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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:
04 April - 30 May 2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2018
Report Date:
2018

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to
Guideline:
EU Method C.4-E (Determination of the "Ready" Biodegradability - Closed Bottle Test)
Version / remarks:
May 30, 2008
Deviations:
no
Qualifier:
according to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Version / remarks:
July 17, 1992
Deviations:
no
Qualifier:
according to
Guideline:
EPA OPPTS 835.3110 (Ready Biodegradability)
Version / remarks:
January 1998

Deviations:
no
GLP compliance:
yes

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
solid: particulate/powder
Details on test material:
Test item: Black DB
Appearance: black powder
Specific details on test material used for the study:
Expiration date:29.09.2020

Study design

Oxygen conditions:
anaerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
Test system
Species:
Activated sludge, microorganisms from a domestic waste water treatment plant.
Origin:
The (controlled) activated sludge was supplied by the sewage plant for domestic sewage in Balatonfüred, Hungary, on 06 April 2018 (seven days before the main test). The prepared activated sludge was continuously aerated (2L/minute) at the test temperature of 22 ± 2 ºC, for about 7 days.
Preparation of Activated Sludge Inoculum:
The activated sludge used for this study was washed by centrifugation and the supernatant liquid phase was decanted. The solid material was re-suspended in isotonic saline solution with shaking and again centrifuged. This procedure was repeated twice. An aliquot of the final sludge suspension was weighed (5.218 g wet weight), dried and the ratio of wet sludge to dry weight (0.4927 g dry weight) determined. Based on this ratio, calculated amount of wet sludge (5 g dry weight that was equivalent to 59.953 g wet sludge) was suspended in mineral medium (Section 5.4; ad. 1000 mL) to yield a concentration equivalent to about 5 g per litre (on dry weight basis). The prepared activated sludge inoculum was aerated under test conditions (for 7 days) until use. The pH of the activated sludge inoculum after preparation was 7.42, just before use the pH was: 7.39. A pH adjustment of activated sludge inoculum was not performed.
Pre-conditioning of Activated Sludge Inoculum:
Pre-conditioning consisted of aerating (2 L/minute) activated sludge (in mineral medium ) for 7 days (from April 06 to 13, 2018) at test temperature (the actual temperature: 20.0 – 20.8 °C). Before use the cell count of inoculum was checked as follows: the viability of the cultured sludge was determined by plating 0.1 mL of the different, 10-1, 10-2, 10-3 and 10-4 dilutions of cultures on nutrient agar plates. Plates were incubated at 37 °C for 24 hours. The viable cell number of the cultures was determined by these plating experiments by manual colony counting. The approximately cell count of aerated inoculum was ~10^8/L; therefore, before the test the inoculum was further diluted 50 000x with mineral medium to reach the necessary ~10^4 – 10^6 cells/L cell concentration. After preparation the sludge was filtered through cotton wool. Pre-conditioning improves the precision of the method. The inoculum was not pre-adapted to the test chemical.
Duration of test (contact time):
28 d
Initial test substance concentration
Initial conc.:
4 mg/L
Based on:
other: was based on the results of the preliminary solubility and toxicity tests
Parameter followed for biodegradation estimation
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
Test Conditions

Environmental Conditions

The test was carried out in a controlled environment room (during the preparation, aeration and incubation of the mineral medium, preparation of test bottles (units), during the formulation, oxygen and pH measuring) at a temperature of 22  2C according to the guideline. The actual temperature range was 20.8 - 21.3 °C.
The test bottles were incubated in an incubator at 22  2 C, in the dark. During the incubation (28 days) of the test units the temperature range was 20.0-20.2 °C.
During the pre-conditioning of activated sludge inoculum the temperature was 20.0 – 20.8 ºC.
Temperature was measured continuously using min/max thermometer (in controlled environment room) or built-in thermometer (in incubator) and recorded at least once a day.
The oxygen concentration of test water (mineral medium) was in the range of 8-9 mg/L. It was measured at the start of the test and found to be 8.24 mg/L.
The pH was checked prior study start and found to be 7.41; further pH adjustment was considered as not necessary. The test conditions were measured with suitable instruments and documented in the raw data.

