Objective To evaluate the in vitro toxicity of non-volatility organic compounds(NOCs)extracted from Hanjiang water disinfected by different sequential treatments.
Methods Hanjiang water was disinfected using ozone, chlorine dioxide or chlorine as the primary disinfectant followed by chlorine as the secondary disinfectant. HepG2 cells were exposed to NOCs extracts of these different treated water samples corresponding to concentrations of 0.2, 1.0, 5.0, 25.0 and 125.0 mL/mL medium. DNA single-strand breaks, chromosome damage and cell survival rates induced by NOCs were investigated via single cell gel electrophoresis(SCGE), cytokinesis-blocked micronucleus(CBMN)test and MTT test respectively.
Results ① Significant and dose-dependent increase of DNA damage induced by NOCs extracted from before and after chlorination, chlorine dioxide and ozone disinfected drinking water were found both in alkaline and neutral comet assay from the doses of 5.0 to 125.0 mL/mL medium (P < 0.05), especially at high dosages(25.0 and 125.0 mL/mL medium)(P < 0.01). NOCs extracted from water sample of chlorine dioxide group caused most serious DNA damage in alkaline comet assay and that of ozone group caused the lowest damage. Extraction from chlorination group caused DNA damage most serious in neutral comet assay.② NOCs extracted from chlorination, chlorine dioxide and ozone disinfected drinking water caused significant and dose-dependent increase of MN frequencies from the doses of 5.0 to 125.0mL/mL medium(P < 0.05)in HepG2 cells;③ NOCs extracted from chlorination, chlorine dioxide and ozone disinfected drinking water caused a significant and dose-dependent decrease of cell viability from the doses of 25.0 to 125.0 mL/mL medium(P < 0.05)in HepG2 cells;④ There were better correlations among cell survival rates, DNA damage(both alkaline and neutral Comet assay)and chromosome damage, either positive or negative.
Conclusion According to Comet assay and Micronucleus assay, chlorination, chlorine dioxide and ozone could cause DNA breaks, both single-and double-strand, but chlorination caused DNA double-strand breaks most seriously and chlorine dioxide caused DNA single-strand breaks most seriously.
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