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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Physical & Chemical properties

Partition coefficient

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Administrative data

Link to relevant study record(s)

Description of key information

Log Kow: 6.6 at 25.3°C (OECD 123)

Log Koa = 3.79± 0.01 at 20.8±0.4°C

Log Kaw = 3.04± 0.20 at 20.8±0.4°C

Key value for chemical safety assessment

Log Kow (Log Pow):
at the temperature of:
25.3 °C

Additional information

Three reliable measured n-octanol/water partition coefficient data are available for octamethyltrisiloxane. An n-octanol/water partition coefficient (log Kow) of 6.6 was determined using OECD 123 and in compliance with GLP. The result is considered to be reliable and selected as key study. Other reliable data reported log Kow values of 6.87 at 20.8°C and 6.6 at 24.1°C. In other secondary sources to which no reliability could be assigned, log Kow values of 4.8 at 25°C and 4.8 - 5.4 were reported for the substance. The study with the highest reliability was assigned as key study.

A disregarded log Kow of 4.6 at 22.3°C (Dow Corning Corporation, 2006) was also determined for the substance because the method used is reportedly associated with a possible under estimation of values of log Kow bearing in mind susceptibility to hydrolysis. The method used was the slow-stirring method with the analytical determination based on 14C-radiolabelled test substance. Liquid scintillation counting was used for the analysis of total radioactivity in each phase. The accuracy of the reported value rested on the assumption that the 14C radioactivity in the aqueous phase represented only 14C-test substance, which was not confirmed during the study. The much greater value of log Kow for the substance determined in the key study (Dow Corning Corporation, 2008) suggests that this assumption was invalid. This is most likely due to the presence of trace level impurities or degradation (radiolysis) products in the radiolabelled test material having lower Kow values than the parent compound.