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Biodegradation in water: screening tests

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Description of key information

Hydrolysis studies show that isobutyric anhydride added to water rapidly converts to isobutyric acid.  Thererfore, isobutyric acid data is being used by read across for all environmental fate and ecotox endpoints.   Isobutyric acid has been demonstrated to be inherently biodegradable in a valid degradation test similar to OECD TG 302 B (Hoechst AG, undated; KS) and to be readily biodegradable in biodegradation test similar to OECD TG 301 E (WoE).

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

The biodegradability of isobutyric acid was tested in four studies. In two of them, anaerobic conditions were applied.

 

study record

Method

Conditions

Reliability

Result

Hoechst AG, undated

Zahn-Wellens test;

similar to OECD TG 302 B

aerobic

(10 days)

2 (KS)

70% and >95% degradation at day 5 and day 10;

inherently biodegradable

Henkel KGaA, 1983

similar to OECD TG 301 E

aerobic

(19 days)

4 (WoE)

97% and 98% degradation at day 5 and day 14;

readily biodegradable

Chou, 1978

anaerobic degradation by acetate adapted domestic activated sludge (metha-nogenic culture, repeated additions of substrate)

anaerobic

4
(not suited for ready biodegradability)

after a 3 day lag period, complete anaerobic degradation of isobutyric acid with a degradation rate of 250 mg/(L*d)

Kameya, 1995

anaerobic biodegradation test using methanogenic bacteria as inoculum

anaerobic

4
(not suited for ready biodegradability)

complete anaerobic degradation of isobutyric acid within 7 days

 

 

The biodegradability of isobutyric acid was tested in a valid Zahn-Wellens test similar to OECD TG 302 B (RL2). After 5 days, the test substance was degraded to 70% and after10 days to >95% demonstrating the inherent biodegradability of the test substance (Hoechst AG, undated).

 

In a test for ready biodegradability similar to OECD TG 301 E, isobutyric acid was shown to be readily biodegradable (Henkel KGaA, 1983). Due to insufficient documentation, the reliability for this test is not assignable. Nevertheless, the results are estimated to represent the real degradation potential of isobutyric acid. Thus, the results of this test are taken as weight of evidence.

  

Based on the results of the key study (Hoechst AG, 1979) in combination with the test results for ready biodegradability (Henkel KGaA, 1983) as weight of evidence, isobutyric acid is assessed to be readily biodegradable. This is in accordance with results for the closely related compound butyric acid, which has been shown to be readily biodegradable.

 

In addition to the results of aerobic biodegradation, isobutyric acid was demonstrated to undergo complete biodegradation under anaerobic conditions as well.

 

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