Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

The distribution in a sewage treatment plant (STP) has been estimated using the SimpleTreat 3.0 model (implemented in EUSES), see table below. Due to the rapid hydrolysis of the parent substance, the distribution calculation is done for the silanol hydrolysis product

Table. Distribution modelling for STP

Assessment entities

dimethylsilanol (Intermediate HP)

dimethylsilanediol (final HP)

Release to water

97.13%

99.98%

Release to air

2.598%

6.15E-4%

Release to sludge

0.266%

9.89E-3%

Release degraded

0%

0%

Summary

1,1,3,3-Tetramethyldisiloxane hydrolyses very rapidly (half-life 11.3 minutes at pH 7 and 25°C) to form dimethylsilanol, which further hydrolyses to form the final hydrolysis product, dimethylsilanediol (half-life 2.5 days). Dimethylsilanediol is not expected to undergo any significant biodegradation, has low Henry’s Law constant and low log Kow/log Koc. Therefore water is the main compartment to which it is expected to partition in a sewage treatment plant.