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Environmental fate & pathways

Biodegradation in soil

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4,4'-MDA is considered to be persistent in soil due to covalent binding to soils organic matter.

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The microbial degradation of MDA in soil was investigated under aerobic and anaerobic conditions using carbon-14C labeled MDA. The results show, that biodegradation started immediately after mixing with the aerobic soil. With the binding of amine to soil the degradation rate decreased later. The test indicates biodegradation of 2.9% after 3 days,. 9.1% after 7 days and 11.6% after 56 days. During the latter period of the incubation some of the 14CO2 was lost, so results for 210 and 365 days must be rejected. The degradation rates after 7 and 56 days indicated that biodegradation is disrupted after MDA had formed covalent bounds with humic substances. From the remaining results it is not possible to calculate a half-life, but it can be assumed that MDA covalently bound to organic matter is degraded almost similar to the humic acids themselves.

Cowen et al (1996) showed that under anaerobic methanogenic conditions no 14CH4 or 14CO2 was recovered after 73 days of incubation. A further study (West et al 2002) was carried out over one year on the degradation of MDA in anaerobic soils under a range of redox conditions. Results indicated that MDA was slowly mineralized to carbon dioxide under denitrifying conditions.

Overall, covalent binding of MDA to natural organic materials present in soil is the dominant process affecting the fate of this substance in soils (see also IUCLID chapter 5.4.4).