Effect of zinc on the transformation of haloacetic acids (HAAs) in drinking water

Suspected carcinogen haloacetic acids (HAAs), as a major class of disinfection byproducts, are widespread in drinking water. Batch experiments were conducted to investigate the effect of zinc, a metal component of galvanized pipe in water distribution systems, on the fate of the HAAs. Results showed that zinc could induce sequential dehalogenation of HAAs. All brominated acetic acids were transformed to acetate ultimately, and chloroacetic acid (MCAA) was the final product for the dehalogenation of trichloroacetic acid (TCAA) and dichloroacetic acid (DCAA). The concentrations of the parent compounds as a function of time were fitted pseudo-first-order kinetic model with R2 > 0.904. Brominated acetic acids were more activated than chlorinated acetic acids in the reaction with zinc and the activity of HAAs decreased with the number of substituents reduced. While flowing through galvanized pipe, brominated and chlorinated acetic acids except MCAA would decrease to 1% of their initial concentrations in 2.11-6.34 h, and the rates would not be affected obviously by the hydrodynamic or duct conditions. The health risk due to TCAA, DCAA in drinking water tends to be magnified, and that due to TBAA, DBAA tends to be first increased and then decreased, also that due to MBAA tends to be decreased.