Mono- to tri-chlorinated dibenzodioxin (CDD) and dibenzofuran (CDF) congeners/homologues as indicators of CDD and CDF emissions from municipal waste and waste/coal combustion

Total homologue concentrations and select congener concentrations from amongst the mono- to tri-chlorinated dibenzodioxins (CDDs) and dibenzofurans (CDFs) are used to model both Total (mono- to octa-) CDD + CDF emissions and the toxicity equivalent (TEQ) of the 2,3,7,8-chlorine-substituted emissions. Analysis of emission data from two facilities indicates that use of total homologue concentrations shows limited, facility-specific correlations with Total CDDs/CDFs and TEQ. Concentrations of select mono- to tri-CDD/CDF congeners show promising correlation with CDD/CDF TEQ across facilities, suggesting that these compounds can act as TEQ indicators.     

Chlorination of dibenzofuran and dibenzo-p-dioxin vapor by copper (II) chloride

Dibenzofuran (DF) is formed from phenol and benzene in combustion gas exhaust streams prior to particle collection equipment. Subsequent chlorination at lower temperatures on particle surfaces is a potential source of chlorinated dibenzofuran (CDF). Gas streams containing 8% O₂ and approximately 0.1% DF vapor were passed through particle beds containing copper (II) chloride (0.5% Cu, mass) at temperatures ranging from 200 to 400 °C to investigate the potential for CDF formation during particle collection. Experiment duration was sufficient to provide an excess amount of DF (DF/Cu=3). The efficiency of DF chlorination by CuCl₂ and the distribution of CDF products were measured, with effects of temperature, gas velocity, and experiment duration assessed. Results of a more limited investigation of dibenzo-p-dioxin (DD) chlorination by CuCl₂ to form chlorinated DD (CDD) products are also presented.

The efficiency of DF/DD chlorination by CuCl₂ was high, both in terms of CuCl₂ utilization and DF/DD conversion. Total yields of Cl on CDF/CDD products of up to 0.5 mole Cl per mole CuCl₂ were observed between 200 and 300 °C; this suggests that nearly 100% CuCl₂ was utilized, assuming a conversion of two moles of CuCl₂ to CuCl per mole Cl added to DD/DF. In a short duration experiment (DF/Cu=0.3), nearly 100% DF adsorption and conversion to CDF was achieved. The degree of CDF chlorination was strongly dependent on gas velocity. At high gas velocity, corresponding to a gas–particle contact time of 0.3 s, mono-CDF (MCDF) yield was largest, with yields decreasing with increasing CDF chlorination. At low gas velocity, corresponding to a gas–particle contact time of 5 s, octa-CDF yield was largest. DF/DD chlorination was strongly favored at lateral sites, with the predominant CDF/CDD isomers within each homologue group those containing Cl substituents at only the 2,3,7,8 positions. At the higher temperatures and lower gas velocities studied, however, broader isomer distributions, particularly of the less CDD/CDF products, were observed, likely due to preferential destruction of the 2,3,7,8 congeners.     

