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Environmental fate & pathways

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Additional information

2,4,6,8 -Tetramethylcyclotetrasiloxane hydrolyses rapidly. The half-life for the initial ring-opening has been determined to be 2.2. min at pH 7 and 22.5°C. The hydroxy siloxanes formed as intermediate hydrolysis products of HD4 are very rapidly hydrolysed to methylsilanediol. This liberated methylsilanediol is oxidised/transformed into the terminal hydrolysis product of methylsilanetriol. Due to the residency time in the waste-water treatment plant, methylsilanetriol is expected to be the main species released to the receiving waters. Therefore, the environmental hazard assessment, including sediment and soil compartments due to water and moisture being present, is based on the properties of the silanol hydrolysis product in accordance with REACH guidance for Chemical Safety Assessment (Chapter R16).

REFERENCE: ECHA (2016). REACH Guidance on Information Requirements and Chemical Safety Assessment Chapter R16: Environmental Exposure Estimation Version: 3.0 February 2016