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EC number: 248-948-6
CAS number: 28299-41-4
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).
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.
The partition coefficient (logPow) of ditolyl ether was determined to be 4.9 at 25 °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 the test item determined within this study also refers to 25
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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