Mechanism of thermal decomposition of a pesticide for safety concerns: Case of Mancozeb

Thermal decomposition under both air and inert atmospheres of a commercial Mancozeb product was investigated through thermogravimetric analysis and laboratory scale thermal treatment from 20 °C to 950 °C, with analysis of gaseous and solid products. The aim of this study is the understanding of the thermal degradation mechanisms of a pesticide under different atmospheres and the chemical identification of the solid and gaseous pollutants which can be emitted during warehouse fires and which can constitute a threat for health and environment. Pyrolysis of Mancozeb takes place between 20 °C and 950 °C and lead essentially to CS2 and H2S emissions with formation at 950 °C of MnS and ZnS. Thermal oxidation of Mancozeb under air occurs between 150 °C and 950 °C with formation of CO, CO2 and sulphur gases (CS2 and SO2). The first step (155-226 °C) is the loss of CS2 and the formation of ethylene thiourea, ZnS and MnS. The metallic sulphides are oxidized in ZnO and MnSO4 between 226 °C and 650 °C (steps 2 and 3). MnSO4 is then oxidized in Mn3O4 during the last step (step 4) between 650 °C and 950 °C. At 950 °C, carbon recovery is close to 95%. Sulphur recovery is close to 98% with an equal partition between SO2 and CS2.