Effects of selected metal oxides on the dechlorination and destruction of PCDD and PCDF

OCDD and OCDF spiked silica/graphite based model fly ash containing various copper compounds and metal oxides were thermally treated under oxygen deficient conditions. All copper compounds tested showed a considerable dechlorination/hydrogenation reaction at 260 °C. After 30 min at 340 °C, less than 1% of the spiked OCDD and OCDF was recovered as T₄CDD/F to OCDD/F. Other compounds tested demonstrated a lower rate of dechlorination compared to the copper compounds. However, all other metal oxides showed a small dechlorination effect at 260 °C, which was considerably increased at 340 °C.

The model fly ash containing the different copper compounds or metal oxides showed comparable PCDD and PCDF isomer patterns after thermal treatment. However, small differences were observed among the different tested compounds. The PCDD and PCDF isomer patterns on the model fly ashes were similar to patterns found during dechlorination experiments on fly ashes from waste incineration processes.

Model fly ash containing Ca(OH)₂ exhibited the highest destruction potential, but a low dechlorination potential. In contrast, model fly ash containing any of the remaining compounds tested, was found to predominantly dechlorinate the spiked OCDD and OCDF.     

Distribution patterns of PCDD/Fs in chlorinated chemicals

The purpose of this research was to determine polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) in five chlorinated chemicals (phthalocyanine copper, phthalocyanine green, chloranil-1 and 2, and triclosan), and to compare their 2,3,7,8-tetrachlordibenzo-IpI-dioxin equivalents (TEQ). The distribution patterns of total PCDD/Fs and 2,3,7,8-substituted PCDD/Fs were elucidated in detail. The TEQ values of toxic PCDD/Fs in all chemicals were in the range of 5.03-1379.55 ng I-TEQ/kg. The contribution of OCDD and OCDF in phthalocyanine green was 75% of the total TEQ. For chloranils, the maximum contribution of toxic PCDD/Fs was from 2,3,7,8-substituted HxCDF and 2,3,7,8-substituted HpCDF. The TEQ of HxCDF and HpCDF in chloranil-1 was 90% and in chloranil-2 was 71%. And the toxic contribution increased with the degree of chlorination for PCDFs.     

PCDD/PCDF,chlorinated pesticides and PAH in Chinese teas

Four samples of Chinese tea (two green teas, and two brick teas) were analyzed for their concentrations of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/PCDF), chlorinated pesticides and PAH. The infusions prepared from these teas were also analyzed for PCDD/PCDF. The levels of DDT and its metabolites in tea leaves were within the safety limit of 0.2 mg/kg. Rather high levels of total PAH were obtained in brick tea (1048–1162 mg/kg), when compared with green tea (497–517 mg/kg). In terms of PCDD/PCDF, the concentrations of green tea and brick tea differed by a factor of 16, while the concentrations of all infusions were within a factor of 2. The dioxin concentrations in green tea leaves can be explained through uptake of atmospheric PCDD/PCDF. The higher concentrations in the brick tea leaves are due the longer exposure time, and to certain extent, the use of old leaves, branches and roots when making the tea, and additional components such as soil particulates through contamination. Certain Chinese populations drinking a large amount of brick tea (>3 l per day) indicated that individuals of these populations consume more tea than Europeans or North Americans result in a comparably higher intake of PCDD/PCDF. Tea consumption can attribute to up to 10% of the TDI recommended by WHO (only PCDD/PCDF considered, no PCB analyzed).     

Pharmacokinetic model of dioxin and furan levels in adipose tissue from Sawmill work involving chlorophenate fungicides

Sawmill workers in British Columbia (B.C.), Canada, have been exposed to chlorophenate fungicides which are known to be contaminated with polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). Due to concern about the potential of these workers to have significant body burdens of PCDD/Fs, and the absence of measurements in these worker, a single-compartment pharmacokinetic model was developed to estimate the concentration of PCDD/Fs in the fat tissue of the sawmill workers. Data from a large cohort of B.C. sawmill workers and literature-based data on chlorophenate exposures and PCDD/F concentrations in chlorophenates were used in Monte Carlo simulations to predict a PCDD/F body burden distribution. The median concentrations of HxCDF and HpCDF predicted using the model for the B.C. sawmill worker population exceeded the range measured in unexposed populations. PeCDF and OCDF concentrations exceeded the range measured in unexposed populations at the 70th percentile of the model-predicted distribution, and PeCDD at the 90th percentile. The primary limitation of the model was the scarcity of input data about actual dermal and inhalation exposures to chlorophenates.     

