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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
Study period:
21 March 2017 - 28 April 2017
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 guidelineopen allclose all
Qualifier:
according to
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Version / remarks:
17 July 1992
Deviations:
no
Qualifier:
according to
Guideline:
other: ISO International Standard 10634. "Water Quality - Guidance for the preparation and treatment of poorly water-soluble organic compounds for the subsequent evaluation of their biodegradability in an aqueous medium"
Version / remarks:
1995
Deviations:
no
GLP compliance:
yes (incl. certificate)
Remarks:
dd. 03 November 2015

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
solid: particulate/powder
Details on test material:
Physical appearance: pink powder
Storage conditions: at room temperature
Specific details on test material used for the study:
Stability in water: stable

Study design

Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: freshly obtained from a municipal sewage treatment plant: 'Waterschap Aa en Maas', 's-Hertogenbosch, The Netherlands, receiving predominantly domestic sewage.
- Storage: not applicable, the freshly obtained sludge was used immediately.
- Preparation of inoculum for exposure: the sludge was allowed to settle (31 minutes) and the supernatant liquid was used as inoculum at the amount of 10 mL/L of mineral medium.
- Pretreatment: the day before the start of the test mineral components, Milli-RO water (ca. 80% of final volume) and inoculum (1% of final volume) were added to each bottle. This mixture was aerated with synthetic air overnight to purge the system of CO2.
- Concentration of sludge: 3.6 g/L
- Water filtered: no
Duration of test (contact time):
28 d
Initial test substance concentrationopen allclose all
Initial conc.:
12 mg/L
Based on:
TOC
Initial conc.:
33 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: mineral medium according to OECD 301
- Test temperature: 22.2 - 23.7°C
- pH: between 7.4 and 7.8 in different test bottles throughout the test
- pH adjusted: no
- Aeration of dilution water: not indicated; tap-water purified by reverse osmosis (Milli-RO) and subsequently passed over activated carbon.
- Continuous darkness: yes
- Other: Test solutions were continuously stirred during the test.

TEST SYSTEM
- Culturing apparatus: 2 litre brown coloured glass bottles
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: synthetic air (CO2 < 1 ppm) sparged through scrubbing solutions at a rate of approximately 1-2 bubbles per second (ca. 30-100 mL/min).
- Measuring method: produced CO2 reacted with barium hydroxide Ba(OH)2 in the gas scrubbing bottle and precipitated out as barium carbonate. The amount of CO2 produced was determined by titrating the remaining Ba(OH)2 with 0.05 M standardized HCl.

SAMPLING
- Sampling frequency: 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 suspension. Titrations for the positive and toxicity control were made over a period of at least 14 days.
- Sampling method: Each time the CO2-absorber nearest to the test bottle was removed for titration; each of the remaining two absorbers was 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.

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes, containing only inoculum (2 bottles)
- Abiotic sterile control: no
- Toxicity control: yes, containing test item, reference item and inoculum (1 bottle).
- Other: positive control: containing reference item and inoculum (1 bottle).

STATISTICAL METHODS: no statistics were used

TEST CONCENTRATIONS:
Test substance (added as weighed amounts to the bottles): bottle A: 32.51 mg/L test substance; bottle B: 32.64 mg/L test substance
Reference control: 40 mg/L reference substance
Toxicity control: 32.50 mg/L test substance and 40 mg/L reference substance

Preparation of test solutions: since the test item was not sufficiently soluble to allow preparationof an aqueous solution at a concentration of 1 g/L, weighed amounts of the test item were added to the 2-litres test bottles containing medium with microbial organisms and mineral components. To this end, 10 mL of Milli-RO water was added to each weighing bottle containing the test item. After vigorous mixing (vortex) the resulting suspension was added quantitatively to the test medium.
Reference substance
Reference substance:
acetic acid, sodium salt
Remarks:
purity: 99.5%

Results and discussion

% Degradation
Key result
Parameter:
% degradation (CO2 evolution)
Remarks:
(mean of duplicate bottles tested)
Value:
12
Sampling time:
28 d
Details on results:
- The relative biodegradation values were 14% and 10% biodegradation of the test substance (based on ThCO2), for the duplicate bottles tested.
- In the toxicity control, more than 25% biodegradation occurred within 14 days (41%, based on ThCO2). Therefore, the test item was assumed not to inhibit microbial activity.
- Functioning of the test system was checked by testing the reference item sodium acetate, which showed a normal biodegradation curve (see attached illustration).
- The theoretical CO2 production of the test substance was calculated to be 1.35 mg CO2/mg and that of the reference substance was calculated to be 1.07 mg CO2/mg.

