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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 21.12.2018 to 17.07.2019
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 310 (Ready Biodegradability - CO2 in Sealed Vessels (Headspace Test)
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
SOURCE
Activated sludge from the aeration tank from the waste water sewage plant Mannheim, Germany
CULTIVATION
A suitable aliquot of the suspension was sieved by a finely woven mesh with a mesh size of about 1 mm. Subsequently, this sludge suspension was aerated for about 4 days at 20 ± 2° C with carbon dioxide free air to reduce the inorganic carbon content in the blank controls.
PREPARATION FOR EXPOSURE
At the day of exposure, the aeration was stopped, the sludge suspension was washed for one time using drinking water and was left to settle. The supernatant was discarded, and the residue of the sludge suspension was filled up again with drinking water and the sludge of the suspension was adjusted to a final concentration 800 mg/L of dry weight. Aliquots of 0.5 mL from this suspension were added to the test vessels to obtain a sludge concentration of 4 mg/L dry substance in the test assays.
Duration of test (contact time):
28 d
Initial conc.:
34 mg/L
Based on:
test mat.
Initial conc.:
20 mg/L
Based on:
TOC
Parameter followed for biodegradation estimation:
inorg. C analysis
Details on study design:
TEST CONDITIONS
- Composition of medium: see table 1
- Test temperature: 20 +- 2°C
- pH: 7.4
- pH adjusted: adjusted to 7.4 with 1 molar sulphuric acid
- Other: samples were shaken on an orbital shaker at a speed of about 150 rpm

TEST SYSTEM
- Method used to create aerobic conditions: bottles were sealed with butyl rubber septa and aluminum caps
- Measuring equipment:
- Details of trap for CO2 and volatile organics if used:
- Other:

SAMPLING
On each sampling days (Day 3, 5, 7, 12, 14, 19, 24, 26) three bottles of each test assay were sacrificed. On the last day (Day 28) of exposure, five bottles were sacrificed for the test substance assay. During sampling, one mL of 7 molar NaOH solution was injected with a syringe through the septum of each bottle. The bottles were shaken for about one hour afterwards. Carbon dioxide present in the headspace that was evolved during biological processes is dissolved in the alkaline solution during this process. Afterwards, the bottles were opened and the total inorganic carbon (TIC) content trapped in the sodium hydroxide solution during the alkalization of the test assays was determined with a carbon analyzer
- Sample storage before analysis: the samples were analyzed on the same day


TEST/ CONTROL SYSTEM
29 blank control assays
31 test substance assays
29 inhibition control test assays
17 reference substance assays
5 assays for abiotic control: (mercuric chloride was added to inhibit the possible microbial growth)
10 test assays for additional pH and oxygen analysis


CALCULATION/ STATISTICAL METHODS:
Single values of these test assays were used for mean value calculation of the biodegradation degree with a limit of confidence limit of 95%. The measured TIC-values were compared with the added amount of TOC and expressed as biodegradation degree and plotted as biodegradation curve.
Reference substance:
aniline
Preliminary study:
Determination of total organic carbon by combustion
Parameter:
% degradation (inorg. C analysis)
Value:
33
St. dev.:
5
Sampling time:
28 d
Details on results:
Duration of the adaptation phase: approx.8 days

Degree of biodegradation of the test substance at the end of
the ten-days window, mean value: approx. 22% TIC/TOC

Degree of biodegradation of the test substance at the end of
exposure (mean value ±SD of five test assays, limit of
confidence 95%): 33 ±5% TIC/TOC

Degree of elimination of the test substance at physical
chemical control at the end of exposure, mean value: <10% TIC/TOC
Results with reference substance:
- Reference substance: aniline
- Degree of biodegradation of the reference substance after 14 days, mean value: 83% TIC/TOC
- Degree of biodegradation in the inhibition control after 14 days, mean value: 50% TIC/TOC
- Test temperature: 20 +- 2 °C
Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
The test item was not readily biodegradable under the conditions of this test over the 28-day exposure to activated sludge according to OECD guideline 310. The required pass level for ready biodegradability i.e., at least 60% of the theoretical TIC/TOC production in a 10- day window exceeding 10% degradation within the 28-day period of the test was not reached.
Executive summary:

The biodegradability of the test item was assessed according to the OECD guideline 310 (headspace test). The test item (34 mg/L) was exposed to 4 mg/l (dry weight) activated sewage sludge for 28 d under aerobe conditions in test bottles closed with  butyl rubber septa. The inoculum was collected from the aeration tank of a municipal sewage treatment plant. As reference substance aniline was used. After day 3, 5, 7, 12, 14, 19, 24 and 26 three test bottle were analyzed, and five bottles were analyzed on day 28. After 28 days 33 ± 5 % were degraded the 10 day window criteria was not met and the substance cannot be considered readily biodegradable according to OECD criteria.

Description of key information

The test item can not be considered readily biodegradable according to OECD criteria.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable, not fulfilling specific criteria
Type of water:
freshwater

Additional information

The biodegradability of the test item was assessed according to the OECD guideline 310 (headspace test). The test item (34 mg/L) was exposed to 4 mg/l (dry weight) activated sewage sludge for 28 d under aerobe conditions in test bottles closed with butyl rubber septa. The inoculum was collected from the aeration tank of a municipal sewage treatment plant. As reference substance aniline was used. After day 3, 5, 7, 12, 14, 19, 24 and 26 three test bottle were analyzed, and five bottles were analyzed on day 28. After 28 days 33 ± 5 % were degraded the 10 day window criteria was not met and the substance cannot be considered readily biodegradable according to OECD criteria.