Study On The Regularity Of NDMA Formation By Chloramine And Its Toxic Effect On Crucian Carp Seedlings

With people's attention to the quality of drinking water,the water treatment system in China is constantly improving.But found that the existence of disinfection by-products continuously in recent years,not only affect the safety of drinking water also affects human health,including NDMA is a kind of polar compounds,are not easily biodegradable,strong hydrophilicity,difficult to remove by usual methods etc,and the material of production means more,therefore has repeatedly detected in the drinking water of NDMA exist.According to the study,the presence of NDMA in urban drinking water is mainly related to the disinfection system in the water treatment process.Therefore,this topic takes dimethylamine(DMA)as the main precursor,and studies the generation rule of NDMA in the chloramine disinfection system,in order to effectively control the production amount of NDMA in the disinfection system;However,in the natural environment,NDMA concentration will be increased to some extent due to the large amount of sewage discharge and algal blooms.However,the current studies on the toxic effects of NDMA on aquatic organisms are relatively few,and the concentration control of NDMA in the environment has not been paid enough attention to.Therefore,in this experiment,crucian carp seedlings common in fresh water were taken as the subject organism to study the toxic effects of NDMA on aquatic organisms,so as to provide a scientific basis for the development of relevant environmental quality standards in the later stage.In this experiment to choose the commonly used chloramine disinfection system as the research background,by changing the types of disinfectants,reaction time,reaction temperature,the p H of the water amount of additive and its precursor DMA to explore the forming rules of NDMA,by observing the test data,as a disinfectant for chloramine(NH₂Cl),the generation and concentration of NH₂Cl were positively NDMA than,When the disinfectant was dichloramine(NHCl₂),the production of NDMA reached a maximum of 623.7ng/L when the concentration of NHCl₂was 1.5mg/L,and then decreased towards equilibrium.Due to the instability of NHCl₂,NH₂Cl was used as a disinfectant in this study.It was found that the maximum yield of NDMA was obtained when the reaction temperature was 25?,the reaction time was 36h,the p H was 7.0,and the molar ratio of NH2Cl to DMA was about 1.And through the orthogonal test data,the five factors on the production of NDMA ranked as the p H value of water>DMA concentration>reaction time>reaction temperature>NH₂Cl concentration.In the study of the toxic effect of NDMA,crucian carp seedlings were selected as the tested organisms.The results showed that the 24h-LC₅₀,48h-LC₅₀,72h-LC₅₀and 96h-LC₅₀of crucian carp seedlings were 21.96mg/L,15.89mg/L,11.93mg/L and 9.69mg/L,respectively,and the safe mass concentration(SC)was 0.97mg/L.The toxicity accumulation degree coefficient(MAC value)of 24h-48h,48h-72h and 72h-96h were49.47%,32.28%and 18.26%,respectively.It was concluded that crucian carp seedlings had a strong sensitivity to NDMA,but their degradation ability was also strong.NDMA was exposed to four concentrations(1.21mg/L,1.61mg/L,2.42mg/L and4.84mg/L)for 1 day,3 days and 5 days,respectively.NDMA mainly induced the protein content of Carassius auratus seedlings.The activity of superoxide dismutase(SOD)was induced by low concentration group and inhibited by high concentration group.The effect on catalase(CAT)activity was mainly induced,but it was inhibited with the increase of toxin concentration.On the whole,the inhibition rate of NDMA on physiological and biochemical indexes of crucian carp seedlings was as follows:SOD activity>CAT activity>protein content.