An isomer prediction model for PCNs, PCDD/Fs, and PCBs from municipal waste incinerators

Isomer patterns of polychlorinated naphthalenes (PCNs), polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated biphenyls (PCBs), and polychlorinated dibenzofurans (PCDFs) from municipal waste incinerators (MWIs) were predicted by a model based on symmetry numbers and preferential chlorination positions. Fly ash isomer patterns from five stoker and seven fluidized bed incinerators were compared to validate the prediction model. The isomer patterns of the highly chlorinated PCN homologues from stoker type incinerators were successfully predicted. The relative equilibrium concentrations of tetrachloronaphthalenes (TeCNs), calculated by an ab initio method, cannot explain the field isomer patterns. Formation pathways involving chlorophenol precursor condensation reactions should be examined to see whether these isomer patterns provide a better fit to the field PCDD data. The PCB isomer patterns were fit reasonably well, but this finding could merely be an artifact of the limited data and the large number of isomers. The prediction equations of PCDFs, revised from prior work to include a symmetry number for each isomer, represented the field data patterns for the higher chlorinated isomers very well. Successful prediction of isomer patterns for partial homologue ranges suggests that these patterns are determined by a mechanism governed by Cl-position-specific preferences.