Chlorination of dibenzofuran and dibenzo-p-dioxin vapor by copper (II) chloride

Dibenzofuran (DF) is formed from phenol and benzene in combustion gas exhaust streams prior to particle collection equipment. Subsequent chlorination at lower temperatures on particle surfaces is a potential source of chlorinated dibenzofuran (CDF). Gas streams containing 8% O₂ and approximately 0.1% DF vapor were passed through particle beds containing copper (II) chloride (0.5% Cu, mass) at temperatures ranging from 200 to 400 °C to investigate the potential for CDF formation during particle collection. Experiment duration was sufficient to provide an excess amount of DF (DF/Cu=3). The efficiency of DF chlorination by CuCl₂ and the distribution of CDF products were measured, with effects of temperature, gas velocity, and experiment duration assessed. Results of a more limited investigation of dibenzo-p-dioxin (DD) chlorination by CuCl₂ to form chlorinated DD (CDD) products are also presented.The efficiency of DF/DD chlorination by CuCl₂ was high, both in terms of CuCl₂ utilization and DF/DD conversion. Total yields of Cl on CDF/CDD products of up to 0.5 mole Cl per mole CuCl₂ were observed between 200 and 300 °C; this suggests that nearly 100% CuCl₂ was utilized, assuming a conversion of two moles of CuCl₂ to CuCl per mole Cl added to DD/DF. In a short duration experiment (DF/Cu=0.3), nearly 100% DF adsorption and conversion to CDF was achieved. The degree of CDF chlorination was strongly dependent on gas velocity. At high gas velocity, corresponding to a gas–particle contact time of 0.3 s, mono-CDF (MCDF) yield was largest, with yields decreasing with increasing CDF chlorination. At low gas velocity, corresponding to a gas–particle contact time of 5 s, octa-CDF yield was largest. DF/DD chlorination was strongly favored at lateral sites, with the predominant CDF/CDD isomers within each homologue group those containing Cl substituents at only the 2,3,7,8 positions. At the higher temperatures and lower gas velocities studied, however, broader isomer distributions, particularly of the less CDD/CDF products, were observed, likely due to preferential destruction of the 2,3,7,8 congeners.     

Influence of combustion conditions on the PCDD/F-, PCB-, PCBz- and PAH-concentrations in the post-combustion chamber of a waste incineration pilot plant

Experiments at a pilot scale waste incinerator (0.5 MW thermal power) showed that the conditions in the post-combustion chamber (650-900 degrees C) are strongly influencing the formation of chlorinated and non-chlorinated aromatics. Non-optimal combustion conditions resulted in increased concentrations of mono- to trichlorinated dibenzo-p-dioxins (PCDD), dibenzofurans (PCDF) and polycyclic aromatic hydrocarbons (PAH), while chlorinated benzenes (PCBz), polychlorinated biphenyls (PCB) and the higher chlorinated PCDD/F are only weakly affected or even decrease. The changes in concentration of the compounds investigated over a time span of hours gave hints on 'memory effects' in this combustion zone. For mono- and dichlorinated benzenes, a high correlation (r2 = 0.80) with the international toxicity equivalent (I-TEQ) value of PCDD/F was observed. As recently has been demonstrated, this correlation can be utilized for an indirect on-line measurement of the I-TEQ by a novel laser mass spectrometric technique (REMPI-TO-FMS).     

Preliminary report: Dioxins and furans in prescribed burns

The Ontario Ministry of Environment (MOE) recently participated in a joint Canadian/U.S. program to monitor the behavior and environmental impact of prescribed fires. Air, soil and ash samples were collected at the burn sites and analyzed for chlorinated dibenzo-p-dioxins (CDD) and dibenzofurans (CDF). Preliminary results indicated that larger air sample volumes were required.     

Source identification of PCDD/Fs in a sewage treatment plant of a German village

The PCDD/F levels in the sewage sludge of a village in North-East Germany were substantially above the limit of 100 pg I-TEq/g for sludge applied to land. A study was initiated to identify the PCDD/F sources in the sewage of this treatment plant. It was found that the PCDD/F contamination entered the plant through the faecal inlet, where the content of faecal storage tanks was emptied into the treatment plant. The isomeric patterns of the higher chlorinated homologues were similar to that of PCP, while incineration showed some influence on the lower chlorinated homologues. Cluster analysis revealed a profile similar to that of PCP.     

Metal-mediated chlorinated dibenzo-p-dioxin (CDD) and dibenzofuran (CDF) formation from phenols

Heterogeneous formation of chlorinated dibenzo-p-dioxins (CDDs) and dibenzofurans (CDFs) on CuCl2 from three phenols without ortho chlorine and one phenol with two ortho chlorines was studied in a flow reactor over a temperature range of 325-450 degrees C. Heated nitrogen gas streams containing 8% oxygen, 1.5% benzene vapor, and equal amounts of phenol, 3-chlorophenol, 3,4-dichlorophenol and 2,4,6-trichlorophenol vapor (700 ppmv, each) were passed through a 1 g particle bed of silica and 0.5% (Cu mass) CuCl2. Maximum product yields of greater than 1.4% phenol conversion to CDD and 5.7% phenol conversion to CDF were observed between 400 and 450 degrees C. CDDs formed with loss of one chlorine atom were favored. While total CDD/F yield varied with temperature, CDD/F homologue and isomer distributions did not vary significantly with temperature. Based on the results of experiments with single phenol precursors, phenol precursors could be assigned to all PCDD/F products. Of the chlorinated phenols without ortho chlorine that were studied, 3,4-dichlorophenol was found to have the greatest propensity to form CDFs.     

