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EC number: 221-906-4
CAS number: 3277-26-7
Table 1. Cumulative immobilization:
Number dead/Number immobile
Number dead/number immobile/number exposed
the negative control appeared normal and healthy throughout the test
with no mortality/immobility or overt signs of toxicity. After
48 hours of exposure, Daphnia magna exposed to dimethylsilanediol
at a concentration of 117 mg/L also appeared normal and healthy with no
mortality or immobility.
Short-term toxicity to aquatic invertebrates: 48-h EC50: 124 mg/l
(measured, arith. mean) (OECD 202), read-across from an
analogous/structurally related substance trimethylsilanol (CAS
A 48-hour EL50value of >100 mg/l has been determined for the
effects of 1,1,3,3-tetramethyldisiloxane (CAS 3277-26-7), on mobility of Daphnia
magna when tested with adjustment of test medium pH and based on
nominal test substance loading rate. The results are above the limit of
solubility of the substance, however, due to the rapid hydrolysis and
length of test media preparation, the organisms would have been exposed
to a fully solubilised hydrolysis product. The back calculated DOC
concentration corresponds to an EL50 of >42 mg/l. It is
possible that the discrepancy may be explained by the volatilisation of
the parent substance from the test medium. The substance has an estimate
Henry’s Law Constant value of 1.86E+5 Pa m3 mol-1
While the data are considered to be reliable, due to the very rapid
hydrolysis of the parent substance, good quality data have been read
across from trimethylsilanol (CAS 1066-40-6), based on the substance
being an analogue of the intermediate hydrolysis product,
dimethylsilanol. Data are also available with dimethylsilanediol (CAS
1066-42-8), the registered substance’s ultimate hydrolysis product.
In the tests with trimethylsilanol and dimethylsilanediol, the
observations are attributed to the exposure of test organisms to the
test substances. Data from tests carried out with the read-across
substances report the following results:
48-hour EC50value of 124 mg/l has been determined for
the effects of trimethylsilanol on mobility/mortality of Daphnia magnabased
on measured (arithmetic mean) concentrations.
48-hour EC50value of >117 mg/l has been determined for
the effects of dimethylsilanediol on mobility of Daphnia magna,
based on measured (arithmetic mean) concentrations.
The study with trimethylsilanol presents a slightly unusual
dose-response curve, where at 48-hours the immobility and mortality
rates observed at 116 mg/l are higher than those at 207 mg/l
concentrations. It is possible this causes the high confidence intervals
(51-203) observed in the study. It is the opinion of the reviewer that
because at 24 hours no unusual observations were observed and the other
study concentrations appear to follow a normal dose-response curve, the
study is considered to be valid and the data are used in the risk
(TMS, CAS 1066-40-6) has the potential to condense to form
hexamethyldisiloxane (HMDS, CAS 107-46-0), which would then contribute
to the species present in the test system. HMDS is classified as Aquatic
Acute 1 H400 and Aquatic Chronic 2 H411 
and therefore its presence may impact the toxicity
results. However, the estimated concentration of HMDS is 0.04, 0.2, 0.3,
0.6 and 0.9 mg/l at 100, 200, 300, 400 and 500 mg/l of TMS respectively,
and there was no reporting of undissolved test material or droplets
being formed, which would otherwise clearly indicate the formation of
HMDS. In addition, the log Kow of
trimethylsilanol (1.62) is such that effects may be observed at high
concentrations in short-term studies.
Therefore the effects seen in the short-term toxicity to invertebrate
be attributable to TMS alone and the study is considered to be
conservative and reliable for the purpose of this assessment.
The registered substance also releases hydrogen during its final
hydrolysis. Hydrogen is not thought to contribute to the toxicity of
the substance and is discussed further in the ecotoxicological
information overview endpoint summary (additional information).
Refer to the discussion in the Section 6 endpoint summary (Section 7.0
of CSR) for further discussion of the approach to chemical safety
assessment for this registration substance, and justification for
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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