Hydrolysis of Phorate Using Simulated Environmental Conditions: Rates, Mechanisms, and Product Analysis

The hydrolysis of phorate, an organophosphorus pesticide, was studied under simulated environmental conditions. Several metal oxides (aluminum hydroxide, hematite, goethite, and ferrihydrite) were chosen to represent the solid phase in natural aquatic systems. Several degradation products were identified using GC-MS in combination with wet chemistry methods. Microtox was used to measure the toxicity of phorate and one of the degradation products, diethyl disulfide. Two potential reaction pathways were proposed for the alkaline hydrolysis of phorate that results in unusual products, such as formaldehyde and diethyl disulfide. No statistically significant catalytic effect was observed for the four metal (hydr)oxides used in the study. However, diethyl disulfide was found to be highly toxic (EC 50 is 2.0 ppm). This study again confirmed the need for the study of the environmental impact of the degradation products of pesticides.