Info

Source: A. K. Djien Diem and J. A. van Zorge, ESPR-Environ. Sci. Pollut. Res., 1995. "Value represents total of incineration of sewage (5) and paper sludge (2). fcValue represents lubrication oil.

cRange represents total of secondary copper smelting (74-740) and secondary lead smelting (0.7-3.5). Value represents diesel only.

eRange represents total of industrial (100-1000) and residential wood burning (13-63).

PCDD/F are formed and emitted from various thermal processes, such as municipal and hazardous waste incinerators and metallurgy. They are transported globally through the atmosphere and precipitated to the surfaces of plants, soils, and water. In Table 8.1 the most important sources and amounts (inventories) for PCDD/F are summarized for six countries.5 PCDD/F is a mixture of 210 compounds (see Figure 8.2). The 17 toxic isomers are expressed as a special sum parameter value, I-TE value (see the following definition). Besides the formation of PCDD/F by thermal processes, these isomers have been found in the past as by-products in technical products like chlorinated biphenyls (PCBs) and in technical grade pentachlorophenol (PCP). It should be mentioned that the amounts of I-TE emitted from technical incinerators have decreased during the last decade in many industrial countries due to strong legislative measures (ordinances such as clean air acts). For example, most European countries have defined limit values of 0.1 ng I-TE/m3 for the emitted flue gas of waste incinerators. As a result, the estimated value of 400 g I-TE for German municipal waste incinerators for the year 1990 decreased to a value of 4 g I-TE in 1998. The United Nations Environmental Program (UNEP) publishes up-to-date inventories of PCDD/F for the most important countries.6 It can be seen from Table 8.1, that pulp and paper mills today play only a minor part in overall dioxin emissions, while PCDD/Fs are emitted by the wastewater from these plants into the water of the rivers and seas.

8.1 FORMATION OF PCDD/F BY ACCIDENTS

All accidents concerned with PCDD/F are related to the production of chlorophenols. The most famous accident happened in Seveso close to Milan, Italy, on July 10, 1976. ICMESA Corp. manufactured 2,4,5-trichlorophenol for production of phenoxy-herbizides by alkaline hydrolysis of 1,2,4,5-tetrachlorobenzene (see Figure 8.1). This

Figure 8.1 Chemistry of the Seveso accident in 1976.

process is a nucleophilic aromatic substitution of one chlorine atom by a hydroxi group. Due to overheating of the vessel, exothermic condensation did occur instead of substitution with the subsequent bursting of the valve of the apparatus. About 2.6 kg of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were released into the close vicinity of the factory.

Dioxins are mainly by-products of industrial processes, but can also result from natural processes, such as volcanic eruptions and forest fires. Besides the anthropogenic (man-made) sources of PCDD/F discussed earlier, biogenic and geogenic sources for dioxins also have been discovered recently. In natural clays of the kaolinite-type found in German mines in Westerwald, considerable levels of PCDD/ F have been detected;7 the same findings were obtained in special ball clays in the Mississippi area of the United States.8 The pattern (isomeric ratios) of this natural type of dioxins is different from the pattern obtained from incineration plants.

8.2 STRUCTURES, PROPERTIES, AND BEHAVIOR OF PCDD/F

The PCDD/F class consists of 210 compounds, 75 isomers of PCDD, and 135 isomers of PCDF. The number of regioisomers are the following according to the number of chlorine atoms in either skeleton (see Table 8.2).

All PCDD/F isomers are solids with high melting points, but low vapor pressure and low solubility in water. The high octanol-water coefficients are an indication of the observed bioaccumulative behavior in plants and animals for these compounds. Detailed environmentally important physicochemical properties can be found in the literature.9 All higher chlorinated compounds are very persistent in the environment with half-lives of 5-10 years; photolysis with sunlight is the only degradation process in the environment.

Identification and quantification is obtained by combined high-resolution gas chromatography/mass spectrometry (GC/MS) methods after special cleanup procedures of the matrix, as shown later for sediments (see Figure 8.2). The cleanup methods for other matrices are similar. Quantification is obtained by addition of 13-C labeled standards before the cleanup procedure. In general, only the toxic isomers are identified and quantified.

