Analysis Of The Degradation Characteristics Of Malathion Under UV/H₂O₂ Advanced Oxidation Process

Organophosphorus pesticides（OPPs）are widely used in modern agriculture.However,most of the OPPs applied will remain on the surface of plants or soil.These pesticides may migrate to surface water and groundwater along with surface runoff or infiltration,causing pollution of natural water bodies.The concentration of OPPs in natural water is at the level of micrograms or even nanograms.Since they cannot be effectively removed by conventional drinking water treatment processes,they may pose a certain risk to drinking water safety.In recent years,various UV-based advanced oxidation processes（UV AOP）have extensively studied the degradation of OPPs.Traditionally,it is believed that OPPs can be mineralized into water and carbon dioxide by UV AOP,and at the same time complete detoxification.However,mineralization is difficult to achieve in actual operation,and the relationship between mineralization and detoxification is not clear.This study analyzed the feasibility of UV AOP（UV/H₂O₂）for the mineralization of common OPPs malathion and assessed the biological toxicity during the process of malathion mineralization.This research has achieved the following results:（1）Developed a new method to assess the biological toxicity of OPPs in water.The detection limit of traditional Ellman colorimetry is too high to detect the biological toxicity of trace OPPs.This method is improved and optimized on the basis of the traditional Ellman colorimetric method,and a more sensitive and efficient biological toxicity detection method has been developed using ultra-high performance liquid chromatography tandem triple quadrupole mass spectrometry.This method uses acetylcholine（ACh）as the substrate of acetylcholinesterase（ACh E）to quickly inactivate the ACh E in the reaction by adjusting the p H.The BEH shield RP18 column is used to separate the ACh in the sample,which can accurately detect the content of ACh.The rate of change was calculated to calculate the ACh E inhibitory effect of trace OPPs.（2）Analyzed the feasibility of UV/H₂O₂on malathion mineralization and assessed the biological toxicity during malathion mineralization.The initial biological toxicity of5mg/L malathion aqueous solution was 28.4%.After UV/H₂O₂treatment,98.7%of malathion was degraded at 15 minutes,and it was mainly converted to the intermediate product malaoxon.At this time,the concentration of malaoxon in the solution was 1.26mg/L,and the toxicity of the solution increased to 94.7%,the salinity is 0;malathion’s main product malaoxon is completely degraded in 2h,at this time the UV radiation is4176 m J/cm2,the toxicity of the aqueous solution is reduced to 2.49%,and the salinity is 1%;continue to UV light,The products of malaoxon,malic acid,diethyl malate and diethyl maleate are completely degraded at 180 min.At this time,the UV radiation is6264 m J/cm2,the aqueous solution toxicity is 0%,and the salinity is 14.15%.The1mg/L standard solution of malaoxon was treated with UV/H₂O₂and found that the initial toxicity of the solution was 98.8%.As the reaction progresses,the amount of malaoxon gradually decreases,and the toxicity of the solution also decreases.When the reaction progressed to 90 minutes,the amount of malaoxon was 0.01 mg/L,and the solution toxicity was 52.9%;when the reaction was 120 minutes,the amount of malaoxon was 0,and the solution toxicity was 1.4%.The results show that UV/H₂O₂can quickly degrade malathion,but it cannot achieve mineralization and consumes a lot of energy;the degree of malathion mineralization has nothing to do with the degree of detoxification;the sharp increase in toxicity of malathion aqueous solution during UV/H₂O₂treatment is mainly derived from malaoxon;the content of malaoxon can be used to characterize the detoxification of the malathion aqueous solution treated with UV/H₂O₂.