LINEAR ALKYLBENZENE SULFONATE (LAS) - UNEP Chemicals

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OECD SIDS LINEAR ALKYLBENZENE SULFONATE (LAS) Test Substance: C10-14 LAS, activity 66.62%; average alkyl chain length = C11.7 Remarks: In most cases, sea water samples showed a similar evolution of bacterioplankton over time, characterized by three phases: (a) a progressive increase in bacterial density; (b) a later decrease; and (c) a fluctuating stationary phase. Bacterioplankton degraded the LAS by growing to populations with a high percentage of viable bacteria. The bacteria were readily grazed by protozoa, preventing anomalous high bacterial growth and ensuring the later channeling of LAS carbon to upper trophic levels. Reference: Vives-Rego, J., Lopez-Amoros, R., Guindulain, T., Garcia, M.T., Comas, J., and Sanchez-Leal, J. 2000. Microbial aspects of linear alkylbenzene sulfonate degradation in coastal water. Journal of Surfactants and Detergents. 3:303-308. Reliability: 2 Valid with restrictions (v) Type: Respirometer Method: Degradation of LAS in Ohio River water collected below the discharge of a municipal wastewater treatment plant (Muddy Creek, OH) was measured in an electrolytic respirometer. Background LAS concentrations were less than 0.5 mg/L. Oxygen consumption over time was determined at five LAS concentrations (5, 10, 20, 40, and 80 mg/L) plus a control until plateau values were reached. The maximum initial rates of oxygen uptake were calculated based on methods described in Larson and Perry (1981). Results: LAS degradation was not affected in river water until the LAS concentration exceeded 10 mg/L. The degradation was partially affected at 20 mg/L but was not completely inhibited until 40 mg/L. Substance: LAS; average chain length C11.6. Remarks: The level at which inhibition of degradation was complete (40 mg/L) is significantly higher than the levels observed in model ecosystem studies conducted by these researchers [see 4.7 (h) and (i)]. Reference: 1) Larson, R.J. and Maki, A.W. 1982. Effect of LAS on the structure and function of microbial communities in model ecosystems. Aquatic Toxicology and Hazard Assessment: Fifth Conference, ASTM STP 766, Pearson, J.G., Foster, R.B., and Bishop, W.E., Eds., American Society for Testing and Materials, pp. 120-136. 2) Maki, A.W. 1981. A laboratory model ecosystem approach to environmental fate and effects studies. Unpublished Internal Report, Environmental Safety Department Procter & Gamble Company, Cincinnati, Ohio. 3) Larson, R.J. and Perry, R.L. 1981. Water Research 15:697-702. Reliability: 2 Valid with restrictions (w) Type: aerobic [X]; anaerobic [ ] Substance: LAS Remarks: The biodegradation of LAS has been thoroughly studied for its primary and total degradation and catabolism. It is mineralized biologically to form carbon dioxide, water and sulphate. Using UV spectroscopic analysis, Swisher (1987) and others showed the aromatic ring to be degradable up to 80%. Using the more reliable tracer technique with 14 C-ring labelled LAS, it was determined that degradation of the ring is predominantly between 50 and 80%. Further studies have shown that LAS degradation proceeds through oxidative conversion of the methyl groups of the alkyl chain into a carboxyl group (ω-oxidation), oxidative shortening of the alkyl chain by 2-carbon units (β-oxidation), oxidative ring splitting, then cleavage of the carbonsulfur bond. This process forms sulfophenyl carboxylates (SPCs) as UNEP PUBLICATIONS 166
OECD SIDS LINEAR ALKYLBENZENE SULFONATE (LAS) biodegradation intermediates. The first detectable degradation product of LAS is ω-carboxylate. For example, Huddleston and Allred (1963) detected sulfophenyl decanoic acid as a catabolite of 2-benzenedecasulfonate. Oxidative degradation of the alkyl chain begins as soon as LAS has been converted into sulfophenyl carboxylic acid. The principal degradation pathway is β-oxidation. The rate of biodegradation is inversely related to the distance between the terminal alkyl-methyl group and the point of benzene ring attachment. Simple branching does not impair the oxidation of alkylbenzene, though more complex branching does decrease the rate. Reference: 1) Swisher, R.D. 1987. Surfactant Biodegradation, second edition. Surfactant Science Series, Volume 18. Marcel Dekker, Inc. New York. 2) Schoeberl, P. 1989. Basic principles of LAS biodegradation. Tenside Surf. Detergents 26:86-94. 3) Huddleston, R.L. and Allred, R.C. 1963. Microbial oxidation of sulfonated alkylbenzenes. Dev. Ind. Microbiol. 4:24-38. Reliability: 2 Valid with restrictions (x) Type: aerobic [X]; anaerobic [ ] Method: Dialkyltetralin sulfonates (DATS) and LAS with single methyl branching on the alkyl chains (iso-LAS) are minor components in commercial LAS. In this study, DATS and iso-lAS were synthesized and exposed to simulated activated sludge, soil, and receiving water environments. In addition, the effluents coming from activated sludge treatment, which contained biodegradation intermediates, were exposed to simulated receiving water environments. Radiolabeled LAS, DATS and iso-LAS were used and all samples were analyzed using chemical-specific HPLC procedures. Surface soils were collected at three locations to represent “pristine” soil, sludgeamended soil, and gray water contaminated soil from the top of a percolation bed that receives surface applications of laundry water from a Laundromat. All samples were screened to remove vegetation, rocks and debris, and mixed with a mineral salts medium containing the test substance. Sediment samples were collected from the upper inch of a small stream that received effluent from a domestic wastewater treatment plant. Periphyton samples were collected as rocks coated with heavy growth from the same stream locations as the water and sediment samples. Each test system consisted of duplicate test flasks and a control flask. Tests lasted at least 30 days. For assessing biodegradation, the porous pot method was used in a simulated wastewater activated sludge modified from ASTM test method E1798-96. A 21-day acclimation phase was followed by a 15-day test phase in which radioactivities in C02, liquids and solids, and effluent total suspended solids and COD were determined each day. Radiochemical recoveries for the porous pot test were calculated. For the die-away tests with porous pot effluents, the combined effluents from individual units were tested for mineralization of radiolabeled parent and intermediate compounds. All tests were run at least 30 days and the radioactivities measured at the end of each test. Results: Results indicate that radiolabeled DATS and iso-LAS is mineralized by indigenous microbial populations in laboratory simulations of aquatic and soil environments. Half-lives ranged from 2 to 20 days. In addition, upon exposure to laboratory activated sludge treatment, most iso-LAS compounds showed >98% parent compound removal, extensive mineralization (>50%), and 79-90% ultimate biodegradation. Activated sludge treatment of DATS resulted in >98% removal, 3-12% ultimate biodegradation, and apparent formation of carboxylated biodegradation intermediates that accounted for 88-97% of the original material. These intermediatel continued to mineralize UNEP PUBLICATIONS 167
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LINEAR ALKYLBENZENE SULFONATE (LAS) - UNEP Chemicals

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