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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:
May 16 - Aug 22, 2019
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Version / remarks:
July 17, 1992
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Version / remarks:
EEC Publication No. L 383 A, December 1992
Deviations:
no
GLP compliance:
yes (incl. certificate)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
Aerobic activated sludge, microorganisms from a domestic waste water treatment plant was supplied by the sewage treatment plant Rossdorf, Germany.

The aerobic activated sludge used for this study was deposited for 15 min, washed by centrifugation and the supernatant liquid phase was decanted. The solid material was re-suspended in test water and centrifuged again. This procedure was done three times. An aliquot of the final sludge suspension was weighed, dried and the ratio of wet sludge to its dry weight was determined. Based on this ratio, calculated aliquots of washed sludge suspension, corresponding to 3.5 g dry material per litre were mixed with test water and aerated overnight. This suspension was used for the experiment.
Duration of test (contact time):
28 d
Initial conc.:
101.8 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
28 d
Details on results:
The mean biodegradation at test end after 28 days was 0% (ThODNH4).
Results with reference substance:
The reference item sodium benzoate was sufficiently degraded to 84% after 14 days after 28 days of incubation.
Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
The degradation rate of the test item did not reach 60 % within the 10-day window and after 28 days of incubation. Thus, the test item is not readily biodegradable.
Executive summary:

The purpose of this study was to determine the ready biodegradability of the test item.The information for this endpoint study record was obtained from an experimental study. The OECD GLP criteria were met and the methods applied are fully compliant with OECD TG  301F.

The test item was exposed to aerobic activated sludge from the aeration tank of a domestic waste water treatment plant for 28 days. The biodegradation was followed by the oxygen uptake of the microorganisms during exposure. As a reference item sodium benzoate was tested simultaneously under the same conditions as the test item, and functioned as a procedure control. This type of study is recognized by the international test guidelines and should provide a rational basis to assess the ready biodegradation properties of the test item when incubated with aerobic activated sludge.

The criterion for ready biodegradability under the conditions of a manometric respirometry test is the degradation of the test item of at least 60%, reached within a 10-day window; the 10-day window starts when the degradation of the test item reaches at least 10% degradation. The test item never reached 10% biodegradation. The mean biodegradation at test end after 28 days was 0% (ThODNH4). Therefore, the test item is considered to be not readily biodegradable based on ThODNH4.

The reference item sodium benzoate was sufficiently degraded to 82% after 14 days and 90% after 28 days of incubation, thus confirming the suitability of the aerobic activated sludge inoculum used.

In the toxicity control containing both, the test item and the reference item sodium benzoate, 29% (ThODNH4) biodegradation was noted within 14 days and 31% after 28 days of incubation. According to the test guidelines, the test item can be assumed to be not inhibitory to the aerobic activated sludge microorganisms because degradation was >25% within 14 days.

Under the conditions of this study the test item is considered to be not readily biodegradable.

Description of key information

OECD 301F: 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 purpose of this study was to determine the ready biodegradability of the test item.

The test item was exposed to aerobic activated sludge from the aeration tank of a domestic waste water treatment plant for 28 days. The biodegradation was followed by the oxygen uptake of the microorganisms during exposure. As a reference item sodium benzoate was tested simultaneously under the same conditions as the test item, and functioned as a procedure control.

The mean biodegradation at test end after 28 days was 0% (ThODNH4). Therefore, the test item is considered to be not readily biodegradable based on ThODNH4.

The reference item sodium benzoate was sufficiently degraded to 82% after 14 days and 90% after 28 days of incubation, thus confirming the suitability of the aerobic activated sludge inoculum used.

In the toxicity control containing both, the test item and the reference item sodium benzoate, 29% (ThODNH4) biodegradation was noted within 14 days and 31% after 28 days of incubation.

Under the conditions of this study the test item is considered to be not readily biodegradable.