Degradation and byproduct formation of parathion in aqueous solutions by UV and UV/H 2O 2 treatment

Abstract

The photodegradation of parathion in aqueous solutions by UV and UV/H 2O 2 processes was evaluated. Direct photolysis of parathion both by LP (low pressure) and MP (medium pressure) lamps at pH 7 was very slow with quantum yields of 6.67 ± 0.33 × 10 −4 and 6.00 ± 1.06 × 10 −4 mol E −1, respectively. Hydrogen peroxide enhanced the photodegradation of parathion through the reaction between UV generated hydroxyl radical and parathion with a second-order reaction rate constant of 9.70 ± 0.45 × 10 9 M −1 s −1. An optimum molar ratio between hydrogen peroxide and parathion was determined to be between 300 and 400. Photodegradation of parathion yielded several organic byproducts, of which the paraoxon, 4-nitrophenol, O, O, O-triethyl thiophosphate and O, O-diethyl-methyl thiophosphate were quantified and their occurrence during UV/H 2O 2 processes were discussed. NO 2 −, PO 4 3−, NO 3 − and SO 4 2− were the major anionic byproducts of parathion photodegradation and their recover ratios were also discussed. A photodegradation scheme suggesting three simultaneous pathways was proposed in the study.