Relationships between congener distribution patterns of PCDDs, PCDFs, PCNs, PCBs, PCBzs and PCPhs formed during flue gas cooling

The congener patterns of mono- to octa-chlorinated dibenzo-p-dioxins (PC1–8DD), dibenzofurans (PC1–8DF), naphthalenes (PC1–8N), mono- to deca-chlorinated biphenyls (PC1–10B), di- to hexa-chlorinated benzenes (PC2–6Bz) and mono- to penta-chlorinated phenols (PC1–5Ph) in flue gas samples collected simultaneously at 450 °C, 300 °C and 200 °C in the post-combustion zone during waste incineration in a laboratory-scale reactor in a previous study, were in this study evaluated using principal component analysis (PCA). To our knowledge this is the most comprehensive chemical and multivariate analysis to date of the thermal formation of dioxins. The PCA indicated that different formation pathways occur in the temperature regions 450–300 °C and 300–200 °C, and reflected a chlorination effect of PCDF and PCDD between 450 °C and 200 °C which could not be discerned or was less pronounced for the other compound groups. Toxic equivalents (TEQs) of PCDDs, PCDFs and PCBs, as well as total TEQ values (TEQTotal) were also calculated, and correlations between changes in levels of specific congeners and the TEQs were explored in the PCA. Levels of four HxCDF congeners and 1,2,3,4,8-, 1,2,3,7,8-PeCDF and 2,3,4,7,8-PeCDF showed the strongest correlations with TEQTotal (R2 ≥ 0.9). In addition, levels of 1,2,4-TriCBz correlated strongly with TEQTotal (R2 > 0.7), supporting previous reports that it may be a potential indicator of the TEQ.

► Different pathways dominating between 450–300 °C and 300–200 °C, respectively.
► Chlorination of PCDD/Fs between 450 °C and 200 °C but not for the other chloroaromatics.
► Best TEQTotal correlations for four HxCDFs, and 1,2,3,4,8-/1,2,3,7,8- and 2,3,4,7,8-PeCDF.
► 1,2,4-TriCBz correlated strongly with TEQTotal (R2 > 0.7) and may be a future TEQ indicator.