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Environmental fate & pathways

Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Deviations:
no
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
not applicable
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
TEST ORGANISM:
- mixed population of aquatic microorganisms, origin from an aeration tank of a waste water plant treating predominantly domestic sewage (Wupper area water authority, WWTP Odenthal, Germany)
- concentration: 30 mg/L suspendid solids

PRETREATMENT OF THE INOCULUM:
- Before use, the inoculum was stored for two days at room temperature under continuous stirring with aeration
- The sludge was washed twice by adding mineral medium and centrifuging for 10 min at 2000 rpm and 20 °C and decanting off the supernatant
- An aliquot of the wet sludge was dried in order to determine the wet weight/dry weight ratio of the sludge and to prepare a stock suspension (activated sludge) of 3 g dw/L
- The calculated amount of sludge, needed to achieve 300 mL of this stock suspension, was dissolved in mineral medium and then filled up to a defined end volume
Duration of test (contact time):
28 d
Initial conc.:
100 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
PRETREATMENT OF THE TEST ITEM/REFERENCE SUBSTANCE:
- 25 mg of the test item were weighed out and added to the test flasks, filled with 200 mL of mineral medium
- the volume was made up to 250 mL with mineral medium containing the inoculum to give a test concentration of 100 mg reference compound /L

PRETREATMENT OF THE TOXICITY CONTROL:
- 25 mg of the test item and 25 mg of the reference compound were weighed out and added to the test flasks, filled with 200 mL of mineral medium
- Afterwards the flask volume was made up to 250 mL with mineral medium containing the inoculum to give a test concentration of 100 mg test item and reference compound/L

EXPOSURE CONDITION:
- Test volume: 250 ml
- Incubation temperature: 22 +/- 1 °C
- Performed in the dark
- Mixing: 1 magnetic stirrer per test vessel
- Test apparatus: OxiTopControl System (WTW)
Reference substance:
benzoic acid, sodium salt
Remarks:
Acros Organics (Purity: 99.9 %; Batch number: A0357641)
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
7 d
Parameter:
% degradation (O2 consumption)
Value:
18
Sampling time:
14 d
Parameter:
% degradation (O2 consumption)
Value:
53
Sampling time:
21 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
64
Sampling time:
28 d
Parameter:
% degradation (O2 consumption)
Value:
1
Sampling time:
9 d
Results with reference substance:
The reference compound showed 86% degradation after 14 days and the theoretical oxygen demand was 1.665 mg O2/mg

Valdity criteria:

- The reference compound has reached the level of higher than 60 % for ready biodegradability within 14 days

- The toxicity control exhibited degradation rates > 25 % within 14 days

- At the end of the test, at the plateau, or the end of the 10-d window, biodegradation in parallels with test item did not differ by more than 20 percentage points

- The oxygen uptake of the inoculum blank was < 60 mg/L

- In cases where the degradation was < 60 %, the pH values were in between 6.0 and 8.5 at the end of the test

Validity criteria fulfilled:
yes
Remarks:
(see "Any other information on results incl. tables")
Interpretation of results:
readily biodegradable, but failing 10-day window
Conclusions:
In the study on ready biodegradability a degradation rate of 64 % was determined within 28 days for the substance. Nevertheless, 10 days after the start of degradation at day 9 only 43 % of the test substance were degraded at day 19. Therefore the substance is readily biodegradable, but failing the 10-day window.
Executive summary:

The study was conducted in accordance with the Council Directive 92/69/EEC Method C.4-D "Manometrie Respirometry Test". This test method is in assential parts identical with OECD Guideline 301 F. A solution of the substance in a mineral medium was inoculated and incubated for 28 d under aerobic conditions. During this period the ready biodegradability was determined. The substance showed 64 % degradation after 28 days. 10 days after the start of degradation at day 9 43 % degradation were observed at day 19. The reference compound showed 86% degradation after 14 days.

Description of key information

In the study on ready biodegradability a degradation rate of 64 % was determined within 28 days for the substance. After 10 days only 3 % degradation was observed.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable but failing 10-day window

Additional information

The substance showed 64 % biodegradation after 28 days, but only 43 % at day 19, 10 days after the start of the degradation process at day 9. Therefore the substance is readily biodegradable, but failing the 10-day window.