Registration Dossier

Environmental fate & pathways

Biodegradation in water: screening tests

Currently viewing:

Administrative data

Link to relevant study record(s)

Description of key information

 The test substance is considered to be inherently biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable

Additional information

A closed bottle test was conducted to assess the ready biodegradability of the read-across substance bisamide (UVCB) according to slightly modified OECD, EU and ISO Test Guidelines in compliance with GLP. A solution of the test substance at 1 mg/L was inoculated with undiluted non-adapted river water activated sludge and placed in closed bottles in the dark for 28 d. Because of the low solubility of the test substance, the test solution was prepared using an emulsion of silicone oil and water (1:1) with 0.5 g/L of Tween 85. The degradation of the test substance was assessed by the determination of the dissolved oxygen concentration (DOC) on Days 7, 14, 21 and 28. Control solutions containing the reference substance, sodium acetate (6.7 mg/L), together with abiotic control and inhibition control were used for validation purposes. The test substance was biodegraded 22% at Day 28 and 37% at Day 60 (during the prolonged closed bottle test). Although the test substance was not readily biodegradable, the level of degradation reached on the last day demonstrates that it should be classified as inherently biodegradable (i.e. > 20% biodegradation). The test was valid as shown by an endogenous respiration of 1.2 mg/L and by the total mineralization of the reference compound, sodium acetate. Sodium acetate was degraded 83% of its theoretical oxygen demand after 14 d. Finally, the most important criterion was met by oxygen concentrations > 0.5 mg/L in all bottles during the test period. Under the study conditions, the test substance was considered to be inherently biodegradable.

Furthermore, a study conducted to increase the bioavailability indicated that the poor water solubility leading to slow desorption and dissolution rates of the test substance at high concentrations was responsible for affecting the biodegradation kinetics. The biodegradation curves of substances with limited bioavailability were linear instead of the anticipated S-shape. The partial degradation (i.e. 37%) was therefore caused by limited bioavailability. However, as the test substance was expected to be present in the environment at concentrations in the range of μg/L or lower, complete degradation can be expected under these conditions within a shorter time period (van Ginkel, 2013).

Further testing (with the read-across substance bisamide (UVCB)) is planned to better characterise the biodegradation potential of this highly insoluble substance in water.