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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:
From 15 January to 14 February 2019
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Version / remarks:
adopted July 17, 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 (e.g. location, sampling depth, contamination history, procedure): activated sludge freshly obtained from a municipal sewage treatment plant: 'Waterschap Aa en Maas', 's-Hertogenbosch, The Netherlands, receiving predominantly domestic sewage

- Pre-treatment: The freshly obtained sludge was kept under continuous aeration until further treatment. The concentration of suspended solids was determined to be 3.6 g/L in the concentrated sludge. Magnetically
stirred sludge was used as inoculum at an amount of 3 mL per litre of mineral medium, leading to a SS concentration of 11 mg/L.
Duration of test (contact time):
28 d
Initial conc.:
21.5 mg/L
Based on:
test mat.
Initial conc.:
12 mg/L
Based on:
TOC
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: mineral medium as described in the OECD guideline
- Test temperature: setpoint of 22°C +/- 2°C, the actual daily mean temperature during the study was 22 to 23°C.
- pH: 7.5
- pH adjusted: no
- Suspended solids concentration: The concentration of suspended solids was determined to be 3.6 g/L in the concentrated sludge.
- Continuous darkness: yes coloured glass bottles, The test media were excluded from light.
- Test duration: 28 days for the inoculum blank and test item (last CO2 measurement on day 29). 14 days for the positive and toxicity control (last CO2 measurement on day 15). During the test period, the test media were aerated and stirred continuously.
- Test vessels: 2 litre brown coloured glass bottles.
- Aeration: A mixture of oxygen (ca. 20%) and nitrogen (ca. 80%) was passed through a bottle, containing 0.5 - 1 litre 0.0125 M Ba(OH)2 solution to trap CO2 which might be present in small amounts. Synthetic air was passed through the scrubbing solutions at a rate of approximately 1-2 bubbles per second (ca. 30-100 mL/min).

TEST SYSTEM
- Pre-incubation medium: The day before the start of the test (day -1) mineral components, Milli-RO water (ca. 80% of final volume) and inoculum were added to each bottle. This mixture was aerated with synthetic air overnight to purge the system of CO2.
- Type and number of bottles:
Test suspension: containing test item and inoculum (2 bottles).
Inoculum blank: containing only inoculum (2 bottles)
Positive control: containing reference item and inoculum (1 bottle).
Toxicity control: containing test item, reference item and inoculum (1 bottle).
- Preparation: At the start of the test (day 0), test and reference item were added to the bottles containing the microbial organisms and mineral components. The volumes of suspensions were made up to 2 litres with Milli-RO water, resulting in the mineral medium described before. Three CO2-absorbers (bottles filled with 100 mL 0.0125 M Ba(OH)2) were connected in series to the exit air line of each test bottle

SAMPLING
- Sampling frequency: Titrations were made every second or third day during the first 10 days, and thereafter at least every fifth day until day 28, for the inoculum blank and test item. Titrations for the procedure and toxicity control were made over a period of at least 14 days.

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes
- Toxicity control: yes
Reference substance:
acetic acid, sodium salt
Key result
Parameter:
% degradation (CO2 evolution)
Value:
14.5
Sampling time:
28 d
Remarks on result:
other: mean of both duplicate (17% and 12%)
Details on results:
- Theoretical CO2 Production:
The ThCO2 of Tributyl(ethyl) phosphonium diethylphosphate was calculated to be 2.06 mg CO2/mg.
The ThCO2 of sodium acetate was calculated to be 1.07 mg CO2/mg.

- Biodegradation:
The relative biodegradation values calculated from the measurements performed during the test period revealed no biologically relevant biodegradation of Tributyl(ethyl) phosphonium diethylphosphate (12% and 17%, based on ThCO2).
In the toxicity control, more than 25% biodegradation occurred within 14 days (46%, based on ThCO2). Therefore, the test item was assumed not to inhibit microbial activity.

Functioning of the test system was checked by testing the reference item sodium acetate, which showed a normal biodegradation curve. The positive control item was biodegraded by at least 60% (84%) within 14 days.
Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
The relative biodegradation values calculated from the measurements performed during the test period revealed no biologically relevant biodegradation of Tributyl(ethyl) phosphonium diethylphosphate (12% and 17%, based on ThCO2).
In the toxicity control, Tributyl(ethyl) phosphonium diethylphosphate was found not to inhibit microbial activity. In conclusion, Tributyl(ethyl) phosphonium diethylphosphate was designated as not readily biodegradable.
Executive summary:

The aerobic biodegradability of the test item Tributyl(ethyl) phosphonium diethylphosphate was investigated in a GLP compliant ready biodegradability test performed in accordance with OECD Guideline No. 301B ('modified Sturm test). The biodegradation of the test item within 29 days was 15% ThCO2 and did not reach the criteria for ready biodegradability (60% ThOD within a 10 -day window). In the toxicity control, the test item was found not to inhibit microbial activity. Since all criteria for acceptability of the test were met, this study was considered to be valid. In conclusion, the test item is considered as not readily biodegradable under the conditions of this test.

Description of key information

The ultimate aerobic biodegradability of the test item was investigated in a GLP-compliant ready biodegradability screening study performed in accordance with OECD Guideline No. 301B. The relative biodegradation values calculated from the measurements performed during the test period revealed no biologically relevant biodegradation of the test item (12% and 17%, based on ThCO2). The test item is thus considered not "readily biodegradable".

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed
Type of water:
freshwater

Additional information

The ready biodegradability of the test item was investigated in one GLP-compliant study performed in accordance with OECD Guideline No. 301B. The study is considered as reliable (Klimisch 1) and is selected as a key study for the endpoint.