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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Under screening test conditions and when tested at low concentration, TDA is not readily biodegradable.

Key value for chemical safety assessment

Additional information

Available data on biodegradation in water

Several experimental results on biodegradation in water are available for: TDA 80/20, 2,4 -TDA and 2,6 -TDA. Those experimental results were obtained in studies performed according to OECD guideline screening tests (ready biodegradability, inherent biodegradability) or other method. Unless the use of biological or wastewater inoculum is always reported, the adaptation of this inoculum is often lacking.

Inherent biodegradation testing

Three studies of reliability (2) are described.

In a MITI(II) test where municipal sludge were not adapted, 4% of biodegradation of TDA 80/20 (Cinitial=30 mg/L) after 28 d was observed. In the two Zahn-Wellens tests where industrial sludge were not adapted, 89% of biodegradation of 2,6 -TDA (Cinitial=104 mg/L) after 28 d and 100% of biodegradation of 2,4 -TDA (Cinitial=160 mg/L) after 6 d were observed.

Ready biodegradation testing - (initial concentration ranging 20 - 200 mg/L)

Four bibliographic references with reliability (2) reported experimental results with initial substance concentration in the range of 20 - 200 mg/L. In those ready biodegradation tests, the observed degradation rates are below the pass level. Therefore, both 2,4 -TDA and 2,6 -TDA are considered not readily biodegradable in water under the conditions of the test.

Non-guideline testing

Two studies using an electrolytic respirometer of reliability (2) are described. In those two studies, the degradation as well as the inhibition of nitrification has been investigated. The sludge was adapted to aromatic amines. The initial concentrations of the test material were 50 and 100 mg/L.

Under the test conditions 2,4 -TDA exhibits 100% of biodegradation at both concentration, the nitrification being partially inhibited at 50 mg/L and completely inhibited at 100 mg/L.

Under the test conditions 2,6 -TDA exhibits a poorly biodegradation (23 and 12% at initial concentration 50 and 100 mg/L respectively) and inhibits completely the nitrification at both concentration.

Ready biodegradation testing - (low initial concentration - 0.5 mg/L)

As both 2,4 -TDA and 2,6 -TDA have been shown to have an inhibitory effect on the microorganisms responsible for the biodegradation, a ready biodegradation test has been performed at low concentration (500 µg/L). This procedure is in accordance with the recommendations of Annex II of OECD guideline 301 on the testing of substances suspected to be toxic to the inoculum.

Under the test conditions 2,4 -TDA was biodegraded at 4% and 7% after 28 and 63 d of exposure, respectively.

Under the test conditions 2,6 -TDA was biodegraded at 12% and 24% after 28 and 63 d of exposure, respectively.

Conclusion

-The origin and the adaptation of microorganisms may have a significant influence on the results of biodegradation screening tests,

-TDA could be degraded by micro-organisms adapted to aromatic amines,

-The low level of biodegradation in screening test is explained by an inhibition effect on the microorganisms responsible for biodegradation,

-TDA is not readily biodegradable under test conditions.