Environ. Sci. Technol. 1986, 20, 1185-1186
CORRESPONDENCE Comment On “Airborne Dioxins and Dibenzofurans: Sources and Fates” SIR: Recently Czuczwa and Hites reported (1) results concerning chlorodibenzodioxins and -furans in the environment. In it, they speculate that the distribution of compounds observed differs from what has been reported for the presumed source, incinerators, because of photolysis. Czuczwa and Hites find that octa- and heptachlor0 compounds overwhelmingly predominate in the lake sediments they studied, while in incinerator emissions tetraand pentachloro compounds dominate the much more variable spectrum of compounds observed. It cannot be ruled out that photolysis contributes to this transformation, but thermal processes occurring as the emitted gas streams cool suffice to explain these changes. Townsend predicted (2) and Eiceman and co-workers confirmed ( 3 ) that chlorodibenzodioxins adsorbed to particulates react to give a mixture strongly enriched in octachlorodibenzodioxin (OCDD). The pattern predicted by Townsend closely resembles those found by Czuczwa and Hites (except in the Lake Ontario sediment). Eiceman and co-workers showed that chlorodibenzodioxinsadsorbed to mineral particulates undergo two reactions, destruction and disproportionation to OCDD: at temperatures between 180 and 250 “C, the total amount of PCDDs recoverable from alumina decreases with residence time, while the relative amount of OCDD increases. In the presence of HC1 vapor, the amount of OCDD increases more rapidly (3). Studies on the composition of incinerator emissions almost always involve sampling the hot exit gas stream somewhere prior to discharge to the atmosphere. The samples are cooled rapidly, in order to obtain a representative sample of that stream (4).Typically, the highest concentrations of PCDDs/PCDFs are found in the vapor phase ( 4 , 5 ) . These studies do not adequately describe the composition of materials adsorbed to particulates that cool slowly to ambient temperature. An argument against photolysis being an important contributor to the compositional change was presented recently by Yokley et al. (6),who observed minimal photolytic change of polynuclear aromatic hydrocarbons adsorbed to dark particulates. However, the solution photolysis results reported by Mill et al. (7) imply that any such change would be in the direction observed by Czuczwa and Hites. It is also worth noting that the composition of trace PCDDs/PCDFs in human adipose tissue reported by Ryan and co-workers (8) and Graham et al. (9) does not closely resemble any of the patterns reported by Czuczwa and Hites (although the closest resemblance is to the sediments). This suggests that the ultimate source of these compounds for the human population has not yet been found. Registry No. OCDD, 3268-87-9; heptachlorodibenzodioxan, 37871-00-4; pentachlorodibenzodioxan,36088-22-9; pentachlorodibenzofuran, 30402-15-4; tetrachlorodibenzodioxan,41903-57-5; tetrachlorodibenzofuran, 55722-27-5. 0013-936X/86/0920-1185$01.50/0
Literature Cited (1) Czuczwa, J. M.; Hites, R. A. Environ. Sci. Technol. 1986, 20, 195. (2) Townsend, D. L. In Chlorinated Dioxins and Related Compounds: Impact on the Environment; Hutzinger, 0.; Frei, R. W.; Merrien, E.; Pocchiari, F., Eds.; Pergamon: Oxford, 1982; pp 265-274 (add other citation). (3) Eiceman, G. A,; Rghei, H. 0. In Chlorinated Dioxins and Dibenzofurans in the Total Environment-II; Keith, L. H.; et al., Eds.; Butterworth: Stoneham, MA, 1985; pp 515-523. Rghei, H. 0.;Eicemann, G. A. Chemosphere 1984, 13, 421. (4) Redford, D. P.; Haite, C. L.; Lucas, R. M. In Human and Environmental Risks of Chlorinated Dioxins and Related Compounds;Tucker, R. E.; et al., Eds.; Plenum: New York, 1983; pp 143-152. (5) Olie, K.; Lustenhower, J. W. A,; Hutzinger, 0.;In Chlorinated Dioxins and Related Compounds: Impact on the Environment; Hutzinger, 0.;Frei, R. W.; Merrien, E.; Pocehiari, F., Eds.; Pergamon: Oxford, 1982; pp 227-244. (6) Yokley, R. A.; Garrison, A. A,; Wehry, E. L., Mamantor, G. Environ. Sci. Technol. 1986, 20, 86. (7) Dulin, D.; Drossman, H.; Mill, T. R.. Enuiron. Sci. Technol. 1986, 20, 72. (8) Ryan, J. J.; Williams, D. T.; Lau, B. P.-Y.; Sakuma, T. In Chlorinated Dioxins and Dibenzofurans in the Total Environment-II; Keith, L. H.; et al., Eds.; Butterworth: Stoneham, MA, 1985; pp 205-214; Chemosphere,in press. (9) Graham, M. A.; Hileman, F. D.; Orth, R. G.; Wendling, J. M.; Wilson, J. D. Chemosphere, in press.
