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EC number: 217-496-1
CAS number: 1873-88-7
1. Results of analysis of sediment exposure concentrations
Nominal Test Concentration
Mean Percent of
Table 2. Test results
Mean Development Time (Days)
was a statistically significant difference (p<0.05) from the negative
control using Dunnett’s t-test.
NOEC 39 mg/kg dwt (89 mg/kg dwt normalised to 5% OC)
No sediment toxicity data are available for the registration substance
A category approach is applied to this endpoint and is detailed in the
updated extract from the Reconsile Siloxane Category report attached to
the endpoint summary in IUCLID Section 6.3.
More than twenty-five sediment toxicity studies for siloxanes are
available and have been reviewed in detail. There is a general trend for
studies using natural sediment, which all have pH <~8, to show no
effects, or higher NOECs than those with artificial sediment. No
significant toxicity (NOEC <100 mg/kg) in any organism is found at pH
near 7 with natural sediment. The data suggest that it is possible to
read across sediment toxicity data between different siloxane
structures, especially where natural sediment data are available, given
that studies which are not suspected to be confounded by extrinsic
factors show relatively minimal effects across the dataset.
In the use of the data set for hazard assessment and derivation of
predicted no-effect concentration (PNEC), the following approaches are
- Where the hydrolysis half-life is >48 hours, the chemical safety
assessment will focus on the parent form.
- Where data are available for a substance with natural sediment and
with artificial sediment for the same species, the natural sediment data
will be given preference over data obtained with artificial sediment.
- PNEC will be determined on a weight-of-evidence basis for each
substance, including use of read-across. Equilibrium partitioning
calculations will be used if necessary.
No measured data are available for the effects of the registration
substance on sediment organisms. Data are read-across from the
structural analogue octamethyltrisiloxane (L3, CAS 107-51-7).
The registered substance (H-L3) and read-across substance (L3, CAS
107-51-7) are members of the Reconsile Siloxanes Category.H-L3and
the source substance L3 are linear siloxanes with three silicon atoms,
alternated by oxygen atoms. In L3, the Si atoms are fully methyl
substituted, whereas in H-L3 the central silicon atom is substituted
with one hydrogen atom and one methyl group.The registration and
read-across substances have similar physicochemical properties (low
water solubility, high log Kowand slow hydrolysis rates), are
not readily biodegradable and have high potential for adsorption to
sediment.A summary of the relevant physicochemical properties of
the registration and read-across substances are reported in the table in
Section 6 of IUCLID.
A 28-day LC50 value of 166 mg/kg dry weight (377 mg/kg dwt
normalised to 5% organic carbon (OC)) has been determined for the
effects of the read-across test substance, L3, on mortality of Chironomus
riparius. A NOEC of 39 mg/kg dry weight (89 mg/kg dwt normalised to
5% OC) for effects on development rate has been determined in the same
test. The test was conducted in artificial sediment under semi-static
water replenishment conditions (Wildlife International 2009b).
28-Day LC50 and NOEC values of >70 and ≥70 mg/kg (>95 and ≥95
mg/kg dwt normalised to 5% OC) have been reported for the effects of L3
on the mortality and growth rate of the freshwater amphipod Hyalella
azteca. The results are based on mean measured concentrations. The
study was conducted in natural sediment, under flow-through conditions
(Smithers Viscient 2013b).
Three studies with Lumbriculus variegatus read across from L3.
In a 28-day study (using artificial sediment under flow-through water
replenishment conditions), an EC50 of >17 mg/kg sediment dry
weight (>45 mg/kg dwt normalised to 5% OC) has been determined for the
effects of the L3 on survival and reproduction of Lumbriculus
variegatus. In the same study, a NOEC of 1.1 mg/kg sediment dry
weight (2.9 mg/kg dwt normalised to 5% OC) was determined for the same
endpoints (Wildlife International 2009a).
In a second study (using natural sediment under static conditions), no
effects on reproduction or growth were observed in Lumbriculus
variegatus at 38 mg/kg dw (measured, initial). The EC50
is therefore >38 mg/kg dwt (61 mg/kg dwt normalised to 5% OC) and
the NOEC ≥38 mg/kg dw (≥61 mg/kg dwt normalised to 5% OC; highest
concentration tested) (Smithers Viscient 2013a).
In the third study (using artificial sediment under static conditions),
no effects of L3 on biomass and reproduction (as total number of
oligochaetes) were observed in Lumbriculus variegatus. The EC50
is therefore >7.8 mg/kg dwt and the NOEC is ≥7.8 mg/kg dwt (both
values normalised to 5% OC as >18.6 and ≥ 18.6 mg/kg dwt, respectively)
(Smithers Viscient 2017).
The Wildlife International 2009a Lumbriculus study derives the
lowest NOEC of all the sediment tests with L3. However, the results of
this study are discounted for the following reasons:
- As discussed in the Reconsile Siloxane Category report extract, there
are a number of possible contributing factors that could have caused
higher toxicity in studies in artificial sediment, particularly the use
of artificial sediment with a peat-based carbon source and elevated pH
in the test system. The result is therefore disregarded because it is
thought that the artificial sediment with peat based carbon source and
high pH values in the study interfered with the test system to exhibit
toxicity that is extrinsic to the actual toxicity of the substance.
- Two further studies of higher reliability with the same species (Lumbriculus
variegatus) are available; one using natural sediment at a lower pH
(Smithers Viscient 2013a), and one in artificial sediment with neutral
pH (Smithers Viscient 2017). No effects were reported in either of these
- In both the Smithers Viscient 2013a and Smithers Viscient 2017
studies, the worms were synchronised prior to testing, whereas the worms
in the Wildlife International 2009a study were not. This can lead to
variability in reproduction and difficulty in interpreting results.
- Reproduction was quite poor in the Wildlife International 2009a study,
with the number of worms at the end of the study (day 28) in the control
vessels not quite meeting the validity criteria outlined in the OECD TG
225 guidance (the average number of living worms per replicate in the
controls should have increased by a factor of at least 1.8 at the end of
exposure compared to the number of worms per replicate at the start of
exposure; the worms in the Wildlife International 2009a study increased
by a factor of 1.73). Although this slight difference in reproductive
increase might not justify disregarding of the study, the combination of
factors discussed above indicates that this study is less reliable than
the Smithers Viscient 2013a and Smithers Viscient 2017 studies.
In view that two further studies with Lumbriculus variegatus are
available with higher reliability, and one of the available studies uses
natural sediment, the Wildlife International 2009a study with Lumbriculus
variegatus is disregarded without detriment to the completeness of
the data set. Hence, the lowest NOEC is taken as 39 mg/kg dwt (89 mg/kg
dwt when normalised to 5% organic carbon content) from the study with Chironomus
riparius (Wildlife International, 2009b). This value is used as the
key value for the CSA.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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