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Partition coefficient

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Description of key information

Partition coefficient n-octanol/water log Pow = -3.6 (at 20°C; pH 9.9)

Key value for chemical safety assessment

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

Additional information

Due to the surface activity of the test substance the shake-flask method according to OECD guideline 107 or the HPLC method according to OECD guideline 117 are not applicable. Therefore the partition coefficient of the test substance was calculated from the individual solubilities in n-octanol and water according to REGULATION (EC) No 440/2008 - A.8. PARTITION COEFFICIENT - Appendix 1 Calculation/estimation methods. The Partition coefficient n-octanol/water is log Pow = -3.6 at 20°C and pH 9.9. The critical micelle concentration was chosen as parameter for the water solubility. This is considered to be a worse case value for the following reasons:

Surfactants show a complex solubility behaviour due to aggregation. They can form different types of solutions in water (e.g. mono-molecular-, micellar-, hexagonal or lamellar solutions) depending on concentration and temperature. The mono-molecular solubility of a surfactant is defined by the critical micelle concentration (cmc). The monomer concentration, and hence the thermodynamic activity, reaches a limiting value at the cmc. It remains approximately constant as the total concnetration is further increased. For ecotocicological models requiring a solubility value, the cmc is therefore the appropriate parameter for water solubility and may be used as a worst-case approach in cases where the resulting log Pow is not critical. The cmc underestimates the total solubility of a surfactant and hence overestimates the partition coefficient.