Study Of Chlorothalonil Photodegradation In Aqueous Solution And On The Surface Of Pepper

The method for determination of chlorothalonil, chlorothalonil-4-hydroxy and EGCGby high performance liquid chromatography and chloridion by ion chromatography wereestablished. And then methods of chlorothalonil photodegradation in aqueous solution andon the surface of pepper were established. The present study examined the effects ofEGCG and nanometer TiO₂on photochemical degradation of chlorothalonil in aqueoussolution and on the plant surface under high-pressure mercury lamp, ultraviolet lamp andsunlight illumination respectively.Results showed that EGCG exhibited strong photosensitizing effect on thedegradation of chlorothalonil in aqueous solution. The photosensitization rate was higherin the sunlight compared to illumination under high-pressure mercury lamp. Underhigh-pressure mercury lamp illumination, the photochemical degradation of chlorothalonilin aqueous solution is mainly through the dechlorination reaction. Due to the reducibilityof EGCG, the concentration of chloridion producing by chlorothalonil increased obviouslywhen mixed with EGCG. That is to say the reducibility of EGCG facilitated completephotodegradation of chlorothalonil under illumination. Moreover,chlorothalonil-4-hydroxy was identified as the main metabolite of chlorothalonil and hashigher toxicity. However, EGCG facilitated complete photodegradation of chlorothalonilwith no detectable accumulation of the intermediate chlorothalonil-4-hydroxy（<LOD）.In addition, nanometer TiO₂also exhibited strong photosensitizing effect on thedegradation of chlorothalonil both in aqueous solution and on the surface of green pepper.The photosensitization rate was the highest in the sunlight compared to illumination underhigh-pressure mercury and UV lamps. Use of distinct hydroxyl radical scavengersindicated that nanometer TiO₂acted by producing hydroxyl radicals with strong oxidizingcapacity. Notably, nanometer TiO₂facilitated complete photodegradation of chlorothalonilwith no detectable accumulation of the intermediate chlorothalonil-4-hydroxy. NanometerTiO₂was also active on the surface of green pepper under natural sunlight both inside andoutside of plastic greenhouse. These results together suggest that nanometer TiO₂can beused as a photosensitizer to accelerate degradation of the pesticides under greenhouseconditions.