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Environmental fate & pathways

Adsorption / desorption

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Description of key information

In the Cowen et al (1996) study Koc values were determined for 2,4-TDA. Under aerobic conditions Koc values were 1339 and 9768 after 8h and 7d respectively. Under anaerobic conditions the determined values were 884 and 4454 after 8h and 7d respectively. Significantly the experiments with radiolabelled 2,4- and 2,6 -TDA revealed that the substances form covalent bonds with the organic fraction in soils and therefore the term Koc is not quite correct.

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Additional information

Initial sorption of both isomers in silt loam soil was rapid under both aerobic and anaerobic conditions. Further, sorption appeared to be slowed and still proceeding after 7 days.

2,4-TDA. Under aerobic conditions, Koc values were determined to be 1339 after 8 hours and 9763 after 7 days. Under anaerobic conditions Koc values were found to be 884 and 4454 after 8 hours and 7 days 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. TDA 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.