Registration Dossier
Registration Dossier
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EC number: 229-929-1 | CAS number: 6843-66-9
Endpoint summary
Administrative data
Description of key information
Additional information
Dimethoxydiphenylsilane (CAS 6843-66-9) is part of a group of organosilicones, the toxicity of which is determined by a non-polar narcosis mechanism. Substances in this group include alkoxy- and chlorosilanes having secondary features that do not affect the toxicity of the substances. The side chain of the registered substance is an aryl. There is evidence that the phenyl (aryl) group’s toxicity is related to the log Kow value. Additional information is given in a supporting report Application of Category - Analogue - QSAR for Reconsile (PFA, 2016) attached in Section 13 of the IUCLID dossier.
READ-ACROSS JUSTIFICATION
Measured aquatic toxicity data were not available for Dimethoxydiphenylsilane. The substance hydrolyses very rapidly (half-life of 0.6 h at pH 7 and 20-25°C) to Diphenylsilanediol (CAS 947-42-2) and methanol.REACH guidance R.16 states that “for substances where hydrolytic DT50 is less than 12 h, environmental effects are likely to be attributed to the hydrolysis product rather than to the parent itself” (ECHA, 2016). TGD (EC, 2003) and REACH guidance R.16 (ECHA, 2016) also suggest that when the hydrolysis half-life is less than 12 h, the breakdown products, rather than the parent substance, should be evaluated for aquatic toxicity testing. Therefore it was considered more environmentally relevant to refer, based on a read across approach, to the aquatic toxicity of the hydrolysis product, Diphenylsilanediol (CAS 947-42-2), on which organisms will be predominately exposed to. Therefore, the hazard assessment for the environment is mainly based in accordance with REACH guidance, on the properties of the hydrolysis product, Diphenylsilanediol.
Supporting information was additionally gained from good quality read-across data of a further analogue substance, that has a similar structure and similar physicochemical properties to the target substance. Read across was conducted based on Article 13 (1) and Annex XI, Item 1.5, of Regulation (EC) No 1907/2006. Since ecotoxicological studies are conducted in aquatic medium, the hydrolysis rate of the substances is particularly taken into account for the selection of read-across surrogates. Moreover, the analogue approach takes into consideration further physicochemical properties such as log Kow, water solubility, vapour pressure, side chains and molecular weight.
In the following paragraphs the read-across approach for Dimethoxydiphenylsilane (CAS 6843-66-9) is assessed for each surrogate substance.
Read-across from Diphenylsilanediol (CAS 947-42-2) to Dimethoxydiphenylsilane (CAS 6843-66-9):
As mentioned above since the substance hydrolyses very rapidly (half-life of 0.6 h at pH 7) it is according to ECHA guidance more environmentally relevant to examine the toxicity of the hydrolysis products. Since methanol is well characterised in the public domain literature (OECD2004 - SIDS for methanol) and is not toxic at the concentrations relevant for the studies, the hazard assessment for the environment, is based on the properties of the hydrolysis product Diphenylsilanediol (CAS 947-42-2).
Experimental data testing the toxicity of Diphenylsilanediol to aquatic invertebrates and algae were available. Algae was found to be the most sensitive trophic level giving the lowest short term effect concentration (72 h - ErC50) of 9.0 mg/L (mean measured).
Read-across from Cyclohexyldimethoxymethylsilane (CAS 17865-32-6) to Dimethoxydiphenylsilane (CAS 6843 -66 -9):
Additional supporting information for the aquatic endpoints was withdrawn from the structural related substance Cyclohexyldimethoxymethylsilane (CAS 17865-32-6). Cyclohexyldimethoxymethylsilane hydrolyses rapidly to Cyclohexylmethylsilanediol and methanol.
Toxicity studies conducted according to appropriate guidelines reported short term effect concentrations EC50) of 35 mg/L (nominal) for algae (based on growth rate) and 24 mg/L (nominal) for aquatic invertebrates and are considered reliable for assessment.
Consideration of the non-silanol hydrolysis product:
Methanol is well characterised in the public domain literature and is not hazardous at the concentrations relevant to the studies; the short-term EC50 and LC50 values for this substance is in excess of 1000 mg/L (OECD 2004a - SIDS for methanol, CAS 67-56-1).
Reference:
OECD (2004): SIDS Initial Assessment Report for SIAM 19, Berlin,
Germany, 18-20 October 2004, Methanol, CAS 67-56-1.
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.
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