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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:
From August 19, 1987 to August 24, 1987
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
according to
Guideline:
other: Methods for the Examination of Waters and Associated Materials
Principles of method if other than guideline:
The principle of the BOD test involves measurement of the reduction in dissolved oxygen in the presence of the test sample and naturally occurring bacteria. The biological seed is obtained from a river, downstream of a sewage plant treating mainly domestic sewage. A bottle is set up containing dilution water seeded with bacteria (the blank). An aliquot of test substance or stock solution is added to dilution water to give the required concentration. Initially two different test concentrations are set up. The dissolved oxygen concentration is measured in all bottles at the start of the test (Day 0) and 5 days after the start, and the oxygen consumption of the test substance is calculated by comparison of the loss of DO with the loss of DO in the blank. The BOD of the sample is calculated in mg O2 consumed per gram of test substance and degradation is reported as a percentage of the COD of the sample. The COD involves oxidation of the test sample under standard conditions by acidified dichromate and titration of the residual dichromate with a ferrous ammonium sulphate solution.
GLP compliance:
yes
Specific details on test material used for the study:
Reference number: NBW 7993/9
Physical state: Red/purple powder contraining 9% moisture
Purity: considered 100%
Storage: in dark and ambient temperature
Inoculum or test system:
activated sludge, domestic, non-adapted
Duration of test (contact time):
ca. 5 d
Initial conc.:
ca. 1 g/L
Details on study design:
Perpetration of standard solutions: A standard solution in distilled water was prepared at a strength of 1 g/L. This same solution was used for the determination of required parameters.

5 day BOD: Thios was carried out on 25 times dilution and 250 times dilution of the standard solution of test substance. The procedure involves incubating test substance in a completely full and stoppred bottle using dilution medium consisting of distilled water containing prescribed inorganic salts and bacterial inoculum prepared from a treated domestic sewage effluent. The incubation carried out at nominal 20˚C and the BOD5 calculated at the end of 5 d measuring the dissolved oxygen in the test bottles in comparison with controls.


COD: The procedure involves the refluxing an aliquot of the substance solution with and excess of acidified potassium dichromate in the presence of silver sulphate and mercury sulphate. After cooling
The excess dichromate was titrated with ferrous ammonium sulphate using ferrous phenanthroline indicator.
Key result
Parameter:
other: BOD5/COD
Remarks:
%
Value:
ca. 13.4
Sampling time:
5 d
Remarks on result:
other: Not readily biodegredable
Details on results:
BOD: The results T the 25 times dilution showed a mean difference of 0.6 mg/L between the test substance and the controls and at the 250 times dilution a mean difference of 0.4 mg/L. These differences corresponds to BOD5 of the substance 0.01 g O2/g and 0.1 g O2/g respectively, but are considered to be below the realistic detection limit of the method, and the BOD5 of the substance therefore recorded as <0.1 g O2/g substance.

COD: The result showed test substance solution had COD strength of 742 mg O2/L corresponding to 0.74 g O2/g substance.
Key result
Parameter:
BOD5
Value:
< 0.1 g O2/g test mat.
Key result
Parameter:
COD
Value:
ca. 7.4 g O2/g test mat.
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
Under the experimental conditions, biodegradation of the test substance was equivalent to 13.5%. The substance is therefore not considered to be readily biodegradable.
Executive summary:

A study was conducted to determine the biodegradability of the test substance based on BOD and COD in a 5 d study. The test involved measuring reduction of dissolved oxygen in the presence of the test substance. Biological inoculum was obtained from a river, downstream of a treatment plant handling mainly domestic sewage. A bottle was set up containing dilution water seeded with the bacteria (blank). An aliquot of the test substance stock solution was added to dilution water to give the required concentration for the study. The dissolved oxygen concentration was measured in all bottles at test start (Day 0) and after 5 d. Oxygen consumption was calculated by comparing dissolved oxygen (DO) loss in the test substance samples versus controls. The BOD of the sample was calculated in mg O2 consumed per gram of test substance and degradation was reported as a percentage of sample COD. The COD involves oxidation of the test substance under standard conditions by acidified dichromate and titration of the residual dichromate with ferrous ammonium sulphate solution. Under the experimental conditions, biodegradation of the test substance was equivalent to 13.5%. The substance is therefore not considered to be readily biodegradable (Brown, 1987).

Description of key information

Key value for chemical safety assessment

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

Additional information

A study was conducted to determine the biodegradability of the test substance based on BOD and COD in a 5 d study. The test involved measuring reduction of dissolved oxygen in the presence of the test substance. Biological inoculum was obtained from a river, downstream of a treatment plant handling mainly domestic sewage. A bottle was set up containing dilution water seeded with the bacteria (blank). An aliquot of the test substance stock solution was added to dilution water to give the required concentration for the study. The dissolved oxygen concentration was measured in all bottles at test start (Day 0) and after 5 d. Oxygen consumption was calculated by comparing dissolved oxygen (DO) loss in the test substance samples versus controls. The BOD of the sample was calculated in mg O2 consumed per gram of test substance and degradation was reported as a percentage of sample COD. The COD involves oxidation of the test substance under standard conditions by acidified dichromate and titration of the residual dichromate with ferrous ammonium sulphate solution. Under the experimental conditions, biodegradation of the test substance was equivalent to 13.5%. The substance is therefore not considered to be readily biodegradable (Brown, 1987).