Degradation of carbendazim by UV/H 2O 2 investigated by kinetic modelling

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The transformation of the fungicide carbendazim (methyl-2 benzimidazole carbamate) induced by hydroxyl radical generated by the UV photolysis of H 2O 2 has been studied in dilute aqueous solution. The efficient reaction of hydroxyl radicals with carbendazim led to the rapid degradation of carbendazim. The study of reaction kinetics yielded a second order rate constant of 2.2±0.3 10 9 M -1 s -1for HO · radicals with carbendazim. This value is in agreement with a high reactivity of HO · radicals with carbendazim. Most degradation products were identified by high performance liquid chromatography mass spectrometry (HPLC-MS). In the presence of hydrogenocarbonate and carbonate ions, hydroxyl radicals were quenched and in turn carbonate radicals CO 3 ·- were formed. Carbonate radicals are indeed known to react efficiently with compounds containing electron-rich sites such as nitrogen or sulfur atoms. The use of a kinetic modelling software gave evidence for the occurrence of such reactions with carbendazim. The second order rate constant of carbonate radical with carbendazim was equal to 6±2 10 6 M -1 s -1.

Keywords: Carbendazim, Hydroxyl radical, Carbonate radical, Transformation, Kinetic modelling

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