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Description of key information

Log Koc was calculated from three representative constituents

2 -methylpropyl dihydrogen phosphate:

LogKoc = 1.55, Koc = 35.87 L/kg (pH 7, pKa= 6.38, ChemProp acid model)

bis(2 -methylpropyl) hydrogen phosphate

LogKoc = 1.78, Koc = 59.65 L/kg (pH 7, pKa= 0.59, ChemProp acid model)

2 -methyltridecan-2 -amine

Log Koc = 4.57, Koc = 37275.87 L/kg (pH 7, pKa= 10.37, calculated manually, bases model)

Key value for chemical safety assessment

Additional information

There is no experimental study available, in which the log Koc of Amines, C12-14-tert-alkyl, mixed sec-Bu and iso-Bu phosphates (CAS 96690-34-5) was assessed. The test item is an UVCB substance, comprising amine and organophosphate components. Representative components were selected for the log Koc calculation. Considering the ionization properties of the components, the adsorption potential has been calculated using Franco and Trapps´ (2008) as well as Franco, Fu and Trapp‘s (2009) expressions on estimation of the organic carbon-water partitioning coefficient of ionisable organic substances, incorporated within the ChemProp software v6.6 (bases and acids, respectively). The log Kow of the neutral molecules, the pH (pH 4, 7 and 9) as well as the pKa values were used as input parameters. The pKa values were calculated using SPARC software v4.6 resulting in pKa values of 6.38 (2 -methylpropyldihydrogenphosphate), 0.59 bis (2 -methylpropyl hydrogen phosphate) and 10.37 (2 -methyltridecan-2 -amine) was calculated. In case of 2 -methylpropyldihydrogenphosphate and 2 -methylpropyl hydrogen phosphate the log Koc calculations were performed with the ChemProp software v.6.6 using the pH dependent soil sorption coefficient model for acids (based on Franco, Fu & Trapp, 2009). The calculation for 2 -methyltridecan-2 -amine was performed manually with the equation given by the same ChemProp model for bases (based on Franco & Trapp, 2008) since the software does not consider other pH than 4.5.

For the 2 -methylpropyl dihydrogen phosphate the log Koc was calculated to be 1.48 at pH 4, 1.55 at pH 7 and 1.61 at pH 9. For the bis(2 -methylpropyl) hydrogen phosphate the log Koc was calculated to be 1.78 at pH 4, pH 7 and pH 9. For 2 -methyltridecan-2 -amine the log Koc was calculated to be 4.57 at pH 4 and pH 7 and 4.56 at pH 9. These values indicate a low adsorption potential for the 2 -methylpropyl dihydrogen phosphate and bis(2 -methylpropyl) hydrogen phosphate in soils and sediments and a high potential for 2 -methyltridecan-2 -amine. According to the Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.7.1.8.5 the log Pn value for the ionized molecule determined around the default pH of 7 is considered more relevant for chemical safety assessment. 2 -methyltridecan-2 -amine with a calculated log Koc of 4.57 (Koc = 37275.87) at pH 7 has been used as key value for the chemical safety assessment.

Reference:

Franco A. & Trapp S., 2008: Estimation of the soil-water partition coefficient normalized to organic carbon for ionizable organic chemicals. Environmental Toxicology and Chemistry, Vol. 27, No. 10, pp. 1995–2004.

Franco A., Fu W., and Trapp S. (2009).Influence of soil pH on the sorption of ionizable chemicals: modeling advances. Environmental Toxicology and Chemistry 3: 458-464, doi: 10.1897/08-178.1