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Biodegradation in water: screening tests

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Description of key information

As the parent compound hydrolyses in water within 10 minutes the assessment of the biodegradability relates to the isobutyric acid and its structurally similar substances butyric acid, pentanoic acid, propionic acid and 2-ethyl hexanoic acid. The hydrolysis product turned out to be readily biodegradable (according to OECD criteria) by the use of a weight-of-evidence approach.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

Parent compound isobutyryl chloride:

No experimental data are available for the parent compound. However, since the substance is known to hydrolyse very quickly to isobutyric acid and HCl, read-across is made to the supporting substances isobutyric acid (CAS 79 -31 -2), butyric acid (107 -92 -6), pentanoic acid (109 -52 -4), propionic acid (79 -09 -4) and 2 -ethyl hexanoic acid (149 -57 -5).

Isobutyric acid was tested in a Zahn-Wellens test similar to OECD TG 302 B (RL2) using activated sludge (source of the activated sludge was not specified). After 5 days, the test substance was degraded to 70% and after 10 days to >95% demonstrating the inherent biodegradability of the test substance (Hoechst AG, 1979).

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 hardly assignable. Nevertheless, the mentioned data was used for weight-of-evidence approach.

Butyric acid, pentanoic acid and propionic acid were evaluated within OECD SIDS dossiers and found to be readily biodegradable. This result is inter alia based on the findings by Dias & Alexander (1971) who tested the substances in Warburg respirometers following standard techniques which are similar to nowadays OECD TG 310 D. Butyric acid was also found to be easily biodegradable in a modified MITI (I) test which was similar to OECD TG 310C (Urano & Kato, 1986). The analogue substance 2 -ethylhexanoic acid, which is a more complex molecule than isobutyric acid, was determined to be readily biodegradable in a Modified OECD Screening Test following OECD 301E (Ekolab, 1998) .

The results above are supported by three QSAR models performed with isobutyric acid.

- EPI Suite v4.10: BIOWIN v4.10: Overall conclusion on ready biodegradability: readily biodegradable

- CATALOGIC v5.11.1: BOD 28 days MITI [OECD 301C] v3.04: ca. 100% after 28 d (domain similarity: 100%) - readily biodegradable

- CATALOGIC v5.11.1: BOD Kinetic [OECD 301F] beta v06.07: ca. 80% after 28 d (domain similarity: 100%) - readily biodegradable but failing

10 -day window

In a weight-of-evidence approach based on the results summmarised above, isobutyryl chloride and its hydrolysis product isobutyric acid are expected to be readily biodegradable.