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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 20 October 2015 to 18 December 2015
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Version / remarks:
(1992)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)
Version / remarks:
(2008)
Deviations:
no
Qualifier:
according to guideline
Guideline:
other: ISO 9439 Water quality - Evaluation of ultimate aerobic biodegradability of organic compounds in aqueous medium - carbon dioxide evolution test
Version / remarks:
(1999)
Deviations:
no
GLP compliance:
yes
Specific details on test material used for the study:
Molecular formula: C16H36PBr (organic carbon content: approx. 57%)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source: The source of test organisms was activated sludge freshly obtained from a municipal sewage treatment plant: 'Waterschap Aa en Maas', 's-Hertogenbosch, The Netherlands, receiving predominantly domestic sewage.
- 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. Before use, the sludge was allowed to settle (86 minutes) and the supernatant liquid was used as inoculum at the amount of 10 mL/L of mineral medium.
Duration of test (contact time):
28 d
Initial conc.:
12 mg/L
Based on:
TOC
Initial conc.:
21 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: 1 litre mineral medium contains: 10 mL of solution (A), 1 mL of solutions (B) to (D) and Milli-RO water (tap-water purified by reverse osmosis (Milli-RO) and subsequently passed over activated carbon)
Stock solutions of mineral components:
A) 8.50 g KH2PO4; 21.75 g K2HPO4; 67.20 g Na2HPO4.12H2O; 0.50 g NH4Cl; dissolved in Milli-RO water and made up to 1 litre, pH 7.4 ± 0.2
B) 22.50 g MgSO4.7H2O dissolved in Milli-RO water and made up to 1 litre.
C) 36.40 g CaCl2.2H2O dissolved in Milli-RO water and made up to 1 litre.
D) 0.25 g FeCl3.6H2O dissolved in Milli-RO water and made up to 1 litre.
- Test temperature: between 21.8 and 22.5°C.
- pH at t=0 d: 7.6
- pH adjusted: no
- pH at t=28 d (test suspensions): 7.5
- pH at t=28 d (blank controls): 7.5-7.6
- pH at t=28 d (positive control): 7.8
- pH at t=28 d (toxicity control): 7.8
- Aeration of dilution water: Overnight prior to the start of the test. During the test the medium was aerated and stirred continously.
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: 2 litre glass brown coloured bottles
- Number of culture flasks/concentration:
Test suspension: containing test substance and inoculum (2 bottles)
Inoculum blank: containing only inoculum (2 bottles)
Positive control: containing reference substance and inoculum (1 bottle)
Toxicity control: containing test substance, reference substance and inoculum (1 bottle)
- Method used to create aerobic conditions: Synthetic air (a mixture of oxygen (ca. 20%) and nitrogen (ca. 80%), with CO2 < 1 ppm) was sparged through the solutions at a rate of approximately 1-2 bubbles per second (ca. 30-100 mL/min).
- Details of trap for CO2 and volatile organics if used: CO2 was trapped in barium hydroxide solution. The amount of CO2 produced was determined by titrating the remaining Ba(OH)2 with 0.05 M standardized HCl (1:20 dilution from 1 M HCl (Titrisol® ampoule). Titrations were made every second or third day during the first 10 days, and thereafter at least every fifth day until the 28th day, for the inoculum blanks and test suspensions. Titrations for the positive and toxicity control were made over a period of at least 14 days. Each time the CO2-absorber nearest to the test bottle was removed for titration; each of the remaining two absorbers was moved one position in the direction of the test bottle. A new CO2-absorber was placed at the far end of the series. Phenolphthalein (1% solution in ethanol, Merck) was used as pH-indicator. On day 28, the pH of all test suspensions was measured and 1 mL of concentrated HCl (37%, Merck) was added to the bottles of the inoculum blank and test suspension. The bottles were aerated overnight to drive off CO2 present in the test suspension. The final titration was made on day 29.

PREPARATION OF TEST SOLUTIONS
Since the test substance was completely miscible in water, the test media were prepared using a stock solution of 1 g/L in Milli-RO water. A weighed amount of 254.8 mg of the test substance was dissolved in Milli-RO water and made up to 250 mL. The final stock solution was clear and colourless. Aliquots of 42 mL of the stock solution were added to the test item bottles A and B and to the toxicity control. These test bottles contained medium with microbial organisms (final volume: 2 litres).The test solutions were continuously stirred during the test, to ensure optimal contact between the test substance and the test organisms.

