Hexamethyldisiloxane

Biodegradation in water and sediment: simulation tests

Description of key information

Sediment degradation half-life [HMDS] : 192 d at 12°C (OECD 308)

Key value for chemical safety assessment

Half-life in freshwater sediment:

192 d

at the temperature of:

12 °C

Additional information

Sediment degradation rates were determined in a reliable study conducted according to an appropriate test method.

The study was conducted under aerobic conditions with two aquatic freshwater sediment systems (Calwich Abbey Lake sediment: 15-18% w/w sand / 63-66% w/w silt / 19% w/w clay [textural class: Silt Loam]. % organic carbon: 4.8 % w/w; Emperor Lake sediment: 63-65% w/w sand / 13-15% w/w silt / 22% w/w clay [textural class: Sandy Clay Loam]. % organic carbon: 1.73 % w/w). A half-life of 192 days was estimated for transformation of HMDS in the Calwich Abbey Lake sediment system. For the Emperor Lake sediment system, a half-life of 53 days was determined. In both cases, the major degradation product was the hydrolytic product, trimethylsilanol; the total amount of CO_2­captured was very small in both systems, suggesting a low rate of mineralisation.

In a preliminary study conducted according to an appropriate test protocol, a sediment degradation half-life of 34 days at 24°C and under aerobic conditions was determined in a preliminary study conducted according to an appropriate test protocol. The major degradation product was the hydrolytic product, trimethylsilanol, while CO2 generation was minimal.