Environ. Sci. Technol. 1985, 79, 942-946
Schniepp, L. E.; Geller, H. H. J. Am. Chem. SOC.1946,68, 1646-1648. Blust, G.; Lohaus, G. Justus Liebigs Ann. Chem. 1953,583, 2-6. Hartung, W. H.; Crossley, F. “Organic Syntheses”, Collect. Vol. 11; Wiley: New York, 1943; pp 363-364. Renaud, R.; Leitch, L. C. Can. J. Chem. 1954,32,545-549. Martinez, R. I.; Herron, J. T.; Huie, R. E. J . Am. Chem. SOC.1981, 103, 3807-3820, and references cited therein. Herron, J. T.; Martinez, R. I.; Huie, R. E. Znt. J . Chem. Kinet. 1982, 14, 201-224. Bailey, P. S. “Ozonation in Organic Chemistry”;Academic Press: New York, 1978 (Vol. l ) , 1982 (Vol. 2). Herron, J. T.; Huie, R. E. J. Am. Chem. SOC.1977, 99, 5430-5435. Herron, J. T.; Huie, R. E.; Int. J . Chem. Kinet. 1978, 10, 1019-1041.
(28) The assignment of HC1s0180Hin IR spectrum was based on the data in the following: Hatakeyama, S.; Bandow, H.; Okuda, M.; Akimoto, H. J . Phys. Chem. 1981, 85, 2249-2254. (29) Santilli, D. S.; Dervan, P. B. J. Am. Chem. SOC.1979,101, 3663-3664. (30) Story, P. R.; Morrison, W. H., 111; Hall, T. K.; Farine, J.-C.; Bishop, C. E. Tetrahedron Lett. 1968, 3291-3294. (31) Story, P. R.; Hall, T. K.; Morrison, W. H., 111; Farine, J. C. Tetrahedron Lett. 1968, 5397-5400. (32) Srinivasan, R. In “Advances in Photochemistry”; Noyes, W. A., Jr., Ed.; Interscience Publishers: New York, 1963; pp 83-113, and references cited therein.
Received for reuiew June 20,1984. Revised manuscript receiued January 30, 1985. Accepted April 22, 1985.
Polychlorinated Biphenyl Emissions to the Atmosphere in the Great Lakes Region. Municipal Landfills and Incinerators Thomas J. Murphy,” Leo J. Formanski, Bruce Brownawell, and Joseph A. Meyer Chemistry Department, DePaul University, Chicago, Illinois 606 14
In an effort to identify sources of polychlorinated biphenyls (PCBs) to the atmosphere, the concentration of PCBs in emissions from several municipal sanitary landfills and refuse and sewage sludge incinerators in the Midwest was determined. Sanitary landfills continuously emit the gaseous products of anaerobic fermentation along with other volatile materials to the atmosphere. Thus, they can be continuing sources of vapor-phase contaminants to the atmosphere. A projection, based on the amount of methane generated annually from landfills and a PCB to methane ratio of 0.3 pg of PCBs/m3 of CH4 found from the landfills sampled, indicates that the annual PCB emissions from sanitary landfills in the U.S. is on the order of 10-100 kg/year. The concentrations of PCBs from the incinerator stacks sampled ranged from 0.3 to 3 pg/m3, and the annual emissions per stack sampled were 0.25 kg/year. The emission rates found here are small compared to the 900 000 kg/year of PCBs estimated to cycle through the atmosphere over the U.S. annually.
