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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Binding to soild soil phase and/or organic matter is possible. 

Key value for chemical safety assessment

Koc at 20 °C:
7 041

Additional information

Experiments with radiolabelled 4,4'-MDA revealed that the substance forms covalent bonds with the organic fraction in soils. Initial sorption of MDA in silt loam was nearly completed by 4 hours under aerobic conditions. Under anaerobic conditions, sorption appeared to still be proceeding at 7 days. The KOC values were determined to 4,848 l.kg-1 after 8 hours and 7,041 l.kg-1 after 7 days for aerobic conditions. The values for anaerobic conditions are 3,828 l.kg-1 and 10,729 l.kg-1 for 8 h and 7 d, respectively. Furthermore, surface adsorption or ion exchange processes were found with minerals without organic content. It should be kept in mind that the term "KOC" generally describes the distribution of a substance between the pore water and the organic matter when the substance is physically bound; if chemisorption occurs the use of this term is not quite correct.

MDA has been shown to irreversibly (i.e. covalently) bind with soils under normal aerobic condition. This binding is suppressed under low redox conditions (i.e. anaerobic). This behaviour is consistent with the literature where aromatic amino groups are known to chemically react with aldehyde and keto groups as well as double bonds of quinoid systems typically found in humic substances present in soils. Under low redox conditions such groups / quinoid systems would not be available for reaction with the amino moiety.

For further assessment, the highest Koc value measured under aerobic conditions was applied.