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Environmental fate & pathways

Biodegradation in water: screening tests

Administrative data

Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
7th April - 8th May 2010
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Study is to current guidelines and was performed in accordance with GLP.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2010
Report date:
2010

Materials and methods

Test guideline
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
GLP compliance:
yes (incl. QA statement)

Test material

Constituent 1
Reference substance name:
PCOC
IUPAC Name:
PCOC
Details on test material:
Test substance supplied by Nufarm UK Limited.

Study design

Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge (adaptation not specified)
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Cambridge Sewage Treatment Works, Cowley Road.
- Preparation of inoculum for exposure: The sludge was sieved, settled, decanted and re-suspended using mineral media.
Centrifuged at 4000rpm for 10 minutes, the supernatant discarded and re-suspended. The above step was repeated. Dry sludge solids determination was conducted on the pellet produced.
Dry sludge solids: 8.6%
Dry sludge solids in test: 0.03 g/L
Volume of mineral medium: 1.5 L per bioreactor.
- Type and size of filter used, if any: 850-micron filter.
Duration of test (contact time):
28 d
Initial test substance concentration
Initial conc.:
> 50.4 - < 51.7 other: mg
Based on:
test mat.
Parameter followed for biodegradation estimation
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Test temperature: 22 +/-2 °C
- pH: not specified
- Aeration of dilution water: Atmospheric air was scrubbed clean of carbon dioxide by passing over soda lime prior to being pumped into the test system
- Continuous darkness: Yes

TEST SYSTEM
- Culturing apparatus: Conical flasks of nominal volume 2000ml.
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: CO2 free air passed through the test medium for the duration of the test.
- Measuring equipment: Tekmar-Dohrmann Phoenix 8000 (UV-Persulphate analyser).
- Details of trap for CO2 and volatile organics if used: Two CO2 traps were placed sequentially post test vessel to trap the evolved CO2.

SAMPLING
- Sampling frequency: The test medium was sampled for analysis on days 2, 5, 7, 9, 14, 19, 23, 28, 29.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes
- Toxicity control: 51.4 mg PCOC and 102.5 mg sodium acetate.


Reference substance
Reference substance:
acetic acid, sodium salt

Results and discussion

% Degradation
Parameter:
% degradation (CO2 evolution)
Value:
ca. 2
Sampling time:
2 d
Remarks on result:
other: 28 days study but for the test substance the highest degradation was observed on day 2.

BOD5 / COD results

Results with reference substance:
The guideline states that the reference material must degrade by at least 60% of its Theoretical Carbon Dioxide (ThCO2) value, a maximum value of 88% degradation of the sodium acetate was achieved on day 29. This is within the guidelines.

Applicant's summary and conclusion

Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
Under the test conditions PCOC is not considered to biodegrade, however due to the stringency of the test , this does not necessarily mean that the test substance is not biodegradable under environmental conditions.
Executive summary:

A guideline study was performed in accordance with GLP, to assess the ready biodegradability of PCOC in freshwater using the CO2 evolution test. A measured volume of inoculated mineral medium containing a known concentration of the test substance (ca 50 mg PCOC) was aerated by the passage of CO2 free air at a controlled rate and in the dark, at 22 +/-2°C. The CO2 evolved from the degradation was retained using sodium hydroxide traps. Degradation was followed over a period of 28 days by determination of the evolved CO2. The CO2 evolved is expressed as a percentage of the organic carbon in the test material.

The CO2 evolution test was also performed on a toxicity control of sodium acetate and inoculum blanks. Test and reference values were corrected for the inoculum blank as appropriate.

On day 28, 1 ml of concentrated HCl was added to drive off the remaining CO2 and a final reading made on day 29.

The results showed that the maximum degradation observed for PCOC was 2% on day 2 of the test.

60% of greater degradation relative to the theoretical CO2 value is required for a substance to be considered biodegradable. Under the conditions of the test, PCOC is not considered to be biodegradable. However due to the stringency of the test, this does not necessarily mean that the test substance is not biodegradable under environmental conditions.

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