LINEAR ALKYLBENZENE SULFONATE (LAS) - UNEP Chemicals

OECD SIDS LINEAR ALKYLBENZENE SULFONATE (LAS)
Remarks: Structure modeled is the pure C12 sodium salt homologue, 2-phenyl isomer,
not the commercial material.
Reference: USEPA. 2000. EPI Suite v3.10.
Reliability: 2 Valid with restrictions. Standard EPA estimation software.
(e)
Log Pow: 3.42
Method: Estimation: EPI Suite
GLP: Yes [ ] No [X] ? [ ]
Test Substance: C13 LAS (CAS #26248-24-8)
Remarks: Structure modeled is the pure C13 sodium salt homologue, 2-phenyl isomer,
not the commercial material.
Reference: USEPA. 2000. EPI Suite v3.10.
Reliability: 2 Valid with restrictions. Standard EPA estimation software.
(f)
Remarks: In its review of LAS and related compounds, IPCS notes that while the
octanol-water partition coefficient can be calculated in practice, it is
impossible to measure Pow for surface-active compounds like LAS. This has
been confirmed by Roberts (2000).
Reference: 1) IPCS. 1996. Environmental Health Criteria 169: Linear Alkylbenzene
Sulfonates and Related Compounds. World Health Organization, Geneva,
Switzerland.
2) Roberts, D.W. 2000. Use of octanol/water partition coefficient as
hydrophobicity parameters in surfactant science. 5 th World CESIO Congress
2:1517-1524, May-June 2000, Firenze, Italy.
(g)
Methods: Acute lethal toxicity data for a range of anionic and non-ionic surfactants
were analyzed with the objective of determining whether QSARs can be
developed relating toxicity to calculated log P values. Approaches to dealing
with the deficiencies in the Leo and Hansch (1979) fragment method for
calculating log P of surfactants (related to mixtures and phenyl isomer
position) were developed and applied to the general narcosis QSAR of
Könemann (1981) as represented by Equation 1:
Log (1/LC50) = 0.87log P + 1.13 (EQ 1)
(for 14-d LC50 tests on guppies; n = 50, r = 0.998, s = 0.237)
Mixtures
Two approaches were taken in this paper to address mixtures. In the first
approach, P was calculated for each component individually then multiplied
by the mole fraction and summed to give a weighted average log P.
Alternatively, when only the overall average composition was known, log P
was calculated for the average structure.
Phenyl isomer position
Since the fragment method gives values for log P that are independent of
branch (i.e., phenyl isomer) position, a position-dependent branch factor
(PDBF) was defined. Branching results in a decrease in the number of water
molecules required to solvate the hydrocarbon chain by allowing water
molecules to be shared between the two branches. Where both branches are
long the water sharing effect should continue, although to a decreasing extent
with increasing distance from the branching position, as long as the branches
can be paired. To model this, a water sharing function log (CP + 1) was
UNEP PUBLICATIONS 124