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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:
2016-11-09 to 2016-12-09
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
according to
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Version / remarks:
July 1992
Deviations:
no
GLP compliance:
yes (incl. certificate)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: municipal wastewater treatment plant Breisgauer Bucht Germany, 600,000 inhabitant equivalents, predominantly domestic wastewater.
- Concentration of sludge: 4.2 g/L after drying at 105°C
- Initial cell/biomass concentration: 30 mg/L
Duration of test (contact time):
28 d
Initial conc.:
ca. 19.9 - ca. 21 mg/L
Based on:
TOC
Remarks:
calculated based on molecular structure
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: mineral medium according to guideline
- Additional substrate: no
- Solubilising agent: no
- Test temperature: 20.5 - 23.1°C
- pH: not registered
- pH adjusted: no
- Aeration of dilution water: 2.5 to 4.3 bubbles/second or 30-100 mL/min with CO2-free air
- Suspended solids concentration: 30 mg dry solids/L
- Continuous darkness: no, diffuse light


TEST SYSTEM
- Number of culture flasks/concentration: 3
- Method used to create aerobic conditions: aeration with CO2-free air
- Measuring equipment: Total organic carbon analyser TOC-5050A with autosampler ASI 5000A, Shimadzu.
- Details of trap for CO2 and volatile organics if used: two 250 mL glass wash bottles in series each filled with 200 mL 0.2 M NaOH, sampling through lateral connecting pieces, through butyl rubber septum using 5 mL PE syringes

SAMPLING
- Sampling frequency: on day 4, 7, 11, 14, 21 and 28
- Sampling method: 4 mL of NaOH sampled from 1st CO2-absorber flasks
- Sample storage before analysis: samples immediately closed with sealing film
- Final sampling: on day 28, 2mL of 4M HCl is added to the reactor to release CO2 dissolved in water. IC-analysis on day 29.

CONTROL AND BLANK SYSTEM
- Inoculum blank: 3 replicates
- Abiotic sterile control: no
- Toxicity control: yes, 1 replicate at 40.1 mg/L TOC
- Reference substance: 3 replicates at 30 mg/L

Reference substance:
benzoic acid, sodium salt
Parameter:
% degradation (CO2 evolution)
Value:
45.9
St. dev.:
7.57
Sampling time:
29 d
Remarks on result:
other: as measured after acidification of the reactor flasks to release CO2 dissolved in water.
Remarks:
mean of 2 replicates
Details on results:
The 10-day window started rapidly, between day 0 and 4, but the biodegradation stagnated at a plateau between 40 and 50 % . As the maximal degradation, 55.2 %, did not exceed the pass level of 60 % it is concluded that the substance is not readily biodegradable. Details on the test results are provided below.

The 3rd replicate containing test item showed remarkable lower degradation, over the whole test duration. This is most probably caused by a leakage of the test reactor.
Results with reference substance:
The reference substance was rapidly biodegraded, with maximal degradation of 87.1%.

Ultimate biodegradation as % of ThCO2

Reactor day 0 day 4 day 7 day 11 day 14 day 21 day 28 day 29
Test item, rep 1 0 20.4 35.3 49.9 47.9 51.3 55.2 51.2
Test item, rep 2 0 20.0 27.1 40.5 34.2 42.4 45.6 40.5
Test item, rep 3 0 6.0 6.4 14.0 10.5 13.5 14.6 13.2
Reference, rep 1 0 71.0 80.8 79.2 83.0 77.1 82.4 84.0
Reference, rep 2 0 77.6 79.1 80.5 85.0 80.2 86.0 87.1
Reference, rep 3 0 68.5 77.6 77.1 84.1 76.7 82.6 84.6
Toxicity control 0 46.7 59.2 68.4 71.5 68.4 72.2 72.6

The test results obtained for Test item, rep 3 are not taken into consideration. The laboratory reported that most likely the bottle leaked during the experiment, resulting in erroneous test results.

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
The biodegradability of the test item was examined in a CO2-evolution test according to OECD 301B. The test item was found to be not readily biodegradable with on average 45.9 % biodegradation after 28 days.
Executive summary:

The biodegradability of the test item was examined in a CO2-evolution test according to OECD 301B. After 28 days, the ultimate biodegradation was found to be 45.9 % (average of 2 replicates). The 10 -day window criteria was not met and the test item should be considered to be not readily biodegradable. The 3rd replicate was not considered for the assessment of the biodegradability of the test item. The degradation in this vessel was remarkably lower than in the other test vesels. This is most probably caused by a leakage in the test reactor.

Up to 72.6 % degradation was observed in the toxicity control containing sodium benzoate and the test item. This result shows that the test item was not inhibitory to the inoculum.

Description of key information

The biodegradability of the test item was examined in a CO2-evolution test according to OECD 301B. The degradation started quickly, but reached plateau after 11 days. After 28 days, the ultimate biodegradation was found to be 45.9 % (average of 2 replicates). The 10 -day window criteria was not met and the test item should be considered to be not readily biodegradable.

Up to 72.6 % degradation was observed in the toxicity control containing sodium benzoate and the test item. This result shows that the test item was not inhibitory to the inoculum.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

The 3rd replicate was not considered for the assessment of the biodegradability of the test item. The degradation in this vessel was remarkably lower than in the other test vesels. This is most probably caused by a leakage in the test reactor.