LINEAR ALKYLBENZENE SULFONATE (LAS) - UNEP Chemicals

OECD SIDS LINEAR ALKYLBENZENE SULFONATE (LAS)
concentration was measured at 9.5 mg/kg (approximately 4%). Very little
reached the 30-40 cm layer, although a value significantly above the limit of
detection (0.050 mg/kg) was determined. No leaching was observed out of
the soil columns and disappearance of LAS in the field trials was attributed to
rapid biodegradation in the soil (approximately 99% of the total LAS was
biodegraded after 42 days). The half-life was determined to be 3 days. There
was a noticeable shift to shorter alkyl chain length homologues in the
percolating water (i.e., longer alkyl chains were retained more strongly).
These shorter chain length homologues have a lower toxicity.
Reference: Kuchler, T. and Schnaak, W. 1997. Behaviour of linear alkylbenzene
sulfonates (LAS) in sandy soils with low amounts of organic matter.
Chemosphere. 35:153-167.
Reliability: 2 Valid with restrictions
(f)
Type : Field trial [ ]; Laboratory [X]; Other [ ]
Radiolabel: Yes [X] No [ ] ? [ ]
Concentration: 250 mg/kg
Soil temperature: 20°C
Soil humidity: 35 g water/100g soil dry weight
Soil pH: 6.9 - 7.1
Dissipation time: DT50 : 15.8 - 25.7 day
Method: Assays were conducted in flow-through microcosms with 15 g (dry wt) of
soil adjusted to a 35% moisture level. The test substances were 14 C ring
labelled LAS pure homologues (C10, C11, C12, C13, C14) which were premixed
with digester sludge and added to flasks at an initial concentration of 2.5, 25
or 250 mg/kg. 14 CO2 evolution was determined by LSC. The first-order
biodegradation rate constant was estimated using non-linear regression
techniques. The study was conducted in both sandy loam and loamy sand
soil types.
GLP: Yes [ ] No [ ] ? [X]
Test substance: Pure LAS homologues C10-14 tested concurrently.
Results: The biodegradation rates followed first order kinetics over a wide range of
concentrations and chain lengths. Half-lives (mineralization) were reported
as C10 21 days; C11 25.7 d; C12 23.1 d; C13 18.2 d; C14 17.8 d
in sandy loam; C10 16.5 d and C14 15.8 d in loamy sand. The degradation rate
constants were C10 0.033/d; C11 0.027/d, C12 0.030/d, C13 0.038/d, C14 0.039/d
in sandy loam; C10 0.042/d C14 0.044/d in loamy sand Mineralisation
efficiency averaged 65%. The remaining radiolabel was incorporated into
microbial biomass or soil humic material.
Remarks: Half-lives for mineralization of the benzene ring, the rate-limiting step for
LAS degradation, ranged from 18 to 26 days.
Reference: Ward, T.E. and Larson, R.J. 1989. Biodegradation kinetics of LAS in
sludge-amended agricultural soils. Ecotox. and Environ. Safety 17:119-130.
Reliability: 2 Valid with restrictions
(g)
Type: Field trial [ ]; Laboratory [ ]; Other [X] Greenhouse pot
Radiolabel: Yes [ ] No [X] ? [ ]
Concentration: 3.7 to 5.1 g/kg dry wt
Soil composition: Clay 3.7 %, Silt 3.1 %, Fine Sand 19.5 %, Coarse Sand 71.4 %
Organic Carbon: 1.3%
Soil pH: 5.9
Cation exchange capacity: 10.7 cm/kg
Microbial biomass: not stated
UNEP PUBLICATIONS 134