Environ. Sci. Technoi’. lQ88,22, 230-231
(2) Changnon, S. A.; Jones, D. M. A. Water Resour. Res. 1972,
8, 360-71. (3) Eichenlaub, V. L. Weather and Climate of the Great Lakes Region; University of Notre Dame Press: Notre Dame, IN,
1979. (4) Cole, H. S.; Lyons, W. A. Proceedings of the 14th Conference on Great Lakes Research; InternationalAssociation for Great Lakes Research Ann Arbor, MI, 1971;pp 436-63. (5) Assel, R. A.; Quinn, F. H.; Leshkevich, G. A.; Bolsenga, S. J. Great Lakes Ice Atlas; Great Lakes Environmental Research Laboratory: Ann Arbor, MI, 1983; Table 2. (6) Murphy, T. J.; Rzeszutko, C. P. J. Great Lakes Res. 1977, 3, 303-12. (7) Doskey, P. V.; Andren, A. W. J. Great Lakes Res. 1981, 7,
15-20. ( 8 ) Hollod, G. J. Ph.D. Thesis, University of Minnesota,
Minneapolis, MN, 1979. (9) Eisenreich,S. J.; Looney, B. B.; Hollod, G. J. Environ. Sci. Technol. 1981, 15, 879-83. (10) Murphy, T. J.; Paolucci, G.; Schinsky, A. W.; Combs, M. L.; Pokojowczyk, J. C. “Inputs of PCBs from the Atmosphere to Lakes Huron and Michigan”;report of U.S. EPA project R-805325; Duluth Environmental Laboratory: Duluth, MN, May 1982. (11) Murphy. T. J. In Toxic Contaminants in the Great Lakes; Simmons, M., Nriagu, J., Eds.; Wiley: New York, 1984.
Thomas J. Murphy Chemistry Department DePaul University Chicago, Illinois 60604
SIR: Murphy questions assumptions made in our estimations of the atmospheric and nonatmospheric contributions of PCBs to Lake Michigan ( I ) . Although we explained our assumptions at some length, we are happy to provide further clarification. Murphy argues that we assumed PCBs from nonatmospheric sources do not evaporate and that this assumption leads to an overestimate of the fraction of the PCB loading to Lake Michigan derived from nonatmospheric sources. However, we did not make this assumption. Clearly, PCBs from nonatmospheric sources are also subject to volatilization. We chose to use the calculated loss to the atmosphere from remote lakes as a conservative estimate of the corresponding loss from Lake Michigan. We did not feel that alternative assumptions, such as Murphy’s suggestion that loss to the atmosphere is directly proportional to loading, were justified. Importantly, our estimate of the nonatmospheric loading to Lake Michigan was presented as the net rather than the total value, representing the amount remaining (in the lake sediments) after losses by volatilization or other processes. As a point of further clarification, we did not obtain the atmospheric loading (7.5 pg m-2 yr-l) on the basis of a ratio of evaporation to sediment accumulation of PCBs, as indicated by Murphy. The atmospheric loading was obtained from a separate investigation (2). We measured sediment accumulation of PCBs in remote lakes and calculated loss to the atmosphere as the difference between atmospheric loading and sediment accumulation of PCBs. Our use of different periods of time for the remote lakes and Lake Michigan in calculating average sediment fluxes of PCBs was also questioned. Fluxes were averaged over the periods for which PCBs were detectable in the sediments. This time interval was longer in Lake Michigan than in the remote lakes. We believe it would be erroneous to use a time period other than the period over which PCBs were actually deposited. In contrast to Murphy’s 230
Environ. Sci. Technol., Vol. 22, NO. 2, 1988
conclusion, we believe PCBs could have been delivered to Lake Michigan earlier than to the remote lakes, i.e., from nonatmospheric sources. As discussed previously ( I ) , the range in sediment fluxes of PCBs in the remote lakes probably reflects uncertainties in time resolution (sectioning sediment cores and calculating sedimentation rates), measurement of low PCB concentrations, and sediment focusing. We did not attempt to correct for differences in sed’,nent focusing among remote lakes. Were sediment focusing occurring in the remote lakes, the difference between the remote lakes and Lake Michigan would be even greater, making our estimates conservative. We share Murphy’s concern regarding meteorological and physical differences between Lake Michigan and the remote lakes and acknowledged this limitation (I). In the absence of a pristine lake identical in size and climate with Lake Michigan, the remote lakes served as a useful first approximation. The suitability of the remote lakes is supported by data from Lake Superior. Lake Superior receives approximately 80% of its PCBs through atmospheric input (3, 4 ) . The average sediment PCB flux in Lake Superior is estimated to be 4 hg m-2 yr-l ( 4 ) , which makes the atmospheric contribution similar to the