| Drinking water chlorine disinfection can kill water environmental pathogenic microorganisms and ensure the safety of drinking water.However,the potential toxicity of chlorination induced disinfection by-products(DBPs),such as trihalomethanes(THMs),haloacetic acids(HAAs),haloacetonitriles(HANs)and mutagenic compounds(MX)and their precursors has become a key problem threatening the safety of drinking water.Generally,natural organic matter is the main source of DBPs precursors for drinking water,while algal organic matter caused by water pollution is the main source of DBPs precursors in the Pearl River Delta region.In addition,along with natural and human factors such as typhoons,heavy rains and dredging of ports,the organic matter adsorbed in the sediment can resuspend into the water,becoming another important source of DBPs precursors.Algal and sediment organic matter during chlorination can generate toxic DBPs such as THMs,HAAs and HANs,etc.Long-term exposure to DBPs may induce cancer.Furthermore,as a precursor of DBPs,polycyclic aromatic hydrocarbons(PAHs)can increase the risk of cardiovascular disease and threaten human health.The DBP characteristics of chlorinated organic matters in the Pearl River Delta and their toxicity mechanism with PAHs are not completely clear until now.Therefore,it is necessary to systematically study the chlorinated algae and sediment organic matter in the water of the Pearl River Delta.Aiming at these problems,the study mainly includes the following five aspects of research:(1)The study of DBP characteristics of chlorinated algal organic matter in the Pearl River Delta regionThe contents of THM(trichloromethane(TCM)),HAAs(dichloroacetic acid(DCAA)and trichloroacetic acid(TCAA)),HANs(dichloroacetonitrile(DCAN)and trichloroacetonitrile(TCAN)),PAHs and chlorinated PAHs of algal organic matter(Chlorella sp.)during chlorination were analysized by gas chromatography,respectively.Compared with DBPs data from report related to chlorinated sediment organic matter,we found that chlorinated algal organic matter can produce DCAN and TCAN,but chlorinated sediment organic matter only generate DCAN in the Pearl River Delta region,suggesting that algal organic matter may be the main source of TCAN precursor in the Pearl River Delta drinking water.In addition,TCM was detected in reported sediment organic matter with or without chlorination,while TCM was not found in algal organic matter and a relatively low content of TCM was detected during chlorination.These results indicate that although TCM can be produced by chlorinated algal organic matter,however,polluted sediment is the main precursor contributor.Moreover,PAHs and chlorinated PAHs in algal organic matter are not detected before and after chlorination,indicating that algal organic matter is not the precursor of chlorinated PAHs and source of PAHs in chlorinated water.This is of great significance to the management of drinking water sources and the optimization of drinking water treatment processes in the Pearl River Delta region.(2)Toxicity characteristics of algal and sediment organic matter after chlorination in the Pearl River Delta regionThe toxic effects of algal and sediment organic matter on Caco-2 cells before and after chlorination were analyzed by SOS chromotest and comet array,respectively.The results demonstrate that the genotoxicity and DNA damage induced by algal and sediment organic matter significantly increased after chlorination.Compared with their precursors,chlorinated DBPs are more toxic.Sediment organic matter induced serious DNA damage after chlorination compared to sediment organic matter,suggesting that DCAN may be an important factor.Furthermore,chlorinated algal organic matter induced higher SOS IP than unchlorinated one,suggesting that DCAA and TCAN may be important contributors.These results lay the foundation for the in-depth toxicity study of chlorinated organic matter in the Pearl River Delta region.(3)The effects of algal and sediment organic matter on the gene expression profile of Caco-2 cells with or without chlorinationMany kinds of DBPs can be produced by algal and sediment organic matter during chlorination,and traditional detection methods are difficult to fully understand their toxic effects.Based on genome-wide expression profile,transcriptomics can comprehensively analyze the toxic effects of algal and sediment organic matter and their chlorinated DBPs.Our study found that sediment organic matter changed Caco-2 cell gene expression,which involved in a set of biological procceses such as cell signal transduction and signal regulation.However,these biological processes were completely inhibited during chlorination,with the emerging of two biological processes including antigen processing and presentation appeared,suggesting that the overall effects of chlorinated sediment organic matter on Caco-2 cells may be reduced although it showed strong toxicity in a single end-point detection.For algal organic matter,the differentially expressed genes(DEGs)in Caco-2 cells induced by algal organic matter enriched on immune response.However,most of those DEGs were reversed and a set of specific DEGs appeared after chlorinaton,focusing on a variety of transcriptional regulation related biological processes,which suggests that DBPs mixture produced by chlorinated algal organic matter increased the toxicity of Caco-2 cells.Transcriptome analysis is helpful to understand the toxicity of algal and sediment organic matter before and after chlorination,providing a broader reference mechanism for the toxicity evaluation of chlorinated DBPs.(4)CYP1A1 and CYP1B1 are potential biomarkers of algal organic matter deriverd DBPsThe detection of chlorinated DBPs of precursor in the Pearl River Delta region is still difficult due to the lack of target indicator(s).Based on the transcriptome data of algal and sediment organic matter,we predicted the upstream regulators of the DEGs induced by algal organic matter with or without chlorination through bioinformatics analysis.It was found that two DEGs,CYP1A1 and CYP1B1 were the common targets of a large number of upstream regulators,and this result was not obtained in chlorinated sediment organic matter.Through qPCR experiment and data integration from DBPs and/or environmental stressors related reports,we found that chlorinated algal organic matter specifically up-regulated the expression of CYP1A1 and CYP1B1.Our study suggests that CYP1A1 and CYP1B1 may serve as potential biomarkers for algal organic matter derived DBPs,which will help for detecting the toxicity of DBPs in disinfected water and further monitor the safety of drinking water in the Pearl River Delta region.(5)Research the toxicity and mechanism of PAH,a precursor of DBPs,and its metabolite on human embryonic stem cell-derived cardiomyocyte(hESC-CMs)Based on hESC-CMs,the toxic effects of benzo[a]pyrene(B[a]P),a precursor of DBPs,and 1-hydroxypyrene,a metabolic marker of PAHs,on cardiomyocytes were studied.It was found that B[a]P and 1-hydroxypyrene didn't effect the activity of hESC-CMs,but increase ROS pruduce and induce DNA damage.Moreover,B[a]P also promote the over-expression of mitochondria related pro-apoptotic gene.These results suggest that oxidative stress and DNA damage are key incidents for the injury of hESC-CMs induced by B[a]P and 1-hydroxy,which to some extent reveals the mechanism of DBPs precursor PAHs and their metabolites leading to cardiac dysfunction. |
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