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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:
2020-04-24 until 2020-05-22
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Version / remarks:
(1992)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
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): sewage treatment plant Ruhrverband Kläranlage, Sunthelle 6, 57392 Schmallenberg, Germany
- Date of sampling: 24th April 2020
- Storage conditions: No storage
- Preparation of inoculum for exposure: Filtered (2 mm) to remove coarse particles, washed once with tap water, the concentration was adjusted to 3.9 g/L and verified by dry mass measurement.
- Pretreatment: Kept aerobic until use
- Concentration of sludge in the test: 29.6 mg dry mass/litre
Duration of test (contact time):
28 d
Initial conc.:
56 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Remarks:
(51.1 mg ThOD/L )
Details on study design:
- The concentration in the test assays were 56 mg per litre mineral test medium (14 mg/250 mL). This amount (56 mg) test item correspond to 51.1 mg theoretical oxygen demand (ThOD). No emulsifiers or solvents were used. The required amount to ensure a final concentration of 56 mg/L (14 mg per 250 mL) was added directly on a weight basis via Teflon discs. Subsequently, the mineral medium was added to the vessels.
- The concentration in the test vessels with reference item (procedural control, toxicity control) was 100 mg per liter mineral test medium (25 mg/250 mL).
- A further solution containing both test and reference item at the same concentrations as in the individual solutions (test item 56 mg/L, reference item 100 mg/L) was prepared to determine the possible toxicity of the test item against the inoculum.
- Further flasks with mineral medium only were prepared for inoculum controls.
- Abiotic controls were also prepared to measure any possible abiotic degradation; a solution of the test item at about 56 mg/L was sterilized by the addition of 10 mL/L NaN3 (100 g/L).
- In all test assays except of the abiotic controls, 1.90 mL of the inoculum stock solution were transferred for inoculation (per 250 mL) resulting in a concentration of 29.6 mg dry mass/litre (7.4 mg dry mass/250 mL).
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
-26.4
St. dev.:
3
Sampling time:
28 d
Details on results:
The average percent biodegradation of the test item in the test media was found to be -26.4% (SD = 3.0%) after 28 days of incubation. No biodegradation within the 10-day-window could be calculated since the start criterium of the window (10% degradation rate) was not reached within the 28 days of incubation.
Results with reference substance:
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 92%.
Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
The test item was not readily biodegradable under the conditions of the test. This study is considered to be relevant, reliable, adequate for risk assessment, and adequate for classification purposes.
Executive summary:

The ready biodegradability of the test item was investigated according to the manometric respirometry test design and carried out according to the OECD guideline for Testing of Chemicals No. 301 F (1992). The ready biodegradability of the test item was investigated at a concentration of 56 mg/L in a manometric respirometry test using domestic aerobic activated sewage sludge incubated at 22 °C in the dark over 28 days under continuous stirring. The biochemical oxygen demand (BOD) was measured daily and the percentage degradation was calculated from the theoretical oxygen demand (ThOD) after correcting for the BOD of inoculum controls. The average percent biodegradation of the test item in the test media was found to be -26.4% after 28 days of incubation. No biodegradation within the 10-day-window could be calculated since the start criterion of the window (10% degradation rate) was not reached within the 28 days of incubation. Since the threshold value of 60% was not surpassed in a 10-day-window within the 28-d period, the test item was not readily biodegradable under the test conditions. The test item had no inhibitory effect on the activity of activated sludge microorganisms at the tested concentration. In the procedural controls, the reference substance sodium benzoate was degraded by an average of 88% by exposure day 14, and reached an average biodegradation of 92% by the end of the test (day 28), thus confirming suitability of the activated sludge.


Description of key information

Not readily biodegradable

Key value for chemical safety assessment

Biodegradation in water:
not biodegradable
Type of water:
freshwater

Additional information

The substance was not degradable in a valid and reliable screening test conducted to OECD TG 301F. It had no inhibitory effect on the activity of micro-organisms in the activated sewage sludge at the tested concentration of 56 mg/L.

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