Decomposition of phorate in aqueous solution by ozonation.

Phorate (O,O-diethyl S-ethylthiomethyl phosphorodithioate) dissolved in aqueous solution was almost completely decomposed by ozonation to form various species within 10 minutes of reaction time for the experimental conditions examined in this research. The generation rate of sulfate was found to be fairly independent of solution pH value. However, the formation of phosphate and carbonate was more favorable for alkaline solutions where hydroxyl free radical is the primary oxidative species. The reaction rates increased with initial gaseous ozone concentrations, indicating the reaction was mass transfer-controlled within the experimental range of this research. Combining the analytical results by various instruments, including gas chromatograph equipped with an electron ionization detector (GC-EID), high performance liquid chromatography (HPLC), ion chromatography (IC), and total organic carbon (TOC), the temporal sequence of phorate ozonation was proposed in this study. The oxidation of sulfur atoms on the phosphorus-sulfur double bond or carbon-sulfur-carbon bond by ozonation was found to occur at first to form sulfate and various intermediates.

Decomposition of phorate in aqueous solution by photolytic ozonation.

The degradation of phorate, a highly toxic organic phosphate pesticide, in aqueous solution by photolytic ozonation was studied under various experimental conditions. The rate constants of phorate decomposition and formation of various anions by photolytic ozonation were roughly independent of the solution's pH value. The initial step of the photolytic decomposition of phorate is considered to be the breakage and subsequent oxidation of the P=S double bond on the phorate molecule, followed by isomerization and consequent oxidation of various organic intermediates.