Revised August 2014
Strictly anaerobic conditions are often defined, for the purpose of laboratory testing, as those in which oxygen is totally excluded. Linear alkylbenzene sulfonate (LAS) can reach several compartments in the environment that are characterized as “anaerobic,” including surface water sediments, septic system tile fields, and landfills where sewage sludge may be disposed. However, recent studies suggest these “anaerobic” environments are actually anoxic, or oxygen-limited, indicating that oxygen diffuses into them but is consumed at a faster rate than it enters.
For a chemical such as LAS, this distinction is significant, for LAS biodegrades in anoxic environments and, once initial biodegradation has occurred, LAS will continue to biodegrade even in strictly anaerobic conditions. Field study data also support this finding, detecting far lower levels of LAS in the environment than laboratory studies conducted under strictly anaerobic conditions would predict. Field studies also confirm that, after more than 50 years of use, LAS has not accumulated in these environments, providing further scientific support for aerobic metabolism through oxygen diffusion into natural anaerobic environments.
• Although several studies have demonstrated that LAS requires oxygen to biodegrade1-7, more recent studies by Lara-Martin30,1,32 have shown that LAS truly degrades in anaerobic sulfate-reducing marine sediment. Laboratory experiments, performed on anoxy marine sediments spiked with 10-50 ppm of LAS, showed that degradation is feasible, reaching a value of 79% in 165 days, with a half-life time of ca. 90 days.
• Anaerobic biodegradation of LAS was also observed in the field with several marine sediment samplings at anoxy depths in the sedimentary column. LAS concentrations in pore waters decreased sharply and the biodegradation intermediates (SPC) reached the maxima. These observations provide the first real evidence of partial degradation of LAS under anaerobic conditions.30,31
• A more recent paper provides for the first time an anaerobic biodegradation pathway for LAS.32
• Standard laboratory tests on anaerobic biodegradability, while predicting fate with no oxygen present, do not reflect the behavior of LAS in real-world environments, which are typically subject to oxygen diffusion.
• Laboratory studies show that LAS will biodegrade under anoxic conditions, presumably by using available oxygen that diffuses into these environments.8-10 River sediments, landfills and subsurface soils are examples of such environments.
• Extensive U.S. monitoring studies found no LAS accumulation on sediments below sewage treatment plant outfalls. In fact, the studies show that the LAS on sediments continues to biodegrade.11-13
• A comprehensive Mississippi River Survey found only very low levels of LAS and biodegradation intermediates in sediments downstream from wastewater treatment plants. Concentrations ranged from less than 0.01 to 5 milligrams per kilogram (mg/kg).14
• Studies in Japan also revealed degradation of LAS in sediments. LAS concentrations in river sediments around outfalls decreased 90 percent in upper estuaries and almost completely (below 0.01 mg/kg) 10 kilometers offshore.15-17
• The vertical distribution of LAS in Japanese lake sediments showed seasonal variations attributed to biodegradation activities.18,19 LAS levels in Japanese lake sediments decreased with increasing depths, indicating biodegradation even though the conditions might be considered anaerobic.19
• Studies involving a German landfill, an ostensibly anaerobic environment, receiving LAS-containing sludge, revealed a 98 percent LAS removal rate over a period of 10 to 11 years.20
• In an extensive series of studies on a domestic septic system, including the subsurface soil and groundwater, LAS was shown to be rapidly and extensively biodegraded by the microbial populations in the soil. In fact, no LAS was detected below the top 2 inches (5 centimeters) of soil in the septic tank percolation field.21-25
• Subsurface soils beneath a drainage field and pond receiving laundromat wastewater were also shown to be effective in biodegrading LAS. No LAS has been detected in the ground-water below the site, despite 25 years of LAS use.26,27
• Studies show that exposure of LAS to oxygen for five to six hours during the treatment process yielded LAS biodegradation products that continued to break down in an anaerobic digester. This indicates that, once aerobic biodegradation of LAS is initiated, it can continue in anaerobic conditions.27,28
KEY REFERENCES
1. Swisher, R.D. Surfactant Biodegradation. (Marcel Dekker, New York, 1987).
2. Little, A.D. “Environmental and Human Safety of Major Surfactants. Volume 1. Anionic surfactants. Part 1. Linear Alkylbenzene Sulfonates.” Final Report To: The Soap and Detergent Association, Ref. 65913 (New York, February, 1991).
3. Painter, H.A. and T.F. Zabel. “Review of the Environmental Safety of LAS.” Water Research Centre, CO-1659-M/1/EV8658 (Medmenham, UK, 1988).
