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Environmental fate & pathways

Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: inherent biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From September 26 to October 28, 2005
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
test procedure in accordance with generally accepted scientific standards and described in sufficient detail
Qualifier:
according to guideline
Guideline:
OECD Guideline 302 C (Inherent Biodegradability: Modified MITI Test (II))
Version / remarks:
1981
Deviations:
yes
Remarks:
not impacting the study outcomes (detail below)
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
No emulsifiers or solvents were used but ultrasound dispersion was employed for 15 minutes to obtain a homogenous suspension of the test item.
Oxygen conditions:
aerobic
Inoculum or test system:
sewage, predominantly domestic (adaptation not specified)
Details on inoculum:
- Source of activated sludge: ARA Ergolz II, Füllinsdorf, Switzerland.
- Pre-treatment: the sludge was washed twice with tap water by centrifugation and the supernatant liquid phase was decanted. A homogenized aliquot of the final sludge suspension was weighed, thereafter dried and the ratio of wet to dry weight was calculated.
- Initial cell/biomass concentration: 4 g dry material per liter.
- Storage: during holding, the sludge was aerated at room temperature until use.
- Preparation of inoculum for exposure: prior to use, the sludge was diluted with test water to a concentration of about 1 g dry material per liter. Based on the determined dry weight of this diluted activated sludge defined amounts were added to test water to obtain a final concentration of 100 mg dry material per liter.
Duration of test (contact time):
28 d
Initial conc.:
65 mg/L
Based on:
test mat.
Initial conc.:
63 - 64 mg/L
Based on:
COD
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Test water: the test water was prepared according to the OECD guideline 301 F, 1992. Analytical grade salts were dissolved in purified water.
- Vessels: 500-ml Erlenmeyer flasks.
- Stirring: continuous stirring.
- Test temperature: 22 °C, maintained with a built-in thermostat and checked once per week.
- pH: the pH measured in all flasks at the start of the test was 7.4. At the end of exposure (day 28) pH values of 7.3 - 7.7 were measured.
- pH adjusted: the pH of test water was adjusted from 7.7 to 7.4 with a diluted hydrochloric acid solution.
- Continuous darkness: yes; darkness.

CONTROL AND BLANK SYSTEM
- Inoculum blank: two replicates.
- Abiotic sterile control: one replicate; poisoned with mercury dichloride at a concentration of 10 mg/l.
- Toxicity control: one replicate.

DETERMINATION OF THE CHEMICAL OXYGEN DEMAND
Due to the complex composition of the test item, its chemical oxygen demand (COD) was determined according to the EU Commission Directive 92/69/EEC, C.6 following DIN 38414-S9 and in compliance with ISO 17025.

MODIFICATION FROM OECD GUIDELINE
- Activated sludge from only one source was used.
- The test water according to OECD Guideline for Testing of Chemicals No. 301 F, Ready Biodegradability: Manometric Respirometry Test, 1992 was used.
- Only the biological oxygen demand (BOD) was monitored.
Reference substance:
benzoic acid, sodium salt
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
28 d
Details on results:
The percent biodegradation of the test item was calculated based on the chemical oxygen demand (COD) of 0.98 mg O2/mg test item.
The oxygen consumption of the test item in the test media was in the normal range of the oxygen consumption in the inoculum controls.
Consequently, was not biodegradable under the conditions of the test within 28 days.

ABIOTIC CONTROL
No degradation of the test item occurred in the abiotic control under the conditions of the test.

TOXICITY CONTROL
The percent biodegradation in the toxicity control containing both the test item and the reference item was calculated based on the COD of the test item and the ThOD of the reference item.
In the toxicity control, the course of biodegradation over the 28-day exposure period was similar to that in the two procedure controls containing the reference item, only. Within 14 days of exposure, biodegradation of 63 % was calculated.
Thus, the test item had no inhibitory effect on activated sludge microorganisms at the tested concentration of 65 mg/l.
Results with reference substance:
The percent biodegradation of the reference item sodium benzoate was calculated based on the theoretical oxygen demand of 1.67 mg O2/mg (ThOD).
In the procedure controls, the reference item was degraded by an average of 73 % and 84 % by exposure day 7 and 14, respectively, thus confirming suitability of the activated sludge. At the end of the test (Day 28), the reference item was degraded by an average of 89 %.

