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Received for review August 6,1990. Revised manuscript received March 15,1991. Accepted May 1,1991. This work is sponsored by U.S. National Science Foundation Grant BCS-8921000.
Polychlorodibenzothiophenes, the Sulfur Analogues of the Polychlorodibenzofurans Identified in Incineration Samples Hans-Rudolf Buser" Swiss Federal Research Station, CH-8820 Wadenswii, Switzerland
Ivan Samuel Dolezal and Max Wolfensberger Swiss Federal Institute for Materials Testing and Research, CH-8600 Dubendorf, Switzerland
Chrlstoffer Rappe Institute of Environmental Chemistry, University of Umei, $90 187 Umei, Sweden
Polychlorodibenzothiophenes (PCDTs), the sulfur analogues of the polychlorodibenzofurans (PCDFs), were identified in fly ash from two municipal solid waste incinerators and from an electric-arc furnace of a carshredding facility. Gas chromatography/mass spectrometry (GC/MS) and MS MS experiments were used to detect the new compoun s in addition to the related polychlorodibenzodioxins (PCDDs) and PCDFs and to differentiate PCDTs from the nominally isobaric PCDDs. Among the PCDTs detected were tetra- and pentachloro isomers including the 2,3,7,8-tetrachlorodibenzothiophene. The concentrat,ions of PCDTs in fly ash were up to 55 ng/g, at or 1magnitude below the concentrations of the PCDDs and PCDFs in these samples. The sources and routes of formation of the new compounds are still unknown. Various pathways seem plausible, and as an example, we report on the formation of PCDTs from the thermal reaction of chloro aromatic compounds [polychlorobiphenyls (PCBs)] with elemental sulfur.
d
Introduction It is more than a decade ago that polychlorodibenzodioxins (PCDDs) and polychlorodibenzofurans (PCDFs) (Figure 1)were detected in incineration samples (fly ash and flue gas) (1, 2). These findings triggered a large number of studies monitoring these compounds in industrial and municipal incinerators (3),and efforts were taken to minimize emissions from such installations. Nevertheless, these emissions are still one of the major 0013-936X/91/0925-1637$02.50/0
sources responsible for the ubiquitous presence of these compounds, especially in the industrialized world (4). Besides the PCDDs and PCDFs, numerous other halogenated organic compounds were detected in emissions from incineration sources. In particular, the presence of polychlorinated biphenyls (PCBs), naphthalenes (PCNs), benzenes, phenols, styrenes, biphenylenes, pyrenes/ fluoranthenes, and other polycyclic aromatic compounds has been reported (5). Other halogenated dibenzodioxins and dibenzofurans were also detected and included the bromo/chloro analogues ( 5 , 6 ) ;polybromodibenzodioxins and polybromodibenzofurans were detected from the burning of brominated flame retardants, present in many plastic consumer products (7). Among all these compounds the PCDDs and the PCDFs are of special importance because of their high toxicity (3, 4, 8). Recently, we reported on the presence of polychlorodibenzothiophenes (PCDTs; Figure 1)in aquatic samples and on analytical methods for the determination of these compounds at trace levels (9). Gas chromatography/mass spectrometry (GC/MS) including MS/MS experiments was investigated for the detection of PCDTs and used to differentiate between PCDTs and the nominally isobaric PCDDs. In that study, individual or mixtures of PCDTs were synthesized by a novel thermal reaction of PCBs with sulfur. Potentially, this or related reactions between chloro aromatic compounds and elemental sulfur (or sulfur compounds) could be of environmental significance and lead to the formation of PCDTs. The analytical methods previously evaluated were now employed to search for
0 1991 American Chemical Society
Environ. Sci. Technol., Vol. 25, No. 9, 1991 1637
Table 1. Operating Conditions and Details on the Incinerators Sampled incinerator
type'
operation
load, tons/h
stack emissn rate, lo3 Nm3/h
flue $as temp, OC
mg/m3
1 2 3 4
MSWI MSWI MSWI EAF
cont cont cont batch
2.8 10.6 3.6 119 (2 h)
39.6 75 50 370
242 255 61 69
200 180 7 31
a MSWI,
municipal solid waste incinerators; EAF, electric-arc furnace of a car-shredding facility.
[SO219
Values measured after electrofilters.
Table 11. Concentrations of PCDDs, PCDFs, and PCDTs in Electrofilter Fly Ashes of Four Incineratorsa I
111
II
IV
Flgure 1. Structures of tetra-CDFs (I) and tetra-CDDs (I I) and their sulfur analogues, tetra-CDTs (111) and tetraCTAs (IV). The substitution
Is not necessarily symmetrical. The PCDTs Mentifled in this study are nominally lsobarlc with the PCDDs.
PCDTs in incineration samples. Here, we report on the finding of PCDTs, the sulfur analogues of the PCDFs, in fly ash samples from several incinerators, and particularily on the presence of the tetra- and pentachloro congeners.
Experimental Section Sample Description. Fly ash samples from three municipal solid waste incinerators (MSWI) and an electric-arc furnace with graphite electrodes of a car-shredding facility were investigated. All installations are located in Switzerland and equipped with emission control units. Fly ash samples were removed from the electrofilters of these installations. In the case of the MSWI facilities, supplementary fuel (low-sulfur heating oil) was used to start incineration; no supplementary fuel was used during operation and sampling. Details on these installations and operating conditions are given in Table I. Sample Preparation. Standard procedures routinely used for the analysis of PCDDs and PCDFs were used (10). They included an acid treatment of 5-100 g of fly ash followed by Soxhlet extraction with toluene and several chromatographies on silica and alumina. Extraction and cleanup were controlled by addition of 13C-labeled surrogate compounds. The chromatographic fractions containing the PCDDs and PCDFs were first analyzed for these compounds; a summary of these results is given in Table 11. The same fractions were then further investigated for the presence of additional chloro compounds. Previous experiments showed that the PCDTs move into the same fraction as the PCDDs and PCDFs and are stable to a sulfuric acid/silica treatment. For analysis, residues were redissolved on toluene. Sample aliquots of 2 FL, corresponding to 30-300 mg of fly ash, were injected. Reference Materials. A series of tetrachlorodibenzothiophenes (tetra-CDTs) was synthesized by the thermal reaction of hexachlorobiphenyls with sulfur at 540 "C (9). Additionally, mono- to penta-, and tri- to hepta-CDTs were obtained as mixtures from the thermal reaction of commercial PCBs (Aroclors 1254 and 1260) with sulfur, respectively, and mono- to octa-CDTs were synthesized as a mixture from the chlorination of dibenzothiophene. The formation of PCDTs from PCBs was determined to proceed via displacement of two ortho C1 substituents by sulfur, a reaction similar to the formation of PCDFs from 1638 Environ. Sci. Technoi., Voi. 25, No. 9, 1991
compounds
incin 1
tetra-CDDs penta-CDDs hexa-CDDs hepta-CDDs octa-CDD tetra-CDFs penta-CDFs hexa-CDFs hepta-CDFs octa-CDF tetra-CDTs penta-CDTs
200 450 1100 600 730 75 140 170 210 100
