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Biodegradation in soil

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"Süß et al. (1978) examined in a laboratory experiment with four soil types the mineralisation of 14C-labelled aniline in a concentration of 1 mg/kg over 10 weeks. In the different soils between 16.2 and 26 .3% of the aniline was mineralised to 14CO2 after 10 weeks. The degradation maximum was already reached after 1 week. After 2 weeks 50% of the totally formed 14CO2 was found. Then the weekly degradation rates remained constant at ca. 1% until the end of the test. After extraction with water between 57.3 and 67.4% of the 14C activity could be detected in the four soils. Biodegradation in soil is impeded by the irreversible bonding of aniline to humic acids. Once those complexes are formed aniline is not accessible to degradation.

The study by Süß et al. (1978) can be used to derive a biodegradation half-life for the reaction product of aniline with humic acids. In this study it was shown that at beginning of the test aniline is degraded relatively rapidly. At this time free aniline is available in the soil. During the test aniline becomes covalently bound to humic acids and the degradation rate decreases significantly.

From the degradation rate of about 1% per week found after 2 weeks a half-life of 350 days can be extrapolated approximately. For the risk assessment it has to be considered that a certain degree of aniline in soil is accessible to biodegradation before irreversible binding occurs. It is therefore assumed that 20% of the aniline in soil is rapidly mineralised and the other 80% are covalently bound to the organic fraction. For this bound aniline the above derived half-life of 350 days is used."

Reference:

ECB (2004). European Union Risk Assessment Report, Aniline, CAS No: 62 -53 - 3, EINECS No: 200 -539 -3, 1st Priority List, Volume 50.