Introduction The presence of measurable concentrations of polychlorinated biphenyls (PCBs) in the atmosphere throughout the northern and southern hemispheres is now well established (1-5). The fact that the PCBs in the atmosphere can exert significant deleterious effects has been demonstrated in the Great Lakes region where it has been shown that the atmosphere is presently a major source of PCB inputs to Lakes Michigan, Superior, and Huron (5-10). Bioaccumulation by the biota in Lake Michigan has led to levels of PCBs in adult sports fish (11) above the FDA limit for interstate commerce of 2 ppm (mg/kg) (12). Levels in adult fish of all species in all of the Great Lakes are above the International Joint Commission criteria of 0.1 mg/kg, and adverse health effects due to their presence have been demonstrated (13). The amount of PCBs transported by the atmosphere is quite large. Concentrations of about 7 ng/m3 of PCBs have been reported in cities and towns of the Midwest (6, 14-16), and concentrations of 0.5-2 ng/m3 have been reported in rural and remote areas (1-5,17). On the basis an estimate of 0.05 ng/m3 in rural areas, 5 ng/m3 urban 942
Environ. Sci. Technol., Vol. 19, No. 10, 1985
areas, and a mixed height in the atmosphere of 2 km, it was calculated that the air over the U.S. at any time contains about 18000 kg of PCBs (18). This estimate is conservative due to the low concentration assumed for rural areas. If an average residence time in the atmosphere is assumed to be 1week, about 900 000 kg/year of PCBs annually cycle through the atmosphere over the U.S. This works out to an average input to, or deposition from, the atmosphere of about 60 g/(km2.year). This deposition rate is in reasonable agreement with that found to be coming into Lake Michigan from the atmosphere (7). Unfortunately, there is little information available on the sources to the atmosphere of this 900 000 kg/year of PCBs. Probable sources include the following: the evaporation of PCBs used in the past for such open uses as paints, wood preservatives, plasticizers, etc.; the evaporation of spilled or leaked PCBs from transformers, large capacitors, hydraulic systems, and equipment containing large volumes of PCBs and still in service or in storage; the evaporation from landfills or incinerators of PCBs from materials disposed of in municipal refuse; the evaporation of PCBs improperly disposed of to open areas such as the use of waste PCB fluids to oil roads etq emissions of PCBs from engines and furnaces burning liquid or gaseous fuels containing or contaminated with PCBs; the reevaporation of PCBs from land areas where they have been deposited by wet and dry deposition from the atmosphere. In the past, PCBs were included in the manufacture of a variety of materials that could end up in municipal waste. Some of these materials are still permitted to be disposed of in municipal waste. This includes carbonless carbon paper and most of the billions of small, PCB-containing capacitors that have been manufactured. Large numbers of these capacitors have been used in the ballasts on fluorescent light fixtures, in consumer electronics, and as the starting capacitor on motors in refrigerators, washing machines, air conditioners, etc. There are still no restrictions on the disposal of these capacitors. It has been estimated that, by 1978,140 x lo6 kg of PCBs had been disposed of in landfills (19). With respect to sanitary landfills, since they continuously generate CHI and C 0 2by the anerobic decomposition
0013-936X/85/0919-0942$01.50/0
0 1985 American Chemical Society
of the organic wastes present, and these gases escape from the landfills, PCBs and all other volatile materials present in the landfills should be carried out along with them. For this reason, sanitary landfills are expected to be a continuing source of PCBs to the atmosphere, in contrast to industrial and hazardous waste landfills in which gases are not being continuously generated and vented. The significance of this source of atmospheric PCBs has not been reported. Multiple hearth incinerators are most commonly used for sewage sludge incineration. These incinerators are cylindrically shaped with a number of horizontal hearths, or stages. Burners are positioned toward the bottom of the incinerator to supply the auxiliary heat necessary to dry and burn the sludge. These burners heat the stage above them to -815 OC. The combustion gases rise through the incinerator and exit at the top at -470 OC. Moist sludge solids enter a t the top and are moved downward through the incinerator, with a residence time on each stage of 5-10 min. As the sludge passes through the hot stages, water and other volatile compounds evaporate, and the remaining combustible matter burns. The point is that multiple hearth incinerators, as sampled in this project, have countercurrent heat and sludge flows. They are then optimally designed to evaporate volatile materials present in the sludge before they get to the high-temperature area of the incinerator. Thus, compounds such as the PCBs, which