CuCl2-catalyzed PCDD/F formation and congener patterns from phenols

Homologue and isomer patterns of polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) in CuCl2-catalyzed formation were studied in an isothermal flow reactor using a distribution of 20 phenols as measured in municipal waste incinerator (MWI) exhaust gases. A mixture of 20 phenols was synthesized and used as reactants for this study because phenols are known to be key precursors in the formation of PCDD/F. Experiments were conducted at 400 degrees C. The 92% of nitrogen (N2) and 8% of oxygen (O2) were used as a carrier gas. PCDD/F homologue and isomer patterns with dibenzo-p-dioxin (DD) and dibenzofuran (DF) were obtained from a mixture of 20 phenols. DF+PCDF formation was favored over DD+PCDD formation. The major homologue groups formed were non-chlorinated DD and DF, and PCDD/F homologue fraction decreased with the degree of chlorination. PCDD/F homologue and isomer distributions were almost constant. Phenol and lower chlorinated phenols present in high amount played an important role in PCDD/F congener distributions. The results presented here can be used as characteristics or fingerprints for homologue and isomer patterns of PCDD/F formation attribution in CuCl2-catalyzed reaction from phenols.     

Alumina as a model support in the formation and dechlorination of polychlorinated dibenzo-p-dioxins and dibenzofurans

Alumina was studied as a model matrix for formation and dechlorination reactions of PCDDs and PCDFs. Only small differences in PCDD and PCDF formation were found between de-novo synthesis on alumina and on fly ash. The amounts of PCDDs and PCDFs formed on acidic alumina were much larger than on neutral and alkaline alumina. OCDD and OCDF were rapidly dechlorinated on basic alumina.     

PCDD/Fs in ambient air collected in Zagreb, Croatia

Levels of PCDD/Fs were measured at four different sites in Zagreb, capital of Croatia. Also one sample was taken during spontaneously initiated open fire on a landfill and one sample where garden waste of unknown content was burnt. Over period 1997–2000, 28 samples were collected and levels ranged between 9 and 306 fg I-TEQ m⁻³, except in the sample collected during landfill fire. Air PCDD/F levels in Zagreb at four sites were different and the highest levels were observed in industrial area. Seasonal variation of levels is also evident with higher levels in winter than in summer. Our results show that PCDD/F levels in ambient air collected in Zagreb are at lower end of the published data range. In general, homologue profiles were quite similar for all locations, the concentration of PCDD homologues increased while the concentration of PCDF homologues decreased with increasing degree of chlorination. PCDD/F levels in the landfill fire sample was 13 200 fg I-TEQ m⁻³ which are much higher than levels in garden waste burning sample or in sample collected at industrial site. During landfill fire, the concentration of 2,3,7,8-TCDF becomes even higher than the concentration of OCDF and is equal to the concentration of 1,2,3,4,6,7,8-HpCDF.     

Formation of PCDF, PCDD, PCB, and PCN in de novo synthesis from PAH: mechanistic aspects and correlation to fluidized bed incinerators

The difference of polychlorinated dibenzofurans (PCDF) isomer patterns between stoker type incinerators and some fluidized bed incinerators (FBI) is a key to understand the formation mechanisms in both types of incinerators. The total yield and the isomer patterns of PCDF, polychlorinated biphenyls (PCB), polychlorinated naphthalenes (PCN), and polychlorinated benzenes (PCBz) formed via de novo synthesis from polycyclic aromatic hydrocarbons (PAH) indicate that chlorinated aromatics in the FBI are formed as a result of PAH breakdown. The detailed analysis of the isomer patterns of PCDF, PCB and PCN gives a first insight into the transformation mechanism of the PAHs and the sequence of degradation, chlorination and oxygen insertion. The major chlorination takes part at the position of the C-C cleavage during degradation of the PAHs. Further chlorination of the hydrogen position of the former PAH takes part preferably in ortho-position to this chlorination or is directed by incorporated oxygen. A perylene structure in soot is proposed as basis for the observed PCDF pattern in the FBI. Polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated phenols (PxCP) were formed in lower concentrations from the de novo experiments indicating an additional formation pathway for these compounds in the FBI.     

