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Environmental fate & pathways

Biodegradation in water: screening tests

Administrative data

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:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2017
Report Date:
2017

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Version / remarks:
adopted July 17,1992
GLP compliance:
yes

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
solid: particulate/powder

Study design

Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: municipal sewage treatment plant: 'Waterschap Aa en Maas', 's-Hertogenbosch, The Netherlands, receiving predominantly domestic sewage.
- Preparation of inoculum for exposure: The freshly obtained sludge was kept under continuous aeration until further treatment
- Pretreatment: Before use, the sludge was allowed to settle (35 minutes) and the supernatant liquid was used as inoculum at the amount of 10 mL/L of mineral medium.
- Concentration of sludge: The concentration of suspended solids was determined to be 3.2 g/L in the concentrated sludge.
Duration of test (contact time):
28 d
Initial test substance concentration
Initial conc.:
1.14 other: mg CO2 mg
Based on:
ThCO2
Parameter followed for biodegradation estimation
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: standard under the guideline
- Test temperature: 22.2 - 23.2°C
- pH: recorded on Day 0 and Day 28 for blanks and test item (Day 14 for positive control); pH adjusted in test item and toxicity control bottles
- Aeration of dilution water: A mixture of oxygen (ca. 20%) and nitrogen (ca. 80%) was passed through a bottle, containing 0.5 - 1 litre 0.0125 M Ba(OH)2 solution to trap CO2 which might be present in small amounts. The synthetic air was passed through the scrubbing solutions at a rate of approximately 1-2 bubbles per second (ca. 30-100 mL/min).
- Continuous darkness: yes

TEST SYSTEM
- Number of culture flasks/concentration: Test suspension: containing test item and inoculum (2 bottles); Inoculum blank: containing only inoculum (2 bottles); Positive control: containing reference item and inoculum (1 bottle).; Toxicity control: containing test item, reference item and inoculum (1 bottle).
- Method used to create aerobic conditions: the synthetic air was passed through the scrubbing solutions at a rate of approximately 1-2 bubbles per second (ca. 30-100 mL/min).
- Test performed in open system: Yes
- Details of trap for CO2: Three CO2-absorbers (bottles filled with 100 mL 0.0125 M Ba(OH)2) were connected in series to the exit air line of each test bottle.

SAMPLING
- Sampling frequency and method : Titrations were made every second or third day during the first 10 days, and thereafter at least every fifth day until day 28, for the inoculum blank and test item. Titrations for the positive and toxicity control were made over a period of at least 14 days.
Each time the CO2-absorber nearest to the test bottle was removed for titration; each of the remaining two absorbers were moved one position in the direction of the test bottle. A new CO2-absorber was placed at the far end of the series. Phenolphthalein (1% solution in ethanol, Merck) was used as pH-indicator.
On the penultimate day, the pH of respective test suspensions was measured and 1 mL of concentrated HCl (37%, Merck) was added to the bottles of the inoculum blank and test suspension. The bottles were aerated overnight to drive off CO2 present in the test suspension. The final titration was made on day 15 (positive and toxicity control) and on day 29 (remaining vessels).

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes
- Abiotic sterile control: no
- Toxicity control: yes


STATISTICAL METHODS: not applicable
Reference substance
Reference substance:
acetic acid, sodium salt

Results and discussion

Preliminary study:
not applicable
Test performance:
This study was considered to be valid.
% Degradation
Key result
Parameter:
% degradation (CO2 evolution)
Value:
5
Sampling time:
28 d
Details on results:
The relative biodegradation values calculated from the measurements performed during the test period revealed no biological relevant biodegradation of Mercaptamine (3% and 7%, based on ThCO2).
In the toxicity control, more than 25% biodegradation occurred within 14 days (38%, based on ThCO2). Therefore, the test item was assumed not to inhibit microbial activity.

BOD5 / COD results

Results with reference substance:
80% degradation after Day 14. Validity criteria met.

Any other information on results incl. tables

Table1          pH Values of Different Test Media

Test medium:

At the start of the test:

On day 14:

On day 28:

Blank control (A)

7.6

-

7.7

Blank control (B)

7.6

-

7.7

Positive control

7.6

7.9

-

Mercaptamine (A)

7.9 → 7.61

-

7.8

Mercaptamine (B)

8.0 → 7.61

-

7.7

Toxicity control

7.9 → 7.61

7.9

-

¹: Adjusted using 1 M HCl (Merck, Darmstadt, Germany)


 

Table 2: Comparison of Biodegradation of the Test Item in Bottles A and B

Day

Biodegradation (%)

Bottle A

Bottle B

Mean A and B

∆ A-B1)

1

0

1

1

1

4

1

1

1

0

6

1

2

2

1

8

1

3

2

2

11

1

3

2

2

15

1

4

3

3

18

1

4

3

3

22

1

5

3

4

25

2

5

4

3

292)

2

6

4

4

292)

2

7

5

5

292)

3

7

5

4

1): Absolute difference in biodegradation between bottles A and B

2): Biodegradation is ended on day 28 by addition of HCl. Therefore, differences observed on day 29 are actually differences of day 28.

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
In conclusion, Mercaptamine was not readily biodegradable under the conditions of the modified Sturm test