Tetradecamethylhexasiloxane

Partition coefficient

Link to relevant study record(s)

Reference

Endpoint:

partition coefficient

Type of information:

(Q)SAR

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification

Justification for type of information:

See attached QMRF/QPRF

Principles of method if other than guideline:

The result was obtained using an appropriate QSAR method (see attached QMRF and QPRF for details).

The model is the publically available KOWWIN v1.68 program (USEPA 2011). KOWWIN is part of EPI Suite v4.1 and may be downloaded from http://www.epa.gov/oppt/exposure/pubs/episuite.htm. The model is based on fragment values. That is, the chemical structure is broken down into its constituent functional groups, and the contribution of each group toward the overall partition coefficient is calculated. The constants used within KOWWIN have been derived by SRC from a wide range of organic chemicals. The authors of this QMRF have carried out additional validation and found the method to be applicable organosilicon compounds, excluding di- and tri-alkoxysilanes.

USEPA 2011. KOWWIN v. 1.68, US EPA. 2011. Estimation Programs Interface Suite™ for Microsoft® Windows, v 4.10. United States Environmental Protection Agency, Washington, DC, USA. Available at http://www.epa.gov/oppt/exposure/pubs/episuite.htm

Partition coefficient type:

octanol-water

Type:

log Pow

Partition coefficient:

> 9

Temp.:

20 °C

pH:

ca. 7

Conclusions:

An octanol-water partition coefficient value of >9 was obtained using an accepted calculation method. The result is considered to be reliable.

Description of key information

log Kow:  >9.268-9.508 (overall weighted average of >9.411) (OECD 123)

Key value for chemical safety assessment

Log Kow (Log Pow):

9.41

at the temperature of:

25 °C

Additional information

The log K_ow of the submission substance (L6, CAS 107-52-8) has been read-across from data available for another structurally-related substance, dodecamethylpentasiloxane (L5, CAS No. 141 -63 -9). Both substances are linear siloxane chains with six and five silicon atoms respectively, with methyl branches and alternated by oxygen. Both substances undergo slow hydrolysis in water to form the same silanol hydrolysis products, dimethylsilanediol and trimethylsilanol. In addition, both substances have similar impurities and the percentage purities of both L6 and L5 are similar (>95% and >93% respectively). It is therefore, considered appropriate to read-across the measured partition coefficient data for L5 to L6.

A measured log K_ow value ranging from 9.268 -9.508, with an overall variance-weighted average value of 9.411was determined for L5 using a relevant test method and in compliance with GLP. Since, L6 has six silicon atoms and higher molecular weight than L5, the log K_ow value of L6 is expected to be >9.41. The result is considered to be reliable and was selected as key study.

For L6, the read-across is supported by a predicted log K_ow value of >9.0 at 20°C which was determined using a validated QSAR estimation method.

In a secondary source to which reliability could not be assigned, a log K_ow value of 6.6 was reported for the submission substance.