Registration Dossier

Administrative data

Hazard for aquatic organisms

Hazard for air

Hazard for terrestrial organisms

Hazard for predators

Additional information

1,3,3,5 -Tetramethyl-1,1,5,5-tetraphenyltrisiloxane (CAS 3982-82-9) has an extremely low estimated water solubility (5.9E-09 mg/l (insoluble)) and very high estimated log Kow (9.0 at 20°C).

The substance is susceptible to hydrolysis with a predicted half-life of >329 hours at pH 7 and 20°C. The reaction products are methyl(diphenyl)silanol (CAS 778-25-6) and dimethylsilanediol (CAS 1066-42-8). The registration substance has a high adsorption potential, and once adsorbed, hydrolysis may not occur.

On the basis that the substance is insoluble, data waivers are in place for short-term toxicity to aquatic invertebrates and algae. The physicochemical properties of the registration substance indicate that maintaining stable aqueous test solutions will be extremely difficult. Furthermore, the substance will have the tendency to adsorb onto the glassware under experimental conditions. This contributes to technical difficulties making reliable experimental studies very difficult to conduct.

In addition:

- Above a log Kow of 6.0 short-term toxicity effects are not expected to occur, because the very limited aqueous solubility prevents toxic concentrations being achieved in exposure media. Similarly, above log Kow of 8, long-term toxicity effects are not expected.1

- Regarding environmental exposure: the chemical properties indicate the substance will have the tendency to adsorb onto dissolved organic matter in the natural environment. Therefore, aqueous exposure is unlikely.

- The physicochemical properties and very high expected Koc value means that if the substance were to enter a wastewater treatment plant in influent waste waters, it would partition mainly to sludges (a small proportion may be volatilised), with a negligible amount passing to water. The result is that exposure of freshwater or marine aquatic compartments is negligible.

1The very high log Kow (9.0) and very low limit of solubility in water mean the substance has very low bioavailability. For substances with these properties, chronic aquatic ecotoxicity is unlikely to be of concern. The principle of log Kow-based cut-off values for toxic effects has been embraced by the ICCA and OECD high Production Volume (HPV) chemical programmes (e.g. UNEP, 2000). The US EPA has also accepted them in its Pollution Prevention Framework (http://www.epa.gov/oppt/p2framework/docs/casestu.htm). The ECOSAR QSAR applies a log Kow cut-off value of 8.0 beyond which chronic toxicity of neutral organics would not be expected because of limitations in bioavailability and uptake of the substance (Clements, 1996). These cut-offs are empirically derived and based on experimental test data.

Consideration of low functionality side chains and reactive groups

Phenyl group: The ecotoxicity of phenyls is related to non-polar narcosis. The ecotoxicity of substances with phenyl groups increases with increasing log Kow. For example, trichlorophenylsilane (CAS 98-13-5) has a very fast hydrolysis rate and the log Kow of the hydrolysis product is -0.2. Short-term toxicity data with trichlorophenylsilane determine no effects up to 100 mg/l (Springborn Smithers 2009a, b and c).

References:

Clements (1996). Estimating toxicity of industrial chemicals to aquatic organisms using structure-activity relationships. Edited by: Richard G. Clements. Contributors: R.G. Clements, J.V. Nabholz, M. Zeeman, Environmental Effects Branch, Health and Environmental Review Division, Office of Pollution Prevention and Toxics, U.S. Environmental Protection Agency, Washington, DC 20460, August 30, 1996.

UNEP (2000). OECD SIDS Alfa Olefins (CAS N°:592-41-6, 111-66-0, 872-05-9,112-41-4, 1120-36-1). UNEP Publications.

Conclusion on classification

The substance has no reliable ecotoxicity data: testing is waived due to the insolubility of the test substance meaning it is technically not feasible to perform the studies and toxic effects are not likely to be expressed at the limit of solubility.

It is therefore proposed that 1,3,3,5-tetramethyl-1,1,5,5-tetraphenyltrisiloxane (CAS 3982-82-9) should not be classified in the EU for acute or chronic toxicity.

According to Regulation (EC) No 1272/2008 (CLP):

Aquatic Acute: Not classified

Aquatic Chronic: Not Classified