are quite resistant to oxidation but reasonably volatile, would be expected to be vaporized in the upper stages of the incinerator before combustion could occur. Any removal of PCBs present in the incoming sludge then would have to occur in the exit-gas cleanup system. Since it has been reported.that sewage sludges (201,stack emissions from municipal refuse and sewage sludge incinerators (16,21),and emissions from sanitary landfills (22-24) contain PCBs, this project was undertaken to determine if municipal sanitary landfills and/or municipal refuse and sewage-sludge incinerators in the Great Lakes basin could be significant sources of PCBs to the atmosphere in this region. Besides being sources of PCBs to the atmosphere, these emissions are from distinct stacks or vents, point sources in contrast to the diffuse nature of the other possible sources of PCBs to the atmosphere. This makes it possible to get estimates of their emission rates. Procedures There are a large number of municipal and private sanitary landfills located in the vicinity of Lake Michigan in Illinois and Wisconsin and upwind of the prevailing winds. Requests for permission to sample were made to the operators of sanitary landfills that had sections that were completed, sealed, and had vent pipes in place. Permission was obtained to collect samples from six municipal landfills in this region. These were located in medium density urban areas whose economy was mostly industrially based. The areas contained numerous paper, chemical, and motor and electrical equipment manufacturing companies. At least one accepted some waste liquors from paper mills that did some waste paper reprocessing, and several accepted sludges from wastewater treatment plants. Because of the number and the variety of industrial and other sources of refuse to these landfills which could contain PCBs, it was thought that their emissions would give some indication of this source of PCBs to the environment. Gas flow from landfills is caused by two different mechanisms. One is the venting of the gases generated by the anaerobic decomposition of organic materials incor-
porated within the landfill. The production rate of the gas depends on a number of factors (25),including the composition of the waste, the temperature and the moisture content of the landfill, and the age of the landfill. It is highest just after filling of the landfill, is reasonably constant for any particular landfill over a period of many months, decreases with time, and can continue for more than 50 years. The last filling date for the landfill sections sampled ranged from 1974 to 1981. Superimposed on this steady flow of gas are variations caused by changes in the barometric pressure. Because of the void air space in a landfill and the presence of only a few vents, a small change in the barometric pressure can cause a relatively large change in the flow rate through the vents. At any time then, the direction and rate of gas flow through the vents is the result of pressure caused by the anaerobic gas production and recent barometric pressure changes. If the increase in the barometric pressure is sufficiently large, the net gas flow can be into the landfill, particularly in older landfills. The variable flow rates, and the air which can be forced into a landfill, greatly complicate the determination of the emissions of PCBs or other gases and vapors. The PCB concentration in the landfill atmospheres should be determined by the equilibrium of the vaporphase PCBs with all of the materials exposed (the fugacity (26) of the PCBs in all of the phases present would be equal). Thus, it was assumed that in the absence of barometric pressure changes, the gas that would be vented from the landfill would have a constant ratio of PCBs to methane. It was also assumed that the gas vented from a landfill would be a mixture of the landfill gas of steady-state composition and air which was drawn into the landfill during times of high barometric pressure. To correct for the air being forced into the landfills during barometric highs, the CH4,air, and C02concentrations of the vented gases were measured as the samples were being collected for PCBs. The PCB concentrations were then normalized to the CH4 concentrations. With respect to the incinerators, requests for permission to sample were made to the operators of municipal refuse and sewage incinerators in the Great Lakes basin state of Illinois, Michigan, Wisconsin, and Ohio. Satisfactory arrangements were made with the operators of two refuse incinerators and three sewage sludge incinerators. Experimental Section Samples of the landfill gases, which were in effect headspace samples, were collected from two or more active vents from each landfill. A clean copper tube (0.8 cm i.d.) was inserted at least 1.5 m into the vent being sampled, and the vent was sealed around the tube to prevent air from being drawn into the vent while sampling. Two metal tubes (2.5 cm i.d. and 20 cm long) containing 20 g each of 6-20 mesh Florisil were connected in series between the copper tube and the pump. A dry gas meter was used to determine the volume of gas drawn through the sampling tubes. Samples of the landfill gases for the determination of the CHI, C02,and air concentrations were collected from the gas stream exiting the sampling pump. A water U-tube was used to check that the pressure in the vent pipe was above atmospheric pressure throughout the sampling period. The techniques and procedures for sampling were the same for the refuse and sewage sludge incinerators. Stack samples were collected by using isokinetic sampling techniques from the discharge stack of the incinerator, after the emission control devices, for the determination of the Environ. Sci. Technol., Vol. 19, No. 10, 1985
