[Occurrence and Risk Assessment of N-nitrosamines and Their Precursors in Qingjiang River Basin]

N-nitrosamines are a type of nitrogen-containing organic pollutant with high carcinogenicity and mutagenicity. In the main drinking water sources of small and medium-sized towns in China, the contamination levels of N-nitrosamines remain unclear. In addition, there is still lack of research on the concentration of N-nitrosamines and their precursors in tributary rivers. In this study, eight N-nitrosamines and their formation potentials （FPs） were investigated in the Qingjiang River, which is a primary tributary of the Yangtze River. The sewage discharge sites were also monitored, and the environmental influencing factors, carcinogenic and ecological risks caused by N-nitrosamines, and their precursors were evaluated. The results showed that six N-nitrosamines were detected in water samples of the Qingjiang River, among which NDMA [（10 ±15） ng·L^-1], NDEA [（9.3 ±9.3） ng·L^-1], and NDBA [（14 ±7.8） ng·L^-1] were the dominant N-nitrosamines, whereas seven N-nitrosamines were detected in chloraminated water samples, among which NDMA-FP [（46 ±21） ng·L^-1], NDEA-FP [（26 ±8.3） ng·L^-1], and NDBA-FP [（22 ±13） ng·L^-1] were the dominant N-nitrosamine FPs. The concentrations of N-nitrosamines in the middle reaches of the Qingjiang River were higher than those in the upper and lower reaches. Furthermore, the concentrations of N-nitrosamines in the sample sites of sewage discharge and tributaries were significantly higher than those in other sampling sites. The monitoring results at the direct sewage discharge points indicated that the main source of N-nitrosamines in river water was the sewage carrying N-nitrosamines and their precursors. In addition, the concentrations of the three dominant N-nitrosamines including NDMA, NDBA, and NDEA were positively correlated with each other, mainly because of their similar sewage sources. The average carcinogenic risk to residents due to N-nitrosamine in drinking water sources was 2.4×10^-5, indicating a potential carcinogenic risk. Moreover, due to the high concentrations of N-nitrosamine formation potentials in the Qingjiang River, the carcinogenic risk of drinking water may be even higher. The ecological risk assessment showed that the ecological risk quotient values of N-nitrosamines in the Qingjiang River watershed were lower than 0.002, which was negligible.