Genotoxicity and effects of nanosilver contamination in drinking water disinfection

This study was conducted to examine the genotoxicity and the influence of silver nanoparticles (AgNPs) contamination when drinking water is exposed to five different disinfection treatments: chlorine, chlorine dioxide, ozone, ozone/chlorine and ozone/chlorine dioxide. Experiments were conducted with water samples of different chemical composition, from three water supply systems in Croatia. AgNPs are of interest because of their use as an antimicrobial in numerous commercial products, and as a drinking water disinfection agent. To examine possible effects of AgNP contamination, the disinfection treatments were repeated with AgNPs in the water samples. AgNP contamination generally caused a decrease in the level of trihalomethanes by up to 59%. Influence of AgNPs on bromide ion incorporation into disinfection by-products (DBPs) was also examined. The most obvious example was the Osi water where ozonation step prior to chlorination increased the bromine incorporation factor from 0.156 to 0.339, while addition of AgNPs limited the increase to 0.249. Also, AgNP presence in almost all disinfection treatments increased dicarbonyl disinfection by-products. All treated waters were tested for genotoxicity using the comet assay and showed similar genotoxic potential. The results are preliminary, but could provide a basis for further studies evaluating the environmental impact of AgNPs in natural aquatic systems.