Description
Total trihalomethanes (TTHMs) are volatile organic
contaminants often referred to as disinfection by-products, or DBPs. TTHMs are chemical contaminants that result when chlorine used to disinfect drinking water interacts with organic matter in the water. TTHMs consist of a sum of the levels
of four closely related chemicals—chloroform, dibromochloromethane, bromoform,
and bromodichloromethane—which occur together at varying ratios when water is
chlorinated. TTHMs are used as an indicator of a complex soup of other
potentially risky DBPs or “chlorination by-products.”
Health Effects
Immediate Health Effects
- If SWALLOWED, trihalomethanes (THMs) is Not Available
- If ABSORBED THROUGH SKIN, trihalomethanes (THMs) is Not Available
- If INHALED (SNIFFED OR BREATHED IN), trihalomethanes (THMs) is Not Available
Longterm or Delayed Health Effects
Other
- CANCER. More than a dozen epidemiological studies of people who drank water containing
chlorination by-products have linked the chemicals to bladder cancer, and several
studies indicate likely links to colorectal, pancreatic, and other cancers.105 National
Cancer Institute epidemiologists found links to brain cancer recently, and a link to
childhood leukemia has been noted in a recent Canadian epidemiological study.106,107
The EPA has classified some individual TTHMs as probable human carcinogens.
- Recent studies have also found that some pregnant women exposed to DBPs in tap
water may have a higher risk of problems with their babies, even after relatively brief
periods of exposure to spikes of the chemicals. The most significant concerns raised
by studies of pregnant women have been about findings of associations between
elevated levels of chlorination by-products (including TTHMs) and low birth weight,
preterm delivery, spontaneous abortions (miscarriages), stillbirths, and birth defects
(central nervous system, major cardiac, oral cleft, respiratory, and neural tube
defects).108 For example, one study in California found a significant association
between women who drank more than six glasses of water a day containing more
than 75 ppb TTHMs and miscarriages by those women.109 Lab studies on animals and
studies of pregnant women exposed to chlorination by-products have also found an
association between TTHMs and low birth weight.110 The evidence that chlorination
by-products cause miscarriages, birth defects, low birth weight, or other reproductive
problems is not conclusive but raises major concerns worthy of preventative action to
reduce or eliminate exposure to these chemicals. As one recent scientific review
concluded, several studies have “shown associations for DBPs and other outcomes
such as spontaneous abortions, stillbirth, and birth defects, and although the
evidence for these associations is weaker, it is gaining weight.”111
Solutions
How to detect trihalomethanes (THMs)
How to minimize exposure to trihalomethanes (THMs)
Alternatives
For More information
Books, articles, factsheets and reports
Other government agencies
Nonprofit organizations
Other websites
