2-Propenoic acid, 2-methyl-, tris(1-methylethyl)silyl ester

PBT assessment

PBT assessment: overall result

PBT status:

the substance is not PBT / vPvB

Justification:

The substance displays properties that indicate persistency within the environment, based on a low ready biodegradability. The substance achieved 8.2% biodegradation in a 28-day closed bottle test indicating that it is unlikely to achieve a half life of less than 40 or 60 days within fresh water attributed to ready biodegradation alone. An experimental study on hydrolytic effects demonstrated that the substance undergoes very rapid hydrolysis at environmentally relevant pHs, with an estimated half life of < 9 minutes at pH 4, 7 and 9. As such, degradation is anticipated via this route. Studies on direct phototransformation in water are not available but it is assumed on the basis of chemical structure that the substance is not degraded by direct photolysis. It is concluded, therefore that abiotic processes would contribute significantly to the depletion of the substance within the environment.

Due to the effects of hydrolysis at environmentally relevant pHs, it is proposed that the substance cannot be considered to have a half life in marine water higher than 60 days, despite the limited ability to biodegrade. Based on its hydrolysis rate at environmentally relevant pH’s, it can be concluded that it is unlikely that the substance could potentially be persistent within the environment. Abiotic effects will result in eventual removal from the environment and hence significant contact with the organisms in the food chain can be considered to be minimised. As such, the substance does not fulfil the requirements of Annex XIII, Para 1.1 based on evaluation of available data, and cannot be considered a “P” and “vP” based in this data.

 

The substance has an estimated log Pow of > 6.5 with an extrapolated value of 7.4. This high log Pow value is considered to be more a consequence of poor water solubility issues than a lipophilic tendency and is considered to be not indicative of the tendency to bioaccumulate in lipid tissues of aquatic organisms. Given the fact that the substance is subject to significant hydrolysis at biologically relevant pH, it is anticipated that bioaccumulation of the substance itself would not occur, as hydrolytic effects in association with metabolic effects would result in removal of the substance.

Based on the physico-chemical data for the substance, it is proposed that the substance does not fulfil the requirement of Annex XIII, Para 1.2 based on evaluation of available data, and cannot be considered a “B” or “vB” based on the available data.

 

The substance is classified as a skin sensitiser. As such, the substance does not fulfil the requirements of Annex XIII, Para 1.3 based on evaluation of available data, and cannot be considered as “T” for the purposes of the assessment.