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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:
19 September - 25 October 2002
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: The study was carried out in accordance with OECD guideline no. 301F and Good Laboratory Practice.
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Version / remarks:
(1992)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
Fresh activated sludge from a biological waste water treatment plant treating predominantly domestic sewage (City of Geneva, Peney-Dessous) was used.
The sludge was collected in the morning, washed three times in the mineral medium (by centrifuging at 1000 g for 10 minutes, discarding the supernatant and resuspending in mineral medium) and kept aerobic until being used on the same day.
Duration of test (contact time):
35 d
Initial conc.:
100 mg/L
Based on:
test mat.
Initial conc.:
292 mg/L
Based on:
ThOD/L
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: Mineral medium according to OECD301F
- Test temperature: 22 °C
- pH: At the start of the test the pH was 7.3 in all flasks. At the end of the test, the pH varied between 7.2 and 7.6.
- pH adjusted: no
- Suspended solids concentration: 30 mg/L

TEST SYSTEM
- Culturing apparatus: 250 mL flasks
- Number of culture flasks/treatment: 2
- Measuring equipment: Respirometer SAPROMAT D 12 (J.M. Voith GmbH, D-7920 Heidenheim, Germany)
- Test performed in closed vessels: Yes
- Details of trap for CO2: stopper with soda lime pellets (this trap was only for adsorbing, it was not analysed)

CONTROL AND BLANK SYSTEM
- Inoculum blank: 2 flasks
- Abiotic sterile control: No
- Toxicity control: 2 flasks

PREPARATION OF THE FLASKS
Test substance samples (25 mg, corresponding to 100 mg/L in a 250 mL flask) were weighed in small aluminium boats and added directly to the test flasks of the SAPROMAT, whereas reference substance samples (sodium benzoate) were added as 1.0 mL of a 25 mg/mL solution in mineral medium.
All flasks were filled with 250 mL of mineral medium. Samples of test or reference substance, or both, were added. Then, a volume of suspended sludge corresponding to 7.5 mg dry weight was added. The pH in each flask was measured at the start and the end of the test. About 2 g of soda lime was placed in an attachment of the stopper, the flasks were closed and placed in the water bath of the SAPROMAT. After temperature and pressure equilibration, the oxygen meters of the instrument were set to zero (time zero of the experiment).

Every day the oxygen consumption of each flask is recorded and correct temperature and stirring were checked
Reference substance:
benzoic acid, sodium salt
Parameter:
% degradation (O2 consumption)
Value:
1
Sampling time:
7 d
Parameter:
% degradation (O2 consumption)
Value:
2
Sampling time:
14 d
Parameter:
% degradation (O2 consumption)
Value:
12
Sampling time:
21 d
Parameter:
% degradation (O2 consumption)
Value:
60
Sampling time:
28 d
Parameter:
% degradation (O2 consumption)
Value:
66
Sampling time:
31 d
Parameter:
% degradation (O2 consumption)
Value:
76
Sampling time:
35 d
Results with reference substance:
Degradation of sodium benzoate was 79% after 7 days and 88% after 14 days: the activity of the inoculum is thus verified and the test is considered as valid.

The test substance underwent 60% biodegradation within 28 days under the test conditions.

Biodegradation started on day 21 days (when the biodegradation exceeded 10%)

after a lag phase, attaining 60% by Day 28 and reached 66% after 31 days and 76% by Day 35 of the incubation. The 10d window criterium was fulfilled.

Thus the substance should be regarded as READILY biodegradable according to this test.

The curves obtained with the reference substance alone and with the test substance + reference substance show no toxic effect of the substance on the microorganisms at the test concentration.

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The substance degraded to 60% within 28 days, and the 10d-window criterion was fulfilled within the initial 28 days of the incubation.
Executive summary:

The ready biodegradability of the test substance was investigated according to OECD guideline no. 301F and Good Laboratory Practice.

The test substance underwent 60% biodegradation by 28 days under the test conditions.

Biodegradation started on day 21 days (when the biodegradation exceeded 10%) following a lag phase, attaining 60% by Day 28 and reaching 66% after 31 days. The 10d window criterium was fulfilled.

A maximal biodegradation of 76% was achieved at the end of the test, after 35 days.

The curves obtained with the reference substance alone and with the test substance + reference substance show no toxic effect of the substance on the microorganisms at the test concentration.

The validity criteria were met and the study is regarded as reliable without restrictions.

Description of key information

The chemical substance has been demonstrated to be READILY Biodegradable and fulfiling the 10-day window criterion under GLP conditions in an OECD 301F biodegradation screening study performed under conservative test conditions.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

The ready biodegradability of the test substance was investigated according to OECD guideline no. 301F and Good Laboratory Practice.

The test substance underwent 60% biodegradation after 28 days under the test conditions.

Biodegradation started on day 21 days after a long lag phase and reached 66% after 31 days. The 10d window criterium was fulfilled.

A maximal biodegradation of 76% was achieved at the end of the test, after 35 days.

The curves obtained with the reference substance alone and with the test substance + reference substance show no toxic effect of the substance on the microorganisms at the test concentration.

The validity criteria were met and the study is regarded as reliable without restrictions.