Degradation Of IMD And THIA In Water Via UV/Chlorine Process

Neonicotinoid insecticides?NIs?have resulted in contamination in global waterenvironment due to their suitable water solubility,environmental persistence and widespreaduse.Previous studies showed that neonicotinoids are recalcitrantconstituents,with insignificant removal during conventional water treatment and neonicotinoid insecticides are frequently detected in sewage,surface water,groundwater,and even chlorine-sterilized tap water.In addition,the adverse effects of neonicotinoids on ecosystems have been reported frequently.Thus,it is of great significance to find an economical and effective technique for removing IMD and THIA from water.The UV/chlorine process,is considered as an alternative advanced oxidation process,has been demonstrated to be efficient for the degradation of micropollutants including herbicides,drugs,personal care productsand DBPs.Meanwhile,UV/chlorineis widely used in drinking water treatment and waste water treatment.In this study,the degradation oftwo typical neonicotinoid insecticides?IMD and THIA?by UV/chlorine was investigatedfor the evaluation of process kinetics,transformation mechanism and toxicity.The details are summarized as follows:?1?The kinetics and influence factors of IMD and THIA degradation via UV/chlorine was investigated:the UV/chlorine process performed synergistic effects on the degradation of IMD and THIA,which deriving from the direct photolysis and reactive radicals-assisted indirect photolysis.Radical scavenging experiments indicated that ClO·and Cl₂^·-played an important role on IMD and THIA degradation,respectively.It is newly found that the existence of Cl^-significantly promoted THIA degradationduring UV/chlorine process,attributed to the formation of Cl₂^·-.The effects of pH,fulvic acid?FA?,and bicarbonate?HCO₃^-?on the degradation of IMD and THIA were evaluated.Low pH was in favor of the degradation of IMD and THIA,while both FA and HCO₃^-had slight inhibitory effects.Meanwhile,the degradation of IMD and THIA via UV/chlorine process were inhibited in real matrices.Br^-exerted a significant inhibition on THIA degradation,which indicated that UV/chlorine process was not suitable for THIA degradation in bromide-containing water.?2?Transformation product identification was performed for IMD and THIA via UV/chlorine process and the biotoxicity removal was also evaluated.The predominant transformation products were tentatively identified using LC-MS and the corresponding pathways were initially proposed.The initial transformation pathways of IMD and THIA involved electron transfer,hydrogen abstraction,and then further disproportionate or the methylene bridge cleavage,yielding hydroxyl and keto derivatives as well as free amine.The amidine nitrogen atoms of IMD and THIA were the preferred attacking sites and?-aminoalkyl radical was important is an important active intermediate.Although the mineralization for IMD?29%?and THIA?35%?was low,the acute toxicity to Vibrio fischeri for the treated samples was lower than that for corresponding parent compounds.In addition,lower eco-toxicity of most transformation product was estimated based on ECOSAR.