Water Disinfection by-Products (DBPs) Such as Trihalomethane or Haloacetic Acid
Millions of people in the U.S. are exposed to these drinking water DBPs (disinfection by-product) every day.While it is vitally important to disinfect drinking water, as thousands of people died from waterborne illnesses before we started disinfection practices in the early 1900s, it is also important to minimize the chemical DBPs formed.
A drinking water disinfection by-product (DBP) is formed when the chemical used for disinfecting the drinking water reacts with natural organic matter and/or bromide/iodide in the source water. Popular disinfectants include chlorine, ozone, chlorine dioxide, and chloramine. Source waters include rivers, lakes, streams, groundwater, and sometimes seawater.
Several DBPs have been linked to cancer in laboratory animals, and as a result, the U.S. EPA has some of these DBPs regulated. However, there are many more DBPs that have still not been identified and tested for toxicity or cancer effects. Currently, we have only identified <50% of the total organic halide (TOX) that is measured in chlorinated drinking water. There is much less known about DBPs from the newer alternative disinfectants, such as ozone, chlorine dioxide, and chloramine, which are gaining in popularity in the U.S. Are these alternative disinfectants safer than chlorine? What kinds of by-products are formed? And, what about the unidentified chlorine DBPs that people are exposed to through their drinking water--both from drinking and showering/bathing? The objective of our research is to find out what these DBPs are--to thoroughly characterize the chemicals formed in drinking water treatment--and to ultimately minimize any harmful ones that are formed.
Previous study from January 1, 1990, through December 31, 1993, to historical water sample data with respect to time and location of maternal residence based on census block groups shown that exposure during pregnancy to disinfection by-products in drinking water has been hypothesized to lead to several adverse reproductive outcomes. We performed a retrospective cohort study to examine the relation of trihalomethane exposure during the third trimester of pregnancy to low birthweight, term low birthweight, and preterm delivery. Using data from a case-control study of miscarriage, preterm delivery, and low birth weight in central North Carolina, we evaluated risk associated with water source, amount, and trihalomethane (THM) concentration. Water source was not related to any of those pregnancy outcomes, but an increasing amount of ingested water was associated with decreased risks of all three outcomes (odds ratios around 1.5 for 0 glasses per day relative to 1-3 glasses per day, falling to 0.8 for 4+ glasses per day). They suggested that the epidemiologic evidence supporting associations between exposure to water disinfection by-products (DBPs) and adverse pregnancy outcomes is sparse, and positive findings should be interpreted cautiously.
But recently, contrary to what has been suggested in some studies, exposure to drinking water disinfection by-products (DBPs) does not seem to raise the risk of pregnancy loss, new research indicates.
The findings, which appear in the American Journal of Epidemiology for December, are based on an analysis of DBP exposure and pregnancy outcomes for 2,409 women. Tap water levels of DBPs were measured in distribution systems weekly or biweekly.
A total of 258 pregnancy losses occurred in the study group, Dr. David A. Savitz, from the University of North Carolina in Chapel Hill, and colleagues note.
There was no evidence that exposure to the DBPs trihalomethane or haloacetic acid increased the risk of pregnancy loss. In the overall analysis, total organic halide exposure was not linked to pregnancy loss, but some sporadic elevations in risk were seen with ingested total organic halide.
"These results provide some reassurance that drinking water DBPs in the range commonly encountered in the United States do not affect fetal survival," the researchers state.
"Relative to previous epidemiologic studies of this issue, the methods of this study are stronger and the evidence for an association weaker," they add.