Genotoxicity testing of surface drinking water from three reservoirs in Sardinia (Italy) subjected to chlorination/chloramination

INTRODUCTION: Sardinia (Italy) is the second-largest island in the Mediterranean Sea, with an area of 24,100 square kilometres. Surface waters collected and regulated in water reservoirs are the main water supplies in this Italian Region. Drinking water disinfection is necessary for prevention of the spread of diseases caused by water borne pathogens; however it has been shown that natural organic substances (e.g. humic and fulvic acids) in surface waters may react with disinfectants to produce volatile and non-volatile disinfection by-products (DBPs) that are potentially harmful to human and aquatic organisms. In particular, it has been demonstrated that chlorination, the most widely used method for water disinfection, leads to the formation of DBPs with mutagenic and/or carcinogenic activity. Water treatment processes used to produce safe drinking water generate heterogeneous mixtures of DBPs, depending on the contaminants in the untreated (raw) source water and chemicals used for water purification. Pretreatment with pre-oxidants is commonly applied in surface waters to improve the removal of dissolved organic matter and thus for controlling the formation of DBPs. AIM OF THE STUDY: In the present study, we evaluated the genotoxic effects of chlorinated drinking water (CDW) processed from raw water (RW) of three reservoirs in North-Sardinia. Drinking water treatment plants (DWTP) used different processes for pre-oxidation/disinfection: (1) Monte Agnese: potassium permanganate/chlorine dioxide, (2) Bidighinzu: potassium permanganate/chlorine dioxide + chloramine, (3) Monte Lerno: chlorine dioxide/chloramine. Three sampling points were considered for each DWTP: (A) raw water, (B) disinfection stage, (C) distribution system (along the pipe-line at least 5 km far from the DWTP). MATERIAL E METHOD: Total organic carbon (TOC), UV absorbance at 254 nm, pH, and residual active chlorine (RAC) were recorded in all water samples. ▪ RW and CDW samples were concentrated through C18 (Sep-Pak Plus tC18 Environmental Cartridges). The eluates were dried and then dissolved in dimethyl sulfoxide (DMSO) to have 3 L of water (Leq) in 50 μl DMSO. ▪ Genotoxicity testing was performed on human hepatoma HepG2 cells using the single-cell microgel-electrophoresis (‘comet’) assay and the micronucleus test. For that, HepG2 cells, sub-cultured in 6-well culture plates, were exposed to 1, 2, and 3 Leq water/well for 4 (comet assay) or 24 (micronucleus test) hours. RESULTS: Chemical parameters evaluated in water samples are shown in Table 1. The analyses showed high concentrations of total organic compounds (TOC) in the water samples (5–11.6 mg/L), whereas UV absorbance (an index of the presence of aromatic compounds) was relatively low. In the comet assay, 10 out of 27 extracts caused a significant increase of DNA strand breakage in HepG2 cells (Figure 3). In particular, the extent of DNA damage was found to be significantly high for all the 3 Leq samples collected at the disinfection stage (treatment plant). Significantly high extent of DNA damage were also observed at the distribution system (pipeline ), with residual genotoxic activity in water from Bidighinzu and Monte Lerno. Genotoxicity was also found in raw water sampled from reservoirs Monte Agnese and Bidighinzu. Notably, very high genotoxic effects were observed for water from Monte Agnese. None of the water extracts significantly increased the frequency of micronuclei (data not shown). These results could help Sardinian health authorities and waterworks managers to improve the quality of distributed drinking water.