Decamethyltetrasiloxane

Partition coefficient

Description of key information

Partition coefficient (decamethyltetrasiloxane): 8.21 at 25.1°C (OECD 123).

Log K_oa= 4.87 ± 0.04 at 19.7 ±0.4°C

Log K_aw= 3.22 ± 0.14 at 19.7 ±0.4°C

Key value for chemical safety assessment

Log Kow (Log Pow):

8.21

at the temperature of:

25.1 °C

Additional information

Two reliable measured n-octanol/water partition coefficient data are available for decamethyltetrasiloxane. An n-octanol/water partition coefficient (log K_ow) of 8.21 at 25.1°C was determined using OECD 123 test method and in compliance with GLP. The result is considered to be reliable and is selected as key study. Other reliable data reported log K_ow value of 8.09 at 19.7°C using a non-standard test method. In other secondary sources to which no reliability could be assigned, log K_ow value of 5.4 was reported for the substance. The study with the highest reliability was assigned as key study.

A disregarded log K_ow of 4.42 at 22.3°C (Dow Corning Corporation, 2006) was also available for the substance. 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 K_ow for the substance determined in the key study (Dow Corning Corporation, 2009) suggests that this assumption was invalid. This is most likely due to the presence of trace level impurities or degradation (radiolysis or hydrolysis) products in the radiolabelled test material having lower K_ow values than the parent compound.