Registration Dossier
Registration Dossier
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EC number: 249-385-9 | CAS number: 29043-70-7
Ecotoxicological Summary
Administrative data
Hazard for aquatic organisms
Hazard for air
Hazard for terrestrial organisms
Hazard for predators
Additional information
The registration substance, dimethylbis(octadecyloxy)silane (CAS 29043-70-7), has an extremely low estimated water solubility (2.5E-14 mg/l at 20-25 °C (insoluble)) and very high estimated log Kow (9.0 at 20°C). The substance is susceptible to hydrolysis with a predicted half-life of >15 hours at pH 7, 25°C. The reaction products are dimethylsilanediol (CAS 1066-42-8) and octadecan-1-ol (CAS 112-92-5). The registration substance has a high adsorption potential and very low water solubility; this means that hydrolysis is likely to be very slow in the environment.
On the basis that dimethylbis(octadecyloxy)silane 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; a water solubility trial with a similar substance (trimethyl(octadecyloxy)silane) was attempted which showed very unstable results (Lange, 2017). 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 8.0, 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 and it has an extremely low water solubility. 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.
The focus of the environmental assessment is based on the properties of the parent substance in accordance with REACH guidance for Chemical Safety Assessment (Chapter R.16), as the estimated hydrolysis half-life for this substance is >12 hours. In addition, the very low water solubility of the substance means that, under environmental conditions, hydrolysis may not occur or will be very slow.
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.
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 Numbers: 592-41-6, 111-66-0, 872-05-9,112-41-4, 1120-36-1). UNEP Publications.
Conclusion on classification
No ecotoxicity data are available for the registration substance and testing is not feasible as the substance has a very low water solubility.
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