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PCB concentration. A RAC Staksampler was used, and the gases and aerosols were drawn through a modified EPA Method 5 sampling train. The sample train was that used by Haile and Baladi (27) for the sampling of PCBs from incinerators, with the exception that none of the impingers used in this project had deflection plates and bicarbonate rather than hydroxide was used in the fourth impinger, Two glass tubes (2 cm i.d.) containing 20 g each of 6-20 mesh Florisil absorbent activated at 450 "C were placed in series between the third and fourth impingers. Separate particulate samples were not collected because a particulate filter created a large pressure drop in the sampling train. The particulates and the PCBs they contained, however, were collected in the sampling train. I t was expected that, at the stack temperatures of the incinerators, PCBs would be chiefly in the vapor phase. After the collection of the stack samples, the water in the first three impingers was combined and extracted 3 times with hexane. The sample probe and other glassware in front of the Florisil tubes were rinsed with methylene chloride, and these washings were added to the water extracts. The Florisil from each sample tube, from either the incinerator or landfill samples, was extracted in a Soxhlet apparatus with hexane/acetone for 16 h (-8 min/cycle). In most cases the extracts from the first Florisil were combined with the impinger extracts and washings from the equipment and treated as one sample. The Florisil from the second collector tube was usually analyzed separately to determine if breakthrough had occurred. In all cases, the organic solutions were dried and chromatographed on Florisil with hexane. The PCBs were separated by temperature-programmed gas chromatography (GC) on a 2 mm X 2 m packed column of 3% SP-2100 on 100-120 mesh Supelcoport. A pulsed current, electron capture detector (ECD) with a 63Nisource was used. The amounts were determined by digital electronic integration of the peak areas (CSI Supergrator 3) and the use of the different response factors determined by the method of Webb and McCall (28) using the standards and Aroclor compositions of Sawyer (29). Samples of the landfill gases were analyzed immediately upon collection for COB,CH4, and air by isothermal GC, with a thermal conductivity detector, on a 1mm X 0.4 m copper column packed with activated charcoal (Carbosphere, Alltech Associates). Air (0, + N,), CHI, and C02 were quantified by the use of response factors determined on pure samples of the gases. Sodium sulfate and Florisil were baked at 450 "C before use. The Florisil was stored at 130 "C. The solvents, rinsings of the glassware, and extracts of the Florisil were checked for the presence of ECD-active materials before use. An average of 14 blank analyses run on the entire extraction and cleanup procedure showed 8.5 f 3.3 ng of PCBs/sample. Overall recovery of PCBs was checked with spiked samples. It averaged 74 f 14%. Portions of Florisil taken on the sampling trips but not used were extracted and used as sample blanks. The amount of PCBs in the incinerator samples was usually more than 100 times the blanks. Therefore, no correction for the blanks was made. The amounts of PCBs in the landfill samples were typically 10-40 times the blank value, and a correction for the blank was made. The PCB standards used to quantify the samples were periodically checked against PCB standards prepared separately and against PCB standard solutions from the US. EPA. Also, two incinerator samples were analyzed by the Grosse Ile laboratory using capillary GC/ECD (30). 944
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Table I. Methane and PCBs in Sanitary Landfill Gases PCB concn, ng/ms 390 135 63 380
130 37 196
% CHI
16 76 30
53
ao
ng of PCBs/ m30f CHI
367 500 433 70 236 285 f 170
Table 11. PCBs in Municipal Refuse and Sewage Sludge Incinerator Emissions
2 (1)
PCBs PCB emitted PCBs concn, per stack, per ton' Wyear burned, g 4 m 3 Municipal Refuse Incinerators 1.5-4.5 0.4 f 0.045 0.35 f 0.045 0.0023 f 0.0003 2.6 0.36 0.265 0.0044
3 (2) 4 (2) 5 (3)
Sewage Sludge Incinerators 0.26 0.0057 2,4 2.0 0.048 0.0033 1.5, 2.25 0.43 b b 1-2 b
volume incin- sampled, erator m3 1 (5)"
Number of SamDles. SamDles contaminated. Metric ton.
