Ultrasonic irradiation of dichlorvos: decomposition mechanism

The sonochemical degradation of dichlorvos in a batch reactor is investigated. Dichlorvos was irradiated with 500 kHz ultrasound at input powers ranging from 86 to 161 W. Acoustic power and sparge gas are two factors which greatly affect sonochemical degradation efficiency. Increasing total acoustic power input from 86 to 161 W resulted in a change in the rate constant from 0.018 +/- 0.001 min-1 to 0.037 +/- 0.002 min-1. The change in rate constant due to sparge gas (Argon, Oxygen, and Argon/Oxygen (60/40% v/v) mixture) at a power of 161 W is also investigated, with the Argon/Oxygen mixture giving the highest rate constant (0.079 +/- 0.005 min-1). Total organic carbon and ion chromatographic analyses are employed to determine and quantify major degradation products, including dimethyl phosphate, formate, carbon dioxide, chloride, and phosphate. The extent of mineralization, indicated by a decrease in the total organic carbon, and the formation of the various intermediates and products, varies with saturating gas. A pathway for dichlorvos decomposition is proposed, based upon formation rates of the various intermediates and products and the rate of decrease of the total organic carbon in the system. The limiting steps in the mineralization pathway appear to be transformation of dimethyl phosphate and formate.