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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:
28 February 2011 to 31 March 2011
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP compliant. Guideline study. Acceptable without restriction.
Qualifier:
according to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
Not applicable
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge : Aerobic activated sludge from a wastewater treatment plant treating predominantly domestic wastewater was used.
- Preparation of inoculum for exposure: The sludge was washed twice with tap water by centrifugation and the supernatant liquid phase was decanted. A homogenized aliquot of the final sludge suspension was weighed, thereafter dried and the ratio of wet to dry weight was calculated. Based on the ratio of wet to dry weight calculated amounts of wet sludge were suspended in test water (see below) to obtain a concentration equivalent to 4 g (±10%) dry material per litre. During the holding period of three days prior to use, the sludge was aerated at room temperature. Prior to use, the sludge was first thoroughly mixed and then diluted with test water to a concentration of 1 g per litre (dry weight basis). Based on the determined dry weight of this diluted activated sludge, defined amounts were added to test water to obtain a final concentration of 30 mg dry material per litre.
- Pretreatment: None reported
- Concentration of sludge: 30 g dry material/L

Duration of test (contact time):
28 d
Initial conc.:
>= 100 - <= 101 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: Purified water with dissolved analytical grade salts
- Test temperature: 22 °C
- pH: start: 7.3-7.4, end: 7.5 - 7.9
- pH adjusted: yes
- Aeration of dilution water: Test media was constantly stirred
- Suspended solids concentration: 30 mg dry material per litre.
- Continuous darkness: yes
- Other: Samples incubated in darkness under continuous stirring

TEST SYSTEM
- Culturing apparatus: 500ml reaction air tight flask containing 250 ml of test medium.
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: Test media was constantly stirred, consumed oxygen replenished daily by electrolytically generated oxygen from a copper sulphate solution.
- Measuring equipment: Oxygen consumption measured by absorbing generated CO2 in soda lime and detecting pressure drop by electrode type manometer. Oxygen consumption recorded manually at least each working day.
- Details of trap for CO2 and volatile organics if used: CO2 trapped in soda lime

SAMPLING
- Sampling frequency: All test solutions sampled at least each working day for 28 days
- Sampling method: CO2 absorbed on soda lime and pressure drop in airtight system measured with electrode type manometer. The consumed oxygen replaced by electrolytically generated oxygen from a copper sulphate solution.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes.
- Abiotic sterile control: No
- Toxicity control: Yes (test item plus sodium benzoate reference item)
- Procedure control: Yes (reference item, sodium benzoate)

% biodegradation = [BOD (mg O2/mg chemical)/ThOD (mg O2/Mg chemical)] x 100%

BOD (Biochemical oxygen demand of the test or reference item) = [(mg O2uptake/L by test/or reference item) - (mgO2 uptake/L by inoculum control)]/mg test and/or reference item per litre


Reference substance:
benzoic acid, sodium salt
Preliminary study:
None reported
Test performance:
In the procedure controls, the reference item was degraded by an average of 88% by Exposure Day 14, thus confirming suitability of the activated sludge.
Parameter:
% degradation (O2 consumption)
Value:
2
Sampling time:
28 d
Remarks on result:
other: Based on a theoretical oxygen demand of 1.67 mg O2/mg test item. Percentage biodegradation corrected for the mean oxygen uptake of the inoculum controls.
Details on results:
Results are given as the average of the degradation in the two replicates.
The biochemical oxygen demand (BOD) of the test item in the test media was in the normal range found for the inoculum controls throughout the study period of 28 days. Consequently, the test item was not readily biodegradable under the test conditions within 28 days.

In the toxicity control the course of biodegradation over the 28-day exposure period was similar to the two procedure controls, containing only the reference item. Within 14 days of exposure, biodegradation amounted to 42%.
Thus, according to the test guidelines, the test item had no inhibitory effect on activated sludge microorganisms at the tested concentration of 100 mg/L because biodegradation in the toxicity control was >25% within 14 days.
Results with reference substance:
In the procedure controls, the reference item was degraded by an average of 88% by Exposure Day 14, thus confirming suitability of the activated sludge. At the end of the test (Day 28), the reference item was degraded by an average of 96%.

Biodegradation in the Test Flask
  Percentage Biodegradation1 
  Test Item  Procedure control  Toxicity control
Time Replicate No. Replicate No. Replicate No.
Days 1 2 1 2 1
0 0 0 0 0 0
1 0 0 13 13 2
2 1 0 56 56 29
3 -- -- -- --  
4 1 0 73 73 37
5 1 0 78 78 40
6 1 0 81 81 41
7 4 0 81 81 41
8 4 0 82 82 41
9 -- -- -- -- --
10 -- -- -- -- --
11 4 0 85 86 42
12 4 0 86 87 42
13 4 0 87 88 42
14 4 0 87 89 42
15 4 0 88 89 42
16 -- -- -- -- --
17 -- -- -- -- --
18 3 0 90 91 42
19 3 -1 91 92 42
20 3 -1 91 93 42
21 3 0 92 93 42
22 3 0 93 94 42
23 -- -- -- -- --
24 -- -- -- -- --
25 3 0 94 96 42
26 3 0 94 96 42
27 3 0 95 96 42
28 4 0 96 97 42
Mean (28 days) 2 96 Not applicable
1  Corrected for mean oxygen uptake of the inoculum controls
--  Not determined
Validity criteria fulfilled:
yes
Remarks:
In the procedure controls, the reference item was degraded by an average of 88% by Exposure Day 14.
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
The test material was found not to be biodegradable under the conditions of the test. The results from the toxicity control show that the test substance is not inhibitory to activated sludge.
Executive summary:

The ready biodegradability of the test substance was determined in a GLP compliant guideline study by observing the oxygen consumption over 28 days. A blank control, procedure control (sodium benzoate) and a toxicity control (sodium benzoate and test material) were also incubated for 28 days. Aerobic activated sludge was used as the inoculum. The validity criteria of the test were met. The test material was found not to be biodegradable under the conditions of the test within 28 days. The results from the toxicity control show that the test substance is not inhibitory to activated sludge.

Description of key information

Not readily biodegradable, OECD 301F, Eisner, 2011

The results from the toxicity control show that the test substance is not inhibitory to activated sludge.

Key value for chemical safety assessment

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

Additional information

Only a single experimental study for biodegradation in water are available for the test substance. The result of the study indicates that the substance is not readily biodegradable. The study is considered reliable and relevant for risk assessment and classification.