Formation of toxic species in thermal decomposition of captan

Captan belongs to an important group of sulfenimide fungicides, commonly used on major crops, fruits and ornamentals. In this study, a laboratory scale apparatus has been constructed to investigate the thermal decomposition of captan in gas phase reactions, similar to those that occur in fires, burning of wood and other biomass treated or contaminated with pesticides. The apparatus comprises a plug flow reactor equipped with sampling systems for gaseous, volatile and condensable products. The gaseous species were detected and quantified by the Fourier transform infra-red spectroscopy (FTIR). The volatile organic compounds (VOC) were trapped in an activated charcoal tube and the condensable products were collected by XAD resin and cold solvent traps. The identification of VOC was performed by means of high resolution gas chromatography-quadrupole mass spectrometry (HRGC-QMS). Under oxidative atmosphere, the thermal decomposition of captan generated gaseous pollutants including carbonyl sulfide, carbon disulfide, thiophosgene and phosgene (the World War I chemical agent). The VOC analysis revealed the formation of tetrachloroethylene, hexachloroenthane (both suspect carcinogens) and chlorinated benzenes. At higher temperature, the decomposition of captan vapour produced, mono to tetra, polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F), with PCDD/F quantified on an HRGC-MS/MS (ion trap) instrument.