4. McEvoy, J. and W. Giger. “Determination of Linear Alkylbenzene Sulfonates in Sewage Sludge by High Resolution Gas Chromatography/Mass Spectrometry.” Environ. Sci. Tech. 20, 376-383 (1986).
5. Janicke, W. and G. Hilge. “Biodegradability of Anionic/Cationic Surfactants Under Aerobic and Anaerobic Conditions of Wastewater and Sludge Treatment.” Tenside Surf. Det. 16, 472-482 (1979).
6. Oba, K.Y., Y. Yoshida and S. Tomiyama. “Biodegradation of Synthetic Detergents: I. Biodegradation of Anionic Surfactants Under Aerobic and Anaerobic Conditions.” Yukgaku 16, 517-523 (1967).
7. Federle, T.W. and B.S. Swab. “Mineralization of Surfactants in Anaerobic Sediments of a Laundromat Wastewater Pond.” Water Res. 26, 123-127 (1992).
8. Pflugmacher, J. “Degradation of Linear Alkylbenzenesulfonates (LAS) Under Laboratory and Field Conditions Using a New HPLC Detection Method.” UWSF-Z. Umweltchem. Oekotox. 4, 329-332 (1992).
9. Britton, L.N. and A.M. Nielsen. “Relevance of Aerobic Biodegradability Testing to Environmental Fate.” 1st SETAC World Congress, Abstract 102P (Lisbon, March 28-31, 1993).
10. Heinze, J.E. and L.N. Britton. “Anaerobic Biodegradation: Environmental Relevance.” Proceedings of the 3rd World Conference on Detergents: Global Perspectives. (ed. A. Cahn) 235-239 (AOCS Press, Champaign, Illinois, 1994).
11. Rapaport, R.A. and W.S. Eckhoff. “Monitoring Linear Alkylbenzene Sulfonate in the Environment: 1973-1986.” Environ. Toxicol. Chem. 9, 1245-1257 (1990).
12. Rapaport, R.A., R.J. Larson, D.C. McAvoy, A.M. Nielsen and M. Trehy. “The Fate of Commercial LAS in the Environment.” 3rd CESIO International Surfactants Congress & Exhibitions — A World Market, Proceedings Section E, 78-87 (London, June 1-5, 1992).
13. McAvoy, D.C., W.S. Eckhoff and R.A. Rapaport. “Fate of Linear Alkylbenzene Sulfonate in the Environment.” Environ. Toxicol. Chem. 12, 977-987 (1993).
14. Tabor, C.F. Jr., L.B. Barber and D.D. Runnells. “Anionic Surfactants in the Mississippi River: A Detailed Examination of the Occurrence and Fate of Linear Alkylbenzene Sulfonate.” 205th Annual Meeting, American Chemical Society, Division of Environmental Chemistry, preprint extended abstracts, pp. 52-55 (Denver, March 28-April 2, 1993).
15. Takada, H. and R. Ishiwatari. “Linear Alkylbenzenes in Riverine Environments in Tokyo: Distribution, Source and Behavior.” Environ. Sci. Tech. 21, 875-883 (1987).
16. Takada, H., N. Ogura and R. Ishiwatari. “Seasonal Variations and Modes of Riverine Input of Organic Pollutants to the Coastal Zone: I. Flux of Detergent-derived Pollutants to Tokyo Bay.” Environ. Sci. Tech. 26, 2517-2523 (1992).
17. Takada, H., R. Ishiwatari and N. Ogura. “Distribution of Linear Alkylbenzenes (LABs) and Linear Alkylbenzene Sulfonate (LAS) in Tokyo Bay Sediments.” Estuarine, Coastal and Shelf Science 35, 141-156 (1992).
18. Amano, K. and T. Fukushime. “On the Longitudinal and Vertical Changes in Lake Estuarine Sediments.” Water Sci. Tech. 20, 143-153 (1988).
19. Amano, K., T. Fukushime and O. Nagasugi. “Diffusive Exchange of Linear Alkylbenzene Sulfonate (LAS) Between Overlying Water and Bottom Sediment.” Hydrobiologia 0, 1-9 (1991).
20. Marcomini, A., P.D. Capel, T. Lichtensteiger, P.H. Brunner and W. Giger. “Behavior of Aromatic Surfactants and PCBs in Sludge-Treated Soil and Landfills.” J. Environ. Quat. 18, 523-528 (1989).
