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Physical & Chemical properties

Partition coefficient

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Description of key information

Key value for chemical safety assessment

Log Kow (Log Pow):
14

Additional information

All of the available information on TNPP, indicated that it will have a very high octanol-water partition coefficient, with log Kow estimates ranging from 6 to >20. This range takes into account both the highest result obtained using QSAR models and the fact that this substance was expected to have a high log Kow based on its structure.

Considering the high hydrophobic potential of TNPP which contains 27 aliphatic and 18 aromatic carbons, this would be expected for this compound. The draft EU Risk Assessment Report (October 2008) considered this endpoint in detail in a senstivity analysis that was provided in Annex 1 of that assesment. The assesment concluded that a log Kow of 14 is appropriate for TNPP.

Reimer (2001d) concluded that it was not appropriate to conduct the partition coefficient measurement because the solubility of TNPP in water was too low and the reaction of TNPP with octanol does not allow the measurement of adequate TNPP concentrations in octanol. Jakupca (2007) determined that a more appropriate approach at estimating the Kow was an HPLC method based on OECD guidelines 117. The analysis of TNPP was conducted with gradient HPLC. Butyl benzene, diethylhexyl phthalate (DEHP), diisononylphthalate (DINP) and diisodecylphthalate (DIDP) were used as standards with known Kow’s to develop a calibration curve. Based on this approach, TNPP was estimated with a log Kow of 14 or greater. A standard could not be found that had a Kow of 14 to test the calibration.

Modelled data results are provided for comparison, though it appears that the models have limitation to be able to accurately predict the octanol-water coefficient.

Kow calculations for TNPP along with the validity domain of the calculation method used

Program

Valid Kow Range*

TNPP value

Remark

CLOGP

0-5

19.918

Very high LogP unrealistic in nature (this remark was associated to the result of the model)

In general, CLOGP gives also better estimates with log Kow < 0.

KOWWIN

Version 1.67

0-5 (clear estimates in this range most of the time)

20.05

 

SPARC

>5

19.02

Better than KOWWIN and CLOGP for Kow >5.

* all estimates for Kow around 10 or above should be considered rather as qualitative than quantitative information.