Equipment

Large glass tank (volume: ~30 L) and large glass bottles (volume: 5 L),
Narrow necked, Winkler bottles with glass stoppers,
Funnels and coarse filter papers,
Oxygen and pH meter with appropriate O2 and pH electrode,
Aeration system, Moisture analyzer,
Temperature controlled (in the range of 22 ± 2 °C with a temperature deviation of ±1 °C) environment room (and/or incubator) with thermometer with exclusion of light,
Balance, Centrifuge, Ultrasonic bath, Freezer,
Spectrophotometer (for nitrate, nitrite and COD determination).

Test Units

Type and Size: Winkler bottles (300 mL, coded) with special neck and glass stoppers.
Identification: Each test bottle was uniquely identified with study number, test group, days of measurement and replicate number.


Preliminary Experiments

The pre-experiments on solubility of the test item, and the 14-day toxicity test were conducted non-GLP, and are excluded from the Statement of Compliance in the final report. The raw data of these tests will be archived under the study code of present study.

Preliminary Toxicity Test

The test item solubility, behavior, and toxicity were tested in a 14-day preliminary experiment. The test design was the same as described at the main experiment. In the preliminary experiment the test item was investigated at the concentration of 4 mg/L. Unequivocal toxic effect of the test item was not found at this investigated concentration (in the toxicity control group 30.6 % (higher than 25 %) degradation occurred within 14 days).
Reference substance
Reference substance:
benzoic acid, sodium salt

Results and discussion

Preliminary study:
The test item solubility, behavior, and toxicity were tested in a 14-day preliminary experiment. The test design was the same as described at the main experiment. In the preliminary experiment the test item was investigated at the concentration of 4 mg/L. Unequivocal toxic effect of the test item was not found at this investigated concentration (in the toxicity control group 30.6 % (higher than 25 %) degradation occurred within 14 days).
% Degradation
Key result
Parameter:
% degradation (O2 consumption)
Value:
14
Sampling time:
28 d
Details on results:
Under the test conditions the percentage biodegradation of the test item reached a mean of 14.0 % after 28 days based on its COD. Based on the dissolved oxygen depletion, the resulting biodegradation values reached a plateau on about the 14th day of the experiment. From this day on, the slight subsequent changes were considered as being within the biological variability range of the applied test system. The test item can be considered to be not readily biodegradable.

BOD5 / COD results

Results with reference substance:
Biodegradation of the Reference Item
The reference item Sodium benzoate was sufficiently degraded to a mean of 71.4 % after 14 days, and to a mean of 73.6 % after 28 days of incubation, based on ThODNH3, thus confirming the suitability of the used activated sludge inoculum.

Biodegradation of the Toxicity Control
In the toxicity control containing both, the test item and the reference item, a mean of 33.1 % biodegradation was noted within 14 days and 34.3 % biodegradation after 28 days of incubation. Thus, the test item can be assumed to not inhibit the activated sludge microorganisms (higher than 25 % degradation occurred within 14 days).

Any other information on results incl. tables

Dissolved Oxygen Concentrations at Different Time Intervals during the Exposure Period of 28 Days

Treatment

Concentration

Bottle

mg O2/L after n days of exposure

[mg/L]

No.

0

7

14

21

28

Test item

 

1a

8.23

6.67

6.36

5.91

5.78

4.0

1b

8.17

6.51

6.17

6.02

5.91

 

mean

8.20

6.59

6.27

5.97

5.85

Reference item

 

2a

8.28

4.37

3.79

3.51

3.35

3.0

2b

8.26

4.10

3.54

3.46

3.39

 

mean

8.27

4.24

3.67

3.49

3.37

Inoculum control

3a

8.23

7.34

7.27

7.21

7.16

3b

8.22

7.22

7.11

6.94

6.85

mean

8.23

7.28

7.19

7.08

7.01

Toxicity control

Test item: 4.0
Reference item: 3.0

4a

8.21

3.21

2.92

2.74

2.47

4b

8.14

3.09

2.81

2.53

2.59

mean

8.18

3.15

2.87

2.64

2.53

Oxygen Depletion at Different Time Intervals during the Exposure Period of 28 Days

Treatment

Concentration

Bottle

mg O2/L after n days of exposure

[mg/L]

No.

