Registration Dossier
Registration Dossier
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EC number: 270-451-8 | CAS number: 68440-34-6
Partition coefficient
Administrative data
Link to relevant study record(s)
Description of key information
not applicable
Key value for chemical safety assessment
Additional information
This study generally does not need to be conducted for inorganic substances (cf. Annex VII, section 7.8, column 2 of Regulation (EC) No 1907/2006). The substance is a salt of fatty acids with an inorganic cation. It is similar to inorganic salts because of its ionic structure. Thus waiving in accordance with Annex VII, section 7.8, column 2 of Regulation (EC) No 1907/2006 is justified.
The octanol/water partition coefficient, Pow, is defined as the ratio of the equilibrium concentrations of a dissolved substance in each of the phases in a two-phase system consisting of octanol and water. It is usually expressed on a log scale. It is a key parameter in studies of the environmental fate of organic substances, indicating the potential for bioaccumulation and soil absorption. However, the mechanisms of absorption of Zn2+into organic matter and living cells are understood to be different from those traditionally attributed to carbon-based substances and the parameter therefore has little relevance to ionic zinc.
In order to measure a log Pow it is necessary to determine an absolute value for the concentration in each phase (as in OECD method 107), or to conduct a HPLC assay (as in OECD method 117). However, zinc is a metallic element that can only exist in solution in a totally dissociated ionic state. The solubility of bivalent zinc cations is low in water and can safely be expected to also be low in organic solvents such as n-octanol.
Because of the unlikely partitioning of zinc cations into the octanol phase, it is not possible to determine the partition coefficient by direct measurement of the zinc concentration in both phases. Similarly, any aqueous HPLC mobile phase will cause dissociation of inorganic zinc compounds, and thus not allow the determination of a log Pow by this method. In conclusion, the conduct of further experimental verification is not considered to be technically or scientifically feasible, and for the reasons stated above derogation from testing is hereby applied for.
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