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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:
2013
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 117 (Partition Coefficient (n-octanol / water), HPLC Method)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Type of method:
HPLC method
Partition coefficient type:
octanol-water
Analytical method:
high-performance liquid chromatography
Type:
log Pow
Partition coefficient:
4.9
Temp.:
40 °C
pH:
7.1
Remarks on result:
other: measured
Type:
log Pow
Partition coefficient:
4.3
Temp.:
25 °C
Remarks on result:
other: calculated (KOWWIN v1.68)
Remarks:
pH is not reported
Type:
log Pow
Partition coefficient:
5.1
Temp.:
25 °C
Remarks on result:
other: calculated (KOWWIN v1.68)
Remarks:
pH is not reported
Details on results:
In order to ensure a stable performance of the HPLC column, the column temperature was set to 40 °C. The reference Pow-values in the OECD guideline presumably refer to 25 °C. Even though the column temperature was 40 °C, this temperature has no influence on the result of the determination. Therefore the Pow -value of the test item determined within this study also refers to 25 °C.

Calculation of the partition coefficient (preliminary estimation):

The log Pow value was calculated with the software KOWWIN v1.68 assuming the nonionic form. KOWWIN is owned by the U.S. Environmental Protection Agency. For two isomeric structures, representative for the test item Ditolylether, were calculated (see results and discussions).

Conclusions:
The partition coefficient (logPow) of ditolyl ether was determined to be 4.9 at 25 °C.
Executive summary:

For ditolyl ether the partition coefficient was determined by the HPLC-method according to OECD TG 117. The partition coefficient was determined to be 4.9 at 40 °C. In order to ensure a stable performance of the HPLC column, the column temperature was set to 40 °C. The reference Pow-values in the OECD guideline presumably refer to 25 °C. Even though the column temperature was 40 °C, this temperature has no influence on the result of the determination. Therefore the Pow -value of ditolyl ether determined within this study also refers to 25 °C.

In a preliminary estimation the log Pow value for two isomeric structures, representative for ditolyl ether, were calculated with the software KOWWIN v1.68 assuming the nonionic form. KOWWIN is owned by the U.S. Environmental Protection Agency. The result was 4.3 and 5.1, respectively.

Description of key information

The partition coefficient (logPow) of ditolyl ether was determined to be 4.9 at 25 °C.

Key value for chemical safety assessment

Log Kow (Log Pow):
4.9
at the temperature of:
25 °C

Additional information

In order to ensure a stable performance of the HPLC column, the column temperature was set to 40 °C. The reference Pow-values in the OECD guideline presumably refer to 25 °C. Even though the column temperature was 40 °C, this temperature has no influence on the result of the determination. Therefore the Pow -value of the test item determined within this study also refers to 25 °C.

Discussion on appropriateness of data to be used for risk assessment

For the partition coefficient of ditolyl ether there is a EPIWIN based QSAR estimation as well as an experimental study which was conducted in accordance with OECD guideline 117 (HPLC method), which give the log Kow was 5.1 and 4.9. The experimental result of 4.9 is more reliable and decisive and was, thus, used for the risk assessment of ditolyl ether.

When thinking about possible methods for experimental determination of log Kow the chosen HPLC method appears to be the most appropriate. With this method log Kow is determined from a correlation between log K (capacity factor) and log Kow for a series of reference substances which were appropriate to determine the partition coefficient with adequate precession. As detailed in ECHA Guidance R.7a (v2.4, Febr. 2014), the HPLC method is also very suitable for measuring the low Kow of chemical homologues mixtures and ditolyl ether is a mixture of isomers. Further on, the log Kow of ditolyl ether is in the HPLC method range: 0 < log Kow < 6 which covers the test item, and the mean of three replicates deviated with less than +/- 0.1 log Kow.

In contrast, the Shake Flask method (OECD 107) is obviously inappropriate as the applicability range is -2 < log Kow < 4. Accordingly, the Slow-Stirring method (OECD 123) is not appropriate as in accordance with ECHA Guidance R.7a it is an alternative to the Shake Flask method which allows to reduce emulsion formation. It could be used for very hydrophobic substances up to log Kow 8.3 but ditolyl ether is not very hydrophobic and the intra-laboratory median standard deviation is described as 0.15-0.3 log Kow which is clearly less precise than the HPLC method.

In conclusion, the most appropriate method to determine the log Kow of ditolyl ether is OECD 117 (HPLC method) and, thus, the available experimental result is reliable and to be used for the risk assessment.

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