SOE, Tsinghua, March 24th, 2021 On March 22, 2021, Chen Chao's team at the Institute of Drinking Water Safety, School of Environment, Tsinghua University, published a paper entitled "Quantitative Analysis of Source and Fate of N-nitrosamines and Their Precursors in an Urban Water System in East China” in the Journal of Hazardous Materials online, an authoritative journal in the field of environment and municipalities. The paper is the first quantitative source analysis of N-nitrosamines and their precursors in the level of urban water system across the world.
N-nitrosamines are a category of strong carcinogens, which are commonly found in many kinds of food, medicine, tobacco, and industrial wastewater. In 1989, nitrosamines were first detected in drinking water in Ontario, Canada, and were identified as a new kind of disinfection by-products due to the reaction of nitrosamine precursors with chloramines and other disinfectants in the water. Ontario of Canada, California as well as Massachusetts of the United States and other developed regions took the lead to regulate N-nitrosodimethylamine (NDMA) and other nitrosamines in drinking water. In 2008, the World Health Organization established a guideline on NDMA in drinking water (100 ng/L). Canada, Australia, the Netherlands and other developed countries and regions have also established the corresponding water quality standards for nitrosamines. In recent years, Shanghai, Shenzhen, Zhangjiakou, etc. in China included NDMA in the local drinking water quality standards, and the limit is 100 ng/L.
Chen Chao, Associate Professor of the Drinking Water Safety Team at Tsinghua University's School of Environment, has focused on nitrosamine research for more than 10 years. He has conducted a lot of investigations on the occurrence of nitrosamines in drinking water, sources tracking of precursors and treatment technologies in China. In recent years, their sampling campaigns have revealed that many cities in China have both nitrosamine precursors and already formed nitrosamines in their water sources, greatly increasing the complexity and urgency of the research.
The team chose one city in East China as the research object, and set up more than 50 representative river network sampling points, more than 30 sampling points of wastewater and 2 water source points in this city. Based on the water quality test results and data of runoff and discharge flow, the loadings of nitrosamines and their precursors in sources and sinks were calculated for each runoff of this river network. Meanwhile, the natural attenuation mechanisms of nitrosamines, such as photolysis and biodegradation in natural water bodies were calculated hour by hour. In addition, the endogenous formation of nitrosamine precursors in urban water systems and water sources was estimated based on the new mechanism of nitrosamines precursors generated by microbial metabolism of amino acids proposed by the team. The results of the above runoff mechanism, natural attenuation mechanism and endogenous generation mechanism were aggregated to finally obtain the material flow of N-nitrosamines and precursors in this urban water system, and to quantify the source analysis.
The results show that upstream surface water contributed 13±4% of NDMA and 21±3% of NDMA precursors to a water source located downstream of the investigated city; domestic and industrial wastewater discharges from the city contributed 30±8% of NDMA and 17±2% of NDMA precursors to the downstream source water. The endogenous formation of the water source itself contributed up to 36% of NDMA precursors. Thus, upstream surface water inflow and local wastewater discharge are important sources of NDMA in downstream water sources; upstream surface water inflow, local wastewater discharge and endogenous formation in water sources are important sources of NDMA precursors. Natural attenuation mechanism only removes part of the pollutant load from runoff mechanism. The paper suggests that attention should be paid not only to the generation of nitrosamines as the emerging disinfection by-products within the water supply system, but also to the discharge of nitrosamines as the emerging pollutants to aquatic environment. The research helps the comprehensive and systematic understanding of the sources of N-nitrosamine in drinking water and the development of the targeted control strategies.
Associate researcher Chen Chao of the School of Environment is the corresponding author of the paper, and PhD candidate Qiu Yu is the first author. This study was supported by the National Natural Science Foundation of China, National Water Special Project, Tsinghua University Independent Research Program, Shenzhen Basic Research Program and the Free Exploration Project of National Key Joint Laboratory of Environmental Modeling and Pollution Control and others. The research has provided technical support for relevant ministries and cities to cope with the risk of N-nitrosamines and improve drinking water quality.
Link to the paper: https://doi.org/10.1016/j.jhazmat.2021.125700
