ULTRATRACE DIOXIN AND DIBENZOFURAN ANALYSIS: 30 YEARS OF ADVANCES Ray E. Clement Ontario Ministry of the Environment Laboratory Services Branch 125 Resources Road (P.O. Box 213) Rexdale, Ontario, Canada M9W 5L1
Enough newspaper headlines have appeared around the world that "dioxins" and "furans" are now household words; among the sources they are associated with are incinerators, the pulp and paper industry, the manufacture of chlorophenols and related products, and accidental PCB fires. Those not working directly in the field of the chlorinated dibenzo^>-dioxins (dioxins) and chlorinated dibenzofurans (furans) may t h i n k that these contaminants are relatively new to e n v i r o n m e n t a l r e search. But, in fact, these compounds have been with us since at least 1872 when their synthesis was first re-
ported by German chemists (1). According to scientists at Dow Chemical Company who have performed extensive studies, dioxins and furans m a y be p r o d u c e d a t t r a c e level amounts by any combustion source (2). If this "trace chemistry of fire" h y p o t h e s i s is t r u e , dioxins a n d furans may have been with us since the first forest fire. Despite tremendous research efforts to ascertain the effects of these chemicals on biological s y s t e m s , there is still much we don't know. Until such issues are resolved (and they may never be!), it is clear that the controversy surrounding dioxins and furans will remain. In fact, new sources of these compounds are still being found. At the 1989 International Dioxin Symposium, Travis used modeling techniques to show t h a t four of the major sources of 2,3,7,8-TCDD (i.e., municipal incin-
1130 A · ANALYTICAL CHEMISTRY, VOL. 63, NO. 23, DECEMBER 1, 1991
erators, automobiles, residential wood combustion, and hospital waste incinerators) accounted for only 13% of the total input to the environment (3). He made a convincing case that a few major sources of dioxins—or many minor sources—have yet to be discovered. The concerns and issues raised above have one thing in common: their resolution requires a tremendous number of analytical measurements, at very low detection limits, in a wide variety of sample types. This is a difficult task: The dioxins and furans in all of the sample types u n d e r i n v e s t i g a t i o n m u s t be extracted from the original matrix; separated from a complex mix of hundreds or thousands of other organic co-extractives, some of which are potential interferences present at concentrations many times greater than that of the analytes; and then mea0003-2700/91/0363-1130A/$02.50/0 © 1991 American Chemical Society
sured accurately at part-per-trillion (pptr) or lower concentrations. Ac complishing this task has challenged the abilities of even the most profi cient analytical laboratories. In this REPORT, I will show that analytical science has made tremendous ad vances in determining dioxins and furans over the past 30 years, but that further refinements are still re quired. What are dioxins and furans? The structures of the chlorinated dibenzo-/>-dioxins (CDDs) and t h e chlorinated dibenzofurans (CDFs) are shown in Figure 1. Up to eight chlorine atoms can be placed on the basic structure, giving rise to 75 dioxin congeners and 135 furan con geners. All of the 75 dioxins are con geners of one another, or members of a like group, and congeners having the same number of chlorines are isomers of one another. Thus there are 22 tetrachlorinated dioxin iso mers. A group of dioxin or furan iso mers is often referred to as a conge ner group. Dioxins or furans containing dif ferent numbers of chlorines are often also called homologues. This is, how ever, incorrect because consecutive members of a homologous group dif fer by a fixed s t r u c t u r a l u n i t , whereas dioxin or furan congener groups differ by the number of hy drogens that have been replaced by chlorine atoms. Although the terms "dioxins" and "furans" are technically incorrect, these short-form names are now so widely used t h a t they have become standard terminology. Some of the difficulties inherent in determining these compounds in en vironmental samples can be pre dicted by considering their struc tures. They are hydrophobic; t h u s their determination in water samples must include a consideration of sus pended particulates. They are not, however, particularly soluble in com mon solvents. Compounds with seven or eight chlorine atoms are difficult to dissolve even in toluene, making the preparation and storage of stan dards difficult. Dioxins and furans are also lipophilic, and are thus sub ject to bioaccumulation and biomagnification in the environment. There fore low detection limits are essential to tracking down sources. In addi tion, dioxins and furans are very sta ble, so their long-term transport in the environment is assured once they are emitted into air or water.
