In Vitro Toxicity And Potential Toxicological Mechanisms Caused By Non-Volatility Organic Compounds Extracted From Surface Water Treated With Different Disinfect Methods

Disinfection of drinking water guarantees an effective protection of humans against pathogens. Chlorination (Cl2) is the most commonly used method of disinfecting drinking water. The economy and effectiveness of chlorine in killing waterborne organisms has made water chlorination a tremendous public health success worldwide. However, chlorination of water can produce trace amounts of carcinogenic and mutagenic by-products, including trihalomethanes (THMs) and halogenated hydrocarbon byproducts (HHBPs) which are potentially harmful to human health. In order to reduce the potential health impact of chlorinated by-products, alternative disinfect methods are under studying. In some cases, chlorine is used as a secondary disinfectant following primary treatment with an alternative disinfection method, particularly for ozone and chlorine dioxide. Using chlorine dioxide (ClO2) and ozone as primary disinfect methods has provided good results and much less formation of the harmful organic by-products. Chlorine dioxide and ozone have oxidizing effects, which can remove iron and manganese by precipitating their insoluble salts and can decompose compounds responsible for flavour and odour. They are also excellent disinfect methods and are able to inactivate even more resistant pathogenic microorganisms such as protozoa (e.g. Cryptosporidium parvum oocysts). Although alternative disinfect methods had advantages, potential toxicity and problems for public health could also exist in these disinfect methods. So toxicity of these disinfect methods were studied. Therefore, the aim of this study was to compare the mutagenic and cytotoxic effects of NOCs extracted from different disinfected drinking water on human hepatoma cells (HepG2) to confirm the main pattern of DNA breaks damage and find out the better disinfect methods for Hanjiang River. In order to indicate the relatively actual toxically effects of the drinking water of Hanjiang River, MTT test and flow cytometry were used to assume the cell survival rates and apoptosis rates of NOCs, while Micronuclei frequency test (MN), single cell gel electrophoreses (SCGE) were used to evaluate the mutagenic potentials of NOCs. Reactive oxygen species (ROS) and the increase of lipid peroxidation were detected to study the mechanine of toxicity of non-volatility organic compounds extracted from surface water treated with different disinfect methods.The whole study is composed of the following two parts:Partâ… : Oxidative stress level caused by non-volatility organic compounds extracted from surface water treated with different disinfect methods in HepG2 cells.Objective: In this part it was invested that ROS level, MDA, GSH and SOD active induced by NOCs in HepG2 cells. Methods: DMSO was used as solvent control. MDA, GSH and SOD which are the product of lipid peroxidation, the representative of antioxidative molecules and the marker of DNA oxidative damage respectively, were detected in HepG2 cells via fluorescence-activated cell sorting (FACS) and lipid peroxidation detected Fits. Results:â‘ ROS showed significant increased among the NOCs from chlorination, chlorine dioxide and ozone disinfected drinking waters at low concentration (1ml NOCs/ml medium)( P<0.05);â‘¡The content of MDA was significantly increased in HepG2 cells exposed to NOCs at the concentration of 0.2, 1, 5 ml NOCs/ml medium in comparison with solvent control (P<0.05). The level of GSH was significantly decreased in HepG2 cells exposed to NOCs at all concentration in comparison with solvent control (P<0.05). There was a striking a negative association between GSH level and MDA level (r=0.761, P<0.01), SOD level and MDA level in HepG2 cells exposed to NOCs with concentration of 0.2, 1, 5 ml NOCs/ml medium. Conclusion: DNA damage stresses frequently accompany cellular accumulation of reactive oxygen species (ROS), NOCs from three disinfected drinking water could induce oxidative stress in HepG2 cells including increase of ROS, lipid peroxidation and DNA oxidative damage, and decrease of antioxidative molecules. DNA oxidative damage in HepG2 cells might be ascribing to NOCs-induced ROS, lipid peroxidation and the weakening of antioxidation ability.Partâ…¡DNA damage and apoptosis level caused by non-volatility organic compounds extracted from surface water treated with different disinfect methodsObjective: The in vitro toxicity and potential mechanisms of non-volatility organic compounds (NOCs) extracted from surface water of Hanjiang River treated with different disinfect methods were compared in order to find the better surface water disinfect ways. Methods: In this part, DNA single-strand breaks, chromosome damage, cell survival rates, and apoptosis rate induced by NOCs were invest via single cell gel electrophoresis (SCGE), cytokinesis-blocked micronucleus (CBMN) test, MTT test and fluorescence-activated cell sorting (FACS) respectively. Results:â‘ NOCs extracted from chlorination, chlorine dioxide and ozone disinfected drinking waters caused a significant and dose-dependent increase of MN frequencies from 5 to 125ml NOCs/ml medium (P<0.05) in HepG2 cells;â‘¡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 5 to 125ml NOCs/ml medium(P<0.05), especially at high dosages (25 and 125ml NOCs/ml medium) (P<0.01). NOCs extracted from chlorine dioxide cause DNA damage most serious in alkaline comet assay and ozone cause the lowest. The order of increase DNA damage was chlorine dioxide>chlorination>ozone>raw water in alkaline comet assay. Extraction from chlorination causes DNA damage most serious in neutral comet assay. The order of increase DNA damage was chlorination>chlorine dioxide>ozone>raw water in neutral comet assay;â‘¢Combined the results of two comet assay and MN test demonstrated that chlorination, chlorine dioxide and ozone all could cause both DNA single- and double- strand breaks, chlorination mainly caused DNA double-strand breaks, chlorine dioxide mainly caused DNA single strand breaks;â‘£There were dose-dependent increased apoptosis rates in three disinfected drinking water from 5 to 125ml NOCs/ml medium (P<0.05) respectively. Conclusion:â‘ According to Comet assay and Micronucleus assay, chlorination, chlorine dioxide and ozone could cause both DNA single- and double- strand breaks, but chlorination mainly caused DNA double-strand breaks; chlorine dioxide mainly caused DNA single-strand breaks. The toxicity of NOCs extrated from chiorination was higher than chlorine dioxide;â‘¡DNA damage of NOCs extracted from ozone disinfected drinking water was lower than chlorine dioxide and chlorination, the order of causing toxicity of NOCs extracted from surface water treated with different disinfect methods were: chlorination>chlorine dioxide>ozone, ozone was better as a disinfect method for Hanjiang River.