Toxicants formed in fires of captafol pesticide

This study presents an investigation into the gas phase thermal decomposition of captafol, a sulfenimide fungicide which consists of a thiotetrachloroethyl (-SCCl₂CHCl₂) group bonded to a tetrahydrophthalimide (C₆H₈(CO)₂N-) moiety. The experiments were performed on a bench type apparatus, under conditions representing both under and well-ventilated non-flaming fires. The analyses of gaseous species relied on Fourier transform infra-red spectroscopy (FTIR) and micro gas chromatography (μGC), resulting in the identification and quantification of 11 gaseous products; among them, phosgene, thiophosgene and hydrogen cyanide. Gas chromatography - quadrupole mass spectrometry (GC-QMS) was employed to analyse the condensed products and volatile organic compounds (VOC), while a GC equipped with an ion trap mass spectrometer (GC-ITMS) was used to quantify polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F). The GC-QMS analysis determined several VOC toxicants; viz., trichloroethylene, tetrachloroethylene, benzonitrile and chlorinated benzenes. At higher temperature (600 °C), the oxidation of captafol led to the formation of mono- to hepta- CDD/F congeners including the most toxic 2,3,7,8-TCDD. In addition, the experimental results were compared to those of the other two sulfenimide fungicides, captan and folpet, both of which contain the thiotrichloromethyl (-SCCl₃) moiety rather than the thiotetrachloroethyl group of captafol. It appears that the thiotetrachloroethyl group in captafol is responsible for the difference in the toxic pollutants formed, particularly influencing the distribution and yields of PCDD/F congeners. Combined with quantum chemical calculations, the results presented in this article provide an insightful understanding of fire chemistry of the sulfenimide fungicides, especially the pathways to the formation of major toxicants during the oxidative thermal decomposition of captafol.