flux for the remote lakes (1). Furthermore, sediment PCB cogener fluxes in Siskiwit Lake on Isle Royale in Lake Superior are similar to those of Lake Superior, even though Siskiwit Lake is ice-covered during winter months (5). Two factors may account for the agreement in fluxes: (1) although possibly enhanced by high wind speeds, dry deposition is not the dominant process involved in transport of atmospheric PCBs to lakes (2), and (2) during winter, vapor exchange from ice-free lakes may be reduced through the influence of low surface water and air temperatures on Henry’s Law constants. In fact, Murphy (6)suggests this temperature effect in a recent publication. Our assumption that atmospheric inputs per unit area are similar for Lake Michigan and the remote lakes is supported by air and rain measurements, including data cited by Murphy. Air concentrations of PCBs over the open waters of Lake Michigan (3, Wisconsin remote sites (8),and Lake Superior ( 4 ) are similar. As we stated previously ( I ) , concentrations in air and rain are higher in urbanized areas in localized regions along the southern shores of Lake Michigan, possibly resulting in higher atmospheric inputs of PCBs to Lake Michigan than to the remote lakes. However, the major portion of the Lake’s surface is apparently influenced by air concentrations similar to those in remote areas. We reemphasize that assumptions made in comparing Lake Michigan and the remote lakes will lead to some uncertainty in the calculated fluxes. We encourage continued examination of the air-water transfer processes to improve the reliability of flux estimates. However, we believe the comparison clearly shows the loss of PCBs from the lake to the atmosphere is significant and that atmospheric and net nonatmospheric inputs of PCBs to Lake Michigan have been of similar magnitude.
Literature Cited (1)
Swackhamer,D. L.; Armstrong, D. E. Enuiron. Sci. Technol.
1986, 20, 879-83. (2) Andren, A. W. In Physical Behavior of PCBs i n the Great
Lakes; Mackay, D., Paterson, S., Eisenreich, S. J., Simmons, M. S., Eds.; Ann Arbor Science: Ann Arbor, MI, 1983; Chapter 8. (3) Eisenreich, S. J.; Looney, B. B.; Thornton, J. D. Environ. Sci. Technol. 1981, 15, 30-38.
Not subject to U.S. Copyright. Published 1988 by the American Chemical Society
Environ. Sci. Technol. 1988,22, 231-231 (4) Eisenreich, S. J. In The Sources and Fates of Aquatic Pollutants; Hites, R. A., Eisenreich, S. J., Eds.; Advances in Chemistry 316; American Chemical Society: Washington, DC, 1987; Chapter 13. (5) Swackhamer, D. L.; McVeety, B. D.; Hites, R. A., unpublished data. (6) Murphy, T. J.; Pokojowczyk, J. C.; Mullin, M. D. In Physical Behavior of PCBs in the Great Lakes; Mackay, D., Paterson, s.,Eisenreich, s. J., Simmons, M. s.,Eds.; Ann Arbor Science: Ann Arbor, MI, 1983; Chapter 3. (7) Doskey, P. D.; Andren, A. W. J. Great Lakes Res. 1981, 7, 15-20. (8) Andren, A. W., personal communication. Deborah L. Swackhamer* Environmental and Occupational Health University of Minnesota Minneapolis, Minnesota 55455
Davld E. Armstrong Water Chemistry Program university of Wisconsin Madison, Wisconsln 53706
Comment on “Reaction Products and Rates of Disappearance of SZmple Bromoalkanes, 1,2-Dibromopropane, and 1,2-Dlbromoethane in Water” SIR A recent article in this journal by T. M. Vogel and M. Reinhard (1)concerned itself with the disappearance, rates, and reaction products of mono- and dibromoalkanes in water. One conclusion of this article was that 1,2-dibromoethane (EDB) degraded to the bromoalkane vinyl bromide as a “main product” causing them to conclude that “...dehydrobromination is the most significant degradation mechanism for alkanes with two bromines in vicinal position, although substitution cannot be ruled out from the data due to analytical limitations”. Since the authors did not specify a t what EDB concentrations their studies were performed, it is impossible to put such observations in perspective with those of ours (2) and Jungclaus and Cohen (3). We have shown that, in natural groundwaters, ethylene glycol and bromide ions account for nearly all the degradation of EDB when studies are done a t EDB concentrations that have been observed in groundwater (2; 10-100 pg/L). Vogel and Reinhard (1) did not look for water-soluble products but concentrated their effors on pentane-soluble ones. When your readers consider the relative mammalian toxicities of ethylene glycol and vinyl bromide, it is important for them to know that the more innocuous ethylene glycol accounts for nearly all the degradation of EDB in groundwaters. Registry No. EDB, 106-93-4; BrCH2CHBrCH3, 78-75-1.
