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EC number: 270-115-0
CAS number: 68411-30-3
The PNEC for water is generally derived from the no observable
effect concentrations (NOEC) for the most sensitive aquatic species, to
which are applied the appropriate assessment factors. In the case of LAS
there are a large number of chronic single species toxicity studies that
have been conducted on a variety of aquatic species over the years.
These data were used to develop a logical progression to evaluation of
LAS in a highest tier model ecosystem study (Belanger et al. 2002).
Prior to conducting the model ecosystem study, assessments of LAS
toxicity using deterministic and probabilistic approaches were performed
(van de Plaasche et al. 1999). Subsequently, most focus has been on
probabilistic (statistical) assessments as warranted by the size of the
data base, including summaries presented in OECD and USEPA HPV (High
Production Volume) assessments).
An SSD assessment was performed using chronic aquatic toxicity
values available from tests with various LAS homolog mixtures. The
dataset of 19 chronic ecotoxicity studies included 4 species of algae, 2
aquatic macrophytes, 8 invertebrates and 5 fish.Development
and analysis of the SSD followed ECHA procedures described in the REACH
Technical Guidance Document R.10.3.1.3 (Calculation of PNEC for
freshwater using statistical extrapolation techniques) supplemented
with additional statistical evidence reflecting the state of the science.
The available chronic toxicity data on LAS
spans a variety of mixtures which vary in their composition of alkyl
chains. As has been previously well described in the peer reviewed
literature and in OECD and USEPA HPV (High Production Volume)
assessments mixtures were first normalized to C11.6LAS by use
of conventional Quantitative Structure-Activity Relationships (see van
de Plaasche et al. 1999; OECD 2005). Similar normalization processes for
environmental risk assessment have also been performed for alcohol
sulfates, alcohol ethoxysulfates, alcohol ethoxylates and long chain
alcohols (van de Plaasche et al. 1999; HERA 2002; Belanger et al., 2006,
2009). The normalization procedures followed the process first described
by van de Plaasche et al. (1999) and replicated for HPV (OECD 2005).
Chronic aquatic toxicity data normalization outcomes are cited in the
respective IUCLID5 entries in the Chemical Safety Report for the
registered substance (LAS: CAS# 68411-30-3).
The C11.6LAS-normalized chronic
data were then fitted to a log-logistical function from which the HC5(the
SSD0.05)of 0.19 mg/L was calculated (95% Lower and Upper
Confidence Limits of 0.06 to 0.36 mg/L), respectively). The HC5value
was equal to or lower than any of the normalized chronic values
contained in the dataset. The quality of the dataset and the sensitivity
and stability of the SSD were validated using recommended criteria and
conventional statistical procedures. These included “leave-one-out” and
“add-one-in” statistical simulations using hypothetical data. These
evaluations demonstrated that the chronic toxicity data were highly
ordered, and strongly adhered to statistical assumptions. The SSD, and
the resulting HC5, were highly stable to either deletion or
addition of new data.
A model ecosystem study of LAS concluded a
NOEC of 0.268 mg/L and is used to derive the PNEC water for LAS. ECHA
describes the interactive roles of statistical extrapolation techniques
with the deterministic based PNECs for mesocosms in the REACH Technical
Guidance Document Sections R.10.3.1.2 (Calculation of PNEC for
freshwater using assessment factors)and R.10.3.1.3 (Calculation
of PNEC for freshwater using statistical extrapolation techniques).
Stream model ecosystems are considered the most appropriate for
assessing this chemical (versus ponds) due to the wide dispersive use
and route of discharge to receiving waters via wastewater treatment
plants. In the case of the model ecosystem study summarized by Belanger
et al. (2002), the following considerations support no additional
application factor to be applied to the result when deriving the PNEC
water (seeECETOC 1997, Giddings et al. 2002, OECD 2006).