in feed fats, and in 1966 X-ray crys tallography techniques led to the identification of one of t h e toxic substances as 1,2,3,7,8,9-hexachlorodibenzo-/>-dioxin. By 1972 the source of the dioxin was traced to fleshing grease from hides contaminated with commercial pentachlorophenol (4). Before 1970, detection limits were in the part-per-million to part-perbillion (ppb) range, and were ob tained using packed-column GC with electron capture detection (ECD). Most work centered on the determina tion of the most toxic dioxin—2,3,7,8TCDD—in industrial chemicals. A typical GC-ECD chromatogram is il lustrated in Figure 2. From 1970 to 1980 the explosive increase in the use of GC/MS meth ods for trace determination of envi ronmental pollutants made GC-ECD somewhat obsolete for use in dioxin determination. The problems with GC-ECD analysis were with specific ity as much as with detection limits: Mixtures obtained from environmen-
REPORT tal sources were so complex t h a t highly specific as well as highly sen sitive detection systems were needed to determine dioxins at low ppb con centrations. In addition, it was be-
Evolution of current methods The development of analytical meth ods w a s complicated by a n o t h e r pressing need, that of the separation of all toxic dioxins and furans from those not considered to be toxic. Un til about 1980 the main challenge consisted of the determination of to tal congener groups (e.g., total tetra chlorinated dioxins and total pentachlorinated dioxins) in addition to the isomer-specific determination of 2,3,7,8-TCDD. However, results from a number of toxicological and bio chemical studies showed that all di oxins and furans with chlorine sub stitution at the 2, 3, 7, and 8 ring positions (Figure 1) were of toxicolog ical concern, not just 2,3,7,8-TCDD. T h u s , for purposes of risk a n d health assessments, those congeners not substituted at the 2, 3, 7, and 8 positions can be ignored; all but 17 of the 75 dioxins and 135 furans fall into this category. Those not consid ered toxic are serious interferences for the 17 that are. For example, of the 22 tetrachlorinated dioxin iso mers, only 2,3,7,8-TCDD is of con cern. But because the 22 isomers are so similar in structure, it is difficult
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Figure 2. GC-ECD chromatogram of dioxins extracted from toxic fleshing grease.
Early detection methods In 1957 millions of broiler chickens in the United States died of "chick edema" disease (4). By 1959 t h e cause was traced to toxic components
coming more i m p o r t a n t to study many different sample types in order to determine the sources and envi ronmental distribution of dioxins and furans. Even GC/MS by itself was in sufficient to produce the desired re sults, and a great deal of front-end chemistry was required to separate trace analytes from potential inter ferences. All of the groundwork for today's state-of-the-art methods was estab lished in the early 1970s, and it can be a r g u e d t h a t most s u b s e q u e n t work h a s simply optimized these early methods.
Figure 1. Structures of the chlorinated dibenzo-p-dioxins and chlorinated dibenzofurans.
The numbers above the peaks represent the numbers of halogen atoms in the individual dioxin molecules. (Adapted with permission from Reference 4.)
ANALYTICAL CHEMISTRY, VOL. 63, NO. 23, DECEMBER 1, 1991 · 1131 A
REPORT to differentiate 2,3,7,8-TCDD from other TCDD isomers in the sample. Conventional MS detection did not help, because the electron ionization mass spectra of dioxin and furan iso mers are almost identical. Other techniques such as FT-IR and NMR spectroscopy, noted for their ability to differentiate among isomers, could not solve this problem because the necessary detection limits were too low. The importance of the correct as signment of identities to dioxin and
furan congeners is further illustrated by Table I, which lists the relative toxicities of the 17 toxic dioxins and fur ans (as determined by toxicological studies) in terms of International Toxicity E q u i v a l e n c y F a c t o r s (ITEFs). More than one set of factors exists, but those shown in Table I are those most commonly used by the in ternational community. The 2,3,7,8TCDD toxicity-equivalent concentra tion for each compound is calculated by multiplying the concentration of the congener by its I-TEF. Summing
