Formation and removal of genotoxic activity during UV/H₂O₂–GAC treatment of drinking water

The objective of this study was to determine the genotoxic activity of water after UV/H₂O₂ oxidation and GAC filtration. Pre-treated surface water from three locations was treated with UV/H₂O₂ with medium pressure (MP) lamps and passed through granulated activated carbon (GAC). Samples taken before and after each treatment step were extracted and concentrated by solid phase extraction (SPE) and analyzed for genotoxicity using the Comet assay with HepG2 cells and the Ames II assay. The Comet assay showed no genotoxic response in any of the samples. In the Ames II, no genotoxic response was obtained with the TAMix (a mix of six strains), but the TA98 strain showed an increase in genotoxic activity after MP-UV/H₂O₂ for all three locations. GAC post treatment effectively reduced the activities to control levels at two of the three locations and to below the level of the pre-treated water at one site. The results indicate that UV/H₂O₂ treatment may lead to the formation of genotoxic by-products, which can be removed by subsequent GAC filtration.