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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:

December 14, 2021 to March 29, 2022

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

conducted under GLP conditions

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)

Version / remarks:

1992

Deviations:

yes

Remarks:

An optional toxicity control as suggested by OECD guideline 301 F was not petiormed. The validity of the study is not adversely affected.

Qualifier:

according to guideline

Guideline:

EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)

Version / remarks:

2008

Deviations:

yes

Remarks:

An optional toxicity control as suggested by OECD guideline 301 F was not petiormed. The validity of the study is not adversely affected.

Qualifier:

according to guideline

Guideline:

EPA OPPTS 835.3110 (Ready Biodegradability)

Deviations:

yes

Remarks:

An optional toxicity control as suggested by OECD guideline 301 F was not petiormed. The validity of the study is not adversely affected.

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

Fresh activated sludge from a biological waste water treatment plant treating predominantly domestic sewage (Bois-de-Bay, Satigny, Switzerland) was used.
The sludge is collected in the morning, washed three times in the mineral medium (by centrifuging at 1000 g for 10 minutes, discarding the supernatant and resuspending in mineral medium) and kept aerobic until being used on the same day.

Determination of the dry weight of suspended solids :
The dry weight of suspended solids is determined by taking two 50 ml samples of the
homogenised sludge, evaporating water on a steam bath, drying in an oven at 105 -
110°C for two hours and weighing the residue.

The dry weight of suspended solids determined in the sludge was 4.46 g/l, which was
then diluted to 1.53 g/l by adding the necessary quantity of mineral medium.
To obtain a concentration of 30 mg/I (dry weight) in 255 ml total volume, 5.00 ml of the
sludge (inoculum) at 1.53 g/L was added to 250 ml of mineral medium.

Duration of test (contact time):

60 d

Initial conc.:

30 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

Test substance samples (7.65 mg, corresponding to 30.0 mg/I in 255 ml of test medium) are weighed in small aluminium boats and added directly to the test flasks of the Oxitop.
For reference substance samples 12.75 mg (corresponding to 50.0 mg/I in 255 ml of test medium) are weighed in small aluminium boats and added directly to the test flasks of the Oxitop.
Flasks are filled with 250 ml of mineral medium. Samples of test or reference substance are added. Then 5.00 ml of suspended sludge diluted to a concentration of 1.53 g/l dry matter is added. Except when the test substance has an acid or alkaline character, the pH of each flask is not measured but assumed to be the same as the mineral medium (see 3.5. in the final report), in order not to remove any loating undissolved test substance from the test medium by dipping a glass electrode in it. Neutral test substances, even sodium benzoate, were shown not to affect the pH of the medium by more than 0.1 pH unit.
Two sodium hydroxide pellets are placed in the quivers on top of the bottle, and the flasks are closed tightly with the measuring heads. The flasks are allowed to equilibrate to the test temperature. The measurement is started by programming the measuring unit of the Oxitop test flasks, and the test flasks are placed in the temperature controlled cupboard of the Oxitop system. After temperature equilibration, the controller of the instrument starts the data acquisition (time zero of the experiment).

Everyday the oxygen consumption of each flask is recorded and correct temperature and stirring are checked.
At the end of the test period, the pH of each flask is measured again.

Reference substance:

benzoic acid, sodium salt

Test performance:

Everyday the oxygen consumption of each flask is recorded and correct temperature and stirring are checked.
At the end of the test period, the pH of each flask is measured again.

The respirometer used during this study is an Oxitop Control System, made by Wissenschaftlich-Technische Werkstatten (WTW), Weilheim, Germany.

Key result

Parameter:

% degradation (O2 consumption)

Value:

81

Sampling time:

28 d

Parameter:

% degradation (O2 consumption)

Value:

85

Sampling time:

60 d

Details on results:

The test item undergoes 81 % biodegradation after 28 days and 85% biodegradation after 60 days in the test conditions. The 10-day window criterion is also fulfilled (28% on day 5 and 74% on day 15).
The test item did not inhibit the intrinsic respiration of the inoculum during the study and can be considered to be non-toxic to the inoculum at the test concentration.
Thus, the test item should be regarded as readily biodegradable according to this test.

Results with reference substance:

Degradation of sodium benzoate exceeded 40% after 7 days (observed = 78%) and 65% after 14 days (observed 85%): the activity of the inoculum was thus verified (validity criterion).
The repeatability validity criterion (not more than 20% difference between replicates) is fulfilled. Therefore, the test is considered valid.

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

The test item undergoes 81 % biodegradation after 28 days and 85% biodegradation after 60 days in the test conditions. The 10-day window criterion is also fulfilled (28% on day 5 and 74% on day 15).
The test item did not inhibit the intrinsic respiration of the inoculum during the study and can be considered to be non-toxic to the inoculum at the test concentration.
Thus, The test item should be regarded as readily biodegradable according to this test.

Executive summary:

The Ready Biodegradability of the test item was determined by the Manometric Respirometry Test (OECD guideline 301F).
The test item undergoes 81 % biodegradation after 28 days and 85% biodegradation after 60 days in the test conditions. The 10-day window criterion is also fulfilled (28% on day 5 and 74% on day 15).
The test item did not inhibit the intrinsic respiration of the inoculum during the study and can be considered to be non-toxic to the inoculum at the test concentration.
Thus, The test item should be regarded as readily biodegradable according to this test.

Description of key information

The Ready Biodegradability of the test item was determined by the Manometric Respirometry Test (OECD guideline 301F).
The test item undergoes 81 % biodegradation after 28 days and 85% biodegradation after 60 days in the test conditions. The 10-day window criterion is also fulfilled (28% on day 5 and 74% on day 15).
The test item did not inhibit the intrinsic respiration of the inoculum during the study and can be considered to be non-toxic to the inoculum at the test concentration.
Thus, The test item should be regarded as readily biodegradable according to this test.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Type of water:

freshwater