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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 26 October 2015 To 18 March 2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.4-E (Determination of the "Ready" Biodegradability - Closed Bottle Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: CY50561001
- Expiration date of the lot/batch: 24 April 2016
- Purity: 65.4% (for the substance in solution)

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: Controlled room temperature (15-25oC, below 70 RH%)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Activated sludge, microorganisms from a domestic waste water treatment plant. The activated sludge was supplied from the sewage plant for domestic sewage in Veszprém, Hungary.
- Conditioning: The activated sludge used for this study was washed by centrifugation (for 10 min.) and the supernatant liquid phase was decanted. The solid material was re-suspended in isotonic saline solution and again centrifuged (for 10 min.). This procedure was repeated twice. 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 4 g dry material per litre were mixed with test water (see below) and then aerated until use (not later than an hour). Before use the sludge was filtered through cotton wool.
- Concentration of sludge: 4 g/l
Duration of test (contact time):
28 d
Initial conc.:
111 mg/L
Based on:
COD
Parameter followed for biodegradation estimation:
O2 consumption
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
0.8
Sampling time:
28 d
Results with reference substance:
The reference item Sodium benzoate was sufficiently degraded to a mean of 71.7% after 14 days, and to a mean of 78.3 % after 28 days of incubation, based on ThODNH4, thus confirming the suitability of the used activated sludge inoculum.

In the toxicity control containing both, the test item and the reference item Sodium benzoate, a mean of 28.1 % biodegradation was noted within 14 days and 29.6% biodegradation after 28 days of incubation.

According to the test guidelines the test item can be assumed to be not inhibitory at the applied concentration level of 11.1 mg/L on the activated sludge microorganisms because degradation was >25 % within 14 days.

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
Under the test conditions the percentage biodegradation of Diquat reached a mean of 0.8 % after 28 days based on the measured COD of the test item. Therefore the test item is considered not readily biodegradable.
Executive summary:

The test item Diquat was investigated for its ready biodegradability in a Closed Bottle Test over a period of 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 test system was a microbial inoculum of good quality, collected from a sewage plant for domestic sewage. The sludge was washed by centrifugation, filtered through cotton wool and aerated until use. Based on the determined dry weight content, the washed sludge suspension contained 4 g dry material per litre.

Under the test conditions the percentage biodegradation of Diquat reached a mean of 0.8 % after 28 days based on the measured COD of the test item. Therefore the test item is considered not readily biodegradable.

According to the test guidelines the pass level for ready biodegradability is removal of 60 % ThOD.

The reference item Sodium benzoate was sufficiently degraded to a mean of 71.7% after 14 days, and to a mean of 78.3 % after 28 days of incubation, based on ThODNH4, thus confirming the suitability of the used activated sludge inoculum.

In the toxicity control containing both, the test item and the reference item Sodium benzoate, a mean of 28.1 % biodegradation was noted within 14 days and 29.6% biodegradation after 28 days of incubation.

According to the test guidelines the test item can be assumed to be not inhibitory at the applied concentration level of 11.1 mg/L on the activated sludge microorganisms because degradation was >25 % within 14 days.

Description of key information

- 0.8 % biodegradation after 28 days (based on the measured COD of the test item)

- OECD TG 301D and EU Method C.4-E under GLP

- No deviation

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

The test item is considered not readily biodegradable.