Investigation of saponification for determination of polychlorinated biphenyls in marine sediments

The effects of saponification conditions (temperature and water content of saponifying solution) on the determination of chlorinated biphenyls (CBs) in marine sediments were investigated. Although highly chlorinated biphenyls (nona- to deca-CBs) decomposed during high-temperature saponification, the degree of degradation was reduced by adding water to the ethanolic potassium hydroxide saponifying solution. Room-temperature saponification yielded quantitative recovery of highly chlorinated biphenyl surrogates but low extraction efficiencies of lightly chlorinated biphenyls (mono- to di-CBs). The same samples were analyzed by other extraction techniques, for example, pressurized liquid extraction, and analytical results were compared. The mono- and di-CB concentrations were correlated with the extraction temperatures of various extraction techniques. In particular, the concentrations of some CB congeners (CB11, CB14) were higher with saponification. The low degree of degradation of highly chlorinated biphenyls and the high recovery of lightly chlorinated biphenyls were compatible when room-temperature and high-temperature saponification were combined. Except for the anomalies of CB11 and CB14, the combined method gave satisfactory results for analysis of PCBs.     

Formation and chlorination of polychlorinated naphthalenes (PCNs) in the post-combustion zone during MSW combustion

Non- to octa-chlorinated naphthalenes (PCNs) were analyzed in flue gas samples collected simultaneously at three different temperatures (450 degrees C, 300 degrees C and 200 degrees C, respectively) in the post-combustion zone during waste combustion experiments using a laboratory-scale fluidized-bed reactor. PCN homologue profiles in all samples were dominated by the lower chlorinated homologues (mono- to triCN), with successive reductions in abundance with each additional degree of chlorination. The isomer distribution patterns reflected ortho-directionality behavior of the first chlorine substituent, and the beta-positions, i.e. the 2,3,6,7-substitution sites, seemed to be favored for chlorination. Injection of naphthalene into the post-combustion zone resulted in increased PCN levels at 200 degrees C, demonstrating the occurrence of chlorination reactions in the post-combustion zone. However, the increases were restricted to the least-chlorinated homologue (monoCN), probably because there was insufficient residence time for further chlorination. In addition, an episode of poor combustion (manifested by high CO levels) was accompanied by extensive formation of 1,8-diCN, 1,2,3- and 1,2,8-triCN; congeners with substitution patterns that are not thermodynamically favorable. These are believed to be products of PAH breakdown reactions and/or chlorophenol condensation. Overall, PCN formation is likely to occur via more than one pathway, including chlorination of naphthalene that is already present, de novo synthesis from PAHs and, possibly, chlorophenol condensation.     

PCB decomposition and formation in thermal treatment plant equipment

In this study we investigated both the decomposition and unintentional formation of polychlorinated biphenyl congeners during combustion experiments of refuse-derived fuel (RDF) and automobile shredder residue (ASR) at several stages in thermal treatment plant equipment composed of a primary combustion chamber, a secondary combustion chamber, and other equipments for flue gas treatment. In both experiments, the unintentional formation of PCB occurred in the primary combustion chamber at the same time as the decomposition of PCB in input samples. By combusting RDF, non-ortho-PCB predominantly formed, whereas ortho-PCB and symmetric chlorinated biphenyls (e.g., #52/69, #87/108, and #151) tended to be decomposed. ASR formed the higher chlorinated biphenyls more than RDF. These by-products from ASR had no structural relation with ortho-chlorine. Lower chlorinated biphenyls appeared as predominant homologues at the final exit site, while all congeners from lower to higher chlorinated PCB were unintentionally formed as by-products in the primary combustion chamber. This result showed that the flue gas treatment equipments effectively removed higher chlorinated PCB. Input marker congeners of RDF were #11, #39, and #68, while those for ASR were #11, #101, #110/120, and #118. Otherwise, combustion marker congeners of RDF were #13/12, #35, #77, and #126, while those for ASR were #170, #194, #206, and #209. While the concentration of PCB increased significantly in the primary combustion chamber, the value of toxicity equivalency quantity for dioxin-like PCB decreased in the secondary combustion chamber and the flue gas treatment equipments.     