TABLE 8.2 Number of Regioisomers for PCDD and PCDF

Chlorine Substitution

PCDD

PCDF

Mono

2

4

Di

10

16

Tri

14

28

Tetra

22

38

Penta

14

28

Hexa

10

16

Hepta

2

4

Octa

1

1

Total

75

135

20 g Sample <- 13Ci2-PCDD/F-Standards

Soxhlet—extraction 24 h with toluene

25 g Aluminum oxide Elution with 80 mL benzene Elution with 200 mL n-hexane:dichloromethane 98:2 Elution with 200mL n-hexane:dichloromethane 1:1

4 g Silica-gel 10 g Silica-gel/44% H2S04 2 g Silica-gel Elution with 250 mL n-hexane

15 g Florisil Elution with 180 mL n-hexane i Elution with 300 mL dichloromethane

HRGC/HRMS

Figure 8.2 Scheme for the cleanup method of PCDD/F in sediments.

All 210 isomers of PCDD/F have been prepared by standard synthetic routes (see recent review.10). But none of the dioxins or furans are used for any practical purpose. OCDD had been prepared in 1872 by Merz and Weith, but without knowledge of the structure. Unsubstituted dibenzodioxin was prepared in 1906 by Ullmann and Stein. 2,3,7,8-TCDD as well as OCDD were synthesized in 1957 by W. Sandermann by electrophilic chlorination of unsubstituted dibenzodioxin. His group prepared about 15 g of 2,3,7,8-TCDD unintentionally and discovered its toxic behavior on themselves. Dr. Sorge, a medical doctor working for Boehringer Corporation in Hamburg showed the toxicity of 2,3,7,8-TCDD prepared and identified by W. Sandermann. At the same time about 30 workers of Boehringer were engaged in commercial production of trichlorophenol for further production of phenoxy herbicides (see Figure 8.1) and suffered from a severe illness that resembled chloracne and related symptoms. Later it was shown that these technical products were contaminated with traces of 2,3,7,8-TCDD. Trace analysis for PCDD/F did not exist at this time. It should be mentioned that the "Vietnam syndrome" can be traced back to the same cause: technical grade Agent Orange, a defoliant used during the war, was contaminated with traces of 2,3,7,8-TCDD, resulting in the severe illness of a large number of veterans.

8.3 TOXICOLOGY

PCDD and PCDF short-term exposure to humans in high levels may result in skin lesions, such as chloracne and patchy darkening of the skin, and altered liver function. Long-term exposure is linked to impairment of the immune system, the developing nervous system, the endocrine system, and reproductive functions. Chronic exposure of animals to dioxins has resulted in several types of cancer. TCDD was evaluated by International Agency for Research on Cancer (IARC) in 1997. Based on human epidemiology data, dioxin was categorized by IARC as a "known human carcinogen." However, TCDD does not affect genetic material and there is a level of exposure below which cancer risk would be negligible.

Toxic behavior of PCDD/F is a complex matter. Contrary to other poisons, LC-50 (lethal concentration) values that were studied for acute toxicity for a variety of mammals depend largely on the species being investigated. The value (in mg/kg) varies from 0.6 for guinea pigs to 300 for hamsters. For man a LC-50 value larger than 2000 has been estimated. In addition, 2,3,7,8-TCDD shows strong cancerogenic effects when administered to mice and rats. The toxic mechanism is a special binding to the Ah receptor of DNA.11 2,3,7,8-TCDD is the most toxic isomer among the 17 isomers with the 2,3,7,8 pattern (see Table 8.3). These values are obtained by enzyme-induction test studies. Properties of endocrine disruption are most likely.

