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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:
2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
GLP compliance:
yes
Oxygen conditions:
anaerobic
Inoculum or test system:
activated sludge (adaptation not specified)
Details on inoculum:
Activated sludge from the municipal wastewater treatment plant Breisgauer Bucht was used as inoculum with a concentration corresponding to 30 mg dry solids per litre. The treatment plant clarifies predominantly domestic wastewater and has a capacity of 600.000 inhabitant equivalents. Sampling date of activated sludge was 28 November 2017. The dry solids (d.s.) content of the activated sludge was 4.7 g/L. It was determined by weight measurements after drying at 105°C for 3.25 hours (mean of triplicate measurements).
Duration of test (contact time):
28 d
Initial conc.:
100 mg/L
Based on:
ThOD
Parameter followed for biodegradation estimation:
other: BOD oxygen demand
Details on study design:
The system OxiTop®- Control from WTW, Weilheim and the Sensomat-System from Aqualytic GmbH & Co., Langen were used as test systems. They consist of narrow-necked glass bottles with rubber sleeve inserts for NaOH pellets, in which the carbon dioxide evolved is absorbed.
The liquid volume was fixed as 164 mL each. Magnetic stir bars were introduced into the bottles which were positioned on a stirrer platform. The bottles were sealed tightly with the measuring heads with a measuring range of 500 – 1350 hPa. Every 112 minutes the current pressure was measured and stored by each measuring head. At the end of the experiment pressure data were read out via an infrared interface to the controller unit and afterwards data were transferred via a RS232 interface using the Achat OC software of WTW to an Excel file where further data processing was carried out. Additionally several measured values were randomly read out and recorded by hand and were afterwards compared with the printed excel table for quality control.

In total three reactors containing the test item, three reactors containing only inoculum (blank), three reactors containing the reference compound (reference) and one reactor containing reference compound and test item (toxicity control) were set up.
The test flasks were filled as described in paragraphs 5.4 - 5.7 and tempered to the incubation temperature for about one hours. Afterwards, 1050 μL of the inoculum were added into each flask, one sodium hydroxide pellet was added to each rubber quiver inserted in the flasks and the flasks were sealed tightly with the measuring heads and the test was started. After 28 days the data were read out and the pH in the flasks was measured on the next day.
Reference substance:
other: sodium acetate
Key result
Parameter:
% degradation (DOC removal)
Value:
2.9
Sampling time:
28 d
Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
There was no biodegradation of the test item observed within 28 days, the degradation extent at the end of the test was 2.9 %. Since the degradation at the end of the 10-d window was below 60%, the criterion of the10-d window was not met.

Therefore the test item did not reach the pass level for ready biodegradability (60% ThOD within 28 days and 10 d-window).
Executive summary:

The test item did not reach the pass level for ready biodegradability (60% ThOD within 28 days and 10 d-window).

Description of key information

There was no biodegradation of the test item observed within 28 days, the degradation extent at the end of the test was 2.9 %. Since the degradation at the end of the 10-d window was below 60%, the criterion of the10-d window was not met.

Therefore the test item did not reach the pass level for ready biodegradability (60% ThOD within 28 days and 10 d-window).

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

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