Degradation and by-product formation of diazinon in water during UV and UV/H2O2 treatment

Kinetics and degradation products resulting from the application of UV and UV/H2O2 to the US EPA Contaminant Candidate List pesticide diazinon were studied. Batch experiments were conducted with both monochromatic (low pressure [LP] UV 253.7 nm) and polychromatic (medium pressure [MP] UV 200–300 nm) UV sources alone or in the presence of up to 50 mg l−1 H2O2, in a quasi-collimated beam apparatus. Degradation of diazinon by both UV and UV/H2O2 exhibited pseudo first order reaction kinetics, and quantum yield of 8.6 × 10−2 and 5.8 × 10−2 mol E−1 for LP and MP lamps respectively. Photolysis studies under MP UV lamp showed 2-isopropyl-6-methyl-pyrimidin-4-ol (IMP) to be the main degradation product of diazinon at aqueous solution pH values of 4, 7 and 10. Trace levels up to 1.8 × 10−3 μM of diazinon oxygen analogue diethyl 2-isopropyl-6-methylpyrimidin-4-yl phosphate (diazoxon) were detected only during the UV/H2O2 reaction. Decay of both products was observed, as the UV/H2O2 reaction prolonged, yet no mineralization was achieved over the UV fluence levels examined. Photolysis kinetics, quantum yield and UV/H2O2 degradation of the reaction product IMP was determined using MP UV lamp at pH values of 4, 7 and 10.