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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Although many screening tests were referenced in the EU Risk Assessment Report, the test according to the protocol of the Dutch Bureau of Standards has been selected. It is considered sufficient and more extensive than the conventional screening methods.This two-phase closed bottle test (oxygen uptake) displayed 21% oxidation after 3 weeks and after repetitive additions of AHTN, an oxygen consumption of 14% was found.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable, not fulfilling specific criteria

Additional information

The EU risk assessment report reported absence of mineralisation under the conditions of the standard tests for ready biodegradation. Mineralisation of AHTN remained low, even though bioavailability was enhanced by use of solvents, dispersants or emulsifiers. Despite all these measures, it is still possible that AHTN does not show degradation in these screening tests due to its low water-solubility or that the inoculum was not fully adapted to AHTN. In order to exclude the latter cause, a test dealing with continuous load of AHTN was selected as the key study. The test demonstrated that AHTN is not toxic to the activated sludge up to a concentration of 22 mg/l. The probability of adaptation was increased by pre-exposure of the inoculums to the test substance or by repetitive additions. Some biodegradation was observed, but it remained poor.

The EU Risk Assessment Report adopted the key value "inherent biodegradable, not fulfilling specific criteria",that was based on all the available information about the environmental degradation of AHTN.