The dioxin toxic equivalency factor (TEF) approach is currently used worldwide for assessing and managing the risks posed by exposure to mixtures of certain dioxin-like compounds (DLCs).12b-12e World Health Organization-TEF (WHO-TEF) values have been established for humans and mammals, birds, and fish.12b,12f (For new, refined values, see Ref. 12g.) It should be mentioned that 16 PCBs, the coplanar isomers with nonortho, monoortho, and diortho substitution by chlorine (overall, there are 209 isomers for this class of compounds) show dioxin-like toxic behavior. I-TE values are smaller, in the range of 0.0001-0.1. The most toxic isomers is 3,3',4,4',5-pentachlorodiphenyl with I-TE of 0.1.13 Polybrominated dibenzodioxins and furans with the 2,3,7,8 pattern also show dioxin-like toxicity, but their I-TE values are lower compared to PCDD/F.

8.4 POLYCHLORINATED DIBENZODIOXINS AND FURANS AS POLLUTANTS FORMED IN INCINERATIONS

8.4.1 Primary and Secondary Measures for Minimization of PCDD/F in Incineration Plants

PCDD/F are emitted by the flue gas of the incineration plants. Primary measures have become very important in the production and technology of chemistry as the

TABLE 8.3 Toxic Equivalency Factors (TEFs) for Toxic PCDD/F Isomers According to NATO/CCMS (1988) and WHO I-TE

Structure

I-TE-value NATO/ CCMS

1988 WHO-TEF

Structure

I-TE-value NATO/ CCMS

1988e WHO-TEF

2,3,7,8-Tetra-CDD

2,3,7,8-Tetra-CDD

CI CI

0.01

0.01

CI CI

CI CI

Octa-CDD

CI CI

Octa-CDD

0.001

0.001

CI CI

2,3,7,8-Tetra-CDF

2,3,7,8-Tetra-CDF

2,3,4,7,8-Penta-CDF

0.05

0.05

CI CI

CI CI

0.01

0.01

(Continued)

8.4 POLLUTANTS IN INCINERATIONS TABLE 8.3 Continued

Source: Landers J. P. and Bunce, N. J. Biochem. J., 1991,12a and van den Berg M. et al., Environ. Health Perspect., 1998.12b

Source: Landers J. P. and Bunce, N. J. Biochem. J., 1991,12a and van den Berg M. et al., Environ. Health Perspect., 1998.12b principal tool for the protection of the environment. They are related to the principles of green chemistry applied in industrial chemistry, called process-integrated protection of the environment.14 The process in itself is designed to run without or with a minimum formation of pollutants. For incineration plants, this goal can be maintained by the following parameters, called good burning praxis (gbp):15a'15b

Optimal burning temperature

Optimal lambda value (air/fuel ratio)

Optimal residence time of fuel in the flame, in general, regulated by turbulence

For either plant type, incineration, or fuel type, these factors must be empirically determined and controlled. Because dioxins as effluents are concerned, it is possible to reduce I-TE values from about 50 ng/m3 to about 1 ng/m3. Additional secondary measures (filter techniques) are therefore necessary for obtaining the lower limit value of 0.1 ng/m3. Secondary measures are special filter techniques for pollutants formed in nongreen processes, also called end-of-pipe technology.16 The main part of technical incineration plants consists of filter devices, mostly coke as adsorbent is used, which must be decontaminated later by itself by burning in hazardous-waste incinerators. The inhibition technology, discussed later, is related on principles of primary (green) measures for a clean incineration method.

8.4.2 Thermal Formation Mechanisms of PCDD/F

The specific mechanisms of PCDD/F formation in incineration processes are very complex.17a'17b Knowledge of the formation mechanisms of micropollutants allows the development of special minimization techniques and improvement of the whole process, therefore the study of formation mechanisms of toxic side products formed in chemical production is also a contribution to green chemistry.

