Occurrence And Health Risk Assessment Of Dimethylnitrosamine In Drinking Water In Parts Of The Yangtze River Basin,China

Object:1.Preliminary understanding of the distribution characteristics of NDMA in drinking water in parts of the Yangtze River Basin.2.Taking the drinking water treatment plants(DWTPs)as the research unit,analyze the causes and influencing factors of NDMA.3.Conduct a health risk assessment of NDMA.Methods:1.A total of 29 DWTPs were selected in the three provinces along the upstream,middle and lower reaches of the Yangtze River Basin.Investigators used questionnaires and field surveys to obtain basic information about DWTPs,including the basic information of the water plant and the pollution situation around the water source.2.According to the given NDMA sampling method and "Standard examination method for drinking water"(GB/T 5750-2006),samples of water source water,water treatment units,factory water and pipe network end water are collected.NDMA was detected by SPE/GC-MS,and other indicators were detected by the method in " Standard examination method for drinking water "(GB/T 5750-2006).3.Use EpiData3.1 to establish a database,enter the collected water quality data and water supply unit questionnaire into the database.Use ArcGis 10.5 to draw maps and spatial analysis.Use Excel,SPSS24.0 and SAS9.2 to test the water quality data and the basic situation of the DWTPs carry out statistical description and statistical analysis,test level ?=0.05.Uncertainty analysis of health risk assessment of NDMA using Oracle CrystalBall software.Results:1.NDMA was detected in drinking water in parts of the Yangtze River Basin in this study.The pollution degree of NDMA was different in different waters,and the pollution concentration in the upstream was higher.2.Of the 29 DWTPs,NDMA was detected in source water samples,treatment process water samples,finished water samples,and tap water samples,with concentrations ranging from ND to 98.40 ng/L.The median was 9.37 ng/L,the interquartile spacing was 4.12?15.68 ng/L,and the detection frequencie of NDMA was 95.3%.3.The concentration of NDMA in the source water samples ranged from 1.55 to 96.70 ng/L,the median was 14.51 ng/L,the interquartile spacing was 6.04?19.85 ng/L,and the detection rate was 100%.Spatially,the degree of NDMA pollution gradually decreased from upstream to downstream.4.The concentration of NDMA in the finished water samples ranges from ND to 74.40 ng/L,the median was 9.90 ng/L,the interquartile spacing was 5.54?14.99 ng/L,and the detection rate was 94.8%.The NDMA values in all finished water samples did not exceed the WHO"Guidelines for Drinking Water Quality"(100 ng/L).The over-standard rates were 51.7%and 44.8%refer to the regional limit of Canada in Ontario(9 ng/L)and the American Massachusetts and California regional limits(10 ng/L),respectively.Spatially,the degree of NDMA pollution gradually decreased from upstream to downstream.5.The concentration of NDMA in each water treatment unit fluctuated slightly between treatment processes,showing a downward trend.The removal rates of pretreatment measures,filtration measures and advanced treatment measures were 20%-26%,25%-33%,30%-78%,respectively.6.The concentration range of seven other disinfection by-products in finished water samples including chloroform,tribromomethane,monobromodichloromethane,dibromochloro-methane,dichloromethane,chlorite and chlorate,were ND-0.0448 mg/L,ND-9.8800 mg/L,ND-0.0110 mg/L,ND-0.0053 mg/L,ND-0.0078 mg/L,ND-0.6000 mg/L and ND-2.0900 mg/L,respectively.Among them,the over-standard rate of tribromomethane was 16.67%,and chlorate was 16.67%.In space,the concentration of chloroform,tribromomethane and dichloromethane gradually decreased from upstream to downstream,and the concentration of monobromodichloromethane and dibromochloromethane gradually increased from upstream to downstream.7.The relationship between pH value and NDMA in source water was good(R2=0.321).Except for pH,the correlations between NDMA concentration in source water and other typical water quality parameters were weak.8.The concentration of NDMA in the finished water samples were significantly related to chloroform and dichloromethane at the 0.05 level,and were significantly related to tribromomethane and dichloromonobromo-methane at the 0.01 level.9.LASSO regression model:The concentration of NDMA in the finished water sample=1.434077 dry season+0.146765 urban pipe network water plant+7.550449 source water quality class ?+ 1.764057 no mixing pool+1.688239 no grid flocculation facility+3.796930 with mechanical flocculation facility+3.545623 no advection sedimentation facility+5.829542 with gravity valveless filtration facility+1.301881 with liquid chlorine disinfection-0.034224 source water turbidity-0.063643 source water nitrite nitrogen content.R2=0.906,the fitting equation is better.10.The total annual carcinogenic risk value of NDMA in the finished water samples from 1.06×10-5 to 3.87×10-4/year,and the average value was 9.84×10-5/year.The risk value of the highest concentration of NDMA was 2.76×10-5/year through the oral route and 3.59×10-4/year through the skin route,and the total risk value was 3.87×10-4/year.The certainty of the health risk assessment results during oral route exposure was 98.11%,and the sensitivity of each parameter to the assessment results was between 0-38.4%and 0-34.4%,respectively.Among them,weight and drinking rate were the key factors that affect the certainty of the assessment results.Conclusion:1.The drinking water in this study area was contaminated with NDMA to varying degrees and it was generally at an acceptable level,but the NDMA level in some areas was relatively high.2.The NDMA concentration in drinking water is mainly affected by the type of source water quality,water treatment facilities,seasonality and type of disinfectant.3.The carcinogenic risk value of NDMA in the finished water from DWTPs along the Yangtze River has a certain carcinogenic risk value and should be taken seriously.