7

14

21

28

Test item

4.0

1a

0.61

0.83

1.17

1.23

1b

0.71

0.96

1.00

1.04

Reference item

3.0

2a

2.97

3.46

3.62

3.71

2b

3.22

3.69

3.65

3.65

Toxicity control

Test item: 4.0
Reference item: 3.0

4a

4.06

4.26

4.32

4.52

4b

4.11

4.30

4.46

4.33

oxygen depletion : (mt0- mtx) - (mbo- mbx), where: 

mt0: oxygen concentration (mg/L) of test group on day 0 (1a, 2a, 4a and 1b, 2b, 4b from Table 2)

mtx: oxygen concentration (mg/L) of test group on day x (1a, 2a, 4a and 1b, 2b, 4b from Table 2)

mb0: oxygen concentration (mg/L) of inoculum blank on day 0 (mean of 3a and 3b from Table 2)

mbx: oxygen concentration (mg/L) of inoculum blank on day x (mean of 3a and 3b from Table 2)

BOD at Different Time Intervals during the Exposure Period of 28 Days

Treatment

Concentration

Bottle

BOD after n days of exposure

[mg/L]

No.

7

14

21

28

Test item

4.0

1a

0.15

0.21

0.29

0.31

1b

0.18

0.24

0.25

0.26

Reference item

3.0

2a

0.99

1.15

1.21

1.24

2b

1.07

1.23

1.22

1.22

Toxicity control

Test item: 4.0
Reference item: 3.0

4a

0.58

0.61

0.62

0.65

4b

0.59

0.61

0.64

0.62

BOD = = mg O2/mg T.i and/or R.i.where:T.i. =test item R.i.  =reference item i.control=inoculum control

Percentage Biodegradation at Different Time Intervals during the Exposure Period of 28 Days

Treatment

Concentration

Bottle

Percent of biodegradation after n days of exposure

[mg/L]

No.

7

14

21

28

Test item

 

1a

7.6

10.3

14.5

15.2

4.0

1b

8.8

11.9

12.4

12.9

 

mean

8.2

11.1

13.4

14.0

Reference item

 

2a

59.3

69.1

72.4

74.2

3.0

2b

64.3

73.7

73.0

73.0

 

mean

61.8

71.4

72.7

73.6

Toxicity control

Test item: 4.0
Reference item: 3.0

4a

31.4

33.0

33.5

35.0

4b

31.8

33.3

34.6

33.6

mean

31.6

33.1

34.0

34.3

Biodegradation % =where: T.i.=test item R.i.=reference item

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
The test item was considered to be not readily biodegradable (14 % biodegradation on day 28).
Executive summary:

The purpose of this study was to determine the ready biodegradability of the test item. The test item was exposed to activated sludge from the aeration tank of a domestic waste water treatment plant. The biodegradation was followed by oxygen uptake of the microorganisms during exposure. As a reference item sodium benzoate (at a concentration of 3.0 mg/L) was tested simultaneously under the same conditions as the test item, and functioned as a procedure control (reference control). Additionally inoculum (containing the filtered inoculum only) and toxicity (containing both the test item and reference item) controls were examined. The chosen test item concentration of 4.0 mg/L investigated in the main test was based on the results of the preliminary solubility and toxicity tests. The chemical oxygen demand (COD) of 2.02 mg O2/ mg of test item was determined at the start of the main experiment. Under the test conditions ready biodegradation of this test item was not noticed. The percentage biodegradation of test item reached a mean of 14.0 % after 28 days based on its COD. Based on the dissolved oxygen depletion, the resulting biodegradation values reached a plateau on about the 14th day of the experiment. From this day the slight changes were considered as being within the biological variability range of the applied test system.

The concurrently conducted analytical determination of possible nitrite and nitrate development showed slight changes in nitrite concentrations in in one parallel 21-day test item sample and in all measured 28-day samples; however the measured dissolved oxygen concentrations in the inoculum control, test item and toxicity control bottles did not correspond to the consumed oxygen of ammonium oxidation processes. Likely technical effects (turbidity and/or discoloration) also influenced the nitrite concentration determinations. Therefore the biodegradability value of the test item was calculated based on its COD; any correction, based on the measured nitrite and/or nitrate content was not performed.

The reference item Sodium benzoate was sufficiently degraded to a mean of 71.4 % after 14 days, and to a mean of 73.6 % after 28 days of incubation, based on ThODNH3, thus confirming the suitability of the used activated sludge inoculum.

In the toxicity control containing both, the test item and the reference item, a mean of 33.1 % biodegradation was noted within 14 days and 34.3 % biodegradation after 28 days of incubation. Thus, the test item can be assumed to not inhibit the activated sludge microorganisms (higher than 25 % degradation occurred within 14 days).