The results were in very good qualitative and quantitative agreement with those reported here. Landfill Results
The results from the landfill samples are shown in Table I. The PCB concentrations found in the emissions were all below 0.5 bg/m3. When corrected for the CHI content, an arithmetic mean ratio of 285 ng of PCB/m3 of CH., was found. The standard deviation of f60% was less than anticipated. The results for landfill1 4 indicate that the methane normalization seems to be correcting for extraneous air in the landfill emissions. Samples collected on different days at this landfill showed a factor of 3 difference in the PCB concentration, but the PCB/methane ratios are within experimental error. The emissions consisted chiefly of chlorobiphenyl compounds containing only a few chlorines per molecule, typical of those found in Aroclor 1242 and 1016. Qualitatively, they are what one would expect from the evaporation of Aroclor 1242,1248, and 1254 type mixtures (31). Incinerator Results
The results of the analyses of the stack samples from the refuse and sewage sludge incinerators are shown in Table 11. The one refuse incinerator was sampled regularly over a period of 2 months, and the results for the five samples are shown. The results are shown as emissions per stack, as well as concentrations. As some of the incinerators had more than one furnace, each with its own stack, the total emissions from the plant would be proportional to the average number of furnaces operated. The refuse incinerators had electrostatic precipitators to lower the particulate emissions, while the sludge incinerators had afterburners and wet scrubbers. Upon analysis, the samples collected from incinerator 5 seem to have been contaminated by Aroclor 1260. This prevented the quantification of those samples, but the pattern of the low molecular weight chlorobiphenyl com-
pounds, which could be seen in the spectra, were similar to those found in the samples collected from the other incinerators. The mean concentration of the PCBs found in the incinerator effluents quantified was below 1pg/m3, and the amounts emitted per stack averaged 0.23 kg/year (see Table 11). The pattern of the PCBs in the incinerator emissions varied. Generally, the tri- to hexachlorobiphenyl compounds dominated (Aroclor 1248 and 1254 type), with the lower molecular weight compounds present in higher amounts. The concentrations of the mono- and dichlorobiphenyls tended to be lower than anticipated on the basis of their volatility. This could be due to a higher destruction rate in the incinerator or to their not being present in the feed. The results from incinerator 1 indicate that the composition and concentration of the emissions from refuse incinerators are variable, and they give some indication of the variability over a 2-month period. On one occasion, samples from incinerator 1 showed higher levels of the penta- to octachlorobiphenyls commonly found in Aroclor 1260, though the relative amount of the compounds present were quite different from virgin Aroclor 1260. This is an expected result and probably reflects the variable composition of the feed. In addition to the above samples, three other types of samples were collected. In 1981 it was reported that PCBs were present in natural gas due to contamination by PCBs in the distribution system (32). An analysis of four samples of natural gas collected in Chicago showed 84 f 14 ng of PCB/m3. Four ambient air samples collected in Chicago outside our laboratory during 1980 and 1981 showed 5.5 f 2 ng of PCB/m3, and four samples of air from our laboratory showed 182 f 34 ng of PCB/m3. These last results support those reported by MacLeod (33) that indoor air environments can have elevated PCB levels. Discussion It is estimated that sanitary landfills in the US.generate 6 X 1O1O (34) or 24 X 1O1O m3/year (35) of methane. By use of the average PCB/methane ratio found above, and these estimates of the amount of methane generated annually, a release in the range 10-100 kg/year of PCBs from sanitary landfills in the U.S. is estimated. Compared to the estimate of 900 000 kg/year of PCBs to the atmosphere, the emissions which were found here to be coming from incinerators (-0.23 kg/year per stack) and landfills are not significant. However, perhaps the largest sources of PCBs to the atmosphere are not point sources, and perhaps not all of the PCBs cycling through the atmosphre are new to the environment. For instance, most of the PCBs deposited from the atmosphere could reevaporate, and there is now even some evidence that particulate PCBs deposited from the atmosphere in large bodies of water may dissolve and reevaporate (31). Thus, the atmospheric concentration of PCBs may be maintained by a high recycle rate, leaving only a smaller loss rate to be made up with new material. This would increase the significance of all sources of PCBs to the atmosphere. On the basis of the results reported here, refuse and sewage sludge incinerators and sanitary landfills are contributing some PCBs to the atmosphere, but they also indicate that the major sources of PCBs to the atmosphere are yet to be identified. Acknowledgments
We would especially like to thank the incinerator and landfill owners for permission to sample and the operators
for their cooperation during the collection of the samples. We would also like to thank Peter Kmet and the Bureau of Solid Waste Management of the Wisconsin Department of Natural Resources for their help and cooperation in this project. Registry No. CH,, 74-82-8.
