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Physical & Chemical properties

Partition coefficient

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Description of key information

In a weight of evidence approch different calculations from database/secondary scources were summarized. The substance is expected to have a very low log Pow between -13.2 and -2.62 at 25 °C. The value of -13.2 was used  in the chemical safety assessment as this value is used in a worst case approach for derivation of PNECsoil and PNEC sediment. 

Key value for chemical safety assessment

Log Kow (Log Pow):
-13.2

Additional information

In a weight of evidence approch different calculations from database/secondary scources were summarized. The substance is expected to have a very low log Pow between -13.2 and -2.62 at 25 °C.

The result of -13.2 was calculated in the most recent study from 2010. In this study, in order to describe the paritioning behaviour of Na3NTA, speciation calculations were performed for NTA with ChemEQL, a speciation computer program that can also handle partitioning behaviour of individual components of the equilibrium system, under the assumption that Na3NTA completely dissociates upon dissolution in water, and that the presence of the sodium ions does not appreciably influence the equilibrium behaviour of NTA.

The partitioning behaviour of Na3NTA is pH-dependent, due to the speciation of the nitrilotriacetate ion, and the fact that only neutral H3NTA will partition into a nonpolar solvent like octanol.

Given an estimated log Kow for H 3 NTA of -3.8 and pKa values for the different NTA species, it was estimated that the apparent log Kow of Na 3 NTA is highest at pH 1.4, with a value of -4.14; at pH 7, the apparent log Kow is already down to -13.2. At pH 14, the apparent log Kow is -31.2.