Health risk assessment of N-nitrosodimethylamine in drinking water in Nanjing, Jiangsu Province

Background N-nitrosodimethylamine (NDMA), a new disinfection by-product in drinking water, has attracted extensive attention due to its high detection rate and concentration.

Objective To investigate the concentration of NDMA in drinking water in Nanjing situated in the lower Yangtze River Basin of China, and to evaluate associated human health risk.

Methods In dry period (January–March) and wet period (July–September) of 2021, raw water, finished water, and tap water from 16 centralized water treatment plants in Nanjing were collected to detect the concentration of NDMA in water samples by solid phase extraction and gas chromatography-triple quadrupole mass spectrometry with programmable temperature vaporizer-based large volume injection. The concentrations of NDMA in water samples of different water types, water periods, and disinfection methods were analyzed, and the daily exposure levels and carcinogenic risk values of NDMA in drinking water of different exposure routes and different exposed populations were calculated. Monte Carlo simulation was implemented with Crystal Ball 11 software to establish a health risk assessment model and conduct sensitivity analysis.

Results A total of 61 drinking water samples were collected in Nanjing, and NDMA was positive in all the water samples, with concentrations ranging from 1.36 to 25.65 ng·L⁻¹ and an overall average concentration of (8.00±4.06) ng·L⁻¹. There were no statistically significant differences in the average concentrations of NDMA among raw water, finished water, and tap water samples (F=2.875, P=0.064), between wet season and dry season (t=−0.855, P=0.397), or among different disinfection methods by liquid chlorine, sodium hypochlorite, and chlorine dioxide (F=0.977, P=0.385). The results of health risk assessment showed that the average carcinogenic risk of NDMA and its P₉₅ were 5.95×10⁻⁶ and 1.12×10⁻⁵ respectively for oral intake of drinking water, and the values for dermal contact were both lower than 1.00×10⁻⁶. The mean carcinogenic risks of exposure to drinking water NDMA in children, adolescents, and adults were 1.84×10⁻⁶, 8.27×10⁻⁷, and 3.28×10⁻⁶, respectively. The results of sensitivity analysis showed that the contributions of daily drinking water volume and NDMA concentration in drinking water to the calculated health risk were high, and the contribution of body weight was negative.

Conclusion There is a potential carcinogenic risk of NDMA in the drinking water of Nanjing section of the lower Yangtze River Basin, but it is within the acceptable range.