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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:
other: Guideline study with GLP.
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 E (Ready biodegradability: Modified OECD Screening Test)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.4-B (Determination of the "Ready" Biodegradability - Modified OECD Screening Test)
Deviations:
no
Principles of method if other than guideline:
The ready biodegradability was determined by the measurement of the dissolved organic carbon at frequent intervals over a 28 d period.
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
sewage, predominantly domestic, non-adapted
Details on inoculum:
Inoculum from the effluent of the sewage treatment works A-2451 Au am Leithagebirge, Austria, which waste-water catchment is predominantly domestic, was collected. On arrival in the laboratory, the sample was aerated by means of filtered compressed air for about 60 minutes before being used for the study.
The inoculum was not acclimatised or adapted to the test substance before exposure in this study.
Duration of test (contact time):
28 d
Initial conc.:
20 mg/L
Based on:
DOC
Parameter followed for biodegradation estimation:
DOC removal
Details on study design:
- Negative controls (blank): 2 vessels (NK1 and NK2), the medium plus inoculum was used.
- Test substance groups: 2 vessels (A3 and A4), test substance (20 mg nominal DOC/L) + inoculum.
- Positive control: the reference substance employed in this study was sodium benzoate (vessel PK).
- Toxicity control (TK): test substance (20 mg nominal DOC/L) + reference substance (sodium benzoate, 20 mg nominal DOC/L) + inoculum.
- Abiotic sterile control (ASK): test substance (20 mg nominal DOC/L) + 5 mL 1 % HgCl2 solution per litre test medium, no inoculum.
- Adsorption control (AK): test substance (20 mg nominal DOC/L) + 5 mL 1 % HgCl2 solution per litre test medium + inoculum.
The DOC of the blanks is that of the test medium plus inoculum.

Procedure
Each 2-litre conical flask reaction vessel was filled with 800 mL mineral medium. Sufficient stock solution of the test and/or the reference substance was added for groups A, PK, TK, ASK and AK. The vessel was then made up to 1 litre with deionised water. The pH value was checked. Each flask was then inoculated with 1.2 mL sewage effluent with ca. 1 x 10^5 cells, (except for group ASK). The number of cells was determined with a Casy Cell Counter, Model DT. The opening of the vessels was covered with aluminium foil in such a way that the exchange of air was guaranteed. The vessels were inserted in a shaking machine and kept there in darkness until the end of the study.
Test duration: 28 days.

Reference substance:
benzoic acid, sodium salt
Parameter:
% degradation (DOC removal)
Value:
3.97
Sampling time:
10 d
Remarks on result:
other: The mean of 2 vessels is reported.
Parameter:
% degradation (DOC removal)
Value:
25.9
Sampling time:
21 d
Remarks on result:
other: The mean of 2 vessels is reported.
Parameter:
% degradation (DOC removal)
Value:
24.4
Sampling time:
28 d
Remarks on result:
other: The mean of 2 vessels is reported.
Details on results:
The test substance was degraded by 24 % within 28 days.
Results with reference substance:
Positive control: The plateau of biodegradation was reached on Day 4 and the degradation of the positive control substance sodium benzoate exceeded the pass level of 70% within 14 days.

Toxicity control: Degradation in the toxicity control, which contained sodium benzoate and the test substance, was not indicative of an inhibition of the microbial activity by the test substance.

Abiotic degradation: On Day 0, the DOC concentration was between 18.15 and 18.60 mg/L and on Day 28 between 16.19 and 16.39 mg/L, therefore no abiotic degradation to inorganic carbon occurred in the abiotic sterile control.

Adsorption control: On Day 0, the DOC concentration was between 18.67 and 18.79 mg/L and on Day 28 between 16.37 and 16.43 mg/L, therefore no adsorption of the test substance to the inoculum occurred.

Environmental control:

- Temperatures recorded were 22.7 ± 0.4 °C.

- No major deviations of the pH were seen during the study.

Validity of the test: The test is considered valid if the difference of extremes of replicate values of the removal of the test substance at the plateau, at the end of the test or at the 10-d window, as appropriate, is less than 20 % and if the percentage degradation of the reference compound has reached the pass levels by day 14.

These criteria were fulfilled.

Validity criteria fulfilled:
yes
Interpretation of results:
other: biodegradable but not readily biodegradable
Conclusions:
MPI-ACA was degraded by 24 % within 28 days.
Executive summary:

The biodegradability of MPI-ACA was determined by measurement of dissolved organic carbon at frequent intervals over a 28 d period. The method used was that described in Part C.4-B of the EC Commission Directive 92/69/EEC and in the OECD Guideline 301 E.

Results

• The reference substance sodium benzoate was degraded by 96.0% within 14 days.

• Degradation in the toxicity control, which contained sodium benzoate and the test substance, was not indicative of an inhibition of the microbial activity by the test substance.

• The biodegradation of MPI-ACA was 24 % within 28 days. MPI-ACA is therefore not regarded as readily biodegradable.

Description of key information

The biodegradation is 24 % within 28 days.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable

Additional information

Inherent biodegradable according to the definition of the OECD. Inherent biodegradable: A classification of chemicals for which there is unequivocal evidence of biodegradation (primary or ultimate) in any test of biodegradability.