James D. Wilson
Monsanto Company St. Louis. Missouri 63167
SIR: To understand the movement of polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofusans (PCDF) through the environment, consider a four-compartment system such as that shown in Figure 1. The first compartment is the atmosphere; it receives PCDD and PCDF from various combustion sources. While in this compartment, PCDD and PCDF seem to undergo various physical and chemical transformations that change the relative concentrations of these compounds. For example, the mixture becomes relatively enriched in octachlorodioxin. The PCDD and PCDF leave the atmosphere by wet and dry deposition processes and enter the sediment and food compartments (see Figure 1). People are the last compartment, and they receive PCDD and PCDF from food. The relative abundances of PCDD and PCDF homologoues in the atmosphere, sediment, and people are virtually identical (see below); this supports the linkage given in Figure 1. In our earlier paper (I), we speculated that the transformations taking place in the atmospheric compartment were caused by photolytic processes. While not disagreeing with this idea, Wilson (2) points out that “thermal processes occurring as the emitted gas streams cool” may also explain our observations. These “thermal processes” have been discussed by Rghei and Eiceman (31, who showed that
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Sediment Figure 1. Four-compartment model of environmental transport of dioxins and dibenzofurans.
Figure 2. Average total concentration of tetra-, penta-, hexa-, hepta-, and octachiorodlbenzofurans (TCDF, PBCDF, HCDF, H7CDF, and OCDF, respectively) and tetra-, penta-, hexa-, hepta-, and octachiorodibenzo-p-dioxins (TCDD, PBCDD, HCDD, H7CDD, and OCbD, respectively) in human adipose tissue. The concentration of OCDD is shown. Data were combined from the following sources: ref 7, Table 1; ref 8, Tables 2, 3, and 5; ref 9, Table 1; ref 10, Table I; ref 11, Table I; ref 12, Table I.
PCDD may react with HCl on fly ash surfaces to give more highly chlorinated PCDD. To distinguish between these processes and photolysis is difficult, and as we stated in our paper, “further study in this area is needed”. Further research, however, must take into account at least three complicating factors. First, there are potential problems in attempting to determine incinerator emissions by sampling the fly ash removed by the electrostatic precipitator or by rapidly cooling the stack gases. These samples may not correctly represent the emissions to the atmosphere. To get a true understanding of atmospheric transformatiosns, the plume leaving the incinerator stack will need to be sampled at varying distances. Second, because the phase in which a compound is present in the atmosphere has a strong influence on its reactivity, one must know about the vapor/particle equilibrium of PCDD and PCDF in the ambient atmosphere. Experiments in our laboratory (4)and elsewhere (5) have shown that PCDD and PCDF exist in both the vapor and particle phases and that this equilibrium is a function of the degree of chlorination and atmospheric temperature. A third complicating factor is the nature of the fly ash surface itself. Experiments in our laboratory have shown that the photolytic degradation of polycyclic aromatic hydrocarbons is highly dependent on the substrate to which they are adsorbed (6). In some cases, photolysis is rapid; in some cases, it is not. We expect this to be the case for PCDD and PCDF as well. Although we agree with Wilson’s comment that photolysis may not be the only process causing atmospheric
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transformations of PCDD and PCDF, we cannot agree with his statement that “the composition of PCDD and PCDF in human adipose tissue ...does not closely resemble any of the patterns reported by Czuczwa and Hites”. Using principle component analysis, we have compared the data available on PCDD and PCDF in human fat (7-12), and we find that all such data fall in region 1 of Figure 4 in reference 1. The human fat data and the sediment and air data fall within a radius of less than 0.3 z units. A bar graph showing the average homologue distribution of PCDD and PCDF in human fat is shown in Figure 2; note the excellent comparison to the air and sediment data given in Figure 3 of reference 1. We can only conclude that the resemblance between the environmental and the human fat samples is excellent and that this resemblance supports the scheme outlined in Figure 1. Based on the arguments presented above, we disagree with Wilson’s conclusion that “the ultimate source of these compounds for the human population has not yet been found”. Combustion is the only source of sufficient size and ubiquity to account for the PCDD and PCDF in human adipose tissue.
Literature Cited Czuczwa, J. M.; Hites, R. A. Environ. Sci. Technol. 1986, 20, 195.
Wilson, J. D. Environ. Sci. Technol., preceding correspondence. Rghei, H. 0.;Eiceman, G. A. Chemosphere 1984,13,421. Eitzer, B. D.; fiites, R. A. Int. J. Environ. Anal. Chem., in press. Oehme, M.; Mano, S.; Mikalsen, A.; Kirschmer, P. Chemosphere 1986, 15, 607. Behymer, T. D.; Hites, R. A. Environ. Sci. Technol. 1985, 19, 1004. Graham, M.; Hileman, F. D.; Orth, R. G.; Wendling, J. M.; Wilson, J. D. Chemosphere, in press. Ryan, J. J.; Lizotte, R.; Lau, B. P.-Y. Chemosphere 1985, 14, 697. Ryan, J. J.; Schecter, A,; Lizotte, R.; Sun, W.-F.; Miller, L. Chemosphere 1985, 14, 929. Ryan, J. J.; Schecter, A. Preprint Extended Abstract; American Chemical Society, Division of Environmental Chemistry: Washington, DC, April 1985; p 158. Nygren, M.; Hansson, M.; Rappe, C.; Dommelloff, L.; Hardell, L. Preprint Extended Abstract; American Chemical Society, Division of Environmental Chemistry: Washington, DC, April 1985; p 160. Hardell, L.; Domellof, L.; Nygren, M.; Hansson, M.; Rappe, C. Preprint Extended Abstract; American Chemical Society, Division of Environmental Chemistry: Washington, DC, April 1985; p 167.
Brian D. Eltzer, Ronald A. Hites” School of Public and Environmental Affairs and Department
of Chemistry Indiana University Bloomington, Indiana 47405