PCDD/F and other chlorinated hydrocarbons observed as micropollutants in incineration plants are products of incomplete combustion like other products such as carbon monoxide, polycyclic aromatic hydrocarbons (PAH), and soot. The thermodynamically stable oxidation products of any organic material formed by more than 99% are carbon dioxide, water, and HCl. Traces of PCDD/F are formed in the combustion of any organic material in the presence of small amounts of inorganic and organic chlorine present in the fuel; municipal waste contains about 0.8% of chlorine. PCDD/F formation has been called "the inherent property of fire." Many investigations have shown that PCDD/Fs are not formed in the hot zones of flames of incinerators at about 1000°C, but in the postcombustion zone in a temperature range between 300 and 400°C.17a Fly ash particles play an important role in that they act as catalysts for the heterogeneous formation of PCDD/Fs on the surface of this matrix. Two different theories have been deduced from laboratory experiments for the formation pathways of PCCD/F:

1. De novo Theory: PCDD/Fs are formed from particulate (elementary) carbon species found in fly ash in the presence of inorganic chlorine of this matrix,

2. Precursor Theory: PCDD/Fs are formed from chemically related compounds as precursors. Chemically related products of PCDD/Fs are chloro-phenols and chlorobenzenes. Both classes of compounds are present in the effluents of incinerators and can adsorb from the stack gas to the fly ash.17b

Both pathways have been shown to be relevant for PCDD/F formation in municipal-waste incinerations. Chlorophenols can be converted to PCDD by copper species known in synthetic chemistry as the Ullmann type II coupling reaction. By use of isotope labeling techniques in competitive concurrent reactions with both reactions performed in laboratory experiments it was shown that precursor theory pathways from chlorophenols may be more important compared to the de novo pathway, but either competing pathway strongly depends on such conditions as temperature, air flow rate, and residence time.17 It may be difficult to model the complex reality of large incinerators using relevant laboratory experiments.

Recently, a general mechanistic scheme for most chlorinated compounds, including PCDD/F, observed in the effluents of incinerators was proposed using a special flow reactor (turbular furnace reactor) with acetylene as the starting material, and CuCl2 and CuO as the most active catalytic components of fly ash (see Figure 8.3). The mechanism is based on ligand transfer chlorination of acetylene by copper chloride, leading to dichloroacetylene as the starting steps. Dichloroacetylene then condenses to a number of condensation products, such as various perchlorinated aliphatic and aromatic compounds,18a-18b (see Figure 8.3).

Hexachlorobenzene, shown in Figure 8.3, reacts further to chlorophenols and PCDD/F, which stay adsorbed on the copper species but can be further extracted19 in the turbular furnace reactor. All low volatile chlorinated compounds shown in Figure 8.3 are eluted with the gas flow. The lower

Ligand-transfer— oxidation

Metal cyclization

-3 CuCI

CI CI

CI CI Hexachlorobutadiene

CI CI Hexachlorobutadiene

Hexachlorobenzene

Figure 8.3 Scheme for global acetylene chlorination/condensation mechanism leading to hexachlorobenzene. (From A. Wehrmeier et al., Environ. Sci. Technol., 1998.)

chlorinated isomers observed in the effluents are the result of subsequent dechlorination processes. Both classes of chlorine compounds have also been detected in the effluents of incinerators, Chlorobenzenes (CBs) and chlorophe-nols (CPs) are found in the stack gas of incinerators, but in much higher concentrations, showing a linear relationship with concentrations of PCDD/F. CBs and CPs have been used as indicator parameters for PCDD/Fs.20a,20b Chlorinated benzenes have been measured on-line by resonance enhanced multi-photon ionization (REMPI) spectroscopy in stack and flue gases of incinerators. This technique allows a direct and easy-to-do indirect estimation of PCDD/F concentrations in the effluents of incinerators.20a PCDD/F values are generally the result of a measurement during a sampling period of 6 hours, yielding an average value for PCDD/F for this time interval. Since a direct time control for PCCD/F is possible by measurement of indicator compounds an affected plant can be cleansed, for example, by the addition of more air (increase of the lambda value).

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1000.00

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00

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00

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CI4DD

Figure 8.4 Ratio of tetrachlorinated dioxin isomers from a large variety and number of incineration samples. (From A. Wehrmeier et al., Chemosphere, 1998.)

ElectrocycNc ring closure +177.0 (disrotatory) '

CI CI CI

cr ci

0.0 Mild thermal +2'8 equilibration

Minor product

Minor product

Figure 8.5 Observed and calculated reaction pathways from aliphatic C6Cl8-species to hexachlorobenzene. Numbers are values (KJ/mol) calculated by B3LYP/6-31G(2d). (From H. Detert et al., to be published.)