Table 1. l-TEFs for 2,3,7,8-substituted dioxins and furans Contaminant Dioxin
Congener 2,3,7,8-TCDD 1,2,3,7,8-P5CDD 1,2,3,4,7,8-H6CDD 1,2,3,7,8,9-H6CDD 1,2,3,6,7,8-H6CDD 1,2,3,4,6,7,8-H7CDD 0BCDD
I-TEF Contaminant 1 0.5 0.1 0.1 0.1 0.01 0.001
Furan
Congener
I-TEF
2,3,7,8-TCDF 0.1 2,3,4,7,8-P5CDF 0.5 1,2,3,7,8-P5CDF 0.05 1,2,3,4,7,8-HgCDF 0.1 1,2,3,7,8,9-H6CDF 0.1 1,2,3,6,7,8-H6CDF 0.1 2,3,4,6,7,8-H6CDF 0.1 1,2,3,4,6,7,8-H7CDF 0.01 1,2,3,4,7,8,9-H7CDF 0.01 0 8 CDF 0.001
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REPORT MS instrumentation, the use of iso tope dilution, quality control proce dures, and other techniques are ap plicable to the study of other trace contaminants. The impact of dioxin/ furan analytical development on the commercial m a n u f a c t u r e of m a s s spectrometer systems illustrates these points very well: Demand for high-resolution systems for dioxin/ furan d e t e r m i n a t i o n s h a s driven manufacturers to greatly improve scan speed and stability, software, and general ruggedness of available instruments. Tough competition be tween various companies has caused the cost of these systems to fall dra matically, enabling many additional laboratories to gain access to this ad vanced technology. Thirty years of dioxin/furan r e search has benefited many fields in addition to significantly advancing analytical science. Studies in toxicol ogy, epidemiology, e n v i r o n m e n t a l transport and fate, and many other fields would be difficult or impossible without the support of analytical chemists and their sensitive, specific methodologies. Although advances to date in dioxin/furan m e a s u r e m e n t capability have been impressive, it
would not be surprising if those in the next decade are equally so. Thanks are extended to Tom Tiernan of Wright State University and Joel Bradley of Cambridge Isotope Laboratories for their valuable com ments in the preparation of this manuscript. This paper is based on a presentation given at the 42nd Pittsburgh Conference and Exposition.
References (1) Long, J. R.; Hanson, D. J. Chem. Eng. News 1983, June 6, 25. (2) Bumb, R. R.; Crummett, W. B.; Cutie, S. S.; Gledhill, J. R.; Hummel, R. H.; Kagel, R. O.; Lamparski, L. L.; Luoma, E. V.; Miller, D. L.; Nestrick, T. J.; Shadoff, L. Α.; Stehl, R. H.; Woods, J. S. Science 1980, 210, 385-90. (3) Travis, C. Α.; Hattemer-Frey, H. A. Chemosphere 1990, 20(7-9), 729-42. (4) Firestone, D. Environ. Health Perspect. 1973 5 59—66 (5) Clement, R. E. Ph.D. Dissertation, University of Waterloo, 1981, p. 202. (6) Baughman, R.; Meselson, M. In ACS Advances in Chemistry Series; American Chemical Society: Washington, DC, 1973; Vol. 120, pp. 92-104. (7) Karasek, F. W.; Clement, R. E. Basic Gas Chromatography-Mass Spectrometry: Principles and Techniques; Elsevier Sci ence: Amsterdam, 1988, p. 126. (8) Bradley, J. C; Nichols, A. W.; Bon aparte, K.; Campana, J. E.; Clement R. E.; Czuczwa, J. M.; DeRoos, F. L. Lamparski, L. L.; Nestrick, T. J. Patterson, D. G.; Phillips, D. L.; Stan
ley, J. S.; Tondeur, Y. G.; Wehler, J. R. Chemosphere 1990, 20, 487-94. (9) Hanson, D. J. Chem. Eng. News 1991, Jan. 28, 7. (10) Hanson, D. J. Chem. Eng. News 1991, Apr. 29, 13-14. (11) Hanson, D. J. Chem. Eng. News 1991, Aug. 12, 7-14.
Ray E. Clement was awarded a Ph.D. from the University of Waterloo in 1981. He joined the Ontario Ministry of the En vironment in 1982 and is currently a se nior research scientist in the Laboratory Services Branch. Clement has published 90 scientific papers, mostly in the dioxin/ furan field, and has published or edited four books. He has a strong interest in teaching environmental and analytical chemistry and holds appointments at Carleton University and the University of Western Ontario. He was recently ap pointed to the ANALYTICAL CHEMISTRY Instrumentation Advisory Panel.
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