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Environmental fate & pathways

Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: screening tests
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Limited data, but performed similar to OECD 311, no GLP
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 311 (Anaerobic Biodegradability of Organic Compounds in Digested Sludge: Measurement of Gas Production)
Principles of method if other than guideline:
The experiment was performed according to ECETOC (1988) with the test substance. The concentration of test substance was 50, 60 and 90 mg/L and the fermentation periods were from 28-61 days with level measurement of background gas (CO2 and methane) and dissolved organic carbon (DIC).

A known volume of (pretreated) anaerobic sludge is suspended in an oxygen free medium and placed in a suitable vessel leaving sufficient headspace into which any gases produced may be evolved. The concentration of solids corresponds to about 10 % of that usually present in a full scale digester. A small amount of test substance of known carbon content is added to each of the test vessels which are then sealed and incubated at a constant temperature and pH for a period of up to 8 weeks. Any carbon dioxide and methane produced by the inoculum is quantified from measurements on control digesters.
GLP compliance:
not specified
Oxygen conditions:
anaerobic
Inoculum or test system:
sewage, predominantly domestic (adaptation not specified)
Details on inoculum:
- Source of inoculum/activated sludge: from a sewage plant treating predominantly domestic sewage
- Pretreatment: The sludge is washed to reduce the inorganic carbon content to an appropriate concentration (< 10 mg IDC/L in the final test solution). The washing procedure consists of centrifuging the sludge in sealed tubes at a relatively low speed (e.g. 3000g) for up to 5 minutes not lower that room temperature. Some treatments are predigested for 2 or 4 days at 35 +/- 2 ℃.
- Concentration of sludge: 1-5 g/L
No additional data available
Duration of test (contact time):
>= 56 d
Initial conc.:
50 other: mg C/L
Based on:
ThIC
Parameter followed for biodegradation estimation:
other: background gas production and DIC
Details on study design:
TEST CONDITIONS
- Composition of medium: deionised water containing per liter: potassium dihydrogen phosphate 0.27 g, disodium hydrogen phosphate 1.12 g, ammonium choride 0.53 g, calsium chloride 0.075 g, magnesium chloride 0.10 g, ferrous chloride 0.20 g, resazurin (redox indicator) 0.0001 g
- Test temperature: 35 ± 2℃
- pH: 6.7-7.1
- pH adjusted: yes


TEST SYSTEM
- Culturing apparatus: closed vessel
- Number of culture flasks/concentration: 3 to 5 replicates
- Method used to create anaerobic conditions: sealing with inert gas septa, incubation at 35 +/- 2 degrees Celsius for one hour
- Measuring equipment: pressure measuring device, carbon analyser (direct DIC determination in range 0-200 mg DIC/L)
Reference substance:
not specified
Preliminary study:
No information provided.
Test performance:
No information provided.
Parameter:
% degradation (CO2 evolution)
Value:
89.5
Sampling time:
35 d
Remarks on result:
other: Washed sludge, inoculum 50 mg/L test material
Parameter:
% degradation (CO2 evolution)
Value:
110.5
Sampling time:
21 d
Remarks on result:
other: Unwashed sludge, inoculum 50 mg/L test material
Details on results:
No information provided.
Validity criteria fulfilled:
yes
Interpretation of results:
other: The biodegration rate is >= 89 % over 21-35 days.
Conclusions:
The biodegration rate is >= 89 % over 21-35 days.
Executive summary:

A known volume of (pretreated) anaerobic sludge is suspended in an oxygen free medium and placed in a suitable vessel leaving sufficient headspace into which any gases produced may be evolved. The concentration of solids corresponds to about 10 % of that usually present in a full scale digester. A small amount of test substance of known carbon content is added to each of the test vessels which are then sealed and incubated at a constant temperature and pH for a period of up to 8 weeks. Any carbon dioxide and methane produced by the inoculum is quantified from measurements on control digesters.

The biodegration rate of the test substance is >= 89 % over 21-35 days under the conditions of this test.

Description of key information

Several non-guideline tests are available that investigate the biodegradability of the test substance under aerobic conditions. The outcome of the tests is indicative for rapid biodegradation in fresh water. Kohei (1985) finds 61-69% degradation (as BOD or DOC) over a priod of 80 hours, MITI (1979) reported 98% degradation (as TOC) over 14 days, Howard (1981) >94.5% (decrease of radioactivity) over 7 days and Freitag (1985) 65.4% (CO2 evolution) over 5 days at a concentration of 0.05 mg/L test substance.

In seawater the test substance degrades 10-80% (DOC removal) over a period of 8-28 days (Shimp 1987), but the test is performed without adding a specific inoculum to the water. Two tests with similarities to simulation testing are available (Junker 2009) that indicate that in a water sediment system the test substance degrades > 74.4% over a 8-day period. These studies are considered to be the key studies.

Several studies indicating that the test substance is completely biodegradable under anaerobic conditions are available (Birch, 1989; Uma, 2007;Nottingham, 1969; Kameya, 1995). The key study for anaerobic degradation (Birch, 1989) is performed according to the methods as described under OECD 311.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

Based on the large number of studies indicating a rapid and almost complete biodegradation, it can be concluded that the test substance is readily biodegradable. Although most tests do not provide information on the passing of the 10-day window, this is considered to be passed, because the overall test duration is in most tests shorter than 10 days.