The group of Haloacetic Acids regulated by the EPA includes five compounds (HAA5):
Monochloroacetic acid (MCAA) ClCH2COOH
Dichloroacetic acid (DCAA) CHCl2COOH
Trichloroacetic acid (TCAA) C2HCl3O2
Monobromoacetic acid (MBAA) BrCH2COOH
Dibromoacetic acid (DBAA) Br2CHCOOH
Chlorinated Haloacetic Acids - MCAA, DCAA and TCAA - form when water containing organic matter is disinfected, usually with chlorine or chloramines. The brominated acetic acids (MBAA and DBAA) form during disinfection when the source water also contains bromide ions.
Haloacetic Acids (HAAs) usually exist in finished water at a lower concentration than the other major group of disinfection byproducts, the Trihalomethanes (THMs).
Chloroform has been studied much more extensively than the other trihalomethanes. Chloroform is normally the trihalomethane (THM) present in drinking water at the highest concentration. The other THMs are expected to be similar in health effects, routes of exposure, and metabolism to chloroform, with a few exceptions as will be noted below. Therefore, much of the data cited in the literature and below is in reference to the Chloroform studies.
Chlorite and bromate are also regulated under EPAs Disinfection By-Product rule. These compounds are considered and measured separately from the HAAs and THMs. Chlorite is also used in industry to etch printed circuit boards, and therefore people employed in this occupation have additive exposure. The maximum contaminant level (MCL) in the water supply allowed is 1 ppm for Chlorite.
Conclusions and Risk Management
The main thing to keep in mind when evaluating possible risks posed by disinfection byproducts is that the risks posed by not disinfecting drinking water are much higher.
Control of microbial waterborne pathogens is the number one priority in any water treatment system. While numerous toxicological studies indicate DBPs can cause cancer when administered at certain dosages to laboratory animals, there is basically no conclusive epidemiological data on the subject. The main hindrance in epidemiological studies is accurate estimation of exposure. DBPs exist as different combinations of chemicals in different water supplies depending on the mode of disinfection used and the organic matter present in the water, and can vary by season. Additionally, people have different water use habits, and the primary routes of exposure differ among the chemicals (i.e. dermal, inhalation, ingestion). The toxicological data currently available on DBPs is useful, but would be more so combined with conclusive epidemiological studies assessing exposure and risk estimates in human populations.
The International Life Sciences Institute held a meeting in 1998 to discuss risks from drinking water. They stated
Owing to the rarity of relevant cancer endpoints and the expectations that, even if there is any effect associated with drinking water, it can lead to only a few extra cancer cases, it seems unlikely that it will ever be possible to establish an association based solely on epidemiological studies between any drinking water contaminant and the induction of cancer. 12
If this is the case, then perhaps it is appropriate to next evaluate where the research, water quality control, and regulatory dollars could be better spent.