LINEAR ALKYLBENZENE SULFONATE (LAS) - UNEP Chemicals

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OECD SIDS LINEAR ALKYLBENZENE SULFONATE (LAS) Remarks: A significant number of additional literature articles report data on the environmental fate of LAS. An additional bibliography of literature citations for LAS can be found in an Appendix to this dossier. (b) Type of Measurement: Background [X]; At contaminated site [ ]; Other [ ] Medium: soil Remarks: Where surfactant and hydrophobic organic compounds (HOCs) co-exist in soil-water systems there are a number of possible interactions which can occur simultaneously: 1) distribution of surfactant between monomeric, hemimicellar and miscellar forms, 2) competition for hydrophobic adsorption sites between the surfactant and HOC and 3) partitioning of HOC among soil hydrophobic adsorption sites, surfactant micelles and hemimicelles. The interaction of HOCs with surfactant monomers is usually very weak and insignificant. At concentrations where micelles and hemimicelles are present interactions can take place. Sorbed HOCs can be solubilised by free micelles, resulting in mobilisation. HOCs in solution are in equilibria between sorption onto hydrophobic adsorptive sites on the soil, partitioning into hemimicelles – both resulting in immobilisation, and partitioning into free micelles. Whether the HOCs are previously sorbed onto soil or are in solution, partitioning into micelles, hence mobilisation, is favoured by increasing surfactant concentration. A model has been put forward describing the effect of non-ionic surfactant on the distribution of HOC in a soil-water system. In simple terms the model illustrates that sorbed surfactant molecules tend to increase HOC sorption onto soil by increasing its fractional organic carbon content, and free surfactant tends to decrease sorption by increasing the apparent aqueous solubility of the HOC. The biodegradation of HOCs in soil can be enhanced by surfactants due to enhanced solubility in the presence of micelles. In some cases however, biodegradation appears to be inhibited by micelles forming a barrier to the degrading organism. Any such inhibition is unlikely to be prolonged due to the biodegradable nature of most modern surfactants. In fact, it is very unlikely that micelles would be present in sludge-amended soils due to the low concentration of surfactants. Although there is evidence that surfactants can effect the fate and behaviour of HOCs in soil, the potential for detergent ingredients to cause significant effects is limited due to the relatively low concentrations found compared with critical micelle concentrations (CMCs). In addition, the effective CMC in environments such as soil and sediments is generally much higher than in clean water systems. Typical soil concentrations of LAS, the most heavily used surfactant in domestic detergents, are significantly lower than those required to produce micelles in pore water. Therefore, it is unlikely that surfactants present in domestic detergents will contribute significantly to the mobilisation of HOCs in sludge-amended soil. Reference: Haigh, S.D. 1996. A review of the interaction of surfactants with organic contaminants in soil. The Science of the Total Environment 185:161-170. UNEP PUBLICATIONS 174
OECD SIDS LINEAR ALKYLBENZENE SULFONATE (LAS) 4. ECOTOXICITY 4.1 ACUTE/PROLONGED TOXICITY TO FISH (a) Type of Test: static [ ]; semi-static [ ]; flow-through [X] Open-system [X]; closed-system [ ] Species: Lepomis macrochirus (Fish, fresh water) Exposure Period: 96 hours Results: LC50 = 1.67 mg/L Analytic Monitoring: Yes [X]; No [ ]; ? [ ] Method: USEPA (1975) Stock solutions were made up in deionized water without the use of a solvent and metered into diluter chambers by peristaltic pump. Mortality was analyzed by four methods: (a) the toxic unit (TU) concept, (b) the additive index, (c) concentration addition, and (d) response addition. GLP: Yes [ ]; No [X]; ? [ ] Test Substance: C11.8 LAS; Average molecular weight 345; 27.3% active; Alkyl chain Composition: C10 9.5%, C11 29.2%, C12 37.7%, C13 19.0%, C14 4.9% Remarks: Average size of individual fish 1.1 g, mean standard length 4.2 cm; water hardness 137 mg/L Ca CO3; temperature 20 ± 2°C; dissolved oxygen 8.4-9.6 mg/L; pH 7.3-8.1. Ten randomly selected fish were exposed to each of the five concentrations and the control. A 16:8 (light:dark) photoperiod was maintained. Fish were not fed during the study. Mortality was recorded at 1, 3, and 5 hours after test initiation and then daily until test termination. Samples were collected at the beginning and end of the study and analyzed for the test substance. Results reported are mean measured concentrations. The LC50 value reported represents the lowest value for this species. In addition to the studies conducted on LAS, the anionic LAS was also tested in binary and ternary equitoxic or equimolar mixtures with non-ionic C14-15 linear alkyl ethoxylate (AE) and cationic C12-14 MDAC. These mixture results are not reported in this robust summary. This is a key study for aquatic toxicity to fish (see SIAR Table 10). Reference: Lewis, M.A. and Perry, R.L. 1981. Acute toxicities of equimolar and equitoxic surfactant mixtures to Daphnia magna and Lepomis macrochirus. Aquatic Toxicology and Hazard Assessment: Fourth Conference, ASTM STP 737, D.R. Branson and K.L. Dickson, Eds., American Society for Testing and Materials, pp. 402-418. Reliability: 2 Valid with restrictions. The studies are very well documented in this peerreviewed publication. (b) Species: Lepomis macrochirus and Pimephales promelas Results: LC50 values ranged from 1.67 to 7.7 mg/L for L. macrochirus (10 records) LC50 value for P. promelas = 4.1 mg/L (1 record) See study (q) below for robust summary Test Substance: C10-13 LAS (CAS #68411-30-3) Remarks: A total of 18 fish studies for these two species were reviewed by HERA in 2004. Seven of these studies were rejected because the test material was not commercial LAS, the study deviated significantly from standard protocols, or non-standard endpoints were measured. The remaining eleven studies were evaluated for reliability and the results reflect the range of acute LC50 values obtained for the most commonly tested fish species. These studies are tabulated and discussed further in the SIAR and SIAP in a weight-of- UNEP PUBLICATIONS 175
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