Degradation of pirimiphos-methyl during thermophilic composting of greenhouse tomato plant residues

Abstract

The effectiveness of invessel thermophilic compo sting on the destruction of pirimiphos-methyl (12, 24, and 36 mg/kg dry matter) was evaluated. The bioreactor operated on a mixture of tomato plant residues, wood shavings, and municipal solid compost. Water was used to adjust the moisture content to 60% (wet basis); urea was used as a nitrogen source to adjust the C:N ratio to 30:1; and used cooking oil was added as a bioavailable carbon source. The compo sting process successfully destroyed 81-89% of pirimiphos¬methyl within the first 54 h of operation. Complete destruction of the pesticide required approximately 438 h. The rate constant (k) for the degradation of pirimiphos-methyl was determined to be a function of the bioreactortemperature. A rate constant of 0.026, 0.003-0.010, and 0.002-0.009 h' was observed for the rising temperature mesophilic phase (25-45°C), thermophilic phase (45-63-45°C), and declining temperature mesophilic phase (45-25°C), respectively. A number of physical, chemical, and biological mechanisms contribute to the degradation of pirimiphos-methyl in the environment including mineralization or hydrolysis, abiotic transformations, adsorption, leaching, humification, and volatization. During compo sting of greenhouse wastes, the degradation of pirimiphos-methyl is accelerated by high temperatures, organic matter content, moisture, and biological activity. Keywords: pirimiphos-methyl, thermophilic, compost, degradation.