Effects Of Routine Water Treatment Technology On Concentrations Of MX And Genetic Toxicity In Drinking Water

3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone (MX), as the most important representative of the family of chlorinated furanones and the new byproduct in chlorine-disinfected drinking water, is mainly produced in process of wood pulp bleaching and chlorinated waters. Though MX occurs in drinking water at the level of ng/L, it has shown extremely strong mutagenicity and can induce genetic damage in variety of mammalian cells. Animal experiments showed that MX not only induced multiple tumors in rats, but also promoted the development of tumor. In view of the MX mutagenicity, carcinogenicity and teratogenicity, The International Agency for Research on Cancer (IARC) has classfied it as possible human carcinogen (group 2B).In the procedure of water chlorination, MX was generated from the reaction of chlorine with the organics (especial humic substance) in source water, which is the main reason for the source of MX. Researches showed that there was direct relation between MX formation and the type and content of the organics, as well as the physics and chemistry factor during routine water treatment technology procedure. So, many researchers focused their attantion on improving water treatment technology to make MX level lower. Up to now, the data about effect of drinking water treatment on formation of MX was limited. More efforts are needed to research how to control the generation of MX and how to protect the human health from the adverse effect of MX.In the first part of our study, we collected water samples from the different treatment steps of drinking water and investigated the correlation between MX formation and chemical indicators including total organic carbon (TOC), pH value and turbidity. Meanwhile we also investigate changes of MX level during drinking water treatment and key steps affecting MX formation.Not only MX but also a large number of chlorination disinfection by-products (CDBPs) were produced in drinking water by using routing water treatment technology. Many researchs indicated that CDBPs enhanced genotoxicity of drinking water. Then, which water treatment steps are responsible for genotoxicity of drinking water? Whether there has correlation between MX level and genotoxicity? In view of such questions, in the second part of our study we used Ames test and single cell gel electrophoresis assay (SCGE) to study genotoxicity of non-volatile organic extracts of water samples collected from routing water treatment steps and to evaluate the relation between MX level and genotoxicity of drinking water. The purpose of the present study is to provide scientific bases for optimization of the routine drinking water treatment technology, for reducing chlorination disinfection by-products, for improving the quality of drinking water and at last achieving the goal of promoting human health.This paper is consisted of two parts:The First Part: Factors influencing MX formation in routine water treatment procedureWater samples including raw water, water from water treatment steps of coagulative precipitation after prechlorination, precipitation, filtration and chlorination disinfection, as well as tap water were collected. After water acidation, TOC, pH and turbidity of water samples were determined by using TOC instrumental analysis, glass electrode method, spectrophotometric method. GC/MS was used to determine MX after water concentration with resin. Our study indicated that, during routing water treatment, levels of MX and TOC were higher in water treated with prechlorination disinfection and lower treated with precipitation than in raw water. After chlorination disinfection, MX and TOC levels increased significantly again. The increase of TOC level after prechlorination and chlorination disinfection was statistic significant. Turbidity showed downtrend with water treatment proceeding and slightly raised only in tap water. There is no change in pH value. MX levels were significantly correlated with TOC levels, but not with pH value and turbidity.The Second Part:The correlation between MX level and genetic toxicityWater sample's collection was the same as mentioned in the first part study. The mutagenicity and DNA damage of organic extracts concentrated from water samples were evaluated by means of the Ames test and SCGE.Ames test was performed as a standard plate incorporation assay with Salmonella typhimurium histidine auxotrophs TA98 and TA100. The tested concentration of water sample was 4L per dish. Dexon (2μg/ml) and sodium azide (NaN3, 15μg/ml) were selected as the positive control reference substances for TA98 and TA100, respectively. Dimethyl sulphoxide (DMSO) was used as solvent control. The results were valued by mutation rate (MR) calculated as revertants per plate / spontaneous revertants per plate. Organic extracts of raw water, water from prechlorination and chlorination disinfection as well as tap water showed the positive mutagenicity for TA98 (+S9) with MR value greater than 2. For TA100 (+S9) only organic extracts of chlorination disinfection water and tap water have MR values greater than 2.The DNA damage was detected by using SCGE. L-02 cells were treated with organic extracts correspondence to 1.2, 6, 30 and 150 ml water / ml culture for 24 hours for analysis of DNA damage. B(a)P (50μmol/L) and DMSO (10 ml/L) were used as positive and solvent control. The results showed that (1) DNA damage was increased at relative high concentrations of water samples (30 and 150 ml/ml culture) from all routine water treatment steps. Their Oliver tail moment (OTM) were statistic significant compared with solvent control (P<0.05). At the water concentration of 6 ml/ml culture, higher OTM was only found in water samples from treatment steps of coagulative precipitation after prechlorination and chlorination disinfection and tap water compared with solvent control (P<0.05). No DNA damage was found at the lowest concentration (1.2 ml/ml culture) of water sample from whole water treatment steps. (2) When concentrations of water sample ranged from 6 - 150ml / ml culture, OTM rose after prechlorination disinfection, descend after precipitation, then rose again after chlorination disinfection. Both MX concentrations and OTM showed the same changes during the process of water treatment. Conclusion: For drinking water treatment technology, chlorination and precipitation were important procedures affecting concentrations of MX and TOC and degree of DNA damage. Water chlorination enhanced MX formation, mutagenic activity and DNA damage in drinking water. Potential health hazard would be increased in peoples who's drinking water contained chlorination disinfection by-products especially MX.