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Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: inherent biodegradability
Type of information:
other: data on Acid Blue 225_constituent 1
Adequacy of study:
key study
Study period:
From May 25 to June 22, 1988
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Justification for type of information:
The experiment was conducted on one of the substance components. It should be noted that the lot tested was characterized by the Acid Blue 225_constituent 1 as main component; however, the impurity profile (which also includes the Acid Blue 225_constituent 2) resulted to be closely similar to that characterizing the substance under assessment (details are given in the document attached to IUCLID section 13.2).
Qualifier:
according to guideline
Guideline:
OECD Guideline 302 B (Inherent biodegradability: Zahn-Wellens/EMPA Test)
GLP compliance:
no
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
Activated sludge were taken from a municipal waste water treatment plant which has been rinsed with municipal water for 2 times. The sediment is taken to estimate the dry weight according to internal method.
The activated sludge was prepared one day before the start of the experiment, ventilated overnight and adjusted to a concentration of 600 mg/l.
Duration of test (contact time):
28 d
Initial conc.:
142 mg/L
Based on:
DOC
Parameter followed for biodegradation estimation:
DOC removal
Details on study design:
PRE-TEST
The day before the main test, a pre-test was conducted. A 3-liter beaker was prepared with 1900 ml of communal water an 100 ml of stock solution. After 1 minute of mixing a 15 ml sample is taken and filtered through a Whatman GF/A filter by centrifugation. Subsequently DOC was measured representing the 0-hour value. Three hours later a second sample is taken from the beaker andevaluated. The zero value was used to validate the DOCvalue, while the 3h-value was used to estimate the adsorption of the test substance to glass.

MAIN TEST
Test solutions and controls were prepared in duplicates.

Analysis of the activated sludge content
At least one day after the main test, 50 ml of the activated sludge was transferred to a measuring cylinder and the dry weight was measured.

Sampling and duration of the test:
Samples for DOC measurement were taken daily on working days until day 28.

Oxygen, pH and temperature measurements:
For oxygen measurements aeration and stirrer were stopped for the time of the measurement (about 30-60 sec.). Oxygen concentration was maintained over 2 mg/l. pH-valuewas taken between 7.0 and 8.0. If the pH-values were outside of this range, the pH was adjusted with NaOH or H2SO4 respectively.
The temperature was maintained in the range of 22 ± 3 °C.
Parameter:
% degradation (DOC removal)
Value:
22
Sampling time:
28 d

DOC removal

Time Substance DOC (mg/l) Blank DOC (mg/l) Substance DOC corrected by control (mg/l) Elimination (%)
Start 142.0 - 142.0 0
3 hours 121.9 9.0 112.9 20.49
Day 2 132.5 9.0 123.5 13.03
Day 5 131.8 9.4 122.4 13.8
Day 7 130.9 9.6 121.3 14.58
Day 9 131.7 7.8 123.9 12.75
Day 12 132.6 7.3 125.3 11.76
Day 14 132.6 8.7 123.9 12.75
Day 16 127.3 10.4 116.9 17.68
Day 19 128.8 10.3 118.5 16.55
Day 21 126.8 9.2 117.6 17.18
Day 23 123.1 9.4 113.7 19.93
Day 26 120.3 8.8 111.5 21.48
Day 28 119.1 8.9 110.2 22.39
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
Biodegradation (28d): 22 %, based on DOC removal.
Executive summary:

The inherent biodegradability of the substance was determined in a 28 days, according to the OECD Guideline for Testing of Chemicals, No. 302B.

The test substance was tested in a concentration of 142 mg/l. Based on the findings of the study, biodegradation after 28 days of the test substance was 22 %.

Conclusion

Biodegradation (28d): 22 %, based on DOC removal.

Description of key information

Not readily biodegradable

Key value for chemical safety assessment

Additional information

Acid Blue 225 is an anthraquinone derivative dye; 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.

The assumption above mentioned is confirmed by the experimental data available on Acid Blue 225_constituent 1. It should be noted that the lot tested was characterized by the Acid Blue 225_constituent 1 as main component; however, the impurity profile (which also includes the Acid Blue 225_constituent 2) resulted to be closely similar to that characterizing the substance under assessment. Therefore, the data can be considered as adequate and the approach can be considered as suitable (details are given in the document attached to IUCLID section 13.2).

The inherent biodegradability of the Acid Blue 225_constituent 1 was determined in a 28 days test, conducted in accordance with the Zahn Wellens testing method, described into the OECD Guideline No. 302B. The test substance was tested in a concentration of 142 mg/l. Based on the findings of the study, biodegradation after 28 days of the test substance was 22 %.

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