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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:
24 November 2015 - 22 December 2015
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.4-E (Determination of the "Ready" Biodegradability - Closed Bottle Test)
Deviations:
no
Qualifier:
according to
Guideline:
EPA OPPTS 835.3110 (Ready Biodegradability)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
Appearance: Blue powder
Purity: ≥85.5%
Manufacture date: 19 November 2014
Storage condition: Controlled room temperature (15-25oC, below 70 RH%)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
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.
Duration of test (contact time):
28 d
Initial conc.:
ca. 3.5 mg/L
Based on:
DOC
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
The incubation period of the closed bottle test was 28 days.
The oxygen concentrations were measured with an oxygen meter with a stirring O2 electrode. Oxygen measurements were performed in duplicate on days 0, 7, 14, 21 and 28.
Reference substance:
benzoic acid, sodium salt
Preliminary study:
not specified
Test performance:
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.
Key result
Parameter:
% degradation (O2 consumption)
Value:
ca. -1.7
Sampling time:
28 d
Details on results:
Under the test conditions the percentage biodegradation of B331 reached a mean of -1.7 % 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 72.5% after 14 days, and to a mean of 80.8 % 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 34.8 % biodegradation was noted within 14 days and 39.4% 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 3.5 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 B331 reached a mean of -1.7 % 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.
According to the test guidelines the test item can be assumed to be not inhibitory at the applied concentration level of 3.5 mg/L on the activated sludge microorganisms because degradation was >25 % within 14 days.

Description of key information

Not readily biodegradable (-1.7% degradation achieved by 28 days, Closed Bottle Test, OECD301D / EC C4-E).

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed
Type of water:
freshwater

Additional information

A ready biodegradability test was conducted to assess the degradation potential of B331 (CiToxLAB, 2016). The study was conducted using the closed bottle test according to OECD test guideline 301D and EC test guideline C4-E) and in compliance with GLP.

The substance was not found to have been significantly degraded over the 28-day monitoring period (-1.7% degradation was recorded, measured in terms of oxygen consumption). The substance was found not to have been inhibitory to the inoculum.

B331 was determined not to be readily biodegradable on the basis of the above result.