UV and UV/H2O2 treatment of diazinon and its influence on disinfection byproduct formation following chlorination

• Influence of UV and UV/H2O2 treatment of diazinon on DBPs formation was analyzed.
• Intermittent oxidation byproducts could yield more DBPs than the parent compound.
• pH and H2O2 affect UV-oxidation byproducts speciation thus altering DBPs formation.
• UV irradiation significantly increased DBPs formation for diazinon solution.

Incomplete oxidation of organic micropollutants may result in diverse intermittent oxidation byproducts, significantly affecting disinfection byproducts (DBPs) formation of the original solutions following chlorination. This study investigated DBPs formation from diazinon in solution due to the formation of intermittent oxidation byproducts by UV and UV/H2O2 pre-oxidation. Monochloroacetic acid (MCAA), dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), chloroform (TCM), dichloroacetonitrile (DCAN) and 1,1,1-trichloroacetone (1,1,1-TCP) were detected for chlorinated diazinon solutions that have been treated by UV and UV/H2O2 oxidation. The DBPs formation was found increased significantly in the treated diazinon solutions with UV dose. Solution pH and H2O2 dose also exhibited distinct influences on the DBPs formation depending on the individual DBP species. Speciation and molecular structures of the oxidation byproducts were analyzed via MS and MS/MS spectra. Four main UV oxidation byproducts, (2-isopropyl-6-methyl-4-pyrimidinol (IMP), O-analog diazinon (diazoxon), diethyl thiophosphate (DETP) and diethyl phosphate (DEP)), were also examined individually to identify their relative contributions to DBPs formation. The increase in total DBPs formation of the treated diazinon solutions was found to be attributable mainly to its oxidation product IMP and its secondary oxidation products, while the other two fragments DETP and DEP had little effect. Moreover, its oxidation fragment diazoxon intensified the formation of MCAA, DCAA and TCAA under UV/H2O2 pre-oxidation condition.

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