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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:
2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Version / remarks:
• OECD Guidelines for the Testing of Chemicals, Part 301 B, adopted 17. Jul. 1992
CO2-Evolution-Test (Modified STURM Test)“
• Council Regulation (EC) No. 440/2008, Method C.4-C, adopted 30. May 2008 “CO2-Evolution-Test”
Deviations:
no
Remarks:
A deviation from the study plan was documented:
GLP compliance:
yes (incl. certificate)
Oxygen conditions:
aerobic
Inoculum or test system:
sewage, predominantly domestic (adaptation not specified)
Details on inoculum:
Activated sludge from a biologic sewage treatment plant was used. The chosen plant is treating mostly domestic sewage
The sludge was taken from the activation basin of the ESN (Stadtentsorgung Neustadt) sewage treatment plant, Im Altenschemel, NW-Lachen-Speyerdorf.

Date of collection: 21. Apr. 2017, batch no: 20170421

The sludge was filtrated, washed with tap water (2x), then washed with and re-suspended in test medium. It was then aerated until use.The dry matter was determined as 4040 mg suspended solids/L.

Preparations:

The medium was prepared from the stock solutions. The stock solution of the positive control was prepared and its DOC was measured. The stock solution of the test item was prepared and its DOC was measured. The inoculum was taken from its source, washed, aerated and the dry matter was determined.
The test vessels were filled with medium and inoculum. Then, all flasks were aerated for 72 hours with purified, CO2-free, moistened air to purge the system of CO2
Duration of test (contact time):
>= 28 d
Initial conc.:
ca. 20 mg/L
Based on:
IC (inorganic carbon)
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
The medium was prepared from the stock solutions. The stock solution of the positive control was prepared and its DOC was measured. The stock solution of the test item was prepared and its DOC was measured. The inoculum was taken from its source, washed, aerated and the dry matter was determined.
The test vessels were filled with medium and inoculum. Then, all flasks were aerated for 72 hours with purified, CO2-free, moistened air to purge the system of CO2

1)Apparatus
The test vessels were aerated with purified (by activated charcoal), CO2-scrubbed, mois-tened air. The scrubbing of carbon dioxide was achieved by bubbling the purified air through a flask containing 1.5 M NaOH. To control the absence of CO2, the air was then led through a flask containing a solution of Ba(OH)2 before reaching the test vessels.
Magnetic stirrers were used to prevent deposition of inoculum.
The emitted CO2 was trapped in 0.25 M NaOH. Two scrubbers containing 100 mL each were connected in series to the test vessels. The initial IC value of the 0.25 M NaOH was separately determined in each flask.
2) Sampling
From each front scrubber flask, 9 samples were taken in order to determine the emitted CO2 (on day 0, 2, 4, 8, 10, 14, 18, 23 and 29). The sample volume was 1 mL. The resulting change in the volume of the front flask was considered in the calculation of emitted CO2 (see also chapter 8.3.1).
On day 28, 5 mL HCl 2 M was added to each test flask in order to drive off dissolved CO2. On day 29, samples from both scrubber flasks were taken.
3) CO2 Determination
Analyses of the emitted CO2 were made by IC measurement using the carbon analyser TOC multi N/C 2100S, Analytik Jena. Each sample was measured in duplicate or tripli-cate, respectively (depending on the variation between the measured values). The carbon analyser was calibrated with freshly prepared reference solutions containing potassium hydrogen phthalate (TC), sodium hydrogen carbonate and sodium carbonate (IC) every month. After every start, quality control samples were measured.
Reference substance:
aniline
Remarks:
positive control
Preliminary study:
In a non-GLP pre-test, the carbon content of a stock solution of the test item was meas-ured in the membrane filtered solution and in the unfiltered solution. The measured con-centrations were in a similar range. For the test a stock solution containing 1000.4 mg/L was prepared. Its carbon content was determined in the unfiltered solution in order to es-timate the amount to be added to the test flasks.
The DOC was 278.15 mg/L, giving an organic carbon content of 27.8 %.
Test performance:
Preparations
The medium was prepared from the stock solutions. The stock solution of the positive control was prepared and its DOC was measured. The stock solution of the test item was prepared and its DOC was measured. The inoculum was taken from its source, washed, aerated and the dry matter was determined.
The test vessels were filled with medium and inoculum. Then, all flasks were aerated for 72 hours with purified, CO2-free, moistened air to purge the system of CO2.
Key result
Parameter:
% degradation (CO2 evolution)
Value:
ca. 0
Sampling time:
28 d
Results with reference substance:
not readily biodegradable