Literature Cited (1) Vogel, M. T.; Reinhard, M. Environ. Sci. Technol. 1986, 20(10),992-997. (2) Weintraub, R. A.; Jex, G. W.; Moye, H. A. Evaluation of Pesticides in Ground Water; Garner, Willa Y., Honeycutt, Richard C., Nigg, Herbert N., Eds.; ACS Symposium Series 315; American Chemical Society: Washington, DC, 1986; Chapter 15. 0013-936X/88/0922-0231$01.50/0
(3) Jungclaus, G. A.; Cohen, S. Z. Extended Abstracts, 191st National Meeting of the American Chemical Society, Division of Environmental Chemistry, New York, NY; American Chemical Society: Washington, DC, 1986: paper 6.
H. Anson Moye,” Randy Welntraub Pesticide Research Laboratory Institute of Food and Agricultural Sciences University of Florida Gainesville, Florida 3261 1
SIR: Weintraub et al. (1)and Jungclaus and Cohen (2) report that 1,2-dibromoethane (EDB) hydrolyzes in aqueous buffers to form ethylene glycol as the primary product. Recent data obtained in this laboratory are consistent with this finding (3). In addition, Vogel and Reinhard ( 4 ) ,Jungclaus and Cohen (2),and recently Haag and Mill (5) have found vinyl bromide as a product of EDB decomposition in water. Haag and Mill (5) have found degradation via elimination to be 9 times slower than hydrolysis. Although ethylene glycol is quantitatively the major product of aqueous EDB degradation, vinyl bromide may be the more significant product because of its elevated toxicity. We specified that the initial EDB concentrations in our studies were 10 mg/L ( 4 ) . However, product distribution is not expected to change with the initial concentration since the rates of both elimination and hydrolysis are first order with respect to organic reactant. Degradation of 100 pg/L EDB (the upper limit in groundwater quoted by Moye and Weintraub) in water may react to form approximately 30 pg/L ethylene glycol via hydrolysis and 6 pg/L vinyl bromide via elimination. For the purpose of comparison, the final maximum contaminant levels set by the U.S. EPA for vinyl chloride (the chlorinated analogue of vinyl bromide) is 2 hg/L. Registry No. EDB, 106-93-4; BrCH2CHBrCH3, 78-75-1,
Literature Cited (1) Weintraub, R. A,; Jex, G. W.; Moye, H. A. Evaluation of Pesticides in Ground Water; Garner, Willa Y., Honeycutt, Richard C., Nigg, Herbert, N., Eds.; ACS Symposium Series 315; American Chemical Society: Washington, DC, 1986; Chapter 15. (2) Jungclaus, G. A,; Cohen, S. Z. Extended Abstracts, 191st National Meeting of the American Chemical Society, Division of Environmental Chemistry, New York, NY; American Chemical Society: Washington, DC, 1986; paper 6. (3) Barbash, J. E.; Reinhard, M. Extended Abstracts, 194th National Meeting of the American Chemical Society, Division of Environmental Chemistry, New Orleans, LA; American Chemical Society: Washington, DC, 1987. (4) Vogel, T. M.; Reinhard, M. Environ. Sci. Technol. 1986, 20,992-997. (5) Haag, W. R.; Mill, T., personal communication, 1987.
Martin Reinhard” Department of Civil Englneering Stanford University Stanford, California 94305
Timothy M. Vogel Environmental Engineering Michigan State University East Lansing, Michigan 48824-1212
0 1988 American Chemical Society
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