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Partition coefficient

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partition coefficient
Data waiving:
study technically not feasible
Justification for data waiving:
the study does not need to be conducted because the substance has a high surface activity
partition coefficient
Type of information:
Adequacy of study:
key study
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
Justification for type of information:
QSAR prediction
equivalent or similar to guideline
other: REACH guidance on QSARs R.6, August 2008
Principles of method if other than guideline:
The Partition coefficient is the ratio of concentrations of a tested substance in a liquid consisting of two immiscible solvents at equilibrium. The n-octanol/water partition coefficient (Kow) is one of the key physico-chemical parameters, and it is used in numerous estimation models and algorithms for environmental partitioning, sorption, bioavailability, bioconcentration/bioaccumulation and also human- and ecotoxicity. As such Kow is a critical parameter for Chemical Safety Assessment (CSA), Classification and Labelling (C&L), and PBT assessment.

The program EpiSuite 4.1 (KOWWIN) predicts logPow values. Up to 89.1 % of the predicted values are within the +/-0.5 log unit of the measured logPow value (standard error of. 0.34 log unit).
GLP compliance:
not specified
Type of method:
calculation method (fragments)
Partition coefficient type:
Analytical method:
other: not applicable, estimated value
Key result
log Pow
Partition coefficient:
25 °C
Remarks on result:
other: calculated logPow value hence no pH
Details on results:
The program EpiSuite 4.0 (KOWWIN v1.68) predicts logPow values. Up to 89.1 % of the predicted values are within the +/-0.5 log unit of the measured logPow value (standard error of. 0.34 log unit).

Total Training Set Statistics:

(i)            number in dataset = 2447

(ii)           correlation coefficient (r2) = 0.982

(iii)          standard deviation = 0.217

(iv)         absolute deviation = 0.159

(v)          average Molecular Weight = 199.98 g/mol


To be effective an estimation method must be capable of making accurate predictions for chemicals not included in the training set. Currently, KOWWIN has been tested on an external validation dataset of 10,946 compounds. The validation set includes a diverse selection of chemical structures that rigorously test the predictive accuracy of any model. It contains many chemicals that are similar in structure to chemicals in the training set, but also many chemicals that are different from and structurally more complex than chemicals in the training set. The average molecular weight of compounds in the validation set is 258.98 versus 199.98 for the training set.


Total Validation Set Statistics:

(i)            number in dataset = 10946

(ii)           correlation coefficient (r2) = 0.943

(iii)          standard deviation = 0.479

(iv)         absolute deviation = 0.356

(v)      average Molecular Weight = 258.98 g/mol

The partition coefficient n-octanol/water (log Pow) of the test item is calculated with the aid of a validated QSAR method (KOWWIN, vers. 1.68).
The result of this calculation is logPow = 3.42.

Description of key information

According to Annex VII section 7.8 Column 2 of Regulation 1907/2006 this study does not need to be conducted for substances with high surface activity.
However, a calculated value as well as details of the calculation method is provided to fulfill the requirements under REACH: logPow = 3.42 (QSAR method, KOWWIN, v1.68).

Key value for chemical safety assessment

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

Additional information