3-[3,3,3-trimethyl-1,1-bis[(trimethylsilyl)oxy]disiloxanyl]propyl methacrylate

Ecotoxicological Summary

Additional information

The registration substance has an extremely low estimated water solubility (5.8E-05 mg/L at 20°C) and very high estimated log K_ow (9.0).

 

The substance is susceptible to hydrolysis, however the low water solubility and high adsorption potential mean that hydrolysis in the environment is likely to be slow. The products of hydrolysis are 3-(trihydroxysilyl)propyl methacrylate and trimethylsilanol.

The registration substance is a member of the Reconsile Siloxanes Category. Substances in this category tend to have low water solubility, high adsorption and partition coefficients and slow degradation rates in the sediment compartment. For substances with a log K_ow of 6.6 and above no effects are seen with aquatic organisms due to the substance low water solubility limiting the effects. In the environment the substances will adsorb to particulate matter and will partition to soil and sediment compartments.

Additional information is given in a supporting report (PFA 2017at) attached in Section 13.

 

On the basis that the substance is insoluble, data waivers are in place for short-term toxicity to fish, 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 K_ow 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 K_ow 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 K_oc 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.

 

⁽¹⁾The very high log K_ow (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 K_ow-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 K_ow 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 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 aquatic ecotoxicity data: testing is waived due to the insolubility of the test substance meaning it is not technically feasible to perform the studies and, based on the very low solubility limit and very high octanol-water partition coefficent, it is predicted that short- or long-term toxic effects are not likely to be expressed at the limit of solubility. Hydrolysis is predicted to be slow under neutral conditions but more rapid at higher or lower pH ranges (half-lives 3.6 h at pH 4, 2.3 h at pH 5, 631 h at pH 7 and 5.3 h at pH 9 and 20-25°C (QSAR)).

 

However taking a conservative interpretation the criteria for the 'safety net' classification, Aquatic Chronic Category 4, could be considered to be met as the substance is of high log Kow, low water solubility and not rapidly degradable. According to Regulation (EC) No 1272/2008 (CLP):

Aquatic Acute: Not classified

Aquatic Chronic: Category 4