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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Biodegradation in water: screening tests: 13% biodegradation in 28 days (OECD Guideline 310). No significant biodegradation expected for the silanol hydrolysis product. 

Key value for chemical safety assessment

Additional information

Two reliable guideline studies are available. The key study was chosen as the most recently conducted study. 13% biodegradation in 28 days was determined in a reliable study conducted according to an appropriate test protocol (OECD 301), and in compliance with GLP. The supporting study indicated 0% to 2% biodegradation in 28 days (OECD 301 F). This study was also conducted in compliance with GLP.

Triethoxy(2,4,4-trimethylpentyl)silane is expected to hydrolyse within the timescale of the ready biodegradation study (half-life 42.5 hours at pH 7 and 20 -25

°C), predicted) to 2,4,4-trimethylpentanesilantriol and ethanol. Ethanol is readily biodegradable (OECD, 2004). Therefore a biodegradation of ~40% would be expected based on the ratio of carbon associated with ethanol and those associated with the non-alkoxy carbons in the silanol side chain.

However, the 2,4,4-trimethylpentyl group may significantly hinder hydrolysis of all three ethoxy groups of the parent substance, and thus formation of ethanol, and this may explain the lower than expected biodegradation results. In addition, triethoxy(2,4,4-trimethylpentyl)silane has a very low solubility (water solubility <0.1 mg/lat 20°C) and may not have fully dissolved and thus not been available for biodegradation in the tests.

The biodegradation observed in the key study is attributable to the biodegradation of the ethanol hydrolysis product. No significant biodegradation is expected for the silanol hydrolysis product.

Reference: OECD (2004): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 19-22 October 2004, Ethanol, CAS 64-17-5.