Thermal Decomposition of Captan and Formation Pathways of Toxic Air Pollutants

This study investigates the thermal decomposition of a widely used fungicide, captan, under gas phase conditions, similar to those occurring in fires, cigarette burning, and combustion of biomass treated or contaminated with pesticides. The laboratory-scale apparatus consisted of a plug flow reactor equipped with sampling trains for gaseous, volatile organic compounds (VOC) and condensed products, with analysis performed by Fourier transform infrared spectroscopy (FTIR) and gas chromatography−mass spectrometry (GC-MS), respectively. Under oxidative conditions, the thermal decomposition of captan generated gaseous pollutants including carbon disulfide, thiophosgene, phosgene, and hydrogen cyanide. The VOC analysis revealed the formation of tetrachloroethylene, hexachloroethane, and benzonitrile. Quantum chemical calculations indicated that captan decomposes unimolecularly, via fission of the C−S bond, with the ensuing radicals reacting with O2. The results of the present study provide an improved understanding of the formation pathways of toxic air pollutants in the accidental or deliberate combustion of captan.