Trihalomethanes

Important factors in THM formation include the type and concentrations of organic materials in the unfiltered water, the chlorine reaction time, water temperature, and chlorination pH of the water. Chloroform is the most common THM, and because of this, is often the most studied and analyzed of the THMs. Many statistics and conclusions regarding THM exposure are extrapolated from studies examining chloroform exposure.

Concentrations of chloroform are generally higher in chlorinated water originating from surface water than in groundwater, because of higher levels of organic matter in surface water. The extent of formation of chloroform varies with different water treatment processes. Concentrations of chloroform in chlorinated water in treatment plants and distribution systems are approximately twice as high during warmer months as during colder months. This is a consequence of the higher concentrations of precursor organic materials and especially of the higher rates of formation of disinfection byproducts in the unfiltered water during the warmer period. Levels can increase as the chlorinated water moves from the water treatment plant through the distribution system, because of the continued presence of residual chlorine throughout the pipes.

Further increases in concentrations of chloroform in water can occur in domestic hot water tanks; however, storage in the hot water tank increases the level of chloroform twice as much in colder months than in warmer months, when more hot water is required to maintain shower and bath temperatures. This demonstrates that, despite higher base water temperatures during warmer months, concentrations of chloroform are relatively constant for both warmer and colder seasonal periods due to the increased usage of hot water during colder months.

Why Do People Need Trihalomethanes Water Filters?

Trihalomethanes are chemicals that are not naturally occurring, and are considered environmental pollutants. The EPA has classified many THMs as Cancer Group B carcinogens, with a possible increase in bladder or colorectal cancer over a lifetime of drinking water with high concentrations of THMs – and particularly the THM dibromochloromethane. Other studies have found links between THMs and damage to the heart, lungs, kidneys, liver, and central nervous system. This is a major reason why it is so important to have a trihalomethane filter for your drinking water. It is not enough to use a basic chlorine water filter when TTHM removal is necessary for the healthfulness of your water.

Pregnant women are particularly at risk of THM exposure, as some studies have linked THMs to reproductive problems, including miscarriage. Expectant mothers should therefore especially consider utilizing filters that remove trihalomethanes in water for their home.

Short-Term (Acute) Effects of THMs

In the past, chloroform was commonly used as an inhaled anesthetic. Evidence of chloroform's acute effects on humans comes primarily from these experiences. In addition to central nervous system effects, chloroform anesthesia was associated with cardiac arrhythmias and abnormalities of the liver and kidneys. Inhalation exposure experiments with animals revealed that high levels of chloroform are toxic to both the liver and the kidneys. Skin contact with undiluted chloroform may cause a burning sensation, redness, and blistering.

Long-Term (Chronic) Effects of THMs

Chronic oral exposure of humans to chloroform at high doses results in adverse effects on the central nervous system, liver, kidneys, and heart. Animal studies have shown decreased body weight in rats and mice given chloroform at high oral doses and an increased incidence of respiratory disease at higher doses. At even higher oral doses, liver abnormalities and decreased size of reproductive organs were observed in rats. In animal studies investigating effects of chronic exposure to each of the other THMS – and particularly bromodichloromethane – liver toxicity was observed.

Carcinogenic Effects of THMs

Chloroform has been demonstrated by several studies to produce kidney and liver tumors in rats and mice when administered orally. In studies of human populations using chlorinated drinking water in which chloroform is the predominant THM, small increases in the incidence of rectal, colon, and bladder cancer have been consistently observed, with evidence strongest for bladder cancer. However, because other possible carcinogens were found in this water, it is impossible to identify chloroform as the sole carcinogenic agent. This is why chloroform has been classified by the U.S. Environmental Protection Agency as a Group B2 or "probable human carcinogen," based on sufficient animal evidence and inadequate human evidence of their carcinogenic nature. Evidence from animal studies now strongly indicates that chloroform exposure causes cancer only after first producing sustained cell toxicity. Because a certain threshold level of exposure is necessary to cause cell toxicity, cancer from chloroform exposure can only occur if that threshold is exceeded.

Bromodichloromethane and bromoform are also classified as Group B2 carcinogens: Bromodichloromethane exposure in animals increased tumors of the large intestine, kidney, and liver, and bromoform exposure in animals increased tumors of the large intestine.

Dibromochloromethane is classified as a Group C carcinogen – "possible human carcinogen" – based on limited animal evidence of an increase in liver tumors.

Developmental / Reproductive Effects of THMs

Published studies in which chloroform was administered to animals indicate that chloroform has the potential to cause birth defects, miscarriages, and delays in fetal development. Results have generally been inconclusive regarding exposure to THMs and adverse developmental or reproductive effects in humans. However, the results of a recent study suggest an increased risk of early-term miscarriage from high levels of THMs in tap water, particularly bromodichloromethane. This reinforces the importance of a trihalomethane filter for drinking water in the home.