Xiaolin Wu

Congener-specific determination of ultratrace levels of chlorinated and brominated polycyclic aromatic hydrocarbons in atmosphere and industrial stack gas by isotopic dilution gas chromatography/high resolution mass spectrometry method

Isotopic dilution gas chromatography combined with high resolution mass spectrometry (GC/HRMS) has overwhelming advantages with respect to the accuracy of congener-specific ultratrace analysis of complex persistent organic pollutants (POPs) in environmental matrices. However, an isotopic dilution GC/HRMS method for analysis of chlorinated and brominated polycyclic aromatic hydrocarbons (Cl-PAHs and Br-PAHs) using 13C-labelled congeners as internal standards has not been established. In this study, a method for identification and quantification of 38 congeners of Cl-PAHs and Br-PAHs in atmosphere and stack gas samples from waste incinerators was developed using the isotopic dilution GC/HRMS technique. The instrumental detection limits of the GC/HRMS method ranged from 0.2pg to 1.8pg for Cl-PAH congeners, and 0.7pg to 2.7pg for Br-PAH congeners, which were about three orders of magnitude lower than those of the GC/quadrupole MS method. This new method developed was also the first to enable determination of Cl-PAH and Br-PAH homologs comprising congeners with the same molecular skeleton and chlorine or bromine substitution numbers. Among the detected congeners, seven Cl-PAH congeners and thirteen Br-PAH congeners that were abundant in the atmosphere and stack gases released from waste incinerators were firstly detected in real samples and reported using the established isotopic dilution GC/HRMS method. The developed isotopic dilution GC/HRMS is significant and needed for better studying the environmental behavior and health risk of Cl-PAHs and Br-PAHs.

Secondary Copper Smelters as Sources of Chlorinated and Brominated Polycyclic Aromatic Hydrocarbons

The generation of and extent to which chlorinated and brominated polycyclic aromatic hydrocarbons (Cl/Br-PAHs) are formed and released from secondary copper smelters remain unknown. This field study, to our knowledge, is the first to identify secondary copper smelters as new sources of Cl/Br-PAHs. Mass concentrations of ∑19Cl-PAHs and ∑19Br-PAHs ranged from 5.8 to 271 ng Nm-3 and 0.59 to 52.4 ng Nm-3, respectively. A comparison of Cl/Br-PAH concentrations in stack gas and fly ash from secondary copper smelters indicated that the use of scrap copper as raw material or the addition of coal or heavy oil as reductant may contribute to the elevated formation and emission of Cl/Br-PAHs. Congener profiles of Cl/Br-PAHs in stack gas and fly ash from secondary copper smelters were different with those of Cl/Br-PAHs from waste incinerations and other previously reported sources, thus could be used as possible fingerprints and source apportionments of environmental Cl/Br-PAHs. Atmospheric levels of Cl/Br-PAHs in the workplace or smelter surroundings were determined and potential exposures were assessed. Although chlorination of PAHs was previously recognized as an important formation pathway of Cl/Br-PAHs, it was not verified to be the major formation pathway for Cl/Br-PAHs from secondary copper smelters in this study.

Molecular Mechanism of Dioxin Formation from Chlorophenol based on Electron Paramagnetic Resonance Spectroscopy

Few studies have investigated the free radical intermediates involved in the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from chlorophenol. This study clarified the reaction pathways during thermochemical formation of PCDDs from 2,3,6-trichlorophenol (TCP) over a Cu(II)O/silica matrix, which was used to simulate fly ash, at 298-523 K. The reaction was studied using electron paramagnetic resonance (EPR) spectroscopy and theoretical calculations. In situ EPR indicated the TCP radical (TCPR) formed by hydrogen abstraction of TCP. Five elementary processes including dimerization of TCPR, ortho-chloride abstraction, Smiles rearrangement, ring closure, and intra-annular elimination of Cl were proposed to occur during formation of PCDDs. The proposed mechanism was further confirmed by the detection of PCDD products from thermochemical experiments in a tube furnace. Several dominant congeners, including 1,2,6,9-tetrachlorodibenzo-p-dioxin (TeCDD), 1,2,6,7-TeCDD, 1,2,8,9-TeCDD, and 1,4,6,9-TeCDD were detected by gas chromatography/quadrupole time-of-flight mass spectrometry, and further confirmed by gas chromatography/high resolution mass spectrometry. The detected PCDD products agree with the proposed PCDD formation mechanism. Relatively high temperatures were found to lead to dechlorination of TCPR to form phenoxy radicals in addition to PCDD/Fs. These radicals will be attached to particles, which will increase their lifetimes. These reactions were further verified by molecular orbital theory calculations. The discovery of persistent phenoxy radicals is of environmental significance because of their potential toxicity. The details of this mechanism could be used for controlling PCDD/F formation during industrial thermal processes.