Literature Cited (1) Bidleman, T. F.; Olney, C. E. Science (Washington,D.C.) 1974,183,517-518. (2) Harvey, G. R.; Steinhauer, W. G. Atmos Environ. 1974,8, 777-782. (3) Atlas, E. L.; Giam, C. S. Science (Washington,D.C.) 1981, 21 I, 163-165. (4) Tanabe, S.; Kawano, M.; Tatsukawa, R. Trans. Tokyo Univ. Fish. 1982, 5, 97-109. ( 5 ) Eisenreich, S. J.; Looney, B. B.; Thorton, J. D. Environ. Sci. Technol. 1981, 15, 30-38. (6) Murphy, T. J.; Rzeszutko, C. P. J. Great Lakes Res. 1977, 3, 305-312. (7) Murphy, T. J.; Paolucci, G.; Schinsky, A. W.; Combs, M. L.; Pokojowczyk, Duluth Environmental Research Laboratory, May 1981, U.S. EPA Project Report R-805325. (8) Swain, W. R. J. Great Lakes Res. 1978, 4 , 398-407. (9) Strachan, W. M.; Huneault, H. J. Great Lakes Res. 1979, 5, 61-68. (10) Eisenreich, S. J.; Hollod, G.; Johnson, T. C. “Atmospheric Inputs of Pollutants to Natural Waters”; Eisenreich, S., Ed.; Ann Arbor Science: Ann Arbor, MI, 1981; pp 425-444. (11) Willford, W. A.; Hesselburg, R. J.; Nicholson, L. W. Conf. Proc.-Natl. Conf. Polychlorinated Biphenyls 1975, EPA56016-75-004, 177-181. (12) Fed. Regist. 1984, 49, 21514-20. (13) Jacobson, J. L.; Jacobson, S. W.; Fein, G. G.; Schwartz, P. M.; Dowler, J. K. Dev. Physchol. 1984, 20, 523-532. (14) Doskey, P. V.; Andren, A. W. J. Great Lakes Res. 1981, 7, 15-20. (15) Eisenreich, S. J. Looney, B. B. In “Physical-Chemical Behavior of PCBs in the Great Lakes”; Mackay, D.; Paterson, S.; Eisenreich, S.; Simmons, M., Eds.; Ann Arbor Science: Ann Arbor, MI, 1983; pp 141-156. (16) Richard, J. J.; Junk, G. A. Environ. Sci. Technol. 1981,15, 1095-1100. (17) Eisenreich, S. J. Bidleman, T. F. Murphy, T. J.; Davis, A. R.; Banning, D. A,; Giam, C. S.; Priznar, F. J.; Mullin, M. D. In “The Potential Atmospheric Impact of Chemicals Released to the Environment. Proceedings of Four Workshops”, Miller, J. M., Ed.; U. S. EPA Office of Toxic Substances, Washington, DC, 1980; EPA 56015-80-001. (18) National Academy of Sciences “Polychlorinated Biphenyls”; National Academy of Sciences: Washington, DC, 1979; p 23. (19) National Academy of Sciences “Polychlorinated Biphenyls”; National Academy of Sciences: Washington, DC, 1979; p 15. (20) Furr, A. K.; Lawrence, A. W.; Tong, S. S. C.; Grandolfo, M. C.; Hofstader, R. A,; Bache, C. A.; Gutenmann, W. H.; Lisk, D. J. Environ. Sci. Technol. 