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thermodynamic Methods; Wiley: New York, NY, 1963. (12) March, J . Advanced Organic Chemistry, Reactions, Mechanisms and Structure; Wiley: New York, NY, 1985. (13) Harris, J. C. In Handbook of Chemical Property Estimation Handbook; Lyman, W. J.; Reehl, W. F.; Rosenblatt, D. H., Eds.; McGraw-Hill: New York, NY, 1982; p p 7-1-7-47. (14) Frost, A. A.; Pearson, R. G. Kinetics and Mechunzsm; Wiley New York, NY, 1961. (15) Cooper, K. A.; Hughes, E. D.; Ingold, C. K.; MacNulty, B. J.; Woolf, L. I. J . Chem. Soc. 1948, 2038-2119. (16) Wolfe, N. L.; Steen, W. C.; Burns, L. A. Chemosphere 1980, 9, 403-408. (17) Mill, T.; Mabey, W. R.; Winterle, J. S.; Davenport, J. E.; Barich, V. P.; Dulin, D. E.; Tse, D. S.; Lee, G. Design and Validation of Detailed Screening Methods for Environmental Processes; EPA Report for Contract 68-01-6325; EPA, Washington, DC, 1982. (18) Thomas, R. G. In Handbook of Chemical Property Estimation Handbook; Lyman, W. J.; Reehl, W. F.; Rosenblatt, D. H., Eds.; McGraw-Hill: New York, NY, 1982; pp 15-115-34. (19) Munz, C. Ph.D. Dissertation, Stanford University, Stanford, CA, 1985.
(20) Lindgren, B. W. Statistical Theory; Macmillan: New York, NY, 1976; pp 533, 546. (21) Pierce, J. R.; Wolfe, N. L. Presented before the Division of Environmental Chemistry, American Chemical Society, Las Vegas, NV, March 1982; Preprint Extended Abstract. (22) Robertson, R. E.; Heppolette, R. L.; Scott, J. M. W. Can. J . Chem. 1959,37,803-824. (23) Laughton, P. M.; Robertson, R. E. Can. J. Chem. 1956,34, 1714-1718. (24) Laughton, P. M.; Robertson, R. E. Can. J. Chem. 1959,37, 1491-1497. Received for review June 19,1984. Revised manuscript received December 23, 1985. Accepted May 13, 1986. This work was supported by the U.S. E P A through the Office of Research and Development, Grant EPA-R-808034-010, and through the R. S. Kerr Environmental Research Laboratory, EPA-R-808851. Although the information i n this article has been funded in part by the U S . Environment Protection Agency, it has not been subjected to the Agency’s review and therefore does not necessarily reflect the views of the Agency, and no official endorsement should be inferred.
Biotransformations of Selected Alkylbenzenes and Halogenated Aliphatic Hydrocarbons in Methanogenic Aquifer Material: A Microcosm Study Barbara H. Wilson* Environmental and Ground Water Institute, University of Oklahoma, Norman, Oklahoma 730 19
Garmon B. Smith R. S. Kerr Environmental Research Laboratory, Ada, Oklahoma 74820
John F. Rees BioTechnica, Ltd., Cardiff, Wales, U.K. ~~
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Leachates from municipal landfills commonly contain a variety of organic contaminants of industrial origin. The behavior of these compounds in anaerobic, and particularly in methanogenic, subsurface materials is poorly understood. The behavior of benzene, toluene, ethylbenzene, o-xylene, 1,l-dichloroethylene, tram-1,2-dichloroethylene, cis-1,2-dichloroethylene,trichloroethylene, and 1,2-dibromoethane was studied in authentic aquifer material known to support methanogenesis. These compounds are frequently found as contaminants in groundwater used for municipal water supplies. The disappearance of all compounds was observed with long lag times required before initiation of degradation of 1,l-dichloroethylene, trans1,2-dichloroethylene7trichloroethylene, benzene, ethylbenzene, and o-xylene. [14C]Toluenedegraded to COP Vinyl chloride was found as a daughter product of 1,ldichloroethylene, trans-1,2-dichloroethylene,and trichloroethylene. 1,2-Dichloroethylene was also observed as a degradation product of trichloroethylene. No daughter products were identified for the remaining compounds.
