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Physical & Chemical properties

Partition coefficient

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Description of key information

Lead styphnate LogKow = -2.19 (at 20°C)

Key value for chemical safety assessment

Log Kow (Log Pow):
-2.19
at the temperature of:
20 °C

Additional information

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 Pb2+ and Pb4+ 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 lead.

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 an HPLC assay (as in OECD method 117). However, lead is a metallic element that can only exist in solution in a totally dissociated ionic state. The solubility of bivalent lead 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 lead cations into the octanol phase, it is not possible to determine the partition coefficient by direct measurement of the lead concentration in both phases. Similarly, any aqueous HPLC mobile phase will cause dissociation of inorganic lead compounds, and thus not allow the determination of a logPow by this method.

In conclusion, the conduct of further experimental verification is not considered to be technically or scientifically feasible.