The relative ratio of regioisomers of PCDD/F and other chlorinated compounds formed in incinerators is called the incineration pattern. The pattern can be derived from statistical analysis of a large number of measurements of the same plants, and can be used for elucidation of thermal formation mechanisms in plants. In principle regioisomers can be formed either by stereospecific chlori-nation or dechlorination processes. The pattern has also been used as a part for explaining of the formation mechanism of PCDD/F and other chlorinated compounds formed in incinerations21 (see Figure 8.4).

A more detailed mechanistic study was performed recently for the thermal conversion of perchlorinated aliphatic C-6 polyenes like C6Cl8 into hexachloroben-zene22 (see Figure 8.5).

8.4.3 Inhibition Technology as Primary Measure for PCDD/F Minimization

As a consequence of the detection of catalytic pathways for formation of PCDD/F, special inhibition methods have been developed for PCDD/F. By this approach the catalytic reactions are blocked by adding special inhibitors as "poisoning" compounds for copper and other metal species in the fly ash. Special aliphatic amines (triethylamine) and alkanolamines (triethanolamine) have been found to be very efficient as inhibitors for PCDD/F, and have been used in pilot plants. The effect can be seen in Figure 8.6. The inhibitors have been introduced into the incinerator by spraying them into the postcombustion zone of the incinerator at about 400oC.23a-c

These amines used as inhibitors show negative side effects (disturbances) when used for larger plants. They can be regarded as pollutants by themselves, and can disturb special devices in the plants, especially, when used on a larger scale, filters like electrostatic precipitators. Therefore, we have improved the inhibition method by the use of much safer inorganic compounds as inhibitors, such as,

Figure 8.6 Effect of aliphatic amines addition as inhibitors on PCDD/F concentration (measured on fly ash). (From D. Lenoir et al., Umweltchem. Okotox1989.)

sulfamide and amido sulfonic acid, which can be added directly to the fuel and survive the hot area of the flames before entering the postcombusting zone.24,25 In a recent study, incineration of lignite coal/solid waste/polyvinyl chloride (PVC) was used in a laboratory-scale furnace in order to study the prevention of PCDD/ F formation by inhibitors.25 Nineteen inhibitors divided into four different types of groups (metal oxides, N-containing compounds, S-containing compounds, and N- and S-containing compounds) according to their chemical nature were tested. The total amounts of PCDD/F generated during the experiments with lignite coal, solid waste, and PVC are high enough to investigate a greater inhibition. The average I-TEQ value of the sum of PCDD/F is about 15 pg/g fuel (see Figure 8.7). A relatively low inhibitory effect is observed for the substances that contain only nitrogen. However, higher reduction effects of PCDD/F can be derived for the S-containing substances present in 10% of the fuel. Sulfur itself shows a very strong inhibition effect for PCDD/F. It is already known that sulfur is converted into SO2 and that it reduces Cl2 to HCl, and therefore dioxin and PCB formation can be reduced.26 Also because of this mechanism, the rest of the S-containing compounds probably, inhibit PCDD/F flue gases. Although the single N- and S-containing compounds are not very effective as inhibitors, all other N- and S-containing substances seem to be able to greatly reduce PCDD/F flue gas emission if used as a 10% additive to lignite coal, solid waste, and PVC as fuel. A mixture of (NH2)2CO+S (1:1) can successfully inhibit PCDD/F toxic gases. However, the most effective inhibitors for PCDD/F are (NH4)2SO4 and (NH4)2S2O3. Both compounds can reduce the PCDD/F emission up to 98-99%. In addition, (NH4)2SO4 and (NH4)2S2O3 were used at 5, 3, and 1% of the fuel. The results show that both substances are still effective inhibitors of PCDD/F formation at 5% and 3% of the fuel (see Figure 8.8).