1976, 10, 683-687. (21) U. S. Environmental Protection Agency, June 1975, Technology Transfer Publication, EPA-62514-75-009. (22) Bidleman, T. F.; Burdick, N. F.; Westcott, J. W.; Billings, W. N. In “Physical-ChemicalBehavior of PCBs in the Great Lakes”; Mackay, D.; Paterson, S.; Eisenreich, S.; Simmons, M., Eds., Ann Arbor Science: Ann Arbor, MI, 1983;p 15-48. (23) Weaver, G. Environ. Sci. Technol., 1984, 18, 22A-27A. (24) Murphy, T. J.; Rzeszutko, C. P. July 1978, U. S. EPA Report EPA-600/3-78-071. (25) McBean, E. A.; Farquhar, G. H. Water Air Soil Pollut. 1980, 13, 157-172. (26) Mackay, D. Environ. Sci. Technol., 1979, 13, 1218-1223. (27) Haile, C. L.; Baladi, E. 1977, U. S. EPA Environmental Monitoring Series Report EPA-60014-77-048. (28) Webb, R. G.; McCall, A. C. J . Chromatogr. Sci. 1973,11, 366-373. (29) Sawyer, L. D. J. Assoc. Off.Anal. Chem. 1978,61,272-281. Environ. Sci. Technol., Vol. 19, No. 10, 1985
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Mullin, M. D.; Pochini, C. M.; McCrindle, S.; Romkes, M.; Safe, S. H.; Safe, L. M. Enuiron. Sci. Technol. 1984, 18, 468-476.
Murphy, T. J.; Pokojowczyk, J. C.; Mullin, M. D. In "Physical-Chemical Behavior of PCBs in the Great Lakes"; Mackay, D.; Paterson, S.; Eisenreich, S.;Simmons, M., Eds.; Ann Arbor Science: Ann Arbor, MI, 1983; pp 49-58. Wall Street Journal; Jan 21, 1981; p 5. MacLeod, K. E. Environ. Sci. Technol. 1981,15,926-928. Pavoni, J. L.; Heer, J. E.; Hagerty, D. J. "Handbook of Solid
Waste Disposal"; Van Nostrand Reinhold New York, 1975; pp 431-443. (35) Sheppard, J. C.; Westberg, H.; Hopper, J. F.; Ganesan, K. J. Geophys. Res. 1982,87 (C2), 1305-1312.
Received for review May 18,1983. Revised manuscript received March 19,1985. Accepted May I , 1985. this project was supported by the U S . Environmental Protection Agency under Cooperative Agreement CR 807412 and by DePaul University.
