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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:
6 July - 4 August 2011
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:
(1992)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)
Version / remarks:
(2008)
Deviations:
no
Qualifier:
according to
Guideline:
ISO DIS 9439 (Ultimate Aerobic Biodegradability - Method by Analysis of Released Carbon Dioxide)
Version / remarks:
(1999)
Deviations:
no
Qualifier:
according to
Guideline:
other: ISO Standard 10634 "Water Quality - Guidance for the preparation and treatment of poorly water-soluble organic compounds for the subsequent evaluation of their biodegradability in an aqueous medium" (1995).
Deviations:
no
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source: 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 4.2 g/L in the concentrated sludge (information obtained from the municipal sewage treatment plant). Before use, the sludge was allowed to settle (60 minutes) and the liquid was decanted for use as inoculum at the amount of 10 mL/L of mineral medium.
Duration of test (contact time):
28 d
Initial conc.:
26 mg/L
Based on:
test mat.
Initial conc.:
12 mg/L
Based on:
other: Total Organic Carbon (TOC)
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: According to OECD Guideline 301 B

- Test temperature: varied between 20.2 and 21.4°C
- pH:
At t=0 d: 7.5 - 7.6
At t=28 d: 7.5 – 7.9
- pH adjusted: No
- Aeration of test medium: Overnight prior to the start of the test. During the test the medium was aerated and stirred continously.
- Suspended solids concentration: The concentration of suspended solids was 4.2 g/L in the concentrated sludge.

TEST SYSTEM
- Culturing apparatus: 2 litre all-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:
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. The synthetic air was sparged through the scrubbing solutions at a rate of approximately 1-2 bubbles per second (ca. 30-100 mL/min).
- Details of trap for CO2:
The CO2 produced in each test bottle reacted with the barium hydroxide in the gas scrubbing bottle and precipitated out as barium carbonate. 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® ampul). 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 blank and test suspension. Titrations for the positive and toxicity control were made frequently until day 14.

SAMPLING
- Sampling frequency: Titration were made on day: 2, 5, 7, 9, 14, 19, 23, 27 and 29

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes
- Positive control: yes
- Toxicity control: yes
Reference substance:
other: Sodium acetate
Parameter:
% degradation (CO2 evolution)
Value:
100
Sampling time:
28 d
Details on results:
- Theoretical CO2 production: The ThCO2 of FDCA was calculated to be 1.69 mg CO2/mg.

- Biodegradation: The relative biodegradation values calculated from the measurements performed during the test period revealed complete biodegradation of FDCA in both test bottles. Furthermore, FDCA biodegradation of at least 60% was reached within a 10-day window.
In the toxicity control more than 25% biodegradation occurred within 14 days (73%, based on ThCO2). Therefore, the test substance was assumed not to inhibit microbial activity.

- Acceptability of the test:
1. The positive control substance was biodegraded by at least 60% (83%) within 14 days.
2. The difference of duplicate values for the %-degradation of the test substance at the plateau, at the end of the test and at the end of the 10-day window, was less than 20.
3. The total CO2 release in the blank at the end of the test did not exceed 40 mg/L (44 mg CO2 per 2 litres of medium, corresponding to 22 mg CO2/L).
4. The Inorganic Carbon content (IC) of the test substance (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 (carbon levels < 500 ppb), IC was less than 5% of TC (mainly coming from the test substance, 12 mg TOC/L).
Results with reference substance:
- Functioning of the test system was checked by testing the reference substance sodium acetate, which showed a normal biodegradation curve. Biodegradation of sodium acetate at 14 days was 83%. The ThCO2 of sodium acetate was calculated to be 1.07 mg CO2/mg.
Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
FDCA was readily biodegradable under the conditions of the modified Sturm test.
Executive summary:
The readily biodegradation of FDCA under the conditions of the carbon dioxide (CO2) evolution test (modified Sturm test) was investigated according to OECD guideline 301 B and GLP principles. The test substance was tested in duplicate at 26 mg/L, corresponding to 12 mg TOC/L. The biodegradation of FDCA was 100% (mean of two bottles) after 28 days. It was concluded that FDCA was readily biodegradable under the conditions of the modified Sturm test. The study is considered to be reliable without restrictions.

Description of key information

The readily biodegradation of FDCA under the conditions of the carbon dioxide (CO2) evolution test (modified Sturm test) was investigated according to OECD guideline 301 B and GLP principles. The biodegradation of FDCA was 100% after 28 days. It was concluded that FDCA was readily biodegradable under the conditions of the modified Sturm test. The study is considered to be reliable without restrictions.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

The readily biodegradation of FDCA under the conditions of the carbon dioxide (CO2) evolution test (modified Sturm test) was investigated according to OECD guideline 301 B and GLP principles. The test substance was tested in duplicate at 26 mg/L, corresponding to 12 mg TOC/L. The biodegradation of FDCA was 100% (mean of two bottles) after 28 days. It was concluded that FDCA was readily biodegradable under the conditions of the modified Sturm test. The study is considered to be reliable without restrictions.