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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:
2017-05-05 to 2017-05-22
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
other: EU method A.8. Partition coefficient n-octanol/water
Version / remarks:
European Commission Regulation (EC) No. 440/2008
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Type of method:
estimation method (solubility ratio)
Partition coefficient type:
octanol-water
Specific details on test material used for the study:
Test item: WARADUR LG
Batch No.: W00004534
Expiry date: April 11, 2018
Certificate: Certificate of analysis No. 28657 dated April 23, 2013
Analytical method:
other: Gravimetric determination
Key result
Type:
Pow
Partition coefficient:
182.36
Temp.:
20 °C
pH:
6.3
Remarks on result:
other: Calculated from individual solubilities in pure n-octanol and pure water
Type:
log Pow
Partition coefficient:
2.26
Temp.:
20 °C
pH:
6.3
Remarks on result:
other: Calculated based on individual solubilities in pure n-octanol and pure water
Details on results:
Externally from the actual study, the partition coefficient n-octanol-water was determined based on the approximate water solubility determined in the key study on water solubility (Study No. Siemens PS20170136-2, Figure 3) of 0.55 mg/L, and the arithmetic mean solubility in n-octanol of 100.3 mg/L determined within this study (single values: 85.1 mg/L; 145.7 mg/L; 70.1 mg/L). The Pow was estimated based on the ratio of saturation concentrations in n-octanol and water as recommended in Appendix I of EU method A.8 for "...cases where the experimental methods cannot be applied for technical reasons." Due to its complex nature this applies to the submission substance.

The original result of this study on determination of Pow is given as
log Pow > 2.2.
This is due to the fact that the original result of the key study on water solubility was
water solubility < 1 mg/L, based on the lower limit of the calibrated concentration range. Extrapolating the perfectly linear calibration curve to lower values, based on the original measurements attached to this study (Study No. Siemens PS20170136-2, Figure 3) a water solubility of 0.55 mg/L can be deduced, which was used to calculated Pow.
Because the determined water solubility refers to TOC analysis, due to oxygen being part of the substance the water solubility based on MW will be still somewhat higher. Consequently, Kow will be somewhat lower.

Preliminary visual estimation of the n-octanol solubility

A defined amount of the test item was stirred with increasing volumes of n-octanol at room temperature and visually checked for any undissolved parts.

Results of the preliminary visual estimation of the n-octanol solubility:

Amount of test item / mg

Added volume of n-octanol / mL

Total volume of n-octanol / mL

Stirring time / min

Appearance of mixture

8.5

5

5

40

not dissolved

5

10

110

not dissolved

90

100

180

not dissolved

According to this preliminary test the solubility of the test item in n-octanol was below 85 mg/L (without correction for the purity).

Determination of the solubility in n-octanol: Flask method

Octanol solubility values as determined according to the flask method described above are given in the following table. The n-octanol solubility was calculated from the measured and unrounded concentration values and not from the rounded values given therein.

n -Octanol solubility experiments of the test item:

Experiment

24 h
experiment

48 h
experiment

72 h
experiment

blank
experiment
(72 h)

Amount of test item / mg

55.2

56.2

54.9

--

Amount of octanol / mL

100

100

100

100

Stirring time at 30 °C / h

24

48

72

72

Measured concentration / mg/L

85.1

145.7

70.1

- / -

n-Octanol solubility / g/L

0.09

0.15

0.07

--

The deviation of the determined n-octanol solubility was approx. 40 %. This was within the accuracy of the applicable analytical method.

The arithmetic mean value for the saturation concentration of the test item in n-octanol (n= 3) is determined as 100.3 mg/L.

Togehter with the water solubility determined based on the key study on water solubility (Study No. Siemens PS20170136-2, Figure 3) of 0.55 mg/L, the Pow is calculated according to Appendix I of EU method A.8 as the ratio of saturation concentrations in n-octanol and water:

Pow = 100.3 mg/L / 0.55 mg/L = 182.36

log Pow = 2.26

Because the determined water solubility refers to TOC analysis, due to oxygen being part of the substance the water solubility based on MW will be still somewhat higher. Consequently, Kow will be somewhat lower.

Conclusions:
Partition coefficient n-octanol-water (EU method A.8) = 182.36 at 20°C; log Pow = 2.26
Executive summary:

In a reliable study (RL 1) performed according to EU method A.8 compliant with GLP the partition coefficient n-octanol-water (Pow) was determined. Due to the complex nature of the submission substance neither the shake-flask method nor the HPLC method could be performed. Instead, Pow was estimated based on the ratio of saturation concentrations in n-octanol and water as recommended in Appendix I of EU method A.8 for "...cases where the experimental methods cannot be applied for technical reasons."

As such, within this study the octanol solubility of Waradur LG was determined following the methodology given in EU method A.6 for determination of the solubility in water according to the flask method. As a result of three replicate determinations, an arithmetic mean solubility in n-octanol of 100.3 mg/L did result (single values: 85.1 mg/L; 145.7 mg/L; 70.1 mg/L).

Togehter with the water solubility determined based on the key study on water solubility (Study No. Siemens PS20170136-2, Figure 3) of 0.55 mg/L, the Pow is calculated according to Appendix I of EU method A.8 as the ratio of saturation concentrations in n-octanol and water:

Pow = 100.3 mg/L / 0.55 mg/L = 182.36

log Pow = 2.26

Because the determined water solubility refers to TOC analysis, due to oxygen being part of the substance the water solubility based on MW will be still somewhat higher. Consequently, Kow will be somewhat lower.

Description of key information

Partition coefficient n-octanol-water (EU method A.8) = 182.36 at 20°C; log Pow = 2.26

Key value for chemical safety assessment

Log Kow (Log Pow):
2.26
at the temperature of:
20 °C

Additional information

In a reliable study (RL 1) performed according to EU method A.8 compliant with GLP the partition coefficient n-octanol-water (Pow) was determined. Due to the complex nature of the submission substance neither the shake-flask method nor the HPLC method could be performed. Instead, Pow was estimated based on the ratio of saturation concentrations in n-octanol and water as recommended in Appendix I of EU method A.8 for "...cases where the experimental methods cannot be applied for technical reasons."

As such, within this study the octanol solubility of Waradur LG was determined following the methodology given in EU method A.6 for determination of the solubility in water according to the flask method. Three replicate determinations led to an arithmetic mean solubility in n-octanol of 100.3 mg/L (single values: 85.1 mg/L; 145.7 mg/L; 70.1 mg/L).

Togehter with the water solubility determined based on the key study on water solubility (Study No. Siemens PS20170136-2, Figure 3) of 0.55 mg/L, the Pow is calculated according to Appendix I of EU method A.8 as the ratio of saturation concentrations in n-octanol and water:

Pow = 100.3 mg/L / 0.55 mg/L = 182.36

log Pow = 2.26

Because the determined water solubility refers to TOC analysis, due to oxygen being part of the substance the water solubility based on MW will be still somewhat higher. Consequently, Kow will be somewhat lower.

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