Comparison of instrumental methods for chlorinated dibenzo-p-dioxin (CDD) determination - interim results of a round-robin study involving GC-MS, MS-MS, and high resolution MS

A study was designed to determine the feasibility of using GC-MS-MS techniques for the determination of chlorinated dibenzo-p-dioxins (CDD) and dibenzofurans (CDF) in difficult environmental samples with reduced cleanup. Three fish and three sediment extracts were provided to six different laboratories with GC-MS-MS capability for analysis. In addition, extracts were analysed by GC-low reduction MS (LRMS) and GC-high resolution MS (HRMS). At the time of this report, all participating GC-MS-MS laboratories had not completed their analysis of the supplied samples. All reporting laboratories found the analysis of these very complex samples difficult without extensive cleanup. GC-HRMS determination of some samples was possible with reduced cleanup compared to GC-LRMS.     

Reporting chlorinated dibenzo-p-dioxin and dibenzofuran data in scientific publications

A literature review of recent work involving the determination of chlorinated dibenzo-p-dioxins (CDD) and dibenzofurans (CDF) in fish and incinerator samples has shown many irregularities and omissions in the reported data. Although some of these result from non-standardized nomenclature and reporting practices and do not affect the overall conclusions reached, in some cases omissions in reporting experimental procedures raise important concerns regarding the validity of data and make comparison of data from different investigations difficult. It is not always necessary or even desirable to report every experimental detail of work performed, however, the ultra-trace determination of CDDs and CDFs in complex environmental samples is still at a stage where omission of key experimental details can affect the interpretation of results.     

Prediction of polychlorinated dibenzofuran congener distribution from gas-phase phenol condensation pathways

A model for predicting the distribution of dibenzofuran and polychlorinated dibenzofuran (PCDF) congeners from a distribution of phenols was developed. The model is based on a simplified chemical mechanism. Relative rate constants and reaction order with respect to phenol precursors were derived from experimental results using single phenols and equal molar mixtures of up to four phenols. For validation, experiments were performed at three temperatures using a distribution of phenol and 19 chlorinated phenols as measured in municipal waste incinerator exhaust gas. Comparison of experimental measurements and model predictions for PCDF isomer distributions and homologue pattern shows agreement within measurement uncertainty. The R-squared correlation coefficient exceeds 0.9 for all PCDF isomer distributions and the distribution of PCDF homologues. These results demonstrate that the distribution of dibenzofuran and the 135 PCDF congeners from gas-phase condensation of phenol and chlorinated phenols can be predicted from measurement of the distribution of phenol and the 19 chlorinated phenol congeners.     

Characterization of polychlorinated naphthalenes in stack gas emissions from waste incinerators

Nine typical waste incinerating plants were investigated for polychlorinated naphthalene (PCN) contents in their stack gas. The incinerators investigated include those used to incinerate municipal solid, aviation, medical, and hazardous wastes including those encountered in cement kilns. PCNs were qualified and quantified by isotope dilution high resolution gas chromatography–high resolution mass spectrometry techniques. An unexpectedly high concentration of PCNs (13,000 ng?Nm^?3) was found in the stack gas emitted from one waste incinerator. The PCN concentrations ranged from 97.6 to 874 ng?Nm^?3 in the other waste incinerators. The PCN profiles were dominated by lower chlorinated homologues, with mono- to tetra-CNs being the main homologues present. Furthermore, the relationships between PCNs and other unintentional persistent organic pollutants involving polychlorinated dibenzo-p-dioxins and dibenzofurans, polychlorinated biphenyls, hexachlorobenzene, and pentachlorobenzene were examined to ascertain the closeness or otherwise of their formation mechanisms. A good correlation was observed between ΣPCN (tetra- to octa-CN) and ΣPCDF (tetra- to octa-CDF) concentrations suggesting that a close relationship may exist between their formation mechanisms. The results would provide an improved understanding of PCN emissions from waste incinerators.     

