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Partition coefficient

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Reference
Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2018-03-29 to 2018-03-30
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
test procedure in accordance with generally accepted scientific standards and described in sufficient detail
Reference:
Composition 0
Qualifier:
equivalent or similar to
Guideline:
other: OECD guideline 105 ("Water Solubility")
Version / remarks:
Adopted July 27, 1995
Deviations:
not applicable
Principles of method if other than guideline:
The determination of the log Pow using the respective OECD guideline methods was technically not feasible due to the intrinsic properties of the test item:
- The test item is a UVCB and the flask-shake (OECD TG 107) and slow-stir method (OECD TG 123) for determination the log Pow are not applicable to complex mixtures.
- The test item cannot be chromatographed under the conditions described in the HPLC-method (OECD Guideline 117) since it is insoluble in the solvents used for the reverse phase HPLC.
- The test item has no defined chemical structure; therefore the calculation of the log Pow with a QSAR tool is not possible.
Hence, the log Pow has to be estimated based on individual solubilities of the test item in water and n-octanol.
GLP compliance:
no
Type of method:
estimation method (solubility ratio)
Partition coefficient type:
octanol-water
Test material information:
Composition 1
Analytical method:
photometric method
other: observation of precipitated substance particles in n-octanol
Key result
Type:
log Pow
Partition coefficient:
-0.1
Temp.:
20 °C
pH:
ca. 3.2
Remarks on result:
other: pH as determined in water solubility study
Key result
Type:
Pow
Partition coefficient:
< 0.25
Temp.:
20 °C
pH:
ca. 3.2
Remarks on result:
other: pH as determined in water solubility study
Details on results:
Undissolved particles were still observed in the test item / n-octanol mixture at the concentration 1 mg test item / 4 L n-octanol after 24 hours.
Based on this observation, the solubility of the test item in n-octanol is less than 0.25 mg/L.
The solubility of the test item in water is 0.35 mg/L as determined in a separate GLP study (see "water solubility")
The Pow value of the test item is calculated by dividing the value for octanol solubility by the value for water solubility: Pow = <0.25 ml/L / 0.35 mg/L = <-0.1.
Conclusions:
Considering the n-octanol/water solubility, the log Pow was estimated to be < -0.1.
Executive summary:

The determination of the log Pow using the respective OECD guideline methods was technically not feasible due to the intrinsic properties of the test item:

- The test item is a UVCB and the flask-shake (OECD TG 107) and slow-stir method (OECD TG 123) for determination the log Pow are not applicable to complex mixtures.

- The test item cannot be chromatographed under the conditions described in the HPLC-method (OECD Guideline 117) since it is insoluble in the solvents used for the reverse phase HPLC.

- The test item has no defined chemical structure; therefore the calculation of the log Pow with a QSAR tool is no possible.

Hence, the log Pow has to be estimated based on individual solubilities of the test item in water and n-octanol. Considering the water solubility of 0.35 mg/L and the n-octanol solubility of < 0.25 mg/L a log Pow of <0.1 has been estimated.

Description of key information

Estimated log Pow based on the individual solubility of the test item in water and n-octanol:

log Pow < -0.1

Key value for chemical safety assessment

Log Kow (Log Pow):
-0.1
at the temperature of:
20 °C

Additional information

The test item is a UVCB substance with an unknown and highly complex composition. Therefore, neither the estimation of the log Pow by QSAR nor its determination with OECD Guideline 107 (shake flask method) is feasible. For the HPLC-method (OECD Guideline 117), which is the recommended method for mixtures, the structural formula of the test item should be known and the test item must be soluble in the mobile phase at a sufficient concentration. The test item does not meet those requirements since its structural formula is not known and it is insoluble in the mobile phases applicable for this method. Consequently, the HPLC-method (OECD Guideline 117) is also not feasible and the log Pow of the test item can only be estimated from its individual solubility in water and in n-octanol. Considering the water solubility of 0.35 +/- 0.01 mg/L (95% confidence interval)  at 20 °C ± 1 °C and the octanol solubility of less than 0.25 mg/L a log Pow of < -0.1 has been estimated.