Source: Tsinghua News Network

Tsinghua news network, June 19 (Xinhua) on June 17, the research group of Chen Chao, Institute of drinking water safety, School of environment, Tsinghua University, published an online publication entitled "Formation of N-nitrosodimethylamine precursors through the microbiological metabolism of nitrogenous substrates in water" on the authoritative journal water research in the field of environment and municipal administration, It is the first time to propose and verify the new mechanism of microbial metabolism of nitrogen-containing substances to produce nitrosamine precursors in the world.

N-nitrosodimethylamine (NDMA) and other nitrosamines are a new type of disinfection by-products, which are produced by the reaction of the precursor of nitrosamine with disinfectant. In 1989, NDMA was first detected in drinking water in Ontario, Canada, and has become one of the hot spots in international research on disinfection by-products of drinking water, sewage and reclaimed water. In 2008, the World Health Organization (who) proposed the guideline value of NDMA for drinking water (100 ng / L). Ontario, California, Canada, Australia and other developed countries and regions have also established corresponding water quality standards. In recent two years, China's Shanghai and Shenzhen took the lead in listing NDMA into the local drinking water health standards, with the standard limit of 100ng / L.

Identification of the source of nitrosamine precursors is an important basis for controlling the formation of nitrosamines in water. Over the past 30 years, researchers have identified dozens of precursors of nitrosamines, including secondary amines, drugs, pesticides, personal care products, etc., but the concentration of these ingredients in water is very low, and the contribution rate is very small. The main source of nitrosamine precursors in water has been an unsolved puzzle in the field of disinfection by-products in the world.

Chen Chao's research group has focused on the research of nitrosamines for more than ten years, and has carried out a lot of research on the status quo, sources and control technologies of nitrosamines in water in China. In 2013, associate researcher Chen Chao put forward the hypothesis for the first time that microorganisms metabolize amino acids and proteins in water to produce precursor nitrosamines. The mechanism has been verified by field testing, laboratory simulation and flux estimation for nearly seven years. The research process is summarized in this paper.

The basic process of nitrosamine precursors produced by microorganisms metabolizing nitrogen-containing substances in water

Firstly, the research group found that the total amount of nitrosamine precursors increased first and then decreased when the samples were not sterilized, indicating the possibility of microbial metabolism to produce nitrosamine precursors; the results of classification and analysis of organic substances in water samples showed that the change trend of amino acid concentration was similar to the total amount of nitrosamine precursors. Subsequently, the research group used amino acid, ammonia nitrogen and peptone as the only nitrogen source, and non-specific inoculation of microorganisms for aerobic or anaerobic culture, also found that there were similar rules. The molar conversion rate of NDMA precursor was between 60 and 200 parts per million for 6 amino acids, and 350 parts per million for peptone. The research group also conducted a preliminary analysis on the precursors of nitrosamines produced by microbial metabolism, and found that extracellular secretion with molecular weight less than 1000 was the main source of nitrosamine precursor, followed by extracellular secretion with molecular weight greater than 10k and intracellular components. Dimethylamine, the known precursor of NDMA, was also detected, but its contribution rate was very low. According to the results of the total amount of precursor nitrosamines in source water and the literature data of amino acid concentration in water, it is estimated that the microbial metabolic mechanism of nitrogen-containing organic matter can contribute up to 38% of the precursor of nitrosamine in source water.

Chen Chao, an associate researcher of the school of environment, is the corresponding author of the paper, and bell, a doctoral student, is the first author. This research is supported by the National Natural Science Foundation of China, the independent research program of Tsinghua University, the basic research program of Shenzhen City and the free exploration project of State Key Joint Laboratory of environmental simulation and pollution control. The related research work of the research group provides technical support for relevant ministries and commissions and some cities to improve the quality of drinking water.

Paper links: https://doi.org/10.1016/j.watres.2020.116055

Contribution: School of environment, Tsinghua University

Editor: Li Huashan

Reviewed by: Cheng Xi

Source: https://news.tsinghua.edu.cn/info/1007/79983.htm

Disclaimer: This article is translated by cpolymer. The translation is for reference only. All contents are subject to the original text.