Evaluation of dioxins and dioxin-like compounds from a cement plant using carbide slag from chlor-alkali industry as the major raw material

Carbide slag produced from chlor-alkali industry contains high amounts of calcium compounds and can potentially be used as raw material for cement production; however, it contains large amounts of chlorine so it is essential to evaluate the emissions of chlorinated organic pollutants, including polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), and polychlorinated naphthalenes (PCNs). A field study of the emission profiles of these pollutants in a cement plant using such slag was performed. The average concentrations of PCDD/Fs, PCBs, and PCNs in stack gases collected at the kiln back end were 6.31, 1.07, and 31.89pg TEQ m-3, respectively. PCDFs dominated over PCDDs in particulate samples. Di- to pentachlorinated biphenyls were dominant homologs in the particulate samples. MonoCBs were the dominant homolog in stack gases from the kiln back end, and homolog concentrations decreased with increasing chlorine numbers. Mono- and diCNs accounted for 48-98% of PCNs. The estimated toxic equivalents of stack gas emissions of PCNs, classified as new persistent organic pollutants under Stockholm Convention, were unexpectedly higher than those of PCDD/Fs and PCBs. A mass balance indicated that all of the toxic equivalents were reduced by this cement kiln system. The highest 2,3,7,8-PCDD/F output is with clinker.

Highly Elevated Levels and Particle-Size Distributions of Environmentally Persistent Free Radicals in Haze-Associated Atmosphere

Levels and particle-size distributions of environmentally persistent free radicals (EPFRs) in haze-associated atmospheric particulate matter (PM) have not been highlighted, even though they may enter the human body along with PM and adversely affect human health. This study quantified the levels of EPFRs in airborne PM with different aerodynamic diameters (dae) using electron paramagnetic resonance (EPR) spectroscopy. EPR spectra showed a single, unstructured signal from persistent semiquinone radicals. The average concentration of EPFRs in the airborne PM during haze events was 2.18 × 1220 spins/g (range: 3.06 × 1019-6.23 × 1020 spins/g), approximately 2 orders of magnitude higher than that reported previously in the US atmosphere. Particle-size distributions of EPFRs in four different PM fractions (dae > 10 μm, 10 μm < dae < 2.5 μm, 2.5 μm <dae < 1 μm, dae < 1 μm) indicated the highest levels of EPFRs in the PM fraction with dae < 1 μm, with average 1/e lifetime of 59.2 days. A significant occurrence of EPFRs in PM samples collected from coal-burning activities (1.52 × 1022 spins/g), automobile exhaust (3.0 × 1022 spins/g), and biomass burning activities (1.14 × 1022 spins/g) was detected, which may be potential primary sources of EPFRs in airborne PM. The results in this study may help to understand the sources and potential risks of EPFRs in airborne fine particles.

