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Environmental fate & pathways

Biodegradation in soil

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Description of key information

Little or no biodegradation was observed in aerobic and anaerobic soils; the main pathway for soil disappearance of TDA was the formation of covalent bonds with organic matter.

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Additional information

Available Soil Biodegradation Data

Experimental results are available form studies quoted by reliability (2). Those studies are well-documented although no guideline was followed. Using radiolabelled TDA, the biodegradation of both isomers were followed in aerobic or anaerobic conditions.

Degradation in Aerobic Conditions

Microbial degradation of both 2,4-TDA and 2,6-TDA using radiolabelled materials was investigated by Cowen et al (1996). Biodegradation of both isomers started immediately after mixing with the soil. Based on 14CO2 measurements, the calculated percentage of biodegradation are:

2,4 -TDA: 1.9% after 3d, 4.0% after 7d, 7.9% after 14d, 10.8% after 28d, 14.8% after 56d

2,6 -TDA: 2.7% after 3d, 6.2% after 7d, 11.1% after 14d, 14.2% after 28d, 18.1 % after 56d

During the latter period, the degradation rates indicate that biodegradation slowed down after TDA had formed covalent bounds to humic substances.

Under the conditions of the test, degradation products were not identified and it was not possible to calculate a half-life (DT50) for TDA in soil. In conclusion, TDA is covalently bound to organic matter and is expected to degrade almost similar to the humic acids themselves.

Degradation in Anaerobic Conditions

Microbial degradation of both 2,4-TDA and 2,6-TDA under anaerobic conditions were investigated by Cowen et al (1996) and by West and Davis (2002).

Under anaerobic conditions, no 14CH4 or 14CO2 was recovered after 73 days of incubation (Cowen et al, 1996).

West and Davis (2002) reported experimental results of the biodegratation of 2,4- and 2,6-TDA in anaerobic soils under a wide range of redox conditions. Very limited biodegradation of 14C-TDA was observed in the sand soil under anaerobic, denitrifying conditions. The maximum yield of 14CO2 was detected after 1 year and was equivalent to 1.3% of the applied 14C-TDA.

Conclusion

-Little or no biodegradation was observed in aerobic and anaerobic soils,

-Consequently no DT50 was calculated for both 2,4 -TDA and 2,6 -TDA,

-Due to bonding to organic matter, biodegradation of TDA is expected to occur in combinaiton with humic acids.