Emissions behavior and distribution of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) from cement kilns in China

The production of cement in China is accompanied by various emissions, such as fine particulate matter, heavy metals, nitrogen oxides, sulfur oxides, carbon dioxide…. Moreover, cement kiln presents a potential health risk to its surroundings, linking to emissions of persistent organic pollutants (POPs), such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), in brief dioxins. Flue gas samples were collected from five typical cement kilns during twelve runs and were used to evaluate the levels and distribution of PCDD/Fs in the emissions from cement kilns. The PCDD/Fs concentrations (136 congeners) and I-TEQ values ranged from 2.3 to >40 ng/m³ and 9.3?～?90.8?×?10^?3 ng I-TEQ/m³, respectively, which were lower than the emission standard in China (0.1 ng I-TEQ/m³). In weight units, the dominant congeners were OCDD, 1,2,3,4,6,7,8-HpCDF, and OCDF; 2,3,4,7,8-PeCDF is the largest contributor (36–66 %) to the total I-TEQ value of twelve runs. HxCDF and TCDF were the first two most abundant homologue groups (12–85 and 4–52 %), and the homologue concentration decreased with rising chlorine number for PCDDs. In addition, there was no marked difference in homologue profiles when solid wastes (refuse-derived fuel and municipal solid waste) and hazardous wastes (DDT and POPs) were combusted as supplemental fuels. The use of various supplemental fuels had no obvious effect on the fingerprint of PCDD/F homologues. Moreover, there was no significant difference in levels of PCDD/Fs emission due to the diversity of production capacity, which were consistent with reported previously. Air pollution control device had effect on the homologue profiles, and cement system with electrostatic precipitators (ESP) had more fractions of octachloro congeners to the total.     

Concentrations,atmospheric partitioning,and air–water/soil surface exchange of polychlorinated dibenzo-p-dioxin and dibenzofuran along the upper reaches of the Haihe River basin,North China

Polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/PCDF) were overall measured and compared in ambient air, water, soils, and sediments along the upper reaches of the Haihe River of North China, so as to evaluate their concentrations, profiles, and to understand the processes of gas–particle partitioning and air–water/soil exchange. The following results were obtained: (1) The average concentrations (toxic equivalents, TEQs) of 2,3,7,8-PCDD/PCDF in air, water, sediment, and soil samples were 4,855 fg/m³, 9.5 pg/L, 99.2 pg/g dry weight (dw), and 56.4 pg/g (203 fg TEQ/m³, 0.46 pg TEQ/L, 2.2 pg TEQ/g dw, and 1.3 pg TEQ/g, respectively), respectively. (2) Although OCDF, 1,2,3,4,6,7,8-HpCDF, OCDD, and 1,2,3,4,6,7,8-HpCDD were the dominant congeners among four environmental sinks, obvious discrepancies of these congener and homologue patterns of PCDD/PCDF were observed still. (3) Significant linear correlations for PCDD/PCDF were observed between the gas–particle partition coefficient (K _p) and the subcooled liquid vapor pressure (P _L ⁰) and octanol–air partition coefficient (K _oa). (4) Fugacity fraction values of air–water exchange indicated that most of PCDD/PCDF homologues were dominated by net volatilization from water into air. The low-chlorinated PCDD/PCDF (tetra- to hexa-) presented a strong net volatilization from the soil into air, while high-chlorinated PCDD/PCDF (hepta- to octa-) were mainly close to equilibrium for air–soil exchange.     

Effects of combustion and operating conditions on PCDD/PCDF emissions from power boilers burning salt-laden wood waste

This paper discusses the effects of combustion conditions on PCDD/PCDF emissions from pulp and paper power boilers burning salt-laden wood waste. We found no correlation between PCDD/PCDF emissions and carbon monoxide emissions. A good correlation was, however, observed between PCDD/PCDF emissions and the concentration of stack polynuclear aromatic hydrocarbons (PAHs) in the absence of TDF addition. Thus, poor combustion conditions responsible for the formation of products of incomplete combustion (PICs), such as PAHs and PCDD/PCDF precursors, increase PCDD/PCDF emissions. PAH concentrations increased with higher boiler load and/or low oxygen concentrations at the boiler exit, probably because of lower available residence times and insufficient excess air. Our findings are consistent with the current understanding that high ash carbon content generally favours heterogeneous reactions leading to either de novo synthesis of PCDD/PCDFs or their direct formation from precursors. We also found that, in grate-fired boilers, a linear increase in the grate/lower furnace temperature produces an exponential decrease in PCDD/PCDF emissions. Although the extent of this effect appears to be mill-specific, particularly at low temperatures, the results indicate that increasing the combustion temperature may decrease PCDD/PCDF emissions. It must be noted, however, that there are other variables, such as elevated ESP and stack temperatures, a high hog salt content, the presence of large amounts of PICs and a high Cl/S ratio, which contribute to higher PCDD/PCDFs emissions. Therefore, higher combustion temperatures, by themselves, will not necessarily result in low PCDD/PCDFs emissions.     