Biodegradation in the test flasks

Time (days) Percentage biodegradation*
Test item Reference substance Toxicity control
0 0 0 0 0 0
1 -- -- -- -- --
2 -7 -7 51 51 42
3 -11 -11 58 56 43
4 -13 -13 64 60 48
5 -17 -17 69 64 51
6 -18 -18 73 68 54
7 -20 -19 77 70 56
8 -20 -20 80 72 56
9 -- -- -- -- --
10 -23 -21 83 75 58
11 -24 -20 85 76 60
12 -22 -19 86 77 60
13 -24 -20 88 78 61
14 -24 -20 89 78 63
15 -- -- -- -- --
16 -- -- -- -- --
17 -25 -17 92 80 64
18 -27 -19 93 80 64
19 -26 -18 93 81 65
20 -28 -18 94 81 64
21 -27 -19 94 81 65
22 -28 -19 94 81 66
23 -29 -18 94 81 66
24 -29 -20 94 81 66
25 -30 -19 95 81 66
26 -29 -18 95 82 67
27 -30 -17 96 82 68
28 -30 -17 96 82 68
Mean (Day 28) -24** 89

*Corrected for the mean oxygen uptake of the inoculum controls

** Negative value due to higher oxygen consumption in the inoculum controls than in the test flasks with test item.

-- Not determined

Oxygen consumption in the test flasks

Time (days) Cumulative oxygen consumption (mg/l)
Test item Inoculum control

Reference substance

Abiotic control

Toxcity control

0

0

0

0

0

0

0

0

0

1

--

--

--

--

--

--

--

--

2

5

5

8

11

95

94

0

106

3

7

7

12

16

111

107

0

112

4

10

10

16

21

126

119

0

128

5

11

11

19

24

137

128

0

138

6

13

13

22

27

147

138

0

148

7

13

14

23

29

154

143

0

154

8

15

15

25

31

161

149

0

158

9

--

--

--

--

--

--

--

--

10

17

18

28

35

170

157

0

166

11

17

19

28

36

174

159

0

170

12

19

21

29

37

177

162

0

172

13

19

22

30

39

181

164

0

176

14

20

23

31

40

184

166

0

180

15

--

--

--

--

--

--

--

--

16

--

--

--

--

--

--

--

--

17

21

26

32

42

191

171

0

184

18

21

26

33

43

193

172

0

186

19

22

27

33

44

194

173

0

188

20

22

28

34

45

196

174

0

188

21

23

28

34

46

197

175

0

190

22

23

29

35

47

198

177

0

192

23

23

30

36

47

199

177

0

194

24

24

30

37

48

200

178

0

194

25

24

31

37

49

201

179

0

196

26

25

32

38

49

202

180

0

198

27

25

33

38

50

204

181

0

200

28

25

33

38

50

205

181

0

200

-- No reading taken

Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
The substance resulted to be not biodegradable under the conditions of the test.
Executive summary:

The test item was investigated for its inherent biodegradability in a manometric respirometry test over 28 days based on the OECD guideline 302 C (1981). The following modifications were made: activated sludge from one source was used; the test water composition was slightly changed; and only the biological oxygen demand (BOD) was monitored.

The oxygen consumption of the test item in the test media was in the normal range of the oxygen consumption in the inoculum controls.

Consequently, the substance resulted to be not biodegradable under the conditions of the test within 28 days.

No degradation of the test item occurred in the abiotic control under the conditions of the test.

In the toxicity control, containing both test item and the reference item sodium benzoate, no inhibitory effect on the biodegradation of the reference item was determined. Thus, had no inhibitory effect on the activity of activated sludge microorganisms at the tested concentration of 65 mg/l.

In the procedure controls, the reference item (sodium benzoate) was degraded by an average of 73 % and 84 % by exposure days 7 and 14, respectively, thus confirming the suitability of the activated sludge.

Conclusion

Not inherently biodegradable.

Description of key information

Neither readily nor inherently biodegradable.

Key value for chemical safety assessment

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

Additional information

The test item was investigated for its inherent biodegradability in a manometric respirometry test over 28 days based on the OECD guideline 302 C (1981).

The oxygen consumption of the test item in the test media was in the normal range of the oxygen consumption in the inoculum controls, consequently, the substance resulted to be not biodegradable under the conditions of the test within 28 days. No degradation of the test item occurred in the abiotic control under the conditions of the test.

In the toxicity control, containing both test item and the reference item sodium benzoate, no inhibitory effect on the biodegradation of the reference item was determined. In the procedure controls, the reference item (sodium benzoate) was degraded by an average of 73 % and 84 % by exposure days 7 and 14, respectively, thus confirming the suitability of the activated sludge (Büche, 2005).

Additionally, an assessment of the ready biodegradability was performed which determined that the substance is not readily biodegradable based on its chemical structure and specific inherent function of a dye.