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Environmental fate & pathways

Adsorption / desorption

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Description of key information

The potential of the substance to sorb on soil or sediment is described by a log Koc between 2.09 and 3.00. Measurements were carried out at pH 6 (Currenta, 2010a). As the three components significantly vary with respect to the peak area, the area % weighted log Koc was calculated as well giving a log Koc value of 2.7 (Koc 501).
According to the classification of Swann et al. (1983), the substance has a medium potential to sorb on soil.

Key value for chemical safety assessment

Koc at 20 °C:
501

Additional information

The HPLC method enables adsorption coefficients to be estimated in the log Koc range from 1.3 to 5 justifying the use of that method for the Koc determination of the substance. The chromatogram of the test item showed resolved bands of 3 signals yielding the following single Koc values: 2.09, 2.50 and 3.00. As the three components significantly vary with respect to the peak area, the area % weighted log Koc was calculated as well giving a log Koc value of 2.7 (Koc 501). The occurance of several peaks might be explained by the hydrolysis of the substance.

As the pH value has a significant influence on sorption behaviour in particular for polar substances, the test was performed at pH 6. In case more than 10 % of the test item is dissociated at pH 6, a second test should normally be performed at a pH where the test item is undissociated. The pKa value of the substance is 6.72 (calculated with the software ACD/pKa v 7.0 based on molecular structure) indicating that the non-ionised form exists at a pH value > 7.7. As the prescribed analytical column for the HPLC method is not suitable for strong basic conditions (outside operating range), the determination was performed solely at pH 6.

Cationic substances in particular adsorb strongly to soil or sediment particles. As measurements were performed at pH 6, approximately 80 % of the substance is present in the cationic form. Therefore, the determined log Koc value covers the sorption behaviour of the ionised form as well, thereby reflecting the most critical species with respect to environmental hazard assessment. An additional measurement at a higher pH value would thus not provide additional information.