Environmental prospection for PCDD/PCDF, PAH, PCB and heavy metals around the incinerator power plant of Reggio Emilia town (Northern Italy) and surrounding main roads

Samples of soil, sediment and pine needles from the Reggio Emilia area were analysed in order to estimate the environmental pollution caused by an MSWI. PCDD/PCDF, PCB, PAH and metals were analysed in the collected samples. The data obtained showed relatively low pollution levels. Indeed, the PCDD/PCDF and PCB data were comparable to the values usually found in the grazing areas of the European Union countries. Metal concentrations in soils and sediments may be related to local geological occurrences and to agricultural activities. PAH values are significantly lower than the limit values set by the Italian law.     

Dechlorination and destruction of PCDD,PCDF and PCB on selected fly ash from municipal waste incineration

The potential of fly ash to dechlorinate and destroy PCDD, PCDF and PCB was tested under oxygen deficient conditions in the laboratory. Specifically, two types of fly ash were compared, originating either from a fluidized bed incinerator using Ca(OH)₂ spray (FA1), or a stoker incinerator without Ca(OH)₂ impact (FA2).

Results from the present study indicate that on FA2 type fly ash, the degradation processes of OCDD, OCDF and D₁₀CB occurred primarily via dechlorination/hydrogenation up to temperature settings of 340 °C. In contrast, FA1 type fly ash was found to effect both dechlorination and destruction of these compounds already at temperature settings of 260 °C.

The dechlorination velocity of PCDD and PCDF did not differ significantly. However, the first dechlorination step of OCDF in the 1,9-position occurred faster compared to the first dechlorination step of OCDD.

The isomer pattern resulting from the dechlorination processes was quite similar on both FA1 and FA2, indicating that differences in alkalinity or elemental composition of the two types of fly ashes do not have a significant influence on the position of dechlorination. PCDD and PCDF dechlorination of the 2,3,7,8-positions was not favoured over dechlorination of the 1,4,6,9-positions on either type of fly ash. In contrast, dechlorination of PCB occurred predominantly on the toxicological relevant 3- and 4-positions.

The dechlorination/destruction processes were completed on both types of fly ash at 380 °C within one hour, which correlates well with results obtained from actual plant operation practices.     

Comparison of PCDD/PCDF levels in soil, grass, cow''s milk, human blood and spruce needles in an area of PCDD/PCDF contamination through emissions from a metal reclamation plant

When in the vicinity of a metal reclamation plant in Tyrol, Austria, increased PCDD/PCDF levels were found in soil and spruce needles, the extent of grass contamination as well as the PCDD/PCDF content in milk of cows fed with hay from this area was determined. The milk samples showed a significant increase in PCDD/PCDF levels compared to control samples. In a blood sample of a farmer a significant increase in PCDD/PCDF levels was found. Correlations in PCDD/PCDF levels between soil, spruce needles, grass, cow's milk and human blood will be presented.     

Search for industrial sources of PCDD/PCDFs: II. Metal chlorides

FeCl₃, AlCl₃, CuCl₂, CuCl, SiCl₄ and TiCl₄ were analysed for their content of PCDD/PCDFs and other chloroaromatic compounds. FeCl₃ and AlCl₃ contain OCDF and H₇CDF in ppb- and hexachlorobenzene in ppm-range; CuCl₂ and CuCl contain lower concentrations of OCDF, H₇CDF and additionally OCDD, H₇CDD and hexachlorobenzene in ppb/ppt-range. SiCl₄ and TiCl₄ contain no measurable quantities of PCDD/PCDFs and hexachlorobenzene. A correlation between the PCDD/PCDF - and hexachlorobenzene-content is postulated for products of industrial sytheses involving high temperatures. The origin of the organic substances in a process of inorganic chemistry could be oils on the waste metals which are used in the manufacture of metal chlorides.     