If the percentage of these substances is decreased further, the suppressing effect of dioxin formation will also decrease. (NH4)2SO4 might also reduce the PCDD/F

Figure 8.7 PCDD/F I-TEQ (pg/g) values of flue gas after the combustion of lignite coal, solid waste, and PVC in the samples without inhibitor and 19 different compounds used with a 10% inhibitor of the fuel. (From M. Pandelova et al., Environ. Sci. Technol., 2005.)
Figure 8.8 PCDD/F I-TEQ pg/g fuel values in flue gas for the samples without an inhibitor and with (NH4)2SO4 and (NH4)2S2O3 as inhibitors of the fuel at 10%, 5%, 3%, and 1%.

flue-gas emission up to 90%, even at 3% of the fuel. (NH4)2SO4 is a low-cost and nontoxic material. That makes it suitable for use in full-scale combustion units.

Inhibition technology also has been used recently by two other groups.27'28 Urea as an aqueous solution added to the fuel has been found to be very effective as an inhibitor of PCDD/F in a pilot and technical plant. Furthermore, other N-compounds and S-compounds, such as sulfur dioxide, ammonia, dimethyla-mine, and methyl mercaptan sprayed as gaseous inhibitors in the flue gas, seem to be a promising technique for preventing the formation of PCDD/F in waste incineration.

8.5 CONCLUSION

An important principle in green chemistry is the avoidance of pollutants formed in chemical processes by the use of primary measures. This approach is shown in this chapter for dioxins formed in incinerations. Concentration of PCDD/F in various parts of the environment has increased during the last few decades as result of an increase in use of different technical thermal processes. Therefore, relevant formation mechanisms for PCDD/F have been studied, showing the importance of copper species in inducing catalytic pathways from aliphatic precursors like acetylene in the postcombustion zone at about 300°C. Now, indicator parameters for PCDD/F like chlorobenzenes can be measured on-line, allowing for the cleansing of the plants. The inhibition technology uses the addition of special compounds to block the active sites of copper in the fly ash of incinerators. PCDD/F concentrations are slowly decreasing in the environment due to primary measures discussed in this chapter in combination with advanced filter devices as secondary measures at incineration plants.

REFERENCES

1. Alloway, B. J.; Ayres, D. C. Schadstoffe in der Umwelt, Chemische Grundlagen zur Beurteilung von Luft-, Wasser-, und Bodenverschmutzungen (Chemical Principles of Environmental Pollutants), Spektrum Verlag, Heidelberg, 1996.

2. Ramamoorthy, S.; Ramamoorty, S. Chlorinated Organic Compounds in the Environment, Regulary and Monitoring Assessment, Lewis Publishers, Boca Raton, Fla.,

1997.

3. Schlottmann, U.; Kreibich, M. Nachrichtenbl. Chem., 2001, 49, 608; see also, www.chem.unep.ch/pops/

5. Djien Diem, A. K.; van Zorge, J. A. ESPR-Environ. Sci. Pollut. Res., 1995, 2, 46.

6. Dioxin and Furan Inventories, National and Regional Emissions of PCDD/PCDF, United Nations Environmental Program, Prepared by UNEP Chemicals, Geneva, Switzerland, most recent issue, May 1999.

7. Jobst, H.; Aldag, R. UWSF-Z. Umweltchem. (Okotox., 2000, 12, 2.

8. Ferrario, J. B.; Byrne, C. J.; Cleverly, D. H. Environ. Sci. Technol., 2000, 34, 4524.

9. Mackay, D.; Shiu, W. Y.; Ma, K. C. Illustrated Handbook of Physical-Chemical Properties and Environmental Fate for Organic Chemicals, Vol. II, Polynuclear Aromatic Hydrocarbons, Polychlorinated Dioxins, and Dibenzofurans, Lewis Publishers, Boca Raton, Fla., 1992.

10. Parlar, H.; Angerhofer, D. Dioxins and annulated derivatives, in Houben-Weyl, Vol. E, Hetarenes IV, Thieme, Stuttgart, 1997.

11. Safe, S.; Hutzinger, O.; Hill, T. A. (Eds.) Polchlorinated Dibenzo-p-Dioxins and -Furans (PCDDs/PCDFs). Sources and Environmental Impact, Epidemiology, Mechanisms of Action, Health Risks, Environmental Toxin Series 3, Safe, S.; Hutzinger, O. (Eds.) Springer, Berlin, 1990.

