THMs), five haloacetic acids (monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid and dibromoacetic acid), bromate and chlorite are currently monitored and regulated (USEPA 2009b). Although water utilities take steps to decrease formation of disinfection byproducts, for example by filtering out some of the organic precursors, short-term spikes of DBPs in tap water still occur.

According to EPA, several DBPs (bromodichloromethane, bromoform, chloroform, dichloroacetic acid and bromate) are carcinogenic in laboratory animals. Several disinfection byproducts, such as bromodichloromethane, bromoform and dichloroacetic acid, are classified as "probable" or "possible" human carcinogens (ATSDR 2005; IARC 2008b; Integrated Risk Information System (IRIS) 1991, 1993, 1996a). In epidemiological studies, exposure to chlorinated drinking water has been associated with certain cancers, especially bladder cancer (USEPA 1998c). EPA estimated that current levels of disinfection byproducts in U.S. tap water may cause up to 9,300 cases of bladder cancer each year (USEPA 1998c). Disinfection byproducts have also been linked to miscarriages, birth defects and other adverse reproductive outcomes in epidemiological studies and in laboratory animals (Klinefelter 1995; MacLehose 2008; USEPA 1998c).

The main causes of DBPs in tap water are sediments, nutrients and pollution from agricultural and urban runoff, and in some small systems, excess use of chlorine. Until Congress and EPA act to limit pollution from farms and urban centers so that the water entering drinking water treatment plants is much cleaner than it is today, CBPs will remain at unacceptably high levels.

In 2004, the U.S. EPA's Toxics Release Inventory (TRI) reported that U.S. industrial facilities released 17,330,728 pounds of chlorine in 2002. The primary metals and chemicals industries account for 91 percent of the total released (USEPA 2009i).