Photodegradation of Insecticide Diazinon under Simulated Solar Light Irradiation Conditions and Identification of Photoproducts

The photodegradation of the organophosphorus insecticide diazinon with a high probability to contaminate aquatic environments under simulated solar light irradiation conditions on natural water of a river in North of Iran has been studied. During exposure to solar natural light, diazinon is broken down and produced photoproducts in environment. The degradation of the insecticide was a 32 hour process and included the formation of several intermediates that were identified using GC/ion-trap mass spectrometry with EI or CI in positive and negative ionization mode and HPLC/mass spectrometry. On the basis of the structurally identified photoproducts a possible degradation pathway is proposed for the photolysis of diazinon in natural water. Since primarily hydroxy derivatives were identified in this solution, the mechanism of degradation was probably based on hydroxyl radical attack. The initial oxidative pathways of the degradation of diazinon involved the substitution of sulfur by oxygen on the P=S bond, cleavage of the pyrimidine ester bond, and oxidation of the isopropyl group. Exact mass measurements of the derivatives allowed the elemental formula of the molecules to be determined confidently.