Chlorination
Chlorination is the process of disinfecting water through the addition of chlorine, a method widely used to purify drinking water, treat wastewater, and maintain hygiene in swimming pools. This practice has significantly contributed to reducing waterborne diseases, such as typhoid, especially noted in the early 20th century when death rates dropped dramatically in the United States. Common agents for chlorination include elemental chlorine gas and sodium or calcium hypochlorite, which generate hypochlorous acid to inactivate harmful microorganisms.
Despite its effectiveness, chlorination raises environmental and health concerns due to the formation of potentially toxic chloro-organic compounds, particularly trihalomethanes (THMs), when chlorine reacts with organic materials in water. Chloroform is one of the most studied THMs due to its carcinogenic properties, leading to regulatory guidelines to minimize its presence in drinking water. While chlorinated water poses some risks, studies indicate that these are significantly lower compared to other health hazards, like cigarette smoking. Overall, chlorination remains a crucial and economical technique in water treatment, but ongoing monitoring of its byproducts is necessary as water pollution increases.
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Chlorination
DEFINITION: Practice of disinfecting water by the addition of chlorine
Although the chlorination of public water in the United States has helped reduce outbreaks of waterborne disease, it has raised concerns about the possible formation of chloro-organic compounds in treated water.
Drinking water, wastewater, and water in swimming pools are the most common water sources where is used to kill and prevent the spread of diseases. Viruses are generally more resistant to chlorination than are bacteria, but they can be eliminated with an increase in the chlorine levels needed to kill bacteria. Common chlorinating agents include elemental chlorine gas and sodium or calcium hypochlorite. In water these substances generate hypochlorous acid, which is the chemical agent responsible for killing microorganisms by inactivating bacteria proteins or viral nucleoproteins.
Public drinking water was chlorinated in most large US cities by 1914. The effectiveness of chlorination in reducing outbreaks of waterborne diseases in the early twentieth century was clearly illustrated by the drop in typhoid deaths: 36 per 100,000 in 1920 to 5 per 100,000 by 1928. Chlorination has remained the most economical method of purifying public water, although it is not without potential risks. Chlorination has also been widely used to prevent the spread of bacteria in the food industry.
In its elemental form, high concentrations of chlorine are very toxic, and solutions containing more than 1,000 milligrams per liter (mg/l) are lethal to humans. According to the Centers for Disease Control and Prevention (CDC) in 2020, chlorine levels of up to 4 mg/l (4 parts per million) are unlikely to harm human health. Chlorine has a characteristic odor that is detectable at levels of 2-3 mg/l of water. Most public water supplies contain chlorine levels of 1-2 mg/l, although the actual of water reaching consumer faucets fluctuates and is usually around 0.5 mg/l.
The greatest environmental concern regarding chlorination has less to do with the chlorine itself than it does with the potential toxic compounds that may form when chlorine reacts with compounds present in water. Chlorine, which is an extremely reactive element, reacts with organic material associated with decaying vegetation (humic acids), forming chloro-organic compounds.Trihalomethanes (THMs) are one of the most common chloro-organic compounds. At least a dozen THMs have been identified in drinking water since the 1970s, when health authorities in the United States came under pressure to issue standards for the identification and reduction of THM levels in drinking water.
Major concern has focused on levels of chloroform because of this compound’s known carcinogenic properties in animal studies. Once used in cough syrups, mouthwashes, and toothpastes, chloroform in consumer products is now severely restricted. A 1975 study of chloroform concentrations in drinking water found levels of more than 300 micrograms per liter (μg/l) in some water, with 10 percent of the water systems surveyed having levels of more than 105 μg/l. In 1984, the World Health Organization set a guideline value of 30 μg/l for chloroform in drinking water.
Although risks are associated with drinking chlorinated water, it has been estimated that the of death from cigarette smoking is two thousand times greater than that of drinking chloroform-contaminated water from most public sources. However, as water sources become more polluted and require higher levels of chlorination to maintain purity, continual of chloro-organic compounds will be needed.
Bibliography
Bull, Richard J. “Drinking Water Disinfection.” In Environmental Toxicants: Human Exposures and Their Health Effects, edited by Morton Lippmann. New York: John Wiley & Sons, 2000.
Crider, Yoshika S. et al. "Adoption of Point-of-Use Chlorination for Household Drinking Water Treatment: A Systematic Review." Environment of Health Perspectives, vol. 13, no. 1, 30 Jan. 2023, doi.org/10.1289%2FEHP10839. Accessed 16 July 2024.
Gray, N. F. Drinking Water Quality: Problems and Solutions. 2d ed. New York: Cambridge University Press, 2008.
"Water Disinfection with Chlorine and Chloramine." Centers for Disease Control and Prevention (CDC), 17 Nov. 2020, www.cdc.gov/healthywater/drinking/public/water‗disinfection.html. Accessed 16 July 2024.