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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:
22 Nov - 27 Dec 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Version / remarks:
17th Jul 1992
Deviations:
no
GLP compliance:
yes (incl. certificate)
Remarks:
National GLP Compliance Monitoring Authority, Gov. of India (22 Jul 2016)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Secondary effluent of JRF Sewage Treatment Plant treating predominantly domestic sewage
- Storage conditions: aerobic (aeration) at 22 ± 2 °C
- Storage length: 7 d
- Pretreatment: The secondary effluent was filtered through Whatman No 1 filter paper.
- Concentration of sludge: 2.01 x 10E+04 CFU/mL (bacteria), 2.00 x 10E+02 CFU/mL (fungus)
- Initial cell/biomass concentration: 1 mL/L
Duration of test (contact time):
28 d
Initial conc.:
5.02 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: Mineral medium according to guideline
- Test temperature: 22 ± 2 °C
- Aeration of dilution water: The mineral medium was strongly aerated for 20 min using aerator and allowed to stand for 20 h at 22 ± 2 °C in a horizontal laminar flow under aseptic conditions.
- Continuous darkness: Yes
- Other: For each test, only one batch of high purity water (Type I Milli-Q) and mineral medium was used.

TEST SYSTEM
- Culturing apparatus: BOD incubator (KB-12, LCI-290)
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: Aeration of mineral medium (20 min) and secondary effluent (7 d)
- Measuring equipment: Dissolved Oxygen / pH Meter (HQ-40d)
- Test performed in open system: No (Closed Bottle Test)
- Other: 10 test bottles each were prepared for the test suspension, inoculum blanc and the procedure control. 6 bottles were prepared for the toxicity control. The bottles of the respective series will be withdrawn in replicate for dissolved oxygen analysis.

SAMPLING
- Sampling frequency: After 0, 7, 14, 21, and 28 d
- Sampling method: The dissolved oxygen of each sample bottle was measured with a Dissolved Oxygen Meter.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes, 2 replicates
- Procedure control: Yes, 2 replicates
- Toxicity control: Yes, 2 replicates
Reference substance:
other: Potassium hydrogen phtalate
Remarks:
C8H5KO4
Parameter:
% degradation (O2 consumption)
Value:
5.99
Sampling time:
28 d
Results with reference substance:
The percent degradation of the reference substance (potassium hydrogen phthalate) on Day 7, 14, 21, and 28 was 80.51, 83.23, 85.11, and 85.79, respectively.

VALIDITY CRITERIA

The validity criteria of the guideline are summarized below (Table 1).

Table 1: Validity criteria for OECD 301.

Criterion from the guideline

Outcome

Validity criterion fulfilled

Difference of extremes of replicate values of the removal of the test chemical at the plateau, at the end of the test or at the end of the 10-d window, as appropriate, is less than 20%.

Mean degradation of the test item did not reach 20% within 28 d.

Criterion cannot be assessed.

-

Percentage degradation of the reference compound has reached the pass levels (60%) by day 14.

83.23% on Day 14

Yes

Oxygen depletion in the inoculum blank should not exceed 1.5 mg dissolved oxygen/L after 28 days.

Oxygen depletion in the inoculum blank was 1.31 mg dissolved oxygen/L after 28 d.

Yes

The residual concentration of oxygen in the test bottles should not fall below 0.5 mg/L at any time.

Residual concentrations were 6.42 mg/L.

Yes

Toxicity control: toxic, if % degradation < 25% within 14 d.

The percent degradation by the toxicity control was 22.58%.

No

 

 BIOLOGICAL RESULTS

The results are summarized in Table 2.

Table 2. Results - percent degradation

Treatment

% degradation

(based on ThOD)

7

14

21

28

Procedure Control

80.51

83.23

85.11

85.79

Test Solution

0.92

1.30

1.45

5.99

Toxicity Control

21.43

22.58

-

-

 

Interpretation of results:
under test conditions no biodegradation observed
Remarks:
For further details on validity criteria please refer to “Any other information on results incl. tables”.

Description of key information

OECD guideline, GLP-complaint study. The biodegradability of the substance was assessed using the Closed Bottle Test. 5.99% biodegradation occurred within the 28 day test period.

The test substance is not rapidly biodegradable under the conditions of the test.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed
Type of water:
freshwater

Additional information