(21) Olie, K.; Berg, M.; Hutzinger, 0. Chemosphere 1983, 12,
627.
Gev H. Eduljee” Rechem International Limited Hardley, Hythe, Southampton SO4 6ZA, U.K. * Address correspondence to this author at Environmental Resources Ltd., 106 Gloucester Place, London WlH-3DB, U.K.
SIR: Eduljee ( I ) suggests that we are overstating the case for combustion as the major source of polychlorodibenzo-p-dioxins (PCDD) and polychlorodibenzofurans (PCDF) for the human population ( 2 , 3 ) . While we agree with some of Eduljee’s comments, we disagree with his conclusion. We will present here quantitative arguments to support our views. Eduljee states that the ambient PCDD and PCDF environmental pattern (air, sediment, and human fat) results from “a set of all-pervasive, nonisomer-specific mechanisms that operate on dioxins in the environment, irrespective of their source”. He also points out that these mechanisms operate in the atmosphere and not in the combustion source and not after deposition. We agree. It is clear from our principle component analysis that the PCDD and PCDF homologue profiles resulting from several different combustion processes are transformed into one profile. In other words, these transformations seem to be controlled by the stabilities of the products rather than the reactants. It is not yet clear if these transformations are thermal or photochemical reactions or are the result of simple physical processes (such as vapor-particulate partitioning). We also agree with Eduljee’s statement that “thermal equilibration has a large role to play in establishing the ‘background’ ratios” of PCDD and PCDF. In fact, we have quantitated this effect by measuring vapor to particulate ratios of PCDD and PCDF as a function of atmospheric temperature (4);there is an excellent correlation between the logarithm of the vapor to particulate ratio and reciprocal temperature, a functional relationship described by Yamasaki et al. (5). Because of these nonspecific reactions, Eduljee states that the linkage between combustion sources and the ambient environmental patterns cannot be made. On this point, we disagree, and we present here some calculations in support of our hypothesis. We have assumed that PCDD and PCDF enter the human food chain via the atmosphere and not directly. For example, we suggest that PCDD and PCDF deposit from the atmosphere into lakes and are bioaccumulated by fish that people eat. We distinguish this route from direct inputs into the lake from, say, dumping or leakage. In other words, we are hypothesizing a diffuse source as opposed to several point sources. Although there are some PCDD and PCDF inputs from point sources, these t e n d to be localized and would not account for the uniform presence of PCDD and PCDF in the environment and people. In our view, this can only be explained by a diffuse source such as atmospheric deposition. What are the possible sources of PCDD and PCDF to ,the atmosphere? We have suggested that combustion is the major source. The only alternate source that has been suggested is pentachlorophenol vaporization. We can compare these two sources quantitatively. The rate at which PCDD and PCDF enter the atmosphere from the use of pentachlorophenol is calculated as follows. The total U S . production of pentachlorophenol in 1976 was 22 X 106 924
Environ. Sci. Technol., Vol. 21, No. 9, 1987
kg (6). The best estimate is that 0.1% of this enters the atmosphere (6) and that the concentration of PCDD and PCDF in this pentachlorophenol averages 130 ppm (7). Thus, the calculated U S . atmospheric load rate from this source is 3 kg/yr. We can compare this rate with that at which PCDD and PCDF leave the atmosphere. We calculate this rate as follows. The total flux of PCDD and PCDF to the surface of the U S . averages 100 pg cmw2yr-l (8,9),and the area of the US. is 9.5 X 106km2. Thus, the measured load rate to the surface of the U.S. is 9500 kg/yr. This is a factor of 3000 more than predicted by pentachlorophenol emissions alone. Even if there are substantial errors in these estimates (and there are), pentachlorophenol vaporization can account for only a very small fraction of the measured fluxes from the atmosphere. [The source of the dramatically different estimate of Hagenmaier et al. (IO) is not clear since no data were given or cited to support their estimate.] Conversely, combustion can account for all of the observed atmospheric concentrations. Eduljee calculates that the atmospheric concentrations of PCDD from refuse incineration should be 0.24-2.4 pg/m3. This range agrees very well with 1.2 pg/m3, which is the average total PCDD concentration in the atmosphere of Bloomington, IN ( 4 ) . Incidentally, the atmospheric measurements of Olie et al. ( I I ) , cited by Eduljee, were made within the maximum emission zone of an incinerator and are certainly too high to be considered ambient values. While we still believe that our qualitative arguments based on homologue patterns are persuasive and suggest combustion as a source of PCDD and PCDF in the ambient environment, we note that the quantitative estimates presented here strengthen our conclusion that “combustion is the only source of sufficient size and ubiquity to account for PCDD and PCDF in human adipose tissue”.
Literature Cited (1) Eduljee, G. H. Enuiron. Sci. Technol., preceding corre-
spondence in this issue. (2) Czuczwa, J. M.; Hites, R. A. Enuiron. Sci. Technol. 1986, 20, 195. (3) Eitzer, B. D.; Hites, R. A. Enuiron. Sci. Technol. 1986,20, 1185. (4) Eitzer, B. D.; Hites, R. A. Int. J.Environ. Anal. Chem. 1986, 27, 215. (5) Yamasaki, H.; Kuwata, K.; Miyamoto, H. Enuiron. Sci. Technol. 1982, 16, 189. (6) U S . Environmental Protection Agency Materials Balance for Chlorophenols; Environmental Protection Agency: Washington, DC, 1980; EPA-560/13-80-004. (7) Buser, H. R.; Bosshardt, H.-P. J . Assoc. Off. Anal. Chem. 1976, 59, 562. (8) Czuczwa, J. M. Ph.D. Thesis, Indiana University, Bloomington, 1984. (9) Czuczwa, J. M.; McVeety, B. D.; Hites, R. A. Science (Washineton. D.C.) 1984. 226. 568. (10) Hagenmaier, H.; Brunner, H:; Haag, R.; Berchtold, A. Chemosphere 1986, 15, 1421. (11) Olie, K.; Berg, M.; Hutzinger, D. Chemosphere 1983, 12, 627.
Brian D. Eltrer, Ronald A. Hites“ School of Public and Environmental Affairs and Department of Chemistry Indiana University Bloomington, Indiana 47405