Introduction The contamination of groundwater by organic compounds disposed in sanitary landfills has been of considerable environmental concern. Historically, landfills have *Address correspondence to this author at the R.S. Kerr Environmental Research Laboratory, Ada, OK 74820. 0013-936X186/0920-0997$01.50/0
been used for the disposal of both industrial and domestic wastes a t thousands of abandoned and currently active sites. Several investigations have surveyed the range of organic pollutants present in groundwater influenced by landfill leachate (1-4). In general, these studies indicate that landfills are a major source of groundwater contamination by the chlorinated solvents and the water-soluble constituents of petroleum. The distribution of organic contaminants in leachate plumes from two sanitary landfills has been carefully studied (1). The majority of the organic compounds identified resulted from the decomposition of plant material and included aliphatic and aromatic acids, phenols, and terpene compounds. However, the plumes also contained chemicals of industrial origin including chlorinated and nonchlorinated hydrocarbons, nitrogencontaining compounds, alkylphenol polyethoxylates, and alkyl phosphates. The compounds indicative of disposal of petroleum products (toluene, benzene, ethylbenzene, and the xylenes) were the most prevalent pollutants identified; among the other common industrial chemicals present were l,l,l-trichloroethane, trichloroethylene, and tetrachloroethylene. The presence of dissolved chlorinated solvents and aromatic hydrocarbons in groundwater is of concern because of their harmful effects even at very low concentrations. The lo4 cancer risk for benzene is 0.67 pg/L and for trichloroethylene is 2.8 pg/L (5). The lo4 cancer risk
0 1986 American Chemical Society
Environ. Sci. Technol., Vol. 20, No. 10, 1986 997
Table I. Characterization of Aquifer Water from the Methanogenic Site" parameter
value
parameter
value
PH Eh, mV conductivity alkalinity total phosphate nitrate
7.3 -50
ammonia total Kjeldahl nitrogen total organic carbon chloride sulfate fluoride
218 229 344 834 27 1.2
6000
2670 0.03 0.7
"All concentrations are in mg/L except pH is in pH units and conductivity is in kmho.
for vinyl chloride, a product of the reductive dehalogenation of trichloroethylene and tetrachloroethylene, is 1pg/L (5). ., Anaerobic conditions are known to exist beneath many landfills, as well as hazardous waste disposal sites and spill situations. An understanding of the potential for biotransformations of aromatic and halogenated aliphatic hydrocarbons under anoxic conditions in subsurface environments is required to predict the behavior of these pollutants in the subsurface. In this study, the behavior of two groups of commonly occurring contaminants was examined in microcosms constructed with authentic aquifer material that receives municipal landfill leachate and is known to support methanogenesis. The alkylbenzenes studied were benzene, toluene, ethylbenzene, and o-xylene,while the halogenated aliphatic hydrocarbons studied were 1,l-dichloroethylene, trans-1,2-dichloroethylene,cis-1,2-dichloroethylene, trichloroethylene, and 1,2-dibromoethane. The alkylbenzenes chosen for study are much more soluble in water than the aliphatic and higher molecular weight constituents of petroleum (6). Also, they do not sorb onto subsurface solids to a significant degree. For these reasons, they are found dissolved in groundwater to a larger extent than other constituents of petroleum distillates and migrate with the moving groundwater. Trichloroethylene and the dichloroethylenes are products of the reductive dehalogenation of tetrachloroethylene (7). Tetrachloroethylene and trichloroethylene are widely used as degreasers and both have become common groundwater contaminants (8). 1,2-Dibromoethane is a constituent of gasoline and is a widely used soil fumigant that has been detected in groundwater. The compounds chosen for study are important contaminants of groundwater supplies of drinking water and frequently are disposed in municipal landfills.
Materials and Methods Site Description. Aquifer material for the anaerobic fate studies was obtained from sites adjacent to the Norman, OK, landfill located on the north bank of the South Canadian River approximately 1.6 km south of the city. The landfill is sited over highly permeable alluvium composed of silt, sand, clay, gravel, and dune sand. The depth of the alluvium varies from 10.7 to 12.2 m and lies over a 91-m layer of dense clay and chert gravel, known locally as the "red b e d . The water table averages from 0.6 to 1.5 m below the original land surface in areas adjacent to the river; the direction of groundwater movement is approximately 7 deg west of south (9). In a previous study of contamination at this landfill ( 4 ) , over 40 organic chemicals were found in the groundwater. Among the compounds detected were various phthalates, p-cresol, several organic acids, and low levels of the xylenes. Currently the landfill is not in use and has been covered with a clay cap. 998
Envlron. Scl. Technol., Vol. 20, No. 10, 1986
Table 11. Disappearance of Halogenated Aliphatic Hydrocarbons from Methanogenic Aquifer Materialn treatment
pg/L of pore water week 0 week 3 week 7 week 16
1,l-DCE trans-1,2-DCE &-1,2-DCE TCE EDB
124 124 123 155 194
Living 135 125 110 104 136 125 151 149 78 35
1,l-DCE trans-1,P-DCE cis-1,2-DCE TCE EDB
136 128 152 127 140
Autoclaved 130 100 124 142 137 129
65 93
