| In recent years,drinking water pollution incidents have been frequently reported.Previous studies have shown that the chemical high-risk pollutants(HRPs)represented by heavy metals and toxic organics and biological HRPs represented by pathogenic bacteria in water may pose serious threats to human health.Water qualities of major partial water sources in Yangtze River,the main drinking water source of Nanjing,have high frequency of not meeting the class ? water quality standard required by China goverment.Although previous studies have been conducted to evaluate the health risk induced by the HRPs in the drinking water of Nanjing City,some important scientific problems still exist and need to be solved,such as the characteristics of health risk induced by the chemical and biological HRPs in drinking water of Nanjing City,and the risk reduction performance of different drinking water treatment processes.Based on the above research background,this study chose the Yangtze River at Nanjing section as the representative region to systematically studied the health risks and their spatial distribution characteristics of source water and drinking water by applying health risk assessment models,biological omics methods,high-throughput sequencing technologies and metagenomics methods;investigated the potential risks of source water and drinking water in Nanjing City;revealed the succession of pathogen bacteria in driking water along conventional water treatment system and distribution pipelines.The main results are summarized as follows:(1)Literature research indicated a high health risk in the lower reaches of the Yangtze River(Nanjing section).Based on the chemical detection of 22 semi-volatile organic compounds(S VOCs)and 24 metal elements in source water and drinking water sampled from a drinking water treatment plant in Nanjing City for three years,this study characterized the reduction of health risk of SVOCs and metal elements by the conventional water treatment processes(coagulation/sedimentation,sand filtration and chlorine disinfection).Total HI of SVOCs in source water and drinking water was 1.08×10-3 and 1.56×10-3,respectively,indicating that traditional treatment processes could not effectively reduce the non-carcinogenic risk.The carcinogenic risk in source water was higher than that of drinking water,but the risk index of drinking water was still over 1.00×10-6.In addition,to effectively reduce the health risks,aerobic biofilters with different backwashing strategies were operated and the reduction ratio of health risks was investigated.Results showed that the biofilter could significantly reduce carcinogenic and non-carcinogenic risks in drinking water.Biofilter backwashing with both air and water under appropriate intensity could increase the ability of reducing the human health risk of drinking water.(2)After exposure with Yangtze River source water and drinking water for 90 days,mice showed no significant changes in body weight and tissue damages in both liver and kidney.However,source water and drinking water caused reproductive toxicity in mice.DNA microarray revealed 5,042 and 828 differentially expressed genes(DEGs)in the liver of the mice fed with source water and drinking water,respectively,indicating that source water posed greater influence on hepatic transcriptome than drinking water.Bioinforamtics analyses showed that the DEGs in source water group were mostly involved in lipid metabolism,followed by neurodegenerative diseases,energy metabolism and endocrine system.Exposure to drinking water mainly affected lipid metabolism,xenobiotics biodegradation and metabolism,and cofactors and vitamins metabolism.Exposure to either source water or source water influenced the lipid metabolism,including fatty acid metabolism,glycerophospholipid metabolism,unsaturated fatty acid biosynthesis,steroid biosynthesis,primary bile acid biosynthesis and steroid hormone biosynthesis,indicating the potential health hazard on lipid metabolism arising from the trace-leve contamination of drinking water.(3)High-throughput sequencing of 16S rRNA gene amplicons revealed the presence of 50 species within 34 genera of potential pathogens in the Yangtze River.Comamonas was the main potential pathogenic bacteria in the upstream of the river,while Mycobacterium and Arcobacter were the main pathogens in the downstream of the river.Sewage treatment plants and the river branches played vital roles in the prevalence of potential pathogenic bacteria.Futhermore,establishment and optimization of bacteria pathogen database and high-throughput sequencing data analysis were conducted to characterize the diversity and abundance of potential pathogenic bacteria in drinking water treatment and pipeline distribution syestems.A total 40 species of putative pathogens were found to be present in the drinking water,among which Mycobacterium smegmatis had the highest abundance.Chlorination significantly increased the relative abundance of Acinetobacter by 3.48 fold,while the relative abundance of Acinetobacter gradually decreased from 1.30%to 0.15%along the drinking water distribution pipelines,revealing the obvious effects of chlorination disinfection and pipeline distribution on the diversity and abundance of potential pathogens in drinking water.In summary,this study indicated that the chemical HRPs in souce water and drinking water of Nanjing City could induce potential human health risk,and hepatic lipid metabolism disturbance might be the crucial damages induced by the drinking water.This study also characterized the health risk reduction and transcriptomic toxicity alteration after drinking water treatment processes,and revealed that bacterial community shift of different pathogens along the drinking water treatment systems and transportation piplines.This study provided a theoretical basis and data support for assessment of the potential health risks of drinking water in Nanjing City and characterization of the reduction of the potential risks by different treatment processes. |
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