LINEAR ALKYLBENZENE SULFONATE (LAS) - UNEP Chemicals

OECD SIDS LINEAR ALKYLBENZENE SULFONATE (LAS)
Discussion
The HC5 values for LAS are considered to be valid estimates of the NOEC since all three meet the
OECD criteria for statistical extrapolation methods (OECD 2002). These include:
1) QSAR method – The approach used to normalize the NOEC data is clearly described (above).
The approach is considered reliable because it’s application to LAS and other major surfactants is
well documented in the scientific literature (Leo and Hansch 1979, Roberts 1991, van de Plassche et
al. 1999).
2) Clear input data – Reliable NOEC values from freshwater single-species chronic studies are
used as described in Table 12A of the SIAR and listed above.
3) Mode of action – LAS has a nonspecific mode of action described as “narcosis toxicity”
(Roberts 1991). As expected from this mode of action, sensitivity of the tested species follows a
log –normal and log-logistic distribution with a high degree of goodness of fit. The best fit of the
data is to the log-logistic distribution.
4) Minimum species requirements – Represented species include fish, crustaceans, insects, a
rotifer, algae, and higher plants.
5) Minimum sample size – The database consists of NOEC values on at least 12 freshwater species.
6) Use of multiple data for same species – In the van de Plassche et al. (1999) review, the
geometric mean value is used for species with multiple values (number of species indicated in Table
12A). For the available data set, the geometric mean value of the valid studies is provided.
7) Statistical fitting procedure – The specified Kolmogorov-Smirnov test was used as described
above. Goodness of fit across distributions (i.e. log-normal versus log-logistic) was compared using
the Cramer-von Mises statistical test as described by Versteeg et al. (1999).
8) Estimation parameter – The reported value is as specified, the HC5 value with 50% confidence
limits.
9) Estimation of NOEC – The HC5 values support the conclusion of the mesocosm studies that no
uncertainty (assessment) factor is needed to determine the NOEC value for LAS. The NOEC for
LAS is derived from the entire database of freshwater chronic data, including the HC5 values and
the mesocosm data, as discussed in the SIAR, section 4.1 Aquatic Effects.
UNEP PUBLICATIONS 105