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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
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
A mixed population of activated sewage sludge micro-organisms was obtained on 9 July 2007 from the aeration stage of the Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK, which treats predominantly domestic sewage.
Duration of test (contact time):
28 d
Initial conc.:
10 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
CO2 evolution
Reference substance:
benzoic acid, sodium salt
Preliminary study:
The results of the preliminary investigation work suggested that the test material did not absorb to filters and/or activated sewage sludge, however the result for the 100 mg/L, inoculated at 30 mg ss/L, filtered sample was lower than expected based on the other analyses conducted. A thorough examination of the data could not reveal an explanation for the low value and hence it was considered likely that it was due to sampling and/or analytical variation. For the purposes of the study, samples taken for DOC analysis were centrifuged to remove the suspended solids rather than filtered as a precautionary measure.
Test performance:
The test material attained 13% degradation after 28 days.
Parameter:
% degradation (CO2 evolution)
Value:
13
Sampling time:
28 d
Details on results:
The total CO2 evolution in the control vessels on Day 28 was 25.99 mg/L and therefore satisfied the validation criterion given in the OECD Test Guidelines.

See 'Attached background material' (OECD 301B Biodegradation Curve) attachment below for the biodegradation curve.

Validity criteria fulfilled:
yes
Remarks:
Total CO2 evolution in the control vessels on Day 28 was 25.99 mg/L.
Interpretation of results:
inherently biodegradable
Conclusions:
The test material attained 13% degradation after 28 days and therefore cannot be considered to be readily biodegradable under the strict terms and conditions of OECD Testing Guideline 301B.
Executive summary:

The ready biodegradability of the test substance was determined in accordance with the OECD Guideline for Testing of Chemicals 301B. The ready biodegradation was measured in an aerobic aqueous medium using domestic activated sludge. 10 mg/L of the test material was exposed to activated sewage sludge micro-organisms with culture medium in sealed culture vessels in the dark at approximately 21°C for 28 days. The degradation of the test material was assessed by the determination of carbon dioxide produced. Control solutions with inoculum and the standard material, sodium benzoate, together with a toxicity control were used for validation purposes. The test material attained 13% degradation after 28 days and therefore cannot be considered to be readily biodegradable under the strict terms and conditions of OECD Testing Guideline 301B. The validation criteria of the study were met.

Description of key information

The substance cannot be considered readily biodegradable using the criteria of OECD Testing Guideline 301B. The substance is inherently biodegradable, with some biodegradation being recorded during the 28 day studies.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable

Additional information

Two ready biodegradation studies and one inherent biodegradation study were conducted to assess the biodegradation of the test substance in water. The studies were considered reliable as they were conducted on the registered substance according to OECD Testing Guidelines 301B and 302B.

The key study on BPA 1-4.5EO (OECD 301B) showed a removal of 13% of the test substance after 28 days, as measured by carbon dioxide evolution. The supporting ready biodegradation study on BPA 2EO (OECD 301B) showed removal of 1% of the test substance after 28 days. Study 301B used carbon dioxide evolution to measure biodegradation, whereas study 301F used oxygen consumption as the measurement. The inherent biodegradation study on BPA 1-4.5EO (OECD 302B) showed 34% removal of the test substance over 28 days, as measured by removal of DOC. The studies on the registered substance show that the substance can be considered inherently biodegradable, but not readily biodegradable.