Initial Decomposition Mechanisms and Products of Dimethyl Methylphosphonate in an Alternating Current Discharge Mark E. Fraser,+ Harold 0. Eaton, and Ronald S. Shelnson" Chemistry Division, Naval Research Laboratory, Code 6 180, Washington, DC 20375-5000
The efficiency of decomposition of dimethyl methylphosphonate (DMMP) vapor from a helium stream in an atmospheric pressure alternating current capacitive discharge has been determined to range from 50 to 100% depending upon the input concentration and flow rate and is improved with trace oxygen addition. In the absence of oxygen the principal discharge products are methane, ethane, formaldehyde, and carbon monoxide, suggesting an initial decomposition mechanism involving the loss of methyl radicals and formaldehyde. The subsequent chemistry of these species is postulated to produce the observed secondary products. Introduction
Interest in electric discharges as air purification systems has recently been renewed (1-4) with emphasis on the toxic organophosphorus compounds. Material breakthrough, failure in a moist or polluted environment, and contamination during unit disposal are the disadvantages of adsorption techniques that have refocused attention on electric discharges. Although the literature on the behavior of various organic and inorganic compounds in electric discharges is extensive ( 5 , 6), very little is known of the electric discharge induced decomposition chemistry of organophosphorus compounds. A cursory study of the microwave discharge decomposition of the G-agent simulants dimethyl methylphosphonate (DMMP) and diisopropyl methylphosphonate (DIMP) has been reported by Bailin et al. (7). In helium, the primary products of the discharge with DMMP were trimethyl phosphite and methanol (7), indicating an initial decomposition mechanism probably involving methyl and methoxy radicals. Mass spectrometric studies performed with real agents (8) and simulants (9) have revealed the electron collison induced fragmentation pattern of the G agents to be by formaldehyde, methyl radical, and methoxy radical loss. The decomposition chemistry of agents (and simulants) in an atmospheric pressure discharge has not yet been examined. The methodology employed in these experiments has been to introduce trace concentrations of an organophosphorus species of interest (dimethyl methylphosphonate or trimethyl phosphate) into a helium bulk carrier gas and monitor the discharge effluent products with GC and GC/MS techniques. In order to study the NRL/NRC Postdoctoral Fellow (1983-1985). Present address: Physical Sciences Inc., P.O. Box 3100, Andover, MA 01810. 946
Environ. Sci. Technol., Vol. 19, No. 10, 1985
discharge-induceddecomposition mechanism, helium bulk carrier gas has been used with and without trace oxygen addition. This was done in order to deconvolute the initial decomposition mechanism from the secondary oxidation reactions. Experimental Techniques
Discharge Apparatus. Figure 1 shows the atmospheric pressure discharge apparatus used in these experiments. Technical grade helium was purified by passage through traps of molecular sieve and activated charcoal immersed in liquid nitrogen baths in order to reduce hydrocarbon, oxygen, and nitrogen impurities. DMMP vapor was introduced into the helium stream from a bubbler immersed in a water bath regulated at 15.0 f 0.1 "C. The impurities in commercial-grade DMMP (Aldrich, 97 % pure), primarily methanol and acetone, were reduced by vacuum distillation. Gold label trimethyl phosphate (Aldrich, 99+ % pure) was used without further purification. A needle valve controlled the flow of added oxygen (0-500 ppm (volume)). Copper sampling lines for O2and N2 analyses were attached to points before and after the discharge. Rubber septum ports for syringe sampling were also located at these points to allow DMMP and discharge product analyses. An alternating current (ac) capacitive "ozonizer" type discharge was constructed by coating the outer and inner walls of a 35 cm long Pyrex Liebig condenser with silver conductive paint. Leads were then attached to a 16-kV, 60-H~ transformer. During normal operation the current was 1 mA with no detectable temperature rise. The outside diameter of the discharge tube was 1.9 cm, and the total volume of the discharge was 25 cm3with a wall-wall separation of 0.3 cm. Analytical System. 02, Nz, and CO separation was performed at 50 "C with a 1.83 m by 3.2 mm 0.d. (6 ft by l/s in.) molecular sieve column. A thermal conductivity detector (TCD) was used to detect oxygen and nitrogen while carbon monoxide was detected by a flame ionization detector (FID) after conversion to methane by a heated nickel catalyst with hydrogen flow. Analysis for methane, ethane, ethene, acetylene, propane, propene, acetaldehyde, dimethyl ether, and methanol was performed by gas chromatography using a 0.91 m by 3.2 mm (3 f t by '/a in.) Porapak-S column with temperature programming (10 "C for 4 min followed by an increase of 8 "C/min to 100 "C) and FID detection. The column temperatures were chosen because we have observed decomposition of DMMP on Porapak producing primarily methanol at column tem-
00 13-936X/85/09 19-0946$01.50/0
0 1985 American Chemical Society
