Distribution and health risk assessment of N-nitrosodimethylamine in urban drinking water in China

Background  Nitrosamines, especially N-nitrosodimethylamine (NDMA), are highly carcinogenic and frequently detected in drinking water systems in China, indicating potential human health risk through drinking water.

Objective  This study aims to analyze the distribution of NDMA in urban drinking water around China and to evaluate relevant human health risk, thus providing recommendations for drinking water safety standards.

Methods  The database of China National Knowledge Infrastructure was searched using nitrosamines and drinking water as key words in Chinese, and PubMed was searched usingN-nitrosodimethylamine or nitrosodimethylamine or NDMA, drinking water, and China as key words in English for relevant literature published from January 1, 2000 to March 1, 2021. Eligible data were extracted to statistically analyze the spatiotemporal exposure levels of NDMA in raw and finished water serving Chinese cities. According to the health risk assessment model for carcinogens recommended by the United States Environmental Protection Agency (US EPA), the cancer risk via drinking water of NDMA in finished water was evaluated for different age groups and different regions.

Results  A total of 102 studies were retrieved, 21 of which met the inclusion criteria and were finally included. The NDMA concentrations in 347 raw water samples and 276 finished water samples were extracted and studied, with positive rates of 82.4% and 67.0%, levels of not detected (ND)-141 and ND-67.1 ng·L⁻¹, and the 95th quantiles of 51.4 and 32.1 ng·L⁻¹, respectively. The level of NDMA in raw water was higher than that in finished water in cities of East and North China (P<0.05). East China had the highest average concentrations of NDMA in raw and finished water (21.4 and 9.0 ng·L⁻¹ respectively). In East China, the average concentrations of NDMA in raw and finished water from 2018 to 2019 (5.9 and 6.1 ng·L⁻¹ respectively) were significantly lower than those from 2015 to 2017 (28.7 and 16.5 ng·L⁻¹ respectively) (P<0.05). The average concentration of NDMA in rivers, lakes, ponds, and streams as drinking water sources (20.8 ng·L⁻¹) was significantly higher than that in groundwater sources (8.0 ng·L⁻¹) and in reservoir sources (6.5 ng·L⁻¹) (P<0.05). The average concentration of NDMA in finished water with pre-chlorination (9.4 ng·L⁻¹) was higher than that without (6.0 ng·L⁻¹) (P<0.05). The cancer risk of NDMA through drinking water for children over 1 year old in China decreased with older age, and the risk of infants aged 1~<2 years (2.52×10⁻⁴) was 23 times higher than that of adults (1.09×10⁻⁵) (P<0.05).

Conclusion  Raw water pollution is the main source of NDMA in urban drinking water in China, and current water treatment technology can partially remove NDMA. The NDMA level in finished water of East China shows a downward trend in recent two years. The carcinogenic risk of NDMA via drinking water for children is higher than that for adults, and their health risk management needs to be strengthened. The study findings recommend 35 ng·L⁻¹ as the limit of NDMA water quality safety standard in China.