Formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F) in fires of arsenic-free treated wood: role of organic preservatives

This article demonstrates that biocidal organochlorines such as tebuconazole and permethrin, employed in formulations of wood preservatives, produce significant quantities of polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran (PCDD/F) when subjected to thermal decomposition under oxidative conditions. Both tebuconazole and permethrin form PCDD/F during gas-phase oxidation, but much greater yields occurred in the presence of surrogate ash corresponding to wood treated with copper-based fungicides. The significant yields have implications for the increased toxicity of PCDD/F emissions during fires of wood impregnated by combination of organic and copper-based preservatives. The oxidative pyrolysis of tebuconazole and permethrin over simulated wood ash generated amounts of PCDD/F exceeding those of untreated wood by 3 orders of magnitude. We obtained yields of 1000 ng WHO97-TEQ/g tebuconazole and 5500 ng WHO97-TEQ/g permethrin when reacting the organochlorines in an oxidizing atmosphere over surrogate wood ash. Gas-phase oxidation also produce measurable quantities of PCDD/F, corresponding to 1 ng WH097-TEQ/g tebuconazole and 36 ng WHO97-TEQ/g permethrin. In the case of tebuconazole, the present measurements correlate well with those obtained from oxidative pyrolysis of CBA-treated wood in the cone calorimeter. It appears that permethrin and tebuconazole provide phenyl and diphenyl precursors to formation of PCDD/F and both constitute a source of chlorine upon fragmentation.