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Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

From 16 April 2021 to 14 May 2021

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)

Version / remarks:

July 17, 1992

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Batch/Lot number: 410752
Purity: 99.9%

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, adapted

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Secondary effluent, microorganisms from a domestic wastewater treatment plant. The secondary effluent was supplied from one of the sewage plant for domestic sewage in Veszprém county, Hungary.
- Storage conditions: After collection of a fresh sample of secondary effluent could settle for approximately one hour, then the decanted effluent or filtrate was aerated until use.

Duration of test (contact time):

28 d

Initial conc.:

2.3 mg/L

Based on:

test mat.

Details on study design:

TEST CONDITIONS
- Composition of medium:
a) Solution: KH2PO4 2.125 g
K2HPO4 5.4375 g
Na2HPO4 x 12H2O 16.795 g
NH4Cl 0.125 g
Deionised water ad 250 mL
b) Solution: MgSO4 x 7 H2O 5.625 g
Deionised water ad 250 mL
c) Solution: CaCl2 x 2 H2O 9.10 g
Deionised water ad 250 mL
 
d) Solution: FeCl3 x 6 H2O 0.25 g
Deionised water ad 1000 mL

- Test temperature: 22 °C
- pH: 7.46
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: BOD bottles (300 mL) with special neck and glass stoppers.
- Number of culture flasks/concentration: 2
- Measuring equipment: The oxygen concentrations were measured with an oxygen meter with a stirring O2 electrode.
- Test performed in closed vessels due to significant volatility of test substance: yes

SAMPLING
- Sampling frequency: Oxygen measurements were performed in duplicate on days 0, 7, 14, 21 and 28.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Only filtered inoculum was added to 3.38 litres of aqueous test medium.
- Toxicity control: The Test Item (7.8 mg) and the reference item stock solution* (34.0 mL) were mixed into 3.40 litres of aqueous test medium corresponding to 2.3 mg/L test item (ThOD of 6.003 mg O2/L) and 3.6 mg/L reference item (ThOD of 6.012 mg O2/L).

STATISTICAL METHODS: Statistical evaluation of data was not performed.

Reference substance:

benzoic acid, sodium salt

Preliminary study:

The concentration of dissolved oxygen resulted a mean of 6.90 mg O2/L after 14 days of incubation in the test item flasks (1a and 1b) in the preliminary test, which resulted a mean of 6.7 % biodegradation within 14 days of the test item.

Key result

Parameter:

% degradation (O2 consumption)

Value:

-2.5

Sampling time:

28 d

Details on results:

The test item was degraded by 0.8% by day 7, then a total of -2.5% biodegradation had occurred by the end of the study period, based on ThOD.

Results with reference substance:

Sodium benzoate was tested simultaneously under the same conditions as the test item and functioned as a procedure control. Sodium benzoate was sufficiently degraded to a mean of 75.8 % after 14 days, and to a mean of 91.7 % after 28 days of incubation, based on ThOD, thus confirming the suitability of the used inoculum.

In the toxicity control, containing both, the test item and the reference item sodium benzoate, a mean of 39.3 % biodegradation was noted within 14 days and 46.8 % biodegradation after 28 days of incubation.

Validity criteria fulfilled:

yes

Interpretation of results:

under test conditions no biodegradation observed

Conclusions:

The percentage biodegradation of Test Item reached a mean of -2.5 % after 28 days based on the ThOD of the test item. The test item is considered not readily biodegradable.

Executive summary:

The test item was investigated for its ready biodegradability in a Closed Bottle Test over a period of 28 days according to OECD Guideline 301D under GLP.

Under the test conditions the percentage biodegradation of Test Item reached a mean of -2.5 % after 28 days based on the ThOD of the test item. According to the test guidelines the pass level for ready biodegradability is removal of 60 % COD/ThOD. Therefore, the test item is considered not readily biodegradable.

Description of key information

The test item was investigated for its ready biodegradability in a Closed Bottle Test over a period of 28 days according to OECD Guideline 301D under GLP.

Under the test conditions the percentage biodegradation of Test Item reached a mean of -2.5 % after 28 days based on the ThOD of the test item. According to the test guidelines the pass level for ready biodegradability is removal of 60 % COD/ThOD. Therefore, the test item is considered not readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Type of water:

freshwater