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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 November 6 to December 4, 1990
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
according to
Guideline:
OECD Guideline 301 A (Ready Biodegradability: DOC Die Away Test)
Version / remarks:
adopted in 1981
Deviations:
yes
Remarks:
not impairing the study results (details below)
Qualifier:
according to
Guideline:
EU Method C.4-A (Determination of the "Ready" Biodegradability - Dissolved Organic Carbon (DOC) Die-Away Test)
Principles of method if other than guideline:
Internal test method: SOP: MBA 001 02
GLP compliance:
yes
Oxygen conditions:
not specified
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
- Source of inoculum: effluent of a domestic treatment plan (ARA-Rein).
- Inoculation: mixture of polyvalent bacteria collected on 06.11.90.
- Initial cell/biomass concentration: 7 x 10^6/ml.
Duration of test (contact time):
28 d
Initial conc.:
40 mg/L
Based on:
DOC
Remarks:
nominal
Details on study design:
TEST CONDITIONS
- Composition of medium: according to the specification of the EEC Annex V, part C.4 resp. OECD 301 A.
- Test temperature: 23 ± 1 °C.
- Lighting: indirect daylight.

TEST SYSTEM
- Number of culture flasks/concentration: 3 flasks per concentration (only one concentration was tested).
- Estimation technique: TOC/DOC Shimadzu TOC-500.

CONTROL AND BLANK SYSTEM
- Inoculum blank: only inoculum, one replicate.
- Abiotic sterile control: test medium, without inoculum, one replicate.
- Toxicity control: test material and glucose, one replicate.
Reference substance:
other: glucose
Parameter:
% degradation (DOC removal)
Value:
0
Sampling time:
28 d
Details on results:
Test item is not readily biodegradable.
From the results of the inhibition control, no inhibition on the activity of the bacteria can be found.
Results with reference substance:
Biodegradation (28 d): 100 % based on DOC removal.
Carbon determination  Flask theor.conc
mg/l
DOC- concentration afte (mg/l)
Culture medium
(nutrient solution..)
0 (Co) 3d 7d 14d 28d
with test material,
with inocolum (Co,Ct)
1 40 47.9 44.8 44.9 45.0 43.2

with test material,

with inocolum  (Co,Ct)

2 40 47.4 44.9 43.9 44.6 42.3
with test material,
with inocolum
 (Co,Ct)
3 40 47.5 46.3 44.1 43.6 42.3
with test medium, without inocolum (sterile control) 4 40 48.6 - - - 43.5
without test material, with glucose, with inocolum (glucose control) 5 40 46.3 9.1 8.7 0 0
with test material, with inocolum, with glucose
(inhibitory action)
6 80 87.3 47.2 50.0 47.5 45.9
with inocolum
(inocolum control ≈ Coi,Cti)
7 - 10.2 6.2 5.5 0 0

Calculation DOC- concentration after (mg/l)
Flask 3d 7d 14d 28d
% DOC removal (corrected
by the black control)
Dt =[((Co-Coi)-(Ct-Cti))/(Co-Coi)]*100
1 0 0 0 0
2 0 0 0 0
3 0 0 0 0
4 0 0 0 0
5 92.0 91.1 100 100
6 46.8 42.3 38.4 40.5
Validity criteria fulfilled:
not specified
Interpretation of results:
not readily biodegradable
Conclusions:
The substance is not readilly biodegradable.
Executive summary:

The biodegradability of the substance was assessed by using an effluent of a domestic sewage tretment plant for 28 days, according to the EU Method C.4 - A and the OECD 301 A. The biodegradation was assessed in terms of elimination of Dissolved Organic Carbon (DOC). For this purpose, the DOC of the solution was measured at fixed time intervals (0, 3, 7, 14 and 28 days). The DOC was assessed in flasks containing the reference substance (glucose), while the inhibitory action of the substance was also evaluated. The amount of dissolved organic carbon removed from the test solutions was corrected for that derived from the blank inoculum.

Biodegradation (28 d): 0 % based on DOC removal.

Biodegradation (28 d): 100 % based on DOC removal.

Conclusion

The substance is not readily biodegradable.

Description of key information

Not readily biodegradable

Key value for chemical safety assessment

Additional information

The biodegradability of the substance was assessed, according to the EU Method C.4 - A and the OECD 301 A. The biodegradation was assessed in terms of elimination of Dissolved Organic Carbon (DOC). Test item resulted as not readily biodegradable, i.e. 0 % of degradation after 28 days, based on DOC removal. From the results of the inhibition control, no inhibition on the activity of the bacteria can be found.

The results of the key study are supported and confirmed also by the Biochemical Oxygen Demand (BOD) test assessed after 5 days. The test item BOD 5 resulted to be 0 mg/O2 g, confirming the conclusion that the substance is not readily biodegradable.

The substance is a polyazo dye, derivative; it is not expected to be ready biodegradable because of its chemical structure and its specific function. Commonly, dyes undergo a primary transformation, i.e. discolourization due to the interrupting the conjugation. Nevertheless, the degradation process involves more steps and take more time.