Registration Dossier
Registration Dossier
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EC number: 242-171-6 | CAS number: 18293-82-8
Toxicity to aquatic algae and cyanobacteria
Administrative data
Link to relevant study record(s)
Description of key information
Algal inhibition: 72 hr EC50 >1170 mg/l (estimated from DOC measured stock solution) (highest concentration tested) (EU Method C.3 (Algal Inhibition test)), read-across from an analogous/structurally related substance, isobutyl(trimethoxy)silane (CAS 18395-30-7). The EC50 is equivalent to >894 mg/l when expressed in terms of the silanol hydrolysis product.
Algal inhibition: 72 hr EC50 437 mg/l (nominal) (EU Method C.3 (Algal Inhibition test)), read-across from an analogous/structurally related substance, 3-chloropropyl(diethoxy)methylsilane (CAS 13501-76-3). The EC50 is equivalent to 321 mg/l when expressed in terms of the silanol hydrolysis product.
Key value for chemical safety assessment
Additional information
There are no reliable algal inhibition data available for isobutyl(dimethoxy)methylsilane (CAS 18293-82-8), therefore good quality data for appropriate structural analogues, isobutyl(trimethoxy)silane (CAS 18395-30-7) and 3-chloropropyl(diethoxy)methylsilane (CAS 13501-76-3), have been read across using a weight of evidence approach. The three substances have structurally similar silanol hydrolysis products, isobutyl(methyl)silanediol, (2-methylpropyl)silanetriol and (3-chloropropyl)(methyl)silanediol respectively. The other hydrolysis products are methanol for the registration substance and isobutyl(trimethoxy)silane, and ethanol for 3-chloropropyl(diethoxy)methylsilane.
A 72 h EC50 value of >1170 mg/l, a NOEC of 221 mg/l and an EC10 value of >1170 mg/l (estimated from DOC measured stock
solution) (highest concentration tested) have been determined for the effects of isobutyl(trimethoxy)silane (CAS 18395-30-7) on growth rate of Scenedesmus subspicatus (new name: Desmodesmus subspicatus). In view of the test media preparation method/exposure regime it is likely that the test organisms were exposed predominantly to the hydrolysis products of the tested substance. The results may be expressed in terms of concentration of the hydrolysis product, (2-methylpropyl)silanetriol, by applying a molecular weight correction: (MW of silanol = 136.22 / MW of parent = 178.31) * >1170 = >894 mg/l.
A 72 h EC50 value of 437 mg/l, a NOEC of 57 mg/l and an EC10 value of 137 mg/l (nominal) have been determined for the effects of
3-chloropropyl(diethoxy)methylsilane (CAS 13501-76-3) on growth rate of Scenedesmus subspicatus (new name: Desmodesmus subspicatus). In view of the test media preparation method/exposure regime it is likely that the test organisms were exposed predominantly to the hydrolysis products of the tested substance. The results may be expressed in terms of concentration of the hydrolysis product, (3-chloropropyl)(methyl)silanediol, by applying a molecular weight correction: (MW of silanol = 154.67 / MW of parent = 210.78) * 437 = 321 mg/l.
The results in terms of (2-methylpropyl)silanetriol and (3-chloropropyl)(methyl)silanediol concentration are read across to isobutyl(methyl)silanediol without further correction.
Refer to the discussion in the Section 6 endpoint summary for further discussion of the approach to chemical safety assessment for this registration substance, and justification for read-across used.
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