21. Larson, R.J., R.W. Federle, R.J. Shimp and R.M. Ventullo. “Behavior of Linear Alkylbenzene Sulfonate in Soil Infiltration and Groundwater.” Tenside Surf. Det. 26, 116-121 (1989).
22. Robertson, W.D., E.A. Sudicky, J.A. Cherry, R.A. Rapaport and R.J. Shimp. “Impact of a Domestic Septic System on an Unconfined Sand Aquifer.” Contaminant Transport in Groundwater. (eds. Kobus & Kenzelbach) 105-112 (Balkema, Rotterdam 1989).
23. Shimp, R.J., E.V. Lapsins and R.M. Ventullo. “Chemical Fate and Transport in a Domestic Septic System: Biodegradation of Linear Alkylbenzene Sulfonate (LAS) and Nitrilotriacetic Acid (NTA).” Environ. Toxicol. Chem. 13, 205-212 (1994).
24. McAvoy, D.C., C.E. White, B.L. Moore and R.A. Rapaport. “Chemical Fate and Transport in a Domestic Septic System: Sorption and Transport of Anionic and Cationic Surfactants.” Environ. Toxicol. Chem. 13, 213-221 (1994).
25. Shutter, S.B., E.A. Sudicky and W.D. Robertson. “Chemical Fate and Transport in a Domestic Septic System: Application of a Variably Saturated Model for Chemical Movement.” Environ. Toxicol. Chem. 13, 223-231 (1994).
26. Federle, T.W. and G.M. Pastwa. “Biodegradation of Surfactants in Saturated Subsurface Sediments: A Field Study.” Ground Water 26, 761-770 (1988).
27. Birch, R.R., W.E. Gledhill, R.J. Larson and A.M. Nielsen. “Role of Anaerobic Biodegradability in the Environmental Acceptability of Detergent Materials.” 3rd CESIO International Surfactants Congress & Exhibition — A World Market, Proceedings Section E, 26-33 (London, June 1992).
28. Larson, R.J., T.M. Rothgeb, R.J. Shimp, T.E. Ward and R.M. Ventullo. “Kinetics and Practical Significance of Biodegradation of Linear Alkylbenzene Sulfonate in the Environment.” J. Amer. Oil. Chem. Soc. 70, 645-657 (1993).
29. Leòn V.M., E González-Mazo, J.M. Forja Pajares and A. Gómez-Parra, “Vertical distribution profiles of LAS and their long-chain intermediate degradation products in coastal marine sediments,” Environ. Tox. Chem. 20: 2171-2178 (2001).
30. Lara-Martín, P.A., Gómez-Parra, A., Köchling, T., Sanz, J.L., Amils, R., and González-Mazo, E. “Anaerobic degradation of linear alkylbenzene sulfonates in coastal marine sediments.” Environ. Sci. Technol. 41, 3573–3579 (2007)
31. Lara-Martín P.A., A. Gómez-Parra, T. Köchling, J.L. Sanz, and E. Gónzalez-Mazo. “Field and laboratory evidences regarding the anaerobic degradation of LAS,” vol. 2, paper O-E11, CESIO 2008: 7th World Surfactants Congress, Paris, France: 22-25 June 2008.
32.Lara-Martín P.A., A. Gómez-Parra, J.L. Sanz, and E. Gónzalez-Mazo. “Anaerobic degradation pathway of linear alkylbenzene sulfonates (LAS) in sulphate-reducing marine sediments,” Environ. Sci. Technol. 44, 1670-1676 (2010).
ADDITIONAL REFERENCES
• Thurman, E.M., L.B. Barber, Jr. and D.J. LeBlanc. “Movement and Fate of Detergents in Groundwater.” Hydrol., 1, 143-161 (1986).
• Field, J.A., L.B. Barber, II, E.M. Thurman, B.L. Moore, D.L. Lawrence and D.A. Peake. “Alkylbenzenesulfonates and Dialkyltetralinsulfonates in Sewage-Contaminated Groundwater.” Environ. Sci. Tech. 26, 1140-1145 (1992).
• “Human and Environmental Risk Assessment on Ingredients of Household Cleaning Products – LAS – Linear Alkylbenzene Sulphonate – CAS No. 68411-30-3”, Revised April, 2013, pages 4, 11-14.
• Cowan-Ellsberry C., S. Belanger, P. Dorn, S. Dyer, D. McAvoy, H. Sanderson, D. Versteeg, D. Ferrer and K. Stanton. “Environmental Safety of the Use of Major Surfactant Classes in North America,” Critical Reviews in Environmental Science and Technology, 44:17, 1893-1993 (2014).
Last updated on August 2014