Thermal oxidation of dieldrin and concomitant formation of toxic products including polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/F)

Abstract

This paper examines the gas phase thermal decomposition of dieldrin and associated formation of toxic combustion products including polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/F). Volatile Organic Carbon (VOC) analysis revealed the formation of pentachlorostyrene (PCS), hexachlorostyrene (HCS) and polychlorinated naphthalene as toxic combustion products generated during the combustion of dieldrin. The thermal pyrolysis of dieldrin resulted in the formation of chlorinated benzenes and chlorinated phenols, which are known PCDD/F precursors. The formation of PCDD/F commenced around 823 K @ 5s residence time and results indicate a preference for the formation of PCDF over PCDD under all experimental conditions studied. Subsequent experiments, to examine the yield of PCDD/F as a function of temperature, reveal the progressive chlorination of PCDD/F with temperatures up to 923 K. Octachlorodibenzofuran (OCDF) was the major dioxin congener detected in the oxidation of dieldrin. The highest toxicity factor for dioxin formation was recorded at 923 K with a 6% O₂ content in the feed gas and corresponds to 6.24 ng TEQ WHO 2005/mg of dieldrin and total PCDD/F concentration of 96.8 ng/mg of dieldrin.

Keywords: Dieldrin; Dioxin; Dioxin precursors; Polychlorinated styrenes; Toxic equivalents factor.