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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
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: No GLP, study according to guidance of German Environmental Agency
Qualifier:
according to guideline
Guideline:
ISO 10708 Water quality - Evaluation in an aqueous medium of the ultimate aerobic biodegradability of organic compounds - Determination of biochemical oxygen demand in a two-phase closed bottle test
Version / remarks:
1990
GLP compliance:
no
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): aeration tank of the municipal sewage treatment plant of Pforzheim, Germany
- Preparation of inoculum for exposure: 2 L of mineral medium were inoculated with 20 mL of activated sludge (3.0 g/L). 200 mL of this solution was transferred into 9 test vessels with magnetic stirring bars. Bottles were closed with glass stoppers and incubated without test item for 1 week in the dark at 20 °C and 100 rpm.
- Pretreatment: activated sludge was washed twice by centrifugation (10 min., 6000 rpm) with mineral solution. Pellet was mixed with mineral solution (final sludge concentration of 3.0 g/L).
- Concentration of inoculum: 30 mg suspended solids per litre
Duration of test (contact time):
28 d
Initial conc.:
20 mg/L
Based on:
ThOD/L
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: in 1 L: KH2PO4 85 mg, K2HPO4 217.5 mg, Na2HPO4*2H2O 334 mg, NH4Cl 5 mg, CaCl2*2H2O 36.42 mg, MgSO4*7H2O 22.5 mg, FeCl3*6H2O 0.25 mg
- Test temperature: 20 °C
- pH: blank: 7.38 - 7.49, reference control: 6.87 - 7.62, test item: 7.36 - 7.46
- Aeration of dilution water: 15 min prior to test start
- Suspended solids concentration: 30 mg/L
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: closed glass bottles with 2/3 aqueous test mixture and 1/3 air
- Number of culture flasks/concentration: 3
- Measuring equipment: oximeter (WTW Oxi 191)
- Other: continuous shaking 100 rpm

SAMPLING
- Sampling frequency: 8, 14, 22, and 28 d alter the start of the experiment
- Sampling method: the remaining O2 concentration in the test vessels was measured

CONTROL AND BLANK SYSTEM
- Inoculum blank: 3 replicates
- Reference control: 3 replicates
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
12.43
Sampling time:
28 d
Results with reference substance:
67.33% degradation after 28 d (more than 60% after 14 d).

Total oxygen uptake in the blanks after 1 week was < 3 mg O2/L and in the following weeks not >= l mg/L per week.

Table 1: Cumulative degradation at day 28.

Sample Cumul. Degradation (%)
28 d
Blank 1  - 
Blank 2  - 
Blank 3  - 
Reference 1 72.089
Reference 2 62.096
Reference 3 67.803
Test item 1 11.099
Test item 2 11.68
Test item 3 14.496
Validity criteria fulfilled:
yes
Interpretation of results:
other: not readily biodegradable under test conditions
Conclusions:
The test item was not readily biodegradable (12.43% based on O2 consumption) under the chosen test conditions.
Executive summary:

There is one study available, in which the ready biodegradability of test item was assessed according to the BODIS test guidance for insoluble substances of the German Environmental Agency (1990).

The test item at a concentration of 20 mg ThOD was inoculated with 30 mg/L of a mixed bacterial inoculum in closed glass bottles with 2/3 of aqueous test mixture and 1/3 headspace for 28 d. The degradation process was followed by weekly measurements of the BOD in the aqueous phase. Degradation was expressed as BOD to ThOD in %. After 28 d, the average degradation rate of the test item was 12.43%. The degradation of the reference substance sodium benzoate reached 67.33% after 28 d, thus confirming the suitability of the inoculum.

Description of key information

Not readily biodegradable (12.43% within 28 d, BODIS test)

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

There is one study available, in which the ready biodegradability of test item was assessed according to the BODIS test guidance for insoluble substances of the German Environmental Agency (1990).

The test item at a concentration of 20 mg ThOD was inoculated with 30 mg/L of a mixed bacterial inoculum in closed glass bottles with 2/3 of aqueous test mixture and 1/3 headspace for 28 d. The degradation process was followed by weekly measurements of the BOD in the aqueous phase. Degradation was expressed as BOD to ThOD in %. After 28 d, the average degradation rate of the test item was 12.43%. The degradation of the reference substance sodium benzoate reached 67.33% after 28 d, thus confirming the suitability of the inoculum.

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