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Partition coefficient

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

partition coefficient

Data waiving:

study technically not feasible

Justification for data waiving:

the study does not need to be conducted because the substance decomposes

Reference 2

Endpoint:

partition coefficient

Type of information:

(Q)SAR

Adequacy of study:

weight of evidence

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

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 an adaptation of the existing SRC model KOWWIN v1.67, which is a component of the EPIWIN Suite. 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. Whilst this method is good in principle, the model was developed using a wide range of organic chemicals and only a few organosilicon compounds. Therefore, a validation procedure was undertaken to assess the applicability of the model to alkoxysilane compounds. It was noted that the model under-predicted log Kow for alkoxysilanes; therefore, a correction factor is applied when this structural feature is present. The adapted model applies to di- and tri-alkoxysilanes.

Partition coefficient type:

octanol-water

Key result

Type:

log Pow

Partition coefficient:

4.2

Temp.:

20 °C

pH:

ca. 7

Remarks on result:

other: the result is for both the cis and trans isomers

Conclusions:

A log Kow value of 4.2 at 20°C for both the cis and trans isomers (Constituent 1a and Constituent 1b) was obtained using an accepted calculation method. The result is considered to be reliable.

Reference 3

Endpoint:

partition coefficient

Type of information:

(Q)SAR

Adequacy of study:

weight of evidence

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

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 an adaptation of the existing SRC model KOWWIN v1.67, which is a component of the EPIWIN Suite. 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. Whilst this method is good in principle, the model was developed using a wide range of organic chemicals and only a few organosilicon compounds. Therefore, a validation procedure was undertaken to assess the applicability of the model to alkoxysilane compounds. It was noted that the model under-predicted log Kow for alkoxysilanes; therefore, a correction factor is applied when this structural feature is present. The adapted model applies to di- and tri-alkoxysilanes.

Partition coefficient type:

octanol-water

Key result

Type:

log Pow

Partition coefficient:

5.4

Temp.:

20 °C

pH:

ca. 7

Conclusions:

A log Kow value of 5.4 at 20°C was obtained for Constituent 2 using an accepted calculation method. The result is considered to be reliable.

Description of key information

log K_ow [constituent 1a and constituent 1b, cis and trans isomers]: 4.2 at 20°C (QSAR)

log K_ow [constituent 2]: 5.4 at 20°C (QSAR)

log K_ow [methylsilanetriol]: -2.4 at 20°C (QSAR)

log K_ow [2-ethylhexyl 3-[dihydroxy(methyl)silyl]propanoate]: 3.0 at 20°C (QSAR)

log K_ow [2-ethylhexyl propanoate]: 4.23 Pa at 20°C

log K_ow [methanol]: -0.82 to -0.64

Additional information

The requirement to conduct an n-octanol/water partition coefficient study for the substance is waived because all the constituents of the substance undergo either rapid or very rapid hydrolysis in contact with water, with half-lives of <12 hours.

In addition, the determination of the log K_ow of the substance as a whole is not scientifically meaningful for the purpose of assessment of exposure or risk. The needs associated with a sound understanding of partition coefficient of the substance are adequately met by the available data on the constituents. The partition coefficient data for constituents of the substance were determined using a validated QSAR estimation method. The estimated log K_ow for constituents 1a and 1b is 4.2 at 20°C and for constituent 2, the log K_ow is 5.4 at 20°C.

A measured log K_ow of >5.79 at 30°C and pH 5 was determined for the substance using a relevant form of HPLC test method according to OECD 117 Test Guideline, but lacking some necessary corrective adjustments that would be necessary to validly interpret the result. The reliability is therefore not assignable.

The log K_ow of the silanol hydrolysis products have been estimated to be -2.4 at 20°C for methylsilanetriol and 3.0 at 20°C for 2-ethylhexyl-3 -[dihydroxy(methyl)silyl]propanoate using a validated QSAR estimation method.

Methanol has a reported log K_ow of -0.82 to -0.64 (OECD 2004).

2-Ethylhexyl propanoate has an estimated log K_ow value of 4.23 at 20°C using a KOWWIN v1.68. The model was not validated for 2 -ethylhexyl propionate, but since there are several propionates in both the training and validation set, the estimated value is considered to be valid and reliable.

References:

OECD (2004): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18-20 October 2004, Methanol, CAS 67-56-1.