12a. Landers, J. P.; Bunce, N. J. The Ah receptor and the mechanism of dioxin toxicity (Review), Biochem. J., 1991, 276, 273.

12b. Van den Berg, M.; Birnbaum, L.; Bosveld, A. T. C. et al., Environ Health Perspect.,

12c. Ahlborg, U. G.; Brouwer, A.; Fingerhut, M. A. et al., Eur. J. Pharmacol., 1992, 228, 179.

12d. DeVito, M. J.; Diliberto, J. J.; Ross, D. G. et al., Toxicol., Appl. Pharmacol., 1997, 147, 267.

12e. Safe, S. H. Crit. Rev. Toxicol., 1990, 21, 519.

12f. Ahlborg, U. G.; Becking, G. C.; Birnbaum, L. S. et al., Chemosphere, 1994, 28, 1049.

12g. van den Berg, M.; Birnbaum, L. S.; Denison, M. et al. The 2005 World Health Organization re-evaluation of human and mammalian toxic equivalency factors for dioxins and dioxin-like compounds, Toxicol. Sci., 2006, 93, 223-241.

13. Ahlborg, U. G.; Becking, G. C.; Birnbaum, L. S. et al., Chemosphere, 1994, 28, 1049.

14. Christ, C. (Ed.) Production-Integrated Environmental Protection and Waste Management in the Chemical Industry, Wiley-VCH, Weinheim, Germany, 1999.

15a. Lenoir, D.; Kaune, A.; Hutzinger, O. et al., Chemosphere, 1991, 23, 1491.

16. Kaune, A.; Lenoir, D.; Nikolai, U. et al., Organohalogen Compounds, 1995, 23, 477. 17a. Stanmore, B. R. Combust. Flame, 2004, 136, 398.

17b. Dickson, L. C.; Lenoir, D.; Hutzinger, O. Environ. Sci. Technol., 1992, 26, 1822. 18a. Wehrmeier, A.; Lenoir, D.; Sidhu, S. et al., Environ. Sci. Technol., 1998, 32, 2741. 18b. Taylor, H. P.; Lenoir, D. Sci. Total Environ., 2001, 269, 1. 19. Taylor, P.; Wehrmeier, A.; Sidhu, S. S. et al., Chemosphere, 2000, 40, 1297. 20a. Kaune, A.; Lenoir, D.; Schramm, K.-W. et al., Environ. Engi. Sci., 1998, 15, 85. 20b. Blumenstock, M.; Zimmermann R.; Schramm K.-W.; Kettrup A. Chemosphere, 2001, 42, 507.

21. Wehrmeier, A.; Lenoir, D.; Schramm, K.-W. et al., Chemosphere, 1998, 36, 2775.

22. Detert, H.; Zipse, H.; Lenoir, D., to be published.

23a. Lippert, T.; Wokaun, A.; Lenoir, D. Environ. Sci. Technol., 1991, 25, 1485. 23b. Dickson, L. C.; Lenoir, D.; Hutzinger, O. et al., Chemosphere, 1989, 19, 1435. 23c. Lenoir, D.; Hutzinger, O.; Mützenich, G.; Horch, K. Umweltchem. Okotox., 1989, 4, 3.

24. Samaras, P.; Blumenstock, M.; Lenoir, D. et al., Environ. Sci. Technol., 2000, 34, 5092.

25. Pandelova, M.; Lenoir, D.; Kettrup, A.; Schramm, K.-W. Environ. Sci. Technol., 2005, 39, 3345.

26. Gullett, B.; Bruce, K. R.; Beach, L. O. Environ. Sci. Technol., 1992, 26, 1938.

27. Ruokojarvi, P. H.; Asikainen, A. H.; Tuppurainen, K. A.; Ruuskanen, J. Sci. Total Environ., 2004, 325, 83.

28. Kuzuhara, S.; Sato, H.; Tsubouchi, N. et al., Environ. Sci. Technol., 2005, 39, 795.

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