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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:
25 February to 28 March 2002
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
Volatility might have influenced the outcome of the test. However, since this would result in underestimation of the potential for biodegradation the outcome is considered worst-case.
Qualifier:
according to
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: 0550109421006
- Expiration date of the lot/batch: Not indicated
- Purity test date: 99.5 %

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: Well ventilated 10 – 20 °C
- Stability under test conditions: Not indicated
- Solubility and stability of the test substance in the solvent/vehicle: practically insoluble (in water)

FORM AS APPLIED IN THE TEST (if different from that of starting material): colourless liquid
Oxygen conditions:
aerobic
Inoculum or test system:
sewage, predominantly domestic (adaptation not specified)
Details on inoculum:
The inoculum used for this test was the secondary effluent from a predominantly domestic sewage treatment works.
Source: Cambridge Sewage Treatment Works.
Date of collection: 21 February 2002.
Storage conditions prior to test: The sludge was used directly upon collection.

Inoculum preparation:
The sludge was passed through a 500μm sieve. This was centrifuged (@4000rpm for 5 minutes) and re-suspended in mineral media. The process was repeated. The solids content of the centrifuged sludge was determined by loss on drying (at 105°C). The sludge was used at 30mg/l (dry weight) in the test vessels.
Duration of test (contact time):
28 d
Initial conc.:
30 mg/L
Based on:
TOC
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
A measured volume of inoculated mineral medium, containing a known concentration of the test substance (10 to 20 mg/litre total organic carbon) as the nominal source of organic carbon, is aerated by the passage of carbon dioxide free air at a controlled rate in the dark at 22 ± 2°C. Degradation is followed over 28 days by determining the carbon dioxide produced. The carbon dioxide is trapped in sodium hydroxide and is measured as Dissolved Inorganic Carbon (DIC) using a Tekmar-Dohrmann Phoenix 8000 (the UV-Persulfate Analyser). The amount of carbon dioxide produced is usually expressed as a percentage of the theoretical carbon dioxide (ThCO2). In practice, carbon dioxide (detennined as DIC) is expressed as a percentage of the organic carbon in the test material. Test and reference values are corrected for inoculum blank.

Insoluble materials are weighed onto microscope cover slips, which are then introduced directly to the bioreactor. Soluble and emulsifiable materials are washed in directly using approximately 10 ml of distilled water. On day 28, 1 ml of concentrated hydrochloric acid is added to each bioreactor, which are aerated
overnight, to drive off the remaining carbon dioxide. One last analysis of evolved carbon dioxide is made on day 29.
Reference substance:
acetic acid, sodium salt
Key result
Parameter:
% degradation (inorg. C analysis)
Value:
25
Sampling time:
29 d
Remarks on result:
other: average value of duplicate
Parameter:
% degradation (inorg. C analysis)
Value:
18
Sampling time:
7 d
Remarks on result:
other: average value of duplicate
Parameter:
% degradation (inorg. C analysis)
Value:
24
Sampling time:
14 d
Remarks on result:
other: average value of duplicate
Parameter:
% degradation (inorg. C analysis)
Value:
25
Sampling time:
25 d
Remarks on result:
other: average value of duplicate
Details on results:
The inoculum blank should not normally produce more than 40 mg/l CO2 (10.9 mg/l C) over the 28 days for the test to be valid.
A value of 12.43 mg/l CO2 (3.4 mg/l C) was recorded.

The reference material reached 61% degradation after a 6 day window.

No toxicity to the inoculum was concluded from the toxicity control data (> 70% biodeg at day 28)
Results with reference substance:
The reference material reached 61%after a 6 day window (estimated graphically).
Validity criteria fulfilled:
yes
Remarks:
see details on results
Interpretation of results:
not readily biodegradable
Remarks:
since volatility might have influenced the results obtained for biodegradability, the result can be considered worst-case and potentially underestimates the true environmental biodegradation.
Conclusions:
Eventhough MNK TECH failed to meet the requirements for a pass in this test, this does not necessarily mean that the test substance is not biodegradable under environmental conditions, but indicates that more work would be necessary to establish biodegradability.
Executive summary:

In order to assess the biodegradation of MNK TECH, a screening test was performed according to OECD TG 301B (CO2 Evolution test) and under GLP conditions. In this study secondary effluent from a predominantly domestic sewage treatment works was used as inoculum. Test substance was dosed at 30 mg/L TOC (based on 77.5% C in test material). Degradation was assessed over 28 days by determining the amount of carbon dioxide produced. MNK TECH was degradaed for 25% after 28d, hence less than the pass level indicating readily biodegradability.

Description of key information

In order to assess the biodegradation of MNK TECH, a screening test was performed according to OECD TG 301B (CO2 Evolution test) and under GLP conditions. In this study secondary effluent from a predominantly domestic sewage treatment works was used as inoculum. Test substance was dosed at 30 mg/L TOC (based on 77.5% C in test material). Degradation was assessed over 28 days by determining the amount of carbon dioxide produced. MNK TECH was degradaed for 25% after 28d, hence less than the pass level indicating readily biodegradability.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information