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

Endpoint summary

Additional information

Environmental fate

The test substance, TIS-M, is a liquid under all environmental conditions and is insoluble in water. It has a low volatility (based on a vapour pressure result of 0.39 kPa at 20 °C and 0.51 kPa at 25 °C). As such, any environmental release will result in virtually all of the substance compartmentalising into soil and water compartments, with little release directly to the atmosphere.

Any potential exposure to the environment is predicted to result in rapid redistribution to soil and water due to its volatility. This is supported by a Level III fugacity model in the US EPA EPISUITE (Mackay), which assumes steady-state but not equilibrium conditions. The Level III model in EPI Suite predicts partitioning between air, soil, sediment and water using a combination of default parameters and various input parameters. This model has been used to calculate the theoretical distribution of TIS-M between four environmental compartments (air, water, soil, sediment) at steady state in a unit world. Partitioning is detailed to be:

1.           Air 4.92 %

2.           Water 51.2 %

3.           Soil 42.4 %

4.           Sediment 1.46 %

TIS-M has a low ready biodegradability in that it 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.

However TIS-M is expected to hydrolyse very rapidly under normal environmental conditions.  Experimental studies on hydrolytic effects demonstrated that the substance does undergo hydrolysis at environmentally relevant pH’s, with a half life estimated to be less than 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 and nature of use that the substance is not degraded by direct photolysis. It is concluded, therefore, that abiotic processes in the aqueous phase would contribute significantly to the depletion of the substance within the environment.

 

TIS-M has an estimated log Pow of > 6.5 (estimated by testing 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 not to be indicative of a tendency to bioaccumulate in lipid tissues of aquatic organisms. No information on bioaccumulation is available; however the use of US EPA EPIWIN programme BCFBAF v 3.00 gave a predicted Log BCF = 3.478 (BCF = 3005 L/kg wet-wt). It is worth noting that the programme calculated this BCF value using an estimated log Pow of 5.78, which is lower than the log Pow value estimated/extrapolated from testing. In addition, TIS-M is subject to rapid hydrolysis at biologically relevant pHs. Therefore, 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.

 

A screening organic carbon-water partitioning coefficient (Koc) is available for the substance, using a HPLC Estimation method. This resulted in a log Koc value of 4.24 at 25 °C with a Koc value of 17259 L/kg. As such, adsorption to soil is deemed to be high, based on this study assessment.

Based on its rapid hydrolysis at pH 4, 7 and 9, it can be concluded that TIS-M is not expected to be persistent within the environment. No PBT/vPvB assessment has been conducted for the products of hydrolysis at this level of registration considering that the substance is imported into the EU only in a polymerised form, and hence exposure to the “neat” form is not anticipated. If an upgrade to the registration level is undertaken, a PBT/vPvB assessment of the degradation products will be conducted.

 

Finally, TIS-M demonstrates low acute toxicity in mammalian studies therefore in the event of exposure to environmental organisms, effects due to secondary poisoning can be excluded.

 

The above is reported for the “neat” test substance and is included for information purposes only. The substance is imported into the EU only in a polymerised form, and hence exposure to the “neat” form is not anticipated.

Reliability

The studies have all been ranked reliability 1 according to the Klimisch et al system. This ranking was deemed appropriate because the studies were all conducted to GLP in compliance with recognised guidelines.

Justification for classification or non classification

The above results triggered no classification under the Dangerous Substance Directive (67/548/EEC) and the CLP Regulation (EC No 1272/2008).