1.1.1   Degradation Values

In the following table, the percentage biodegradation is presented:

Degradation values in %

Day

Positive Control 1

Positive Control 2

Positive Control Mean

Test 1

Test 2

Test Mean

Abiotic Control

Toxicity Control

2

-0.6

1.5

0.5

0.6

-1.2

-0.3

0.6

1.5

4

17.9

21.2

19.5

0.4

0.3

0.3

1.7

7.0

8

55.6

69.1

62.3

0.3

0.5

0.4

1.6

26.7

10

68.8

80.7

74.7

-0.2

1.9

0.9

1.4

30.0

14

84.4

86.7

85.5

0.3

0.9

0.6

0.8

34.0

18

85.0

84.7

84.8

-2.0

-1.3

-1.6

1.0

34.0

23

86.8

85.4

86.1

-1.9

-1.8

-1.9

0.7

34.2

29

86.4

82.9

84.6

-5.3

-5.3

-5.3

0.7

33.1

 

Because the values of day 29 are the sum of the IC values in scrubber flasks A and B, an increase (IC values in flasks B of the test flasks higher than in those of the control) or a decrease (IC values in flasks B of the test flasks lower than in those of the control) of degradation can be observed.

As the measured IC values in the test flasks are very low, measurement uncertainties lead to negative degradation values while in

fact no degradation has taken place

Validity criteria fulfilled:
yes
Remarks:
No observations were made which might cause doubts concerning the validity of the study outcome. The result of the test can be considered valid
Interpretation of results:
not readily biodegradable
Conclusions:
The test item Blendazol Red Blendwell is considered as “not readily biodegrada-ble“.
For the test item Blendazol Red Blendwell no biodegradation was observed after 28 days. The 10-day window could not be determined
The criterion of reaching 60% of degradation after 28 days was not met. Blendazol Red Blendwell is therefore con-sidered as
“notreadilybiodegradable”.
The abiotic degradation reached 0.7 %.
Executive summary:

The aerobic ready biodegradability of Blendazol Red Blendwell in the CO2Evolution Test was determined following OECD 301B resp.

EU C.4-C, the biodegradability was determined after a duration of 28 days

The following data were determined for the test item Blendazol Red Blendwell:

10-day-window:                                                             not detected
degradation at the end of 10-day-window                        0 %
degradation at the end of the test                                      0 %
pass level following guideline:          
                                  60% at the end of 10-day-window for pure

respective 60 % at the end of the test for mixtures

For the test item Blendazol Red Blendwell no biodegradation was observed after 28 days.

Blendazol Red Blendwell is therefore considered a“not readily biodegradable”.

Description of key information

Degradation behaviour of positive control and toxicity control was normal. Abiotic degradation reached 0.7 %. Both replicates of the test item showed very good correspondence.

If degradation in the toxicity flask is below 25% after 14 days, the test item can be considered as toxic towards the inoculum. As degradation in the toxicity flask was 34.0% after 14 days, the test item can be stated as “not toxic towards the inoculum in a concentration of 72.0 mg/L”.

Ready biodegradability is defined in the guidelines as degradation surpassing 60% within 10 days after reaching a level of 10%.

For the test item Blendazol Red Blendwell no biodegradation was observed after 28 days.Blendazol Red Blendwell is therefore considered as “not readily biodegradable

Key value for chemical safety assessment

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

Additional information