Pivotal Roles of Metal Oxides in the Formation of Environmentally Persistent Free Radicals

Environmentally persistent free radicals (EPFRs) are emerging pollutants that can adversely affect human health. Although the pivotal roles of metal oxides in EPFR formation have been identified, few studies have investigated the influence of the metal oxide species, size, or concentration on the formation of EPFRs. In this study, EPFR formation from a polyaromatic hydrocarbon with chlorine and hydroxyl substituents (2,4-dichloro-1-naphthol) was investigated using electron paramagnetic resonance spectroscopy. The effect of the metal oxide on the EPFR species and its lifetime and yield were evaluated. The spectra obtained with catalysis by CuO, Al2O3, ZnO, and NiO were obviously different, indicating that different EPFRs formed. The abilities of the metal oxides to promote EPFR formation were in the order Al2O3 > ZnO > CuO > NiO, which were in accordance with the oxidizing strengths of the metal cations. A decay study showed that the generated radicals were persistent, with a maximum 1/e lifetime of 108 days on the surface of Al2O3. The radical yields were dependent on the concentration and particle size of the metal oxide. Metal oxide nanoparticles increased the EPFR concentrations more than micrometer-sized particles.

Emissions of 2,3,7,8-substituted and non-2,3,7,8-substituted polychlorinated dibenzo-p-dioxins and dibenzofurans from secondary aluminum smelters

The secondary aluminum smelting industry is an important source of polychlorinated dibenzo-p-dioxin and dibenzofurans (PCDD/Fs). However, the formations and emissions of non-2,3,7,8-PCDD/Fs have rarely been studied. Non-2,3,7,8-PCDD/Fs may also be metabolically toxic to mammalians. In this study, four typical secondary aluminum smelters were selected as demonstration smelters and the composition of the raw material they used was adjusted to investigate the influence on PCDD/F emissions and profiles. In addition to 17 congeners of 2,3,7,8-PCDD/Fs, 64 congeners of non-2,3,7,8-PCDD/Fs were firstly reported. Strong, positive correlations were found between non-2,3,7,8-PCDD/Fs and 2,3,7,8-PCDD/Fs. The concentrations of 2,3,7,8-PCDD/Fs in stack gas and fly ash samples were 120.7-870.4 pg/Nm3 and 13.40-292.9 ng/g, respectively. Those of non-2,3,7,8-PCDD/Fs in the stack gas and fly ash samples were 84.03-1183.7 pg/Nm3 and 7.20-344.7 ng/g, respectively. The raw material composition was a key factor affecting PCDD/F emissions and profiles. An analysis of Gibbs free energies (ΔGf) showed that non-2,3,7,8-PCDD/Fs could be transformed into 2,3,7,8-PCDD/Fs, which would increase the PCDD/F environmental risks. The emission inventories of 2,3,7,8-PCDD/Fs, non-2,3,7,8-PCDD/Fs, and International Toxic Equivalents from Chinese secondary aluminum smelters in 2013 were 8247 g, 7253 g, and 608.6 g, respectively. The results of this study could contribute to potential risk evaluations and effective reduction of non-2,3,7,8-PCDD/Fs.

Chlorinated and Brominated Polycyclic Aromatic Hydrocarbons from Metallurgical Plants

In this study, we investigated several metallurgical industries, including iron ore sintering, secondary aluminum smelting, and secondary lead smelting, as potential sources of Cl-PAHs and Br-PAHs. Stack gas emissions of 19 Cl-PAH and 19 Br-PAH congeners from the investigated metallurgical plants were in the ranges of 68.3-156 ng Nm-3 and 2.9-13.5 ng Nm-3, respectively. Cl/Br-PAHs in ambient air surrounding the investigated metallurgical plants were also quantified, and the ranges were 7.0-554 pg m-3 for Cl-PAHs and 3.0-126 pg m-3 for Br-PAHs. Toxic equivalent (TEQ) concentrations of Cl-PAHs and Br-PAHs in the ambient air samples were in the ranges of 0.03-3.61 pg TEQ m-3 and 0.001-0.23 pg TEQ m-3, respectively. These TEQs were slightly higher than or comparable to those of dioxins and dioxin-like compounds. Congener profiles of Cl-PAHs emitted from iron ore sintering, secondary aluminum smelting, and secondary lead smelting facilities were clarified and their congener profiles were obviously different from that from waste incinerators. Comparisons of Cl/Br-PAH congener profiles between surrounding air samples and stack gas emissions indicated that metallurgical emissions affected the surrounding environment to some extent.