The most important factors are knowledge of the biological complexity,
sensitivity, study duration, exposure determination, and relevance to
natural systems for the specific system being assessed. For the model
ecosystem study of LAS
1) The model
ecosystem was biologically complex, containing a highly diverse
community with 117 invertebrate genera assessed (including ~500 insect
species). Approximately 150 algal species were studied, dominated by
sensitive diatom flora. Protozoa which were not studied in this
particular investigation historically accounted for an additional 300
2) The model
ecosystem was sensitive. The system was optimized for statistical
and biological sensitivity. Key endpoints evaluated possessed Minimum
Detectable Differences using inferential statistics of 5-20% (change
needed to be identified as statistically different from the control).
Use of PRC, Principal Response Curve Analysis, corroborated use of
repeated measure ANOVAs on single population endpoints and coincides
with NOECs on the most sensitive taxa and taxonomic groups. The dominant
invertebrate taxa were sensitive species of the EPT group (mayflies,
stoneflies, and caddisflies; a total of 28 genera were represented).
Dominant algae were diatoms, many known as sensitive species. Functional
endpoints were also investigated including photosynthesis, organic
matter processing, in situ biodegradation, organism drift, insect
3) The model
ecosystem study was longer than most chronic toxicity tests(approximately
4 months duration). Colonization of the streams, leading to stable,
consistent and testable communities, was for 10 weeks with exposure of
stream communities to LAS was for 8 weeks. Repeated sampling insured
ecological and toxicological shifts were tracked.
4) The exposure
to LAS was verified weekly and found to be nearly 100% of nominal.
For example the streams exposed to nominal concentrations of 0.300 and
3.000 mg/L were measured at 0.293 mg/L and 2.973 mg/L, respectively. A
dynamic sorption model based on detailed weekly investigations of
sorption, daily evaluations of suspended solids, and weekly assessments
of DOC, TOC were used to express exposure based on the free fraction of
5) The study is
relevant to natural systems. Studies by the sponsor demonstrated the
model ecosystem was nearly indistinguishable from the source system and
representative streams that were relatively uninfluenced by man. Dyer
and Belanger (1999) showed ESF stream communities were as or more
sensitive than >80% of streams in Ohio surveyed at >1200 locations from
the period of 1985-1995. The more sensitive systems were Appalachian
mountain slope, first or second order systems that never have seen
effect or been exposed to human influences to any degree. Peterson et
al. (2001) and Morrall et al. (2006) demonstrated community function of
the test system was similar to that of low order streams across the
globe (including systems outside of the United States) and that
predator-prey relationships in the ESF were equivalent to the source
river used to deliver water to the streams.
In summary, the NOEC of LAS
measured from the ESF model ecosystem study was equal to 293 µg LAS/L
which corresponds to 268 µg LAS/L as free (dissolved and not associated
with organic or particulate matter). Further, an Application Factor (AF)
of 1 is justified, especially when viewed in concert with the chronic
toxicity Single Species Sensitivity Distribution (SSD) of 0.19 mg/L).Based
on this data, the PNECfreshwaterwas
calculated as the model ecosystem study NOEC/1 or 0.268 mg LAS/L.
To calculate the PNECmarinethe
aquatic NOEC of 0.268 mg/L from the model ecosystem study was used as a
starting point.The AF for the marine PNEC is generally 10 applied to
the PNECaquaticresulting in a PNECmarineof 0.0268
mg/L.This AF is considered appropriate given the detailed literature
reviews regarding marine and freshwater organism sensitivity to LAS
(Temara et al. 2001). Temara et al. (2001) provided conclusions that
were similar to observations from van de Plaasche et al. (1999), but
with additional data to derive a chronic marine SSD to compare with a
chronic freshwater SSD. In these investigations, the sensitivity of
marine taxa versus freshwater is typically 10-fold, consistent with the
AF consistent with principals described in the REACH
Technical Guidance Document Sections R.10.3.2.3 (Calculation of PNEC
for marine water).
Finally, the PNECintermittentreleaseswas
calculated as normal by using the lowest acute LC50 value and applying
an AF of 100 to get a finalPNECintermittentreleasesvalue
of 0.0167 mg/L.
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