Effect of Solution pH on the Hydrolysis and Photolysis of Diazinon in Aqueous Solution

The hydrolytic and photolytic decomposition of diazinon were found to be highly dependent on the solution pH and can be adequately described with a two species distribution model. At light intensities less than 60 W m^-2, the photolytic decomposition rate of diazinon increased linearly with the UV light intensity. Both the hydrolytic and photolytic product of diazinon was identified to be 2-isopropyl-4-methyl-6-pyrimidinol (IMP). No further decomposition of IMP was found by hydrolysis, but the S-P bond of the other portion of diazinon molecule after production of IMP (which could be a thiophosphonate) may be ruptured by UV photolylsis to release a sulfate ion.