Hazardous air pollutants formation from reactions of raw meal organics in cement kilns

Thermally induced chlorination, condensation, and formation reactions of raw meal organic surrogates were investigated on different types of surfaces. The System for Thermal Diagnostic Studies provided a powerful tool to study these reactions under defined reaction conditions, which were related to typical conditions in the preheater zone of cement kiln. Experiments were conducted with benzene and benzene/myristic acid (C6H6/C13H27COOH) mixtures in a quartz reactor containing different chlorinating catalysts/reagents over a temperature range of 300-500 degrees C. Reaction products were trapped in-line and analyzed by GC-MS. A mixture of chlorides of calcium, potassium, aluminium and iron was highly effective for chlorination/condensation reactions of benzene and benzene/myristic acid mix at temperatures above 300 degrees C. The same behavior was observed only when calcium chloride and potassium chloride were used as chlorinating catalyst/reagent. This result showed that transition metal chlorides like FeCl3 are not necessary for chlorination/condensation of organics under post-combustion conditions. Methylene chloride was the major chlorinated product followed by chloroform and various other C1, C2 and C6 chlorinated products. Yields of chlorinated aliphatics were highest at 400 degrees C for both benzene and benzene/myristic acid mix. C6 products were mainly mono- to hexa-chlorinated benzenes with trace amounts of chlorinated phenols. The major chlorinated products observed in this study (i.e., methylene chloride, chloroform, chloroethanes and monochlorobenzene) were also present as major chlorinated hydrocarbons in the cement kiln field emission data.     

The distribution of polychlorinated dibenzo-p-dioxins and dibenzofurans in Jackfish Bay, Lake Superior, in relation to a kraft pulp mill effluent

Samples of whole effluent and effluent suspended solids from a kraft pulp mill and sediments and biota from Jackfish Bay, Lake Superior were analyzed for polychlorinated dibenzo-p-dioxins (CDDs) and dibenzofurans (CDFs). Tetra-CDFs (4CDF) were consistently detected in whole effluent at levels ranging between 0.3 and 1.3 ng/L. Effluent suspended solids also contained 4CDFs as well as traces of 4CDD, 5CDF, 8CDF and 8CDD. The horizontal sediment distribution suggests that the effluent was the only active source of 4CDF in the area but that 8CDD originated from a more general source such as the atmosphere. An abrupt appearance of 4CDF in the more recent sections of a core profile taken in the bay suggests that an operational change at the pulp mill resulted in the formation of 4CDFs in the mill effluent some time after 1973. Moderate values of 4CDF and low values of 4CDD were found in samples of the shrimp confirming the presence of an active source of 4CDF in Jackfish Bay.     

Reductive dechlorination of polychlorinated dibenzo-p-dioxins by zerovalent iron in subcritical water

A new method for reductive dechlorination of polychlorinated dibenzo-p-dioxins (PCDDs) and remediation of contaminated soils is described that uses zerovalent iron as the dechlorination agent and subcritical water as reaction medium and extractive solvent. It is found that the zerovalent iron can be applied for stepwise dechlorination of octachlorinated dibenzo-p-dioxin (OCDD) on various matrixes in subcritical water. By using iron powder as matrix higher chlorinated congeners were practically completely reduced to less than tetra-substituted homologues. A significant part of residual OCDD, when it was spiked in to soils, and formed less chlorinated congeners are extracted with water in the given conditions. The solubility of OCDD was increased by a 4–6 orders over its solubility at ambient conditions. The new method of contentious-flow extraction is described.     