Kinetics of carbon degradation and PCDD/PCDF formation on MSWI fly ash

The native carbon oxidation and PolyChloroDibenzo-p-Dioxins and PolyChloroDibenzoFurans, PCDD/F, formation were simultaneously studied at different temperatures (230-350 degrees C) and times (0-1440 min) in order to establish a direct correlation between the disappearance of the reagent and the formation of the products. The kinetic runs were conducted in an experimental set up where conditions were chosen to gain information on the role of fly ash deposits in cold zones of municipal solid waste incinerators in PCDD/F formation reaction. The carbon oxidation measured as the decrease of total organic carbon of fly ash was in agreement with the carbon evolved as sum of CO and CO(2). The carbon mass balance indicated an increase in the efficiency of carbon conversion in CO and CO(2) with temperature. The CO and CO(2) formation was the result of two parallel pseudo first order reactions thus giving significant information about the reaction mechanism. PCDD/F formation as a function of temperature showed that the maximum formation was achieved in a narrow range around 280 degrees C; the time effect at 280 degrees C was a progressive formation increase at least up to 900 min. The PCDF:PCDD molar ratio increased with temperature and time, and the most abundant homologues were HxCDD, HpCDD, OCDD for PCDD, and HxCDF, HpCDF within PCDF. These experimental results supported the hypothesis that the formation mechanism was the de novo synthesis.     

PCDD/PCDF Isomer patterns in waste incinerator flyash and desorbed into the gas phase in relation to temperature

The influence of temperature on the PCDD and PCDF isomer profiles of a municipal waste incinerator flyash and the PCDD/PCDF desorbed from the ash under an inert atmosphere was investigated using a bench-scale reactor. Exposure to temperatures of 250 degrees C and above resulted in significant changes in the distribution of isomers within most dioxin and furan congener groups. The PCDD content tended to become more evenly distributed across the range of isomers than was the case for the raw flyash, while the PCDF content became concentrated across a relatively lower number of isomers. In most cases the desorbed PCDD/PCDF were mainly mono- to tri-chlorinated, and hence had a relatively low I-TEQ value. The isomer profiles of the desorbed species were also influenced by temperature. There were some significant differences between the PCDF isomer profiles of the desorbed species and those of the treated flyashes under the same conditions, but no clear differences between the PCDD isomer profiles.     

Surface catalyzed formation of polychlorinated dibenzo-p-dioxins/dibenzofurans during municipal waste incineration

A series of reactions was carried out on different surfaces using carbon and CuCl₂, and KCl or HCl as a Cl-source. The PCDD/PCDF congener distribution was seen to vary to a great extent but the isomer distribution remained fairly constant. It is concluded that thermodynamic properties are largely responsible for the PCDD/PCDF isomer distribution. With pentachlorobenzene Cl₂ elimination, assisted by oxygen, appears to be the major pathway for PCDD/PCDF formation.     

Comparison of PCDD and PCDF in flyash collected from muncipal incinerators of different countries

Flyash samples were collected from the electrostatic precipitators of seven municipal refuse incinerators of four different countries. Analytical results of PCDD and PCDF in these samples shows a very similar iosmer distribution pattern for all PCDD/PCDF although concentrations of PCDD and PCDF vary. These results imply that PCDD/PCDF were formed through the same mechanism in those incinerators regardless of garbage composition or incinerator design.     

Correlation of PCDD/PCDF and CO values in a MSW incinerator--indication of memory effects in the high temperature/cooling section

The correlation of PCDD/PCDF levels with the CO emissions in a full-scale municipal waste incinerator was assessed during a four-week measurement effort. PCDD/PCDF concentrations in fly ashes-containing more than 99% of the total PCDD/PCDF burden of the fluidized bed incinerator (FBI)-were measured and compared with the emitted CO concentrations. The CO concentration during the sampling time showed no significant correlation to the PCDD/ PCDF amount in fly ash (R2 = 0.078). However, a comparison of the time integrated CO concentration several hours before sampling lead to a correlation with the PCDD/PCDF burden. Maximum correlation was found for the time integrated CO values of 3 and 4 h before sampling (R2 = 0.467 and R2 = 0.457 respectively). This indicates a memory effect in the high temperature cooling section of several hours. Possible mechanisms leading to the memory effect are discussed. The correlation of PCDD/PCDF with CO concentration demonstrate that the combustion conditions play an important role for PCDD/PCDF formation in FBIs. However the variability in the correlation of CO to PCDD/PCDF levels show that other factors have a significant influence on PCDD/PCDF formation.