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Partition coefficient

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Description of key information

Partition coefficient n-octanol/water log Pow = -0.57 (at 20°C; pH 6.8)

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 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 = -0.57 at 20°C and pH 6.8. 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.