Trihalomethanes, or THMs, are a group of chemical byproducts commonly found in treated drinking water. These compounds, including chloroform, bromodichloromethane, dibromochloromethane, and bromoform, are a result of the necessary disinfection processes that make our water safe to drink. While water disinfection protects against harmful microorganisms, it can unintentionally lead to the formation of these substances.
How Trihalomethanes Form
Trihalomethanes are formed when disinfectants, primarily chlorine, react with naturally occurring organic matter present in source water. This organic matter often includes decaying leaves and other vegetation. The reaction creates various disinfection byproducts, with THMs being a prominent group.
The extent of THM formation is influenced by several factors, including the type and amount of disinfectant used, the concentration of organic matter, water temperature, pH levels, and the contact time between the disinfectant and the water. The presence of bromide in water, for example, can lead to the formation of brominated THMs.
Health Implications of Trihalomethanes
Chronic exposure to trihalomethanes in drinking water has been linked to various health concerns. Studies suggest an increased risk of certain cancers, such as bladder and colon cancer. For example, a meta-analysis of 29 studies indicated that high THM levels could increase bladder cancer risk by 1.33 times. Some research suggests an association with colon cancer at THM concentrations above 19 micrograms per liter.
Prolonged THM exposure has also been associated with reproductive and developmental issues. Studies suggest links to pregnancy complications, including low birth weight and miscarriage. While research continues, organizations like the International Agency for Research on Cancer classify some THMs, such as chloroform, as possibly carcinogenic to humans.
Ensuring Water Safety
Public water systems actively manage and monitor THM levels to ensure drinking water safety. Regulatory bodies, such as the Environmental Protection Agency (EPA) in the United States, establish standards for total trihalomethanes (TTHMs). The EPA has set a Maximum Contaminant Level (MCL) for TTHMs at 0.080 milligrams per liter, or 80 parts per billion (ppb), measured as a running annual average. This standard balances potential health risks with the need for effective water disinfection.
Water utilities regularly test their water to comply with these standards, often conducting quarterly sampling from various points in the distribution system. To reduce THM formation, utilities optimize disinfection processes, such as adjusting disinfectant dosage or delaying chlorination to limit chlorine’s contact time with organic materials. They implement treatment methods to remove organic precursors from the source water before disinfection. These methods include coagulation, flocculation, sedimentation, and filtration, which cause organic matter particles to clump together and be removed.
Reducing Exposure at Home
Individuals can take steps to reduce their exposure to THMs within their homes. Activated carbon filters are effective for removing THMs from drinking water. These filters work through adsorption, where porous carbon material traps THMs and other organic compounds as water passes through. Pitcher filters, faucet-mounted filters, and whole-house filtration systems are available options, and verifying a filter’s certification for THM reduction, such as NSF/ANSI Standard 53, is advisable.
Boiling water can also significantly reduce THM concentrations due to their volatile nature. Boiling water for one minute can reduce trihalomethane concentration by up to 75%. Boiling water for three to five minutes can achieve nearly 100% removal of some THM species like chloroform and dibromochloromethane. Good ventilation during showering and bathing is also helpful, as THMs can vaporize and be inhaled or absorbed through the skin. Reducing shower time and temperature can further minimize exposure.