SAMPLING
- Sampling frequency (blanks and test suspensions): Titrations were made on day: 1, 4, 6, 8, 11, 14, 18, 22 (test suspension bottle B only; the barium hydroxide in the CO2-absorber of test suspension bottle A was in advertently discarded before measurement), 27 and 29
- Sampling frequency (positive and toxicity control): Titrations were made on day: 1, 4, 6, 8, 11 and 14
- Sampling method: Titration of the whole volume of CO2-absorber

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes
- Abiotic sterile control: no
- Toxicity control: yes
Reference substance:
acetic acid, sodium salt
Key result
Parameter:
% degradation (CO2 evolution)
Value:
9
Sampling time:
29 d
Remarks on result:
other: HCl added on the 28th day (last CO2-measurement on the 29th day). Result based on replicate B. On day 22 the CO2 produced in replicate A was not measured, but the curves on both replicates were comparable.
Details on results:
- Theoretical CO2 production:
The ThCO2 of the test substance was calculated to be 2.07 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 ≥7% and 9% biodegradation of the test substance, for A and B, respectively (based on ThCO2). A ≥ value for bottle A as on day 22 the CO2 produced in this bottle was not measured. Thus, the criterion for ready biodegradability was not met.
In the toxicity control, more than 25% biodegradation occurred within 14 days (36%, based on ThCO2). Therefore, the test substance was assumed not to inhibit microbial activity.
Functioning of the test system was checked by testing the reference substance sodium acetate, which showed a normal biodegradation curve.
Results with reference substance:
The positive control substance was biodegraded by at least 60% (75%) within 14 days.

Acceptability of the test:

- The positive control substance was biodegraded by at least 60% (75%) within 14 days.

- The difference of duplicate values for %-degradation of the test item was always less than 20 (≤4%).

- The total CO2 release in the blank at the end of the test did not exceed 40 mg/L (36.8 mg CO2 per 2 litres of medium, corresponding to 18.4 mg CO2/L).

- The Inorganic Carbon content (IC) of the test item (suspension) in the mineral medium at the beginning of the test was less than 5% of the Total Carbon content (TC). Since the test medium was prepared in tap-water purified by reverse osmosis (Milli-RO water (Millipore Corp., Bedford, Mass., USA, carbon levels <500 ppb)), IC was less than 5% of TC (mainly coming from the test item, 12 mg TOC/L).

Since all criteria for acceptability of the test were met, this study was considered to be valid.

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
Under the conditions of the modified Sturm test the substance was determined to be not readily biodegradable.
Executive summary:

The ready biodegradation of the substance under the conditions of the carbon dioxide (CO2) evolution test (modified Sturm test) was investigated according to OECD guideline 301 B and GLP principles. A test concentration of 12 mg/L (as TOC) was tested in duplicate during 28 days. The relative biodegradation values calculated from the measurements performed during the test period revealed ≥7% and 9% biodegradation of the substance, for replicate A and B, respectively (based on ThCO2). A ≥ value for bottle A as on day 22 the CO2 produced in this bottle was not measured. In the toxicity control, the substance was found not to inhibit microbial activity. The study is considered to be reliable without restrictions. In conclusion, the substance was determined to be not readily biodegradable under the conditions of the modified Sturm test.

Description of key information

The ready biodegradation of the analogue substance under the conditions of the carbon dioxide (CO2) evolution test (modified Sturm test) was investigated according to OECD guideline 301 B and GLP principles. A test concentration of 12 mg/L (as TOC) was tested in duplicate during 28 days. The relative biodegradation values calculated from the measurements performed during the test period revealed ≥7% and 9% biodegradation of the substance, for replicate A and B, respectively (based on ThCO2). A ≥ value for bottle A as on day 22 the CO2 produced in this bottle was not measured. In the toxicity control, the substance was found not to inhibit microbial activity. The study is considered to be reliable without restrictions. In conclusion, the substance was determined to be not readily biodegradable under the conditions of the modified Sturm test.

Key value for chemical safety assessment

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

Additional information