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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
Siloxane Category report (PFA, 2017a). The hypothesis for read-across of
sediment ecotoxicity evidence within the Siloxanes Category is that no
structure-based or property-based pattern is evident from the category
dataset of existing studies, although patterns are identifiable
associated with extrinsic aspects of test design to which effects may be
attributed. The approach will be revisited in the event that reliable
new data become available. With this in mind, a single overall
interpretation is made across the category. To fulfil the requirements
of REACH, a conservative approach is made by reading across on a
nearest-neighbour basis the reliable data within the category.
In the context of the RAAF, Scenario 6 is expected to apply to this
endpoint. It is considered that effects observed in benthic organisms
are associated primarily with extrinsic factors associated with test
design and not to structural similarities as such.
A total of twenty-four sediment toxicity studies for siloxanes are
available and nineteen results from studies of standard duration in
standard test species 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 the studies which are not suspected to be confounded by extrinsic
factors show relatively minimal effects across the dataset.
Data available for the substance:
No data are available for the effects of the registration substance on
sediment organisms. Data are read-across from the structural analogue
octamethyltrisiloxane (L3; 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-L3 and
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 Kow and 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 Section 6
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 sediment incorporated
test substance 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 under semi-static water replenishment conditions (Wildlife
A 28-day LC50 and
NOEC value of >70 and ≥70 mg/kg, respectively, (>95 and ≥95 mg/kg dwt,
respectively, 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
(Smithers Viscient, 2013b).
Two studies with Lumbriculus
variegatus are available for 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 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,
2009b). 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).
Outlier analysis was performed on the four NOEC values obtained from
these studies (Dow Corning Corporation, pers. comm., August 2015). The
scores of the lowest L3 benthic invertebrate NOEC value (i.e., 1.1 mg/kg
dw on artificial sediment) showed the largest deviation from the whole
distribution and the datum is an outlier via both the Dixon Q test and
Grubbs’ (z) test. In
addition, differences between measured and nominal
concentrations were observed at the start and over the course of this
study. Measured concentrations at the start of the test showed that they
were in the range of approximately 13-25% (more generally 22-25%) of
nominal. Over the course of the test they declined further to between
approximately 12 and 20% (more generally 12-14%) of nominal. These
difference might be explained as follows:
- The relatively high vapour pressure and Henry’s Law
Constant of the substance would suggest that volatile losses from the
test system are likely even during the media preparation phase.
- Under the test conditions (pH 8.2-8.4 and temperature
22-24°C), the hydrolysis half-life of approximately 4 days would explain
the further decline in measured concentration of parent substance over
the duration of the study.
In view that a second study with the same species (L. variegatus),
is also available, using natural sediment and at a lower pH, this
outlier value 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 C.
riparius (Wildlife International, 2009a). 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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