Study On The Mechanisms Of Typical Pesticides Degradation And Byproducts Formation During Photolysis Of Nitrate

Water environmental problems have been widely concerned by human society.Pesticide and nitrate have always coexisted in agricultural runoff with the increasing use of pesticides and nitrogen fertilizer.With widely distributed,high toxic and difficult to degrade,it becoming a stubborn disease of water treatment,threatening the water environment and the safety of drinking water.The current research mostly focuses on the removal of pesticides or nitrate alone,without considering the conversion mechanism under the combined pollution of the pesticides and nitrate.Due to the photosensitive of nitrate It can generate a variety of active ingredients including hydroxyl radicals and nitrogen-containing free radicals after exposure to light,which achieve the purpose of degrading organic pesticides.Therefore,this paper conducted a systematic study of the degradation mechanism of organic pollutants in nitrate photolysis system and the generation mechanism of harmful by-products.This paper first investigated the degradation efficiency and mechanism of Atrazine（ATZ）under different UV wavelengths（255 nm,285 nm,365 nm）due to the difference in molar absorptivity of nitrate at different ultraviolet wavelengths.We found out that the degradation rate of ATZ is 285 nm,255 nm,and 365 nm in order from fast to slow and the corresponding calculated reaction rate constans are 0.0158min^-1、0.0008 min^-1和0.0005 min^-1,which confirms that the degradation of ATZ in this system mainly depends on the effects of ultraviolet radiation,active nitrogen free radicals and hydroxyl free radicals.The probe method was used to measure the contribution rate of the three above in the ultraviolet/nitrate（UV/NO₃^-）system to the degradation of ATZ,and it was found that the UV₂₈₅/NO₃^-system mainly depended on RNS（84.9%）,while the UV₂₅₅/NO₃^-system was mainly based on·OH（55.8%）.And the influence of natural organic matter and bicarbonate on the degradation of ATZ in the UV/NO₃^-was investigated.The results show that the UV₂₈₅/NO₃^-system is less affected by water matrix than the UV₂₅₅/NO₃^-system,which indirectly proved that the selectivity of RNS is relatively stronger than·OH The degradation products of ATZ（DEA,DIA,OEIT,OAIT,AIT）in the UV/NO₃^-system were detected by liquid chromatography-triple quadrupole mass spectrometer,and the possible degradation pathways were proposed.Vibrio fischeri was used to monitor the changes in toxicity of the system during the degradation of ATZ.In addition,the transformation mechanism of nitrate and diuron under solar-light was investigated.Similar to the UV/NO₃^-system,the solar-light//NO₃^-system can also generate a large amount of RNS and·OH.Electron paramagnetic resonance（EPR）was the first time used to qualitatively detected the·OH and NO·in this system and directly confirmed the generation of RNS and·OH with high proportion.Furthermore,in this part the study explores the nitrate concentration,dissolved oxygen,p H,bicarbonate,and natural organic matter on the degradation of Diuron was investigated.It was found out that the higher the concentration of nitrate and dissolved oxygen,the lower the concentration of bicarbonate and natural organic matter,the higher degradation efficiency of Diuron in the solar-light/NO₃^-system is achieved.And the p H affected the degradation of diuron by affecting the distribution of HONOO and ONOO^-in the system.At p H of 7,the removal efficiency was up to 82%.The degradation products（TP1-TP6）of Diuron in the solar-light/NO₃^-system were detected by liquid chromatography-triple quadrupole mass spectrometer.Diuron in water.However,with the DMA structure.In this part we further research the potential risk of the by-products（nitrite and NDMA）formed in solar-light/nitrate system during the degradation of Diuron.The study found that under different conditions,the generation trends of nitrite and NDMA were basically the same,confirming that nitrite is an important precursor for the formation of NDMA.Finally,Vibrio fischeri was used to monitor the acute toxicity changes during the reaction system.The nitrate photolysis system proposed in this paper provides a new method for the remediation of polluted water bodies with nitrate and organic pesticide contaminated water bodies.At the same time,the potential risks of the conversion of nitrate and Diuron to nitrite and NDMA under solar-light exposure were evaluated,providing new insights for analyzing the risks of the system.