Haloacetic acids

Haloacetic acids or HAAs are carboxylic acids in which one or more halogen atoms take the place of hydrogen atoms in the methyl group of acetic acid. Those acids have a general chemical formula |X^{1}X^{2}X^{3}C\sCO2H|auto=1, where X is hydrogen or halogen, and at least one X is a halogen. In a monohaloacetic acid (|XCH2\sCO2H), a single halogen replaces a hydrogen atom: for example, in bromoacetic acid (|BrCH2\sCO2H). Further substitution of hydrogen atoms with halogens can occur, as in dichloroacetic acid (|Cl2CH\sCO2H) and trichloroacetic acid (|Cl3C\sCO2H). Haloacetic acids are a common contaminant in treated drinking water, particularly water subjected to chlorination.

Haloacetic acids (HAAs) are a common undesirable by product of water treatment by chlorination. Exposure to such disinfection by products in drinking water, at high levels over many years, has been associated with a number of health outcomes by epidemiological studies. HAAs can be formed following chlorination, ozonation, or chloramination of water, as chlorine from the water disinfection process can react with organic matter and small amounts of bromide present in water. A study published in August 2006 found that total levels of HAAs in drinking water were not affected by storage or boiling, but that filtration was effective in decreasing levels.

The inductive effect caused by the electronegative halogens often results in the higher acidity of these compounds by stabilising the negative charge of the conjugate base.