Abstract:Samples of stack gas were collected from two typical municipal waste incinerators, i.e., mechanical stoker incinerator and fluidized-bed incinerator, and the concentrations of PCDDs/PCDFs in these samples were determined with internal standard-calibrated isotope dilution method in combination with high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS). Average percentages of PCDDs/PCDFs and their toxicity equivalents were both above 85% in condensate water phase, which were much higher than that in filter thimble phase and in XAD-2 resin phase for the two incinerators; the ratio of ∑PCDFs to ∑PCDDs was as low as 0.77 in stack gas from mechanical stoker incinerator, but turned out to be as high as 5.28 in stack gas from fluidized bed incinerator. Among the three phases of stack gas from the mechanical stoker incinerator, the PCDDs/PCDFs were found to be dominated by OCDD, with the concentration of OCDD being up to 51.1% particularly in the filter thimble phase. However, among the three phases of stack gas from the fluidized-bed incinerator, the PCDDs/PCDFs were found to be not dominated by a single congener. In stack gas from both incinerator types, PCDFs showed the highest contribution to toxicity equivalent (I-TEQ), and particularly, 2,3,4,7,8-PeCDF made higher than 30% contribution to the total toxicity equivalent.