Assessing influence of experimental parameters on formation of PCDD/F from ash derived from fires of CCA-treated wood

Ash residues from fires of radiata pine timber, both untreated and treated with chromated copper arsenate (CCA), were analyzed for the presence of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F). Fire conditions were simulated using a cone calorimeter. The sensitivity of the magnitude and profile of PCDD/F in the ash under controlled experimental conditions were examined to gain an insight into the formation of PCDD/F in a system containing CCA. The total amount of PCDD/F increased from 2.0 ng/kg of ash (0.05 ng of TE/kg of ash, using WHO-TEF) for untreated radiata pine to a maximum of 2700 ng/kg of ash (78 ng of TE/kg of ash) for 0.94% CCA. Ash containing CCA showed a distinct preference for formation of PCDFs, particularly the tetrachloro homologue. It is concluded that PCDD/F formation predominantly occurred via de novo synthesis during smoldering of the char rather than during the initial flaming and pyrolysis. Furthermore, the composition of the CCA constituents present in the timber was controlled to assess whether the physical presence of Cu, a known catalyst in PCDD/F production, was sufficient to account for the formation of PCDD/F in fires of timber impregnated with CCA.