Author Archive for: fisraeli@kellencompany.com

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 biodegrade^1-7, more recent studies by Lara-Martin^30,1,32 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

There are two types of alkylbenzene sulfonates, ABS (branched alkylbenzene sulfonate) and LAS (linear alkylbenzene sulfonate). LAS had not been discovered when ABS was first introduced as a detergent surfactant in the late 1940s. While ABS has served consumers well, foam-related environmental problems began to appear in surface waters, groundwater, drinking water and in wastewater treatment plants. Investigation of these problems led to the discovery that ABS is resistant to biodegradation.^1,2,3 This resistance caused ABS to be known as non-biodegradable or a “hard detergent.” LAS is known as biodegradable or a “soft detergent” because it quickly and completely biodegrades^2,3,4 and does not cause such environmental problems.

Environmental Benefits

As ABS was replaced with LAS beginning in the mid-1960s, extensive data, compiled in the book by R.D. Switzer⁵, have confirmed the positive environmental effects. Among the well-documented examples:

United States: Surfactant concentrations in river waters dramatically decreased. The Illinois River at Peoria, Illinois, was highly polluted because of sewage and industrial plant effluents and storm water runoff from the greater Chicago area. From 1959 to 1965, the average MBAS (Methylene Blue Active Substance) concentration in the river was 0.54 parts per million (ppm). The MBAS test measures anionic surfactants (including LAS and ABS) and related anionic substances. These substances generally affect the taste of water and cause foaming at concentrations above 0.5 ppm. Consequently, the U.S. and other countries adopted standards for water quality of MBAS < 0.5 ppm. In the year following the conversion to LAS, the average MBAS value dropped to 0.22 ppm. By the spring of 1968, it had dropped even lower, averaging 0.05 ppm. In addition, analytical work showed that only 20 percent of the MBAS present was actually LAS. A U.S. monitoring study of 50 river sites directly below wastewater treatment plants showed that the average LAS concentration was 0.035 ppm.⁶ Furthermore, 90% of over 500,000 U.S. river miles in the U.S. have less than 0.004 ppm LAS.

England: When ABS was replaced with LAS in England, the surfactant concentration in river waters dropped by a factor of five. By 1966, surfactant levels had reached the lower limits of analytical detection. Today they are almost certainly lower. These changes occurred even though the volume of detergents used, and therefore the amount entering the environment, had greatly increased.

Germany: From 1958 to 1964, MBAS residues in surface waters of the Rhine River basin increased constantly, paralleling the rapid increase in ABS consumption. The conversion to LAS in 1964 resulted in the immediate reduction of MBAS levels. Average MBAS concentrations continued to drop until pre-1958 levels were observed by the late 1970’s. This overall reduction occurred despite a population increase of approximately 6 million people and a two-fold increase in detergent consumption over 1958 levels. From 1978 to 1987 the MBAS levels dropped to below 0.05 ppm. LAS specific analyses suggest that only about 0.01 ppm LAS is currently present in the Rhine River.

Japan: Similar results were observed in Japan. One example is that of the Tama River, which passes through heavily populated areas and receives large quantities of untreated domestic sewage. Even though the levels of organic pollutants in the river had reached the 8-10 ppm BOD level by the early 1980’s, the yearly average MBAS residues had steadily decreased from a high of about 2.5 ppm in 1968 to 0.3 ppm in 1981 as a result of the use of LAS.

Thailand: In July-August 1983, the average MBAS residual over the 10-48 kilometer zone of the Chao Phraya River was 0.34 ppm. After switching to LAS, the average value over the same zone had decreased by 72 percent to 0.095 ppm by July of 1984.

Thus while there is extensive evidence that ABS causes environmental problems, there is now also overwhelming evidence that these problems are solved by changing to the use of LAS. This remains true regardless of geographical location, climate or environmental conditions.

Processing

The same plant process units, transfer and storage equipment, and similar operating conditions can be used for LAS as is used for ABS. No new plant investment or other significant changes are required in switching to the biodegradable LAS.

Performance Advantages

Both the cleaning power and the foam properties of LAS are equal or superior to ABS under most washing conditions. These performance advantages offer the detergent manufacturer possibilities of reducing the level of active ingredient and/or phosphate in the detergent product without sacrificing performance. (The actual amount of these reductions will depend, of course, on the particular formulation and the local washing conditions.) The detergency performance advantage of LAS over ABS is due to two factors. First the carbon distribution of LAS is at the optimum for performance (C12 average). This is not the case for ABS which gives optimum performance at C13 average. Second, LAS is less sensitive to water hardness than ABS in, for example, Latin American washing conditions.⁷ This greater cleaning property of LAS offers the detergent formulator possibilities for either a superior cleaning product or for surfactant and phosphate reductions in the detergent product when changing from ABS to LAS.

Conclusion

The change for ABS to LAS detergents has not only eliminated the environmental problem of non-biodegradability, but has given manufacturers and consumers a superior product with performance benefits. This has been thoroughly documented in countries throughout the world that have changed from ABS to LAS. As a result, LAS has become the leading detergent active ingredient in the world.

Key References

1. Sallee, E. M., J.D. Fairing, R.W. Hess, R. House, P.M. Maxwell, F.W. Melpolder, F.W. Middleton, J. Ross, W.C. Woelfel, and P.J. Weaver. “Determination of trace amounts of alkyl benzene-sulfonates in water.” Anal.Chem., 28, 1822–1826 (1956).

2. Swisher, R.D., Surfactant Biodegradation, Second Ed., Marcel Dekker, New York, 1987, pp. 1-2.

3. 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).a>

4. Serrano, L.I., C.A.P. Velasco and A.S.C. Malagon. “Ultimate Biodegradation of Commercial Linear Alkylbenzene Sulphonates (LAS) under ISO 14593 Headspace CO2 Test: Compliance with EU Detergent Regulation 648/2004.” Tenside Surf. Det. 48, 390-394 (2001).

5. Swisher, R.D., ibid., pp. 5-6 and section 5.XI.E (pp. 400-401) and tables and references therein.

6. 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).

7. Matheson, K.L. “Detergency Performance Comparison between LAS and ABS Using Calcium Sulfonate Precipitation Boundary Diagrams.” J. Am. Oil Chem. Soc. 62, 1269-1274 (1985).

Revised August 2014