Registration Dossier
Registration Dossier
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EC number: 939-487-8 | CAS number: -
Endpoint summary
Administrative data
Description of key information
Additional information
Phenyl silsesquioxanes (EC No. 939-487-8) is considered a multiconstituent substance, and is a reaction mass of the monomer, dimer and oligomers of phenyltris(trimethylsiloxy)silane. The linear oligomers of phenyl silsesquioxanes contain a siloxane chain, where the terminal Si atoms are fully methyl substituted, and the repeating unit contains a Si atom substituted with a phenyl and a trimethylsiloxy group. The major constituents comprise 70-80% of the linear oligomers n=1-5; the minor constituents comprise 10-20% cyclic (n=3-7) and linear (n=6-7) oligomers. The combined purity of both linear and cyclic oligomers is about 85-95%. The remaining impurities are higher polymerised material and alkoxy substituted oligomers.
There are no short-term toxicity test data available for fish or aquatic invertebrates for the registration substance. Data waivers are applicable to these endpoints on the grounds that in accordance with Annex VII and VIII of the REACH Regulation 1907/206 the studies do not need to be conducted because the very low water solubility of the substance indicates that short term effects would not be expected up to the limit of solubility, and long-term data are available for analogue substances. Algal toxicity data are read across from suitable analogues, and adequate information exists for environmental classification and labelling.
A 72-hour NOEC value of ≥2 μg/l based on growth rate of Pseudokirchneriella subcapitata was obtained with read-across substance dodecamethylcyclohexasiloxane (D6, CAS 540 -97 -6). The results are read-across to the registration substance.
A 21-day NOEC value of ≥0.00605 mg/l has been determined for the effects of phenyl silsesquioxanes on reproduction of Daphnia magna based on geometric mean measured concentrations (sum of the three major constituents).
A 32-day (28 days post-hatch) NOEC ≥0.11 mg/l (mean measured) has been determined for the effects of phenyl silsesquioxanes on survival and growth in an early-life stage toxicity test in fathead minnow (Pimephales promelas).
All constituents of phenyl silsesquioxanes are above the log Kow threshold at which chronic ecotox effects are expected to be expressed. For substances with a log Kow of 8 and above no long-term toxicity effects are seen with aquatic organisms due to the low water solubility limiting the effects seen. In the environment the substances will adsorb to particulate matter and will partition to soil and sediment compartments.
The conclusion of no effects at the limit of solubility is further supported by a peer-reviewed study by Redman et al (Redman 2012). A tissue based risk assessment was performed, with measured tissue concentrations of D4, D5 and D6 compounds in fish and benthic invertebrates compared with critical target lipid body burdens (CTLBBs) as estimated with the target lipid model (TLM). Acute and chronic toxicity data for these compounds were compared with data for nonpolar organic chemicals to validate application of the TLM in this effort. The analysis was extended to estimate the contribution from metabolites to the overall tissue residues using a food chain model calibrated to laboratory and field data. Concentrations of the compounds in biota from several trophic levels, including fish, are well below the estimated CTLBBs associated with acute and chronic effects. The data support the use of the TLM model (which assumes a non-polar narcosis mode of action) for D4, D5 and D6 (substances that are used as read-across for phenyl silsesquioxanes) and demonstrate their generally low bioavailability.
No data are available assessing the toxicity of the substance to sediment organisms. Sediment toxicity is considered to be related to the log Kow and adsorption potential of the substance. Data are read-across from the structurally related substances decamethylcyclopentasiloxane (D5, CAS 541-02-6, EC No. 208-764-9) and dodecamethylcyclohexasiloxane (D6, 540-97-6, EC No. 208-762-8).
A 3 hour EC50 value of >1000 mg/l and NOEC value of ≥1000 mg/l (OECD 209) were determined for phenyl silsesquioxanes in an activated sludge respiration inhibition (ASRI) reliable study conducted according to an appropriate test protocol, and in compliance with GLP.
References
Redman et al (2012). Tissue-Based Risk Assessment of Cyclic Volatile Methyl Siloxanes. Environmental Toxicology and Chemistry Volume 31, Issue 8, pages 1911–1919, August 2012
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