Disinfection By-Products
Fate and Transport of DBPs in the Environment
Characterization of DBPs
DBPs are currently regulated by the United States Environmental Protection Agency (USEPA) as two separate classes of compounds under the National Primary Drinking Water Regulations: Disinfectants and Disinfectant By-Products Final Rule (40 CFR Parts 9, 141 & 142). The first group is called the trihalomethanes (THMs) of which there are a total of four compounds:
- Trichloromethane (chloroform) CHCl3
- Dibromochloromethane CHClBr2
- Bromodichloromethane CHCl2Br
- Tribromomethane (bromoform) CHBr3
The EPA has limited the average annual maximum contaminant level (MCL) of Total Trihalomethanes (TTHMs) in most municipal water supplies to 80 parts per billion (ppb) or 0.1 milligram per liter. This measure of TTHMs is equal to the sum of the mass concentrations of all four chemicals in a water supply.
The second group of DBPs that has received attention is the haloacetic acids (HAAs). This group consists of five separate compounds:
- Monochloroacetic acid ClCH2COOH
- Dichloracetic acid CHCl2COOH
- Trichloroacetic acid C2HCl3O2
- Monobromoacetic acid BrCH2COOH
- Dibromoacetic acid Br2CHCOOH
The maximum annual average of HAAs permitted under EPA regulations is 60 ppb. It should also be noted that chlorite and bromate are also regulated under the DBP rule. These compounds are considered separate from the THMs and HAAs, with a MCL of 1 ppm for chlorite and 10 ppb for bromate.