Effects of injected activated carbon and solidification treatment on the leachability of polychlorinated dibenzo-p-dioxins and dibenzofurans from air pollution control residues of municipal waste incineration

To assess the effectiveness of the injected activated carbon, cement, and sulfur-containing chelating agent in controlling polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) release from the surface of air pollution control (APC) residues, this study examined the leachability of PCDD/Fs from APC residues generated by municipal solid waste incinerators. Results showed that PCDD/Fs were stably retained in the APC residues when the samples were leached with acetic acid solution. Highly chlorinated PCDD/F homologues (i.e., hepta- and octa-CDDs and CDFs) were relatively easy to leach. The leaching percentages of PCDD/Fs from raw APC residue samples containing activated carbon were smaller than those from samples without activated carbon, especially when n-hexane was used as the leachant. These results indicate that the flue gas injected activated carbon not only controls PCDD/F emissions, but also suppresses the leachability of PCDD/Fs from the APC residues. Solidification/stabilization (S/S) processes with 30wt% cement and 5wt% sulfur-containing agent can additionally decrease the leachability of PCDD/Fs with humic acid. Using n-hexane as the leachant, S/S processes increased the leachability of PCDD/Fs. Various low chlorinated PCDD/F congeners were moreover leached out of the APC residue samples, markedly increasing the leachate toxicity. The enhancement of leachability and toxicity owing to S/S processes may negatively impact the environment when APC residues are exposed to nonpolar organic solvents.     

Chloroperoxidase-mediated chlorination of aromatic groups in fulvic acid

The aim of the present study is to investigate whether exo-enzymatically mediated chlorination of fulvic acid (FA) results in the formation of chlorinated groups within the macromolecules which correspond to those which were previously detected in soil and surface water samples. The chlorination was carried out by exposing FA to a commercial chloroperoxidase (CPO) in the presence of chloride and hydrogen peroxide. The exposed FA was then chemically degraded using an oxidative technique and finally analysed for four different aromatic groups and their chlorinated analogues. The particular aromatic groups included were the methyl esters of 4-ethoxybenzoic acid, 3-methoxy-4-ethoxybenzoic acid, 3,4-diethoxybenzoic acid, and 3,5-dimethoxy-4-ethoxybenzoic acid, along with their mono- and dichlorinated analogues. Prior to the chemical degradation procedure, the FA was analysed for AOX (adsorbable organic halogens) and chlorinated acetic acids. The original FA contained 1.4 mg Cl(org) g(-1) and detectable amounts of two chlorinated aromatic groups. After exposure to the enzyme, the concentration of AOX increased to 44.3 mg Cl(org) g(-1) and detectable amounts of four chlorinated aromatic groups as well as di- and trichloroacetic acid were found.     

Identification of surrogate compounds for the emission of PCdd/F (I-TEQ value) and evaluation of their on-line real-time detectability in flue gases of waste incineration plants by REMPI-TOFMS mass spectrometry

Correlations between products of incomplete combustion (PIC), e.g., chloroaromatic compounds, can be used to characterise the emissions from combustion processes, like municipal or hazardous waste incineration. A possible application of such relationships may be the on-line real-time monitoring of a characteristic surrogate, e.g., with Resonance-Enhanced Multiphoton Ionization-Time-of-Flight Mass Spectrometry (REMPI-TOFMS). In this paper, we report the relationships of homologues and individual congeners of chlorinated benzenes (PCBz), dibenzo-p-dioxins (PCDD), dibenzofurans (PCDF) and phenols (PCPh) to the International Toxicity Equivalent (I-TEQ) of the PCDD/F (I-TEQ value) in the flue gas and stack gas of a 22 MW hazardous waste incinerator (HWI). As the REMPI detection sensitivity is decreasing with the increase of the degree of chlorination, this study focuses on the lower chlorinated species of the compounds mentioned above. Lower chlorinated species, e.g., chlorobenzene (MCBz), 1,4-dichlorobenzene, 2,4,6-trichlorodibenzofuran or 2,4-dichlorophenol, were identified as I-TEQ surrogates in the flue gas. In contrast to the higher chlorinated phenols, the lower chlorinated phenols (degree of chlorination <4) were not reliable as surrogates in the stack gas. The identified surrogates are evaluated in terms of their detectability by REMPI-TOFMS laser mass spectrometry. The outcome is that MCBz is the best suited surrogate for (indirect) on-line measuring of the I-TEQ value in the flue gas by REMPI-TOFMS. The correlation coefficient r of the MCBz concentration to the I-TEQ in the flue gas was 0.85.