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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Adsorption/desorption: Predicted Log Koc trimethylsilanol 1.6; ammonia 1.1

Key value for chemical safety assessment

Additional information

The substance hydrolyses very rapidly to trimethylsilanol and ammonia. Trimethylsilanol has a low log Kow value (<3) and thus has low potential for adsorption, and the requirement for testing is waived.

Based on its solubility, ammonia (unionised) is not expected to adsorb to soil particulate matter, suspended solids or sediment. (Environment Agency, 2007).

The ammonia ion is bound in soil by the attraction of the positive charge on the ammonium ion to the negatively charged soil micelles. In

soil, ammonium is adsorbed primarily by four mechanisms: chemical (exchangeable), fixation (non-exchangeable), reaction with organic matter

and physical attractive forces.

For environmental exposure assessment, adsorption is predicted for the hydrolysis products, trimethylsilanol and ammonia, using the EU TGD (Technical Guidance Document) ‘non-hydrophobics’ log Kowprediction method (EC, 2003),also referred to in REACH Guidance R7a (ECHA, 2008).

Environment Agency, 2007. Proposed EQS for Water Framework Directive Annex VIII substances: ammonia (un-ionised).

Science Report: SC040038/SR2. SNIFFER Report: WFD52(ii)

EC (2003). European Union Technical Guidance Document on Risk Assessment for New and Existing Substances, Part II, European Chemicals Bureau, 2003.

ECHA (2008) Guidance on information requirements and chemical safety assessment Chapter R.7a: Endpoint specific guidance. Section R. Evaluation of available information on adsorption/desorption