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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

According to a screening test under TG OECD 301D and GLP, the test substance is readily biodegradable (63% at Day 28; 10 day-window criterion waived for a multiconstituant).

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable
Type of water:

Additional information

Three screening tests assessing the biodegradability of the test substance are available.

In the first one, the degradation of the substance was determined to be 63 % after 28 days in the Closed Bottle test.  It is noted that the registered substance is a multiconstituent consisting of three main constituents and the degradation of different constituents may differ.  Since almost complete degradation of the entire substance was observed, and considering that the constituents are structurally relatively similar (they mainly differ in the length of the linear alkyl chains), it can be assumed that the three constituents have degraded either almost completely or at least to a significant extent. Therefore the substance being a complex substance, the 10-day window criterion is waived. The pass level being applied at Day 28, the substance meets the ready biodegradable criterion (>60% at day 28) according to OECD guideline (301D).


In the second test almost 60% (i.e. 52) biodegradation was reached after 28 days in the Closed Bottle test. Furthermore, the biodegradation at day 42 was 61% which indicates total mineralization, therefore the registered substance should not be classified as persistent.


The lack of biodegradation is assumed to be related to lack of bioavailability due to the very low solubility of the substance in water. In the first and second screening tests, experimental conditions were designed to improve the bioavailability of the substance using surfactants and/or silicon oil.


In the third test, the biodegradation reached 14% at Day 28 and 34% at Day 112 with direct addition. The low degradation observed in the tests may be due to low bioavailability of the substances to the microorganisms. Given that ready biodegradability tests may sometimes fail because of the stringent test conditions, positive test results should generally supersede negative test results.