Study On Microbial Transformation Of Nitrosamine Precursors In Actual Water Sources

In recent years,nitrosamine disinfection by-products have received extensive attention due to their strong carcinogenicity.Proteins and amino acids as important nitrogen-containing organic substances in water can produce nitrosamine precursors through microbial metabolism,but the specific route is still unclear.It is of great significance to carry out research on the source of nitrosamine precursors to control the formation of nitrosamines and ensure the safety of water supply.In this paper,an analytical method for the determination of 17 amino acids in water by ultra-high liquid chromatography tandem mass spectrometry(UPLC-MS/MS)was established by exploring the conditions of sample pretreatment and instrumental analysis.The detection limit of the method was 0.2-6.0 nmol/L,and the correlation coefficient(R2)was greater than 0.99.On this basis,the amino acid concentrations in different source water sources were studied.The total concentrations of amino acids in the Yangtze,Hanjiang,Dongjiang and Qiandao Lakes were 1296 nmol/L,1348 nmol/L,885 nmol/L and 55 nmol/L,respectively..The amino acid content of the actual water body is related to the degree of soil erosion,algae,large aquatic plants and zooplankton activities.Proteins,amino acids are closely related to the production of nitrosamine precursors.Nitrosamine precursors are produced during microbial culture in a medium in which beef extract peptone is the sole source of nitrogen.The NDMA precursor is mainly produced in the low concentration medium,and the nitrosamine precursor is mainly a nitrogen-containing organic substance having a non-polar group.A variety of precursors are produced in the high concentration medium,and the precursors are mainly nitrogen-containing organic compounds having positively charged groups.The carbon-nitrogen ratio index under aerobic conditions can better reflect the content of nitrosamine precursors in water,and the effect of biomass on precursors is more significant under anoxic conditions.The experiment of culturing the raw water by using the microorganisms contained in the actual water body found that the anabolic precursor of the microorganisms is also one of the sources of the nitrosamine precursors in the water.Microorganisms use organic substances such as proteins in water to release amino acid organic substances and easily degradable biogenic amines,some of which are nitrosamine precursors.When the nutrients in the water are exhausted,the secondary metabolic reaction of the microorganisms increases,which leads to an increase in the content of the precursors.The final nitrosamine precursor in the water is degraded,leaving a refractory nitrosamine precursor.