BOD5 / COD results

Results with reference substance:
85% within 14 days

Any other information on results incl. tables

Table 1 CO2 Production and Percentage Biodegradation of the Test Item (Bottle A)

Day

HCl(0.05 N) titrated (mL)

Produced

CO2

(mL HCl)

Produced

CO2

(mg)

Cumulative

CO2

(mg)

Biodegradation1)

(%)

Blank

(mean)

Bottle A

1

49.14

49.56

0.00

0.0

0.0

0

4

46.08

45.96

0.12

0.1

0.1

0

6

47.20

46.51

0.69

0.8

0.9

1

8

48.12

46.65

1.47

1.6

2.5

3

11

47.06

46.84

0.22

0.2

2.7

3

15

47.31

46.50

0.81

0.9

3.6

4

19

46.36

45.97

0.39

0.4

4.1

5

22

46.66

45.68

0.98

1.1

5.1

6

25

47.16

45.04

2.12

2.3

7.5

9

29*)

44.77

43.66

1.11

1.2

8.7

10

29*)

46.91

45.31

1.60

1.8

10.4

12

29*)

48.16

46.81

1.35

1.5

11.9

14

1): Calculated as the ratio between CO2produced (cumulative) and the ThCO2of the test item: 87.8 mg CO2/2L.

*): CO2measured on day 29 is actually part of CO2production of day 28, since microbial activity was ended on day 28 by addition of HCl.

 

Table 2 CO2 Production and Percentage Biodegradation of the Test Item (Bottle B)

Day

HCl (0.05 N) titrated (mL)

Produced

CO2

(mL HCl)

Produced

CO2

(mg)

Cumulative

CO2

(mg)

Biodegradation1)

(%)

Blank

(mean)

Bottle B

1

49.14

49.11

0.03

0.0

0.0

0

4

46.08

44.53

1.55

1.7

1.7

2

6

47.20

46.72

0.48

0.5

2.3

3

8

48.12

47.18

0.93

1.0

3.3

4

11

47.06

47.48

0.00

0.0

3.3

4

15

47.31

47.20

0.11

0.1

3.4

4

19

46.36

46.77

0.00

0.0

3.4

4

22

46.66

46.04

0.62

0.7

4.1

5

25

47.16

45.41

1.75

1.9

6.0

7

29*)

44.77

45.26

0.00

0.0

6.0

7

29*)

46.91

46.61

0.30

0.3

6.3

7

29*)

48.16

46.01

2.15

2.4

8.7

10

1): Calculated as the ratio between CO2produced (cumulative) and the ThCO2of the test item: 88.1 mg CO2/2L.

*): CO2measured on day 29 is actually part of CO2production of day 28, since microbial activity was ended on day 28 by addition of HCl.

 

Table 3 CO2 Production and Percentage Biodegradation of the Toxicity Control

Day

HCl (0.05 N) titrated (mL)

Produced

CO2

(mL HCl)

Produced CO2

(mg)

Cumulative CO2

(mg)

Biodegradation1)

(%)

Blank

(mean)

Toxicity

control

1

49.14

49.81

0.00

0.0

0.0

0

4

46.08

27.12

18.96

20.9

20.9

12

6

47.20

32.19

15.01

16.5

37.4

22

8

48.12

40.96

7.15

7.9

45.2

26

11

47.06

40.65

6.41

7.1

52.3

30

15*)

47.31

30.83

16.48

18.1

70.4

41

1): Calculated as the ratio between CO2produced (cumulative) and the sum of the ThCO2of the test item and positive control: 173.3 mg CO2/2L (ThCO2test item: 87.8 mg CO2/2L + ThCO2sodium acetate: 85.5 mg CO2/2L).

*):  CO2measured on day 15 is actually part of CO2production of day 14, since microbial activity was ended on day 14 by addition of HCl.

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Remarks:
see 'overall remarks' section.
Interpretation of results:
not readily biodegradable
Conclusions:
Based on the results of a ready biodegradation test (Modified Sturm test), performed according to OECD 301B and GLP principles, C.I. Pigment Red 81:2 is not readily biodegradable (mean degradation of 12%).
Executive summary:

In a Modified Sturm Test, according to OECD guideline 301 B and GLP principles, C.I. Pigment Red 81:2 was assessed for its ready biodegradability. The test substance was tested in duplicate at a target concentration of 33 mg/L, corresponding to 12 mg TOC/L. The exposure period was 28 days and two inoculum blanks, a positive control and a toxicity control were included. The test substance was not sufficiently soluble to prepare an aqueous solution of 1 g/L. Therefore, weighed amounts were directly added to medium, containing medium with microbial organisms and mineral components, and Milli-RO water was added. After vigorous mixing, the suspension was added to the test medium. The test solutions were continuously stirred during the test to ensure optimal contact between the test item and test organisms. CO2 measurements showed that the test substances biodegraded for 14% and 10%, in the duplicate bottles measured. Based on these results, the criterion for ready biodegradability was not met. C.I. Pigment Red 81:2 is therefore considered to be not readily biodegradable in the Modified Sturm Test.

The test itemwas found not to inhibit microbial activity and all validity criteria were met, thus the study was considered to be valid.