Objective To describe the pollution of nitrosamines(NAs)in the drinking water in the downstream Baiyun Section of Liuxi River and study the health risks and environmental factors.Methods From July 2021 to June 2022,the contents of nine NAs in the raw water of the Liuxi River water source,the finish water,and the pipe network water of the water supply system were monitored for four quarters.The carcinogenic health risk model of the US Environmental Protection Agency(US-EPA)was used to evaluate the cancer risk of NAs exposure in people of different ages through drinking water.The NAs monitoring results were compared with the five environmental factors for redundancy analysis(RDA).Results The detection rate of NAs was 40.83％,and N-dimethylnitrosamine(NDMA)(33.33％)was the highest.The total NAs(∑NAs)concentration ranged from undetected(ND)to 27.63 ng/L,with an average of 5.54 ng/L.The average concentration of ∑NAs was finished water＞pipe network water＞raw water(H=9.12,P＜0.05).In different types of water,NAs were detected in raw water only in summer,and the ∑NAs concentration in finished water in spring was about 1.0 times lower than in other seasons.The average ∑NAs concentration in peripheral water was the highest in summer(6.32 ng/L)and the lowest in winter(4.17 ng/L).Friedman test found that only the seasonal difference of NDEA in peripheral water was statistically significant(x2=8.00,P＜0.05).RDA results show that Nitrate Nitrogen,pH value,and Oxygen Consumption were the main environmental factors,wherein Nitrate Nitrogen was always positively correlated with ∑NAs(α was displayed as an acute angle).In contrast,covariates such as pH value and oxygen consumption showed seasonal differences in the influence of ∑ NAs.pH value was positively correlated with Σ NAs content in autumn and winter,while Oxygen Consumption was conducive to∑ NAs formation in summer.The carcinogenic risk of exposure to NAs in different age groups was infants＞children＞adolescents＞adults;the median cancer risk was 3.36X10-5.Conclusions NAs pollution was positive in the water source and water supply system of Liuxi River.The carcinogenic risk of exposure to Σ NAs through drinking water for infants aged 0 to 2 years exceeded the maximum acceptable level(10-4).In order to control the source of NAs and their precursors,it is necessary to focus on regulating the unreasonable emission of sources of rural living sources,livestock breeding,and farming along the Liuxi River.
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