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Environmental fate & pathways

Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: inherent biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
Oktober 1992 - January 1993
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reference:
Composition 0
Qualifier:
according to
Guideline:
OECD Guideline 302 B (Inherent biodegradability: Zahn-Wellens/EMPA Test)
Deviations:
no
Qualifier:
according to
Guideline:
ISO 9888 Water quality - Evaluation of ultimate aerobic biodegradability of organic compounds in aqueous medium - Static test (Zahn-Wellens method)
Version / remarks:
1991
Deviations:
no
Qualifier:
according to
Guideline:
other: 88/302/EWG (Teil C)
Version / remarks:
EG Amtsblatt L 133, 30.5.1988
Deviations:
no
GLP compliance:
yes
Test material information:
Composition 1
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, industrial, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: sewage treatment plant of Höchst and Kelsterbach, ratio 1:1
- Pretreatment: no
- Concentration of sludge: 9.4 g dry substance /L
- Initial cell concentration: 70 mL sludge
Duration of test (contact time):
> 0 - < 28 d
Initial conc.:
192.6 mg/L
Based on:
DOC
Parameter followed for biodegradation estimation:
DOC removal
Details on study design:
TEST CONDITIONS
- Composition of medium: as discribed in EEC-Directive, 1.6.1.4
- Additional substrate: no
- Test temperature: 21 + /- 2 °C
- pH: 7.4
- pH adjusted: yes, with NaOH
- Aeration: yes
- Suspended solids concentration: 70 mL sludge suspension


TEST SYSTEM
- Culturing apparatus: 3L beaker
- Number of culture flasks/concentration: 3
- Method used to create aerobic conditions: aeration
- Measuring equipment: pH-Meter Portamess, OXI-Meter 196

SAMPLING
- Sampling frequency: after 0, 1, 4, 7, 11, 15, 19, 27 and 28 days
- Sampling method: 15 mL for detection of DOC with
- Sample storage before analysis: no
- Pretreatment: Filtration with folded filters


CONTROL AND BLANK SYSTEM
- Inoculum blank: Inoculum and Reaction medium without test substance
- Toxicity control: Inoculum and Reaction medium with Diethylenglykol (DOC 220.5 mg/L)

Reference substance:
diethylene glycol
Preliminary study:
no preliminary study
Key result
Parameter:
% degradation (DOC removal)
Value:
9
Sampling time:
28 d
Details on results:
The degradation of the test item had a maximum of 13 % on day 15 and day 19, with an end value of 9% after 28 days.
Validity criteria fulfilled:
yes
Interpretation of results:
not inherently biodegradable
Conclusions:
The biodegradation of the test substance was 9% after 28 days. Therefore, the test substance is not inherently biodegradable in the Zahn-Wellens test.
Executive summary:

In order to assess the biotic degradation, a inherent biodegradability test was performed which allows the biodegradability to be measured in an aerobic medium. The inherent biodegradability was determined in the Zahn-Wellens test according to OECD 302B and ISO 9888, and in compliance with the OECD principles of Good Laboratory Practice. In the biodegradability tests, sludge was inoculated into a chemically defined liquid medium containing the test substance as sole carbon and energy source. The test compound is exposed to the inoculum, consisting of relatively low numbers of microorganisms from an activated sludge plant, under aerobic conditions for a period of at least 28 days. The biodegradation of the test substance was 9% after 28 days. Hence, the test substance is not inherently biodegradable in the Zahn-Wellens test (28 days) and should therefore not be classified as readily biodegradable. The reference substance, Diethylenglykol, was degraded more than 75% after 14 days.

Description of key information

The biodegradation of the test substance was 9% after 28 days. Therefore, the test substance is not inherently biodegradable in the Zahn-Wellens test.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

In order to assess the biotic degradation, an inherent biodegradability test was performed which allows the biodegradability to be measured in an aerobic medium. The inherent biodegradability was determined in the Zahn-Wellens test according to OECD 302B and ISO 9888, and in compliance with the OECD principles of Good Laboratory Practice. In the biodegradability tests, sludge was inoculated into a chemically defined liquid medium containing the test substance as sole carbon and energy source. The test compound is exposed to the inoculum, consisting of relatively low numbers of microorganisms from an activated sludge plant, under aerobic conditions for a period of at least 28 days. The biodegradation of the test substance was 9% after 28 days. Hence, the test substance is not inherently biodegradable in the Zahn-Wellens test (28 days) and should therefore not be classified as readily biodegradable. The reference substance, Diethylenglykol, was degraded more than 75% after 14 days.

Two additional studies are available with very limited documentation, but supporting the above mentioned result (biodegradation < 10 % in 28 days).