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Physical & Chemical properties

Partition coefficient

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Description of key information

The partition coefficient of this substance is not considered to be relevant.

Key value for chemical safety assessment

Additional information

In accordance with Annex XI of Regulation (EC) No 1907/2006, this study does not need to be conducted for this substance, as it is considered to be neither scientifically necessary nor technically possible.

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 a key parameter in studies of the environmental fate of organic substances, indicating the potential for bioaccumulation and soil absorption. Whereas this may also be applicable for organometallic substances, it does not pertain to the substance in question here because of its inorganic nature.

For inorganic substances, the determination of a partition coefficient is not considered to be required (ECHA Guidance on information requirements and chemical safety assessment Chapter R.7a: Endpoint specific guidance, section R.7.1.8; December 2013); since the substance is similar to inorganic salts because of its ionic structure, waiving in accordance with Annex VII section 7.8 Column 2 of regulation (EC) 1907/2006) is also justified.

Instead of the determination of a Pow value, the environmental fate and distribution of the dissociation products of this substance in water are better assessed according to the dissociation products in water as follows:

(i) the mechanisms for partitioning of ionic lead in environmental media, including the adsorption and/or absorption by organic matter and living cells, are understood to be different from those traditionally attributed to carbon-based substances (see IUCLID section 5.4 for information on the partitioning of lead in the environment). Thus, and in accordance with ECHA final decision: CCH-D-0000003912-74-02/F, partition coefficient n-octanol/water information is not relevant for the lead ion. In order to measure an octanol/water partition coefficient, 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 log Pow by this method.

(ii) regarding the partitioning behaviour of organic acid constituent, peer-reviewed handbook or collection of data report for phthalic acid a log Pow of 0.73 [Hansch C, Leo A, Hoekman D (1995) and US NIOSH [http://www.cdc.gov/niosh/ipcsneng/neng0768.html] respectively the IPCS INCHEM International Chemical Safety Card (ICSC) for phthalic acid [http://www.inchem.org/documents/icsc/icsc/eics0768.htm]. The corresponding estimate for the log Pow of phthalic acid based on an atom/fragment contribution method is 1.07 [KOWWIN™ Program Version 1.68; EPI Suite™ v.4.11, 2012].

In conclusion, the conduct of further experimental verification is considered to be neither technically nor scientifically feasible, and for the reasons stated above derogation from testing is hereby applied for.