In this work, three commercial diazinonemulsifiable concentrate (EC) formulations 60% were collected from the Egyptian market (manufactured from three different companies ) to investigate the degradation of diazinon after storage at 54 ?2 oC for 70 days , at room temperature for 12 months, and exposure to sunlight for 6 months, also identification of some degradation products by GC-MS. In addition to find the causes of the formation of toxicological impurities of diazinon, O,S-TEPP and S,S-TEPP and study the relation between the water content and the amount of impurities . The obtained results showed that, diazinon was more stable after storage at 54 ?2 oC and at room temperature, while the rate of degradation increased after exposure to sunlight. Analysis of samples after exposure to sunlight using GC-MS identified three degradation products: diazoxon, hydroxydiazinon and 2-isopropyl-6-methyl-4-pyrimidinol (IMP). There was a positive correlation between water content and the amount of O,S-TEPP. Whereas S,S-TEPP didn’t affect by storage or water content in diazinon , but it produced during the production process. - See more at: http://www.journalijar.com/article/3694/study-the-relation-between-storage-and-stability-of-diazinonemulsifiable-concentrate-formulations-in-the-formation-of-its-impurities-and-major-degradation-products/#sthash.X1Jkelbd.dpuf