LINEAR ALKYLBENZENE SULFONATE (LAS) - UNEP Chemicals

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OECD SIDS LINEAR ALKYLBENZENE SULFONATE (LAS) than 99% of the LAS load was removed by biodegradation, showing that the adsorbed fraction as well as the soluble fraction of LAS is readily available for biodegradation. Mackay et al. (1996) conducted five-stage Level III fugacity modelling that included evaluative, regional and local-scale models. The level I and II models each resulted in LAS partitioning in air, water, soil and sediment at percentages of 0, 26, 56 and 18%, respectively. The overall residence time of LAS is predicted to be 100 hours with removal primarily by biodegradation in water (76%) and partitioning to sediment (13%). Impacts of LAS are predicted to be restricted to local receiving waters and their sediments and biota. In the Level III Fugacity Model, when discharges are directly to water, the residence time is predicted to be 33 hours and more than 99% remains in the water. However, in shallower receiving water more partitioning to sediments might be expected. When discharge is to soil, the residence time is predicted to be 28 days because of the slower biodegradation rate (compared to water) and little transfer to other media. Using the ChemCAN 4 model and assuming 90% LAS discharge to soil and 10% to water, LAS partitioning in air, water, soil and sediment is predicted to be 0, 0.64, 99.35 and 0.004%. Level III fugacity modelling was also conducted by ECETOC (1993; reliability not assigned due to uncertainty regarding the input parameters) to predict LAS concentrations in air, biota, sediment, arable soil, suspended solids and water. LAS concentrations were predicted to be highest in soil and suspended solids. 2.2.6 Biodegradation Biodegradation is the primary mechanism by which LAS is transformed, with the formation of sulfophenyl carboxylates (SPCs) as biodegradation intermediates (Swisher 1987; Schoeberl 1989; Huddleston and Allred 1963; dossier 3.5w). Longer alkyl chain LAS homologues undergo more rapid primary biodegradation to SPCs than shorter chain homologues (Bock and Wickbold 1966). SPC toxicities are several orders of magnitude lower than that of the parent material (Kimerle and Swisher 1977; dossier 4.1r, 4.2Af). SPCs also biodegrade as demonstrated by the rapid and complete biodegradation of LAS (to CO2, SO42-, and water) under aerobic conditions documented below. An extensive database of studies is available demonstrating rapid and complete biodegradation of LAS in freshwater under aerobic conditions (e.g., Ruffo et al. 1999; Nielsen and Huddleston 1981; dossier section 3.5). The studies summarized in Table 4 demonstrate that LAS passes standard tests for ready biodegradability, including the 10-day biodegradation window (Add refs). Rapid biodegradation of the iso-LAS components of LAS was also demonstrated by Cavalli et al. (1996) in a modified OECD 301E biodegradation study in which C11.6 LAS containing 5-6% iso-LAS was the sole source of carbon and the bacterial biomass was obtained from soil. Preliminary tests showed that more than 90% of the LAS disappeared within 4 days so additional LAS was added to the test system every fourth day over a 80-day test period. No accumulation of iso-LAS was observed in this study demonstrating that the iso-LAS components are just as biodegradable as LAS. Rapid biodegradation of LAS has also been demonstrated in marine systems, as shown by measured loss of LAS in salt water samples collected off the coast of Spain in which half-lives ranged from 3.4 to 13.8 days, with 4-9 days being the most frequent values (Vives-Rego et al. 2000). UNEP PUBLICATIONS 16
OECD SIDS LINEAR ALKYLBENZENE SULFONATE (LAS) Table 4. Results of Aerobic Ready Biodegradation Studies on LAS Study, Protocol Endpoint DOC Die-Away, Directive 79/83/EEC, Appendix V, C.4-A (OECD 301A) DOC Die-Away, Directive 79/83/EEC, Appendix V, C.4-A (OECD 301A) DOC Removal C11.6 DOC Removal C11.6 OECD 301B, Modified Sturm Test CO2 Production C11.6 OECD 301B, Modified Sturm Test CO2 Production C11.6 Modified OECD Screening Test, Directive 84/449/EEC, C.3 (OECD 301E) OECD Screening Test according to “Verordnung ueber die Abbaubarkeit anionischer und nichtionischer grenzflaechenaktiver Stoffe in Wasch- und Reinigungsmittel vom 30.1.1977”. Bundesgesetzblatt Teil I, S. 244. 1977 DOC Removal C11.6 DOC Removal C11.6 Test Material Description (Average Alkyl Chain Length) Degradation 93%; meets 10day window criterion 94%; meets 10day window criterion 66.7%; 10-day window not met 83%; meets 10day window criterion 76%; meets 10day window criterion 95%; meets 10day window criterion Duration (days) Reference UNEP PUBLICATIONS 17 28 28 28 28 28 19 Schoeberl 1993b, dossier 3.5e; reliability = 1 Schoeberl 1993c, dossier 3.5f; reliability = 1 Ruffo et al., 1999, dossier 3.5b; reliability = 1 Enste-Diefenbach, 2002, dossier 3.5z; reliability = 1 European Commission 2000, dossier 3.5g; reliability = 4 European Commission 2000, dossier 3.5i; reliability = 4 While LAS degrades rapidly under aerobic conditions, it does not degrade under anaerobic conditions, except under special conditions. Denger and Cook (1999) showed that strains of anaerobic bacteria capable of degrading LAS (using it as a sulfur source) under sulfur-limiting conditions are present in nature. Sanz et al. (1999) were the first to demonstrate that LAS anaerobic biodegradation does occur under conditions that are not sulfur-limited, using anaerobic digester sludge and specific HPLC methods to measure the loss of the parent material. Prats et al. (2000) confirmed with specific HPLC analysis (loss of LAS) that LAS biodegrades anaerobically in the ECETOC-28 test, although increased gas production (mineralization) was not observed. Angelidaki et al. (2000a) demonstrated that degradation (loss of LAS) occurred under anaerobic conditions when exposed to inocula obtained from lake sediments or aerobic environments such as compost and activated sludge from a wastewater treatment plant. Anaerobic stabilized sewage sludge in continuous stirred reactors also showed a capacity to anaerobically degrade LAS, as measured by loss of parent material (Angelidaki et al. 2000b). Measurement of radiolabeled biogas and/or intermediates would be required for confirmation of these preliminary results. Degradation of LAS in soils has also been reported – see section 2.2.4 above.
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LINEAR ALKYLBENZENE SULFONATE (LAS) - UNEP Chemicals

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