Registration Dossier
Registration Dossier
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EC number: 242-042-4 | CAS number: 18162-48-6
Endpoint summary
Administrative data
Description of key information
Additional information
The Chemical Safety Assessment focuses on the silanol assessment entity due to rapid hydrolysis. Reliable data are available for this silanol itself; the registered substance (in conditions under which organisms would have been predominantly exposed to silanol (Daphnia only)); and an analogous chlorosilane (in conditions under which organisms would have been predominantly exposed to an analogous silanol).
The key data are as follows in terms of the silanol:
Fish: WoE: 96 hr LC50 >100 mg/l, tert-butyl(dimethyl)silanol, mortality of Oryzias latipes;
WoE: 96-hour LC50 >26 mg/l as butyl(dimethyl)silanol, mortality of Cyprinus carpio.
Daphnia: Key: 48-h EC50 6.49 mg/l tert-butyl(dimethyl)silanol, mobility of Daphnia magna.
Algae: Key: 72-h EC50 84.0 mg/l and NOEC 12.5 mg/l, tert-butyl(dimethyl)silanol, growth rate of Pseudokirchneriella subcapitata.
Reliable short-term toxicity tests results are available for freshwater fish (Oryzias latipes), invertebrates (Daphnia magna) and algae (Pseudokirchneriella subcapitata) for the silanol hydrolysis product of the registration substance, tert-butyl(dimethyl)silanol (CAS 18173-64-3). The relevant short-term values are:
Fish: LL50 (96 h) >100 mg/l (nominal).
Daphnia: EC50 (48 h): 6.49 mg/l; (nominal).
Algae: ErC50 (72 h): 84.0 mg/l; NOEC 12.5 mg/l (nominal).
The fish data with the silanol hydrolysis products are used as weight of evidence in conjunction with the data for the structurally analogous substance butyl(chloro)dimethylsilane (CAS 1000-50-6).
The Daphnia and algal data with the silanol hydrolysis product are used as key.
A reliable short-term toxicity to aquatic invertebrates test is available for the registration substance. An EC50 value of >100 mg/l has been determined for the effects of tert-butyl(chloro)dimethylsilane on mobility of Daphnia magna. The results are based on nominal concentrations. Due to the rapid hydrolysis rate of the test substance, it is likely that the test organisms were exposed to the hydrolysis products of the test substance.
If the results are expressed in terms of the silanol hydrolysis product, by adjusting for the respective molecular weights, the EC50 value for short-term toxicity to aquatic invertebrates is >88 mg/l as tert-butyl(dimethyl)silanol. The data with the silanol hydrolysis product are used as key since the result is more conservative in respect of the silanol assessment entity than this study with the parent substance.
No reliable studies for toxicity to fish and aquatic algae and cyanobacteria are available for tert-butyl(chloro)dimethylsilane (CAS 18162-48-6). Aquatic toxicity test results are, however, available from an analogous substance butyl(chloro)dimethylsilane (CAS 1000-50-6). The relevant values are:
Fish: An EC50 value of >30 mg/l was determined for the effects of butyl(chloro)dimethylsilane on mortality of Cyprinus carpio. The results are based on nominal concentrations. Due to the rapid hydrolysis rate of the test substance, it is likely that the test organisms were predominantly exposed to the hydrolysis products of the substance.
If the results are expressed in terms of the silanol hydrolysis product, by adjusting for the respective molecular weights, the EC50 value for toxicity to fish is >26 mg/l as butyl(dimethyl)silanol. This study is used as weight of evidence in conjunction with the data for the silanol hydrolysis product, tert-butyl(dimethyl)silanol (CAS 18173-64-3).
Algae: An ErC50 value of 10 mg/l and an ErC10 value of 3.8 mg/l were determined for the effects of butyl(chloro)dimethylsilane on growth rate of Desmodesmus subspicatus. The results are based on nominal concentrations. Due to the rapid hydrolysis rate of the test substance, it is likely that the test organisms were predominantly exposed to the hydrolysis products of the substance.
If the results are expressed in terms of the silanol hydrolysis product, by adjusting for the respective molecular weights, the ErC50 value for toxicity to aquatic algae is 8.8 mg/l as butyl(dimethyl)silanol and the ErC10 value is 3.3 mg/l as butyl(dimethyl)silanol.
A toxicity to aquatic algae QSAR prediction EC50 result of 24 mg/l for tert-butyl(dimethyl)silanol (the hydrolysis product of the read-across substance), derived from ECOSAR v.1.1, supports the algal toxicity study result carried out with butyl(chloro)dimethylsilane.
These values are used as supporting information.
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