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Environmental fate & pathways

Adsorption / desorption

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Description of key information

The QSAR determination of the carbon partition coefficient for o-toluidine using the model KOCWIN included in the Estimation Program Interface (EPI) Suite v4.11 revealed values of 47.63 L/kg (logKow method) and 115 L/kg (MCI method) for the unaffected molecule.

Key value for chemical safety assessment

Koc at 20 °C:

Additional information

The organic carbon partition coefficient (Koc) for o-toluidine was predicted using the QSAR calculation of the Estimation Program Interface (EPI) Suite v 4.11. The Koc was estimated to be 47.63 L/kg (logKow method), and 115 L/kg (MCI method). The results relate to the unaffected molecule of the substance as any decomposition (e.g. hydrolysis) of the substance is not taken into account by the program.

The coefficient of distribution (Kd) between the sediment extracted from an aquifer situated in Germany and the water from the river Elbe was measured in columns. o-Toluidine together with other aromatic amines were pumped in the columns and then analysed with HPLC. The fraction of organic carbon contained in the sample of sediment was ca. 0.015 %. A Kd of 0.013 was observed for o-toluidine, therefore the Koc can be calculated to 87. This value is in the same range of the calculated values. During the ICCA initiative the content of organic carbon for the sediment used in this study was misinterpreted. Therefore, in the OECD SIDS (2004) the reported value for o-toluidine was undervalued for two orders of magnitude.

However, adsorption of o-toluidine in soil is influenced by ion-ion interactions. The mechanism responsible for adsorption of o-toluidine and other amines was investigated on montmorillonite. The adsorption in soil rich in Ca2+ ion was higher than in soil with K+. This reflects the formation of an amine water bridge with the exchangeable Ca2+ . Adsorption also depends on pH conditions. The maximum adsorption occurs when the pH is approximately equal to the pKa (4.44 - 4.45) of the protonation reaction.