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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:
07 August 2009 - 11 November 2009
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Version / remarks:
1992
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum sludge: fresh activated sludge from a biological waste water treatment plant treating predominantly domestig sewage (Bois-de-Bay, Satigny, Switzerland) was used.
- Preparation of inoculum for exposure: the sludge was collected in the morning, washed three times in the mineral medium, by centrifuging at 1000 g for 10 minutes, discarding the supernatant and resuspending in mineral medium, and kept aerobic until being used on the same day.
- Dry weight of suspended solids: 1.53 g/L, determined by drying two 50 mL samples of homogenised sludge in an oven for two hours after water was evaporated on a steam bath
Duration of test (contact time):
36 d
Initial conc.:
100 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: mineral medium according to OECD 301
- Test temperature: 22 °C
- pH: at the start: 7.6, at the end: 7.45 - 8.03
- pH adjusted: yes, the pH of the mineral medium was measured and if necessary adjusted to 7.4 +/- 0.2 with phosphoric acid or potassium hydroxide. The pH in the test solutions was not measured at the start and assumed to be the same as the pH in the mineral medium.
- Suspended solids concentration: 30 mg/L

TEST SYSTEM
- Culturing apparatus: Oxitop Control System (Wissenschaftlich-Technische Werkstätten (WTW), Weilheim, Germany)
- Number of culture flasks/concentration: 2
- Measurements: the consumption of oxygen is determined by measuring the pressure drop in the respirometer flask. The Biological Oxygen Demand (BOD), amount of oxygen taken up by the microbial population during biodegradation of the test chemical (corrected for uptake by blank inoculum, run in parallel) is expressed as a percentage of ThOD (Theoretical Oxygen Demand, calculated from the elemental composition, assuming that carbon is oxidized to carbon dioxide, hydrogen to water and nitrogen to ammonium, nitrite or nitrate).

SAMPLING
- Sampling frequency: daily recording of the oxygen consumption of each flask
- Sampling method: automatic by the respirometer

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes, 2 replicates
- Toxicity control: yes, 2 replicates
- Other: positive control: yes, 2 replicates

STATISTICAL METHODS: none
Reference substance:
benzoic acid, sodium salt
Remarks:
purity: min. 99.0%
Key result
Parameter:
% degradation (O2 consumption)
Value:
76
Sampling time:
28 d
Parameter:
% degradation (O2 consumption)
Value:
83
Sampling time:
36 d
Details on results:
- The test substance showed 76% biodegradation after 28 days and 83% degradation after 36 days in the test conditions (12% biodegradation on day 4 and 55% on day 14). .
Results with reference substance:
89% biodegradation within 14 days

Functioning of the test system was checked by testing the reference substance sodium benzoate which showed a normal biodegradation curve (see attached illustration).

The toxicity control showed that the test substance was not inhibitory for the inoculum used, since O2 uptake of the toxicity control was higher than the flasks containing only mineral medium, reference substance and inoculum.

Table 1 Biodegradation results



Days

3

4

5

7

14

17

21

28

36

O2 uptake
(mg O2/L)

Inoculum blank

1a

15.5

17.3

 

 

26.4

27.3

 

31.0

32.8

2a

13.7

15.5

 

 

27.3

29.2

 

34.6

37.4

Mean

14.6

16.4

 

 

26.9

28.3

 

32.8

35.1

Test substance + inoculum

5a

31.5

36.8

 

 

137.0

147.0

 

184.0

195.0

6a

36.8

47.3

 

 

146.9

157.9

 

199.8

220.8

Test substance

5a-mean inoculum

16.9

20.4

 

 

110.2

118.8

 

151.2

159.9

6a-mean inoculum

22.2

30.9

 

 

120.0

129.6

 

167.0

185.7

Reference substance + inoculum

13a

 

 

136.1

146.2

178.5

 

178.4

188.5

193.5

14a

 

 

141.2

152.3

172.4

 

172.4

178.4

172.3

Reference substance

13a-mean inocolum

 

 

118.4

125.7

151.6

 

148.3

155.7

158.4

14a-mean inoculum

 

 

123.4

131.7

145.6

 

142.3

145.6

137.2

Toxicity control

17a

 

 

172.5

188.6

262.3

 

314.8

341.0

361.2

18a

 

 

178.5

198.7

283.4

 

324.7

345.9

361.0

Mean

 

 

175.5

193.7

272.8

 

319.7

343.4

361.1

Biodegradation
(%)

Test substance

 

8

10

 

 

53

57

 

73

77

 

11

15

 

 

58

62

 

80

89

Mean

9

12

 

 

55

60

 

76

83

Reference substance

 

 

 

71

75

91

 

89

93

95

 

 

 

74

79

87

 

85

87

82

Mean

 

 

73

77

89

 

87

90

89

Degradation of test substance in presence of reference substance (%)

 

10

17

 

 

40

50

 

73

81

 

8

13

 

 

53

61

 

81

91

Mean

9

15

 

 

47

56

 

77

86

Validity criteria fulfilled:
yes
Remarks:
The positive control degraded for 89% within 14 days, the difference of duplicate values for % degradation was <20% (i.e. 12%), mean oxygen uptake of the inoculum blank at day 28 was <60 mg/L (i.e. 32.8 mg O2/L)
Interpretation of results:
readily biodegradable
Conclusions:
The substance showed 76% biodegradation in an OECD TG 301F test after 28 days, therefore it is considered to be readily biodegradable.
Executive summary:

The ready biodegradability of the test substance was investigated in a study conducted in accordance with OECD TG 301F (Manometric Respirometry Test) and GLP. The concentration tested was 100 mg/L test substance, with an activated sludge concentration of 30 mg/L. The test substance biodegraded for 76% in 28 days and can be considered ready biodegradable because it is a multi-constituent, despite failing the 10 -day window (CLP, 2016, 4.1.2.9.5). The substance was not toxic to the inoculum (89% biodegradation of the benzoic acid reference substance within 14 days).

Description of key information

The ready biodegradability of the test substance was investigated in a study conducted in accordance with OECD TG 301F (Manometric Respirometry Test) and GLP. The concentration tested was 100 mg/L test substance, with an activated sludge concentration of 30 mg/L. The test substance biodegraded for 76% in 28 days and can be considered ready biodegradable because it is a multi-constituent, despite failing the 10 -day window (CLP, 2016, 4.1.2.9.5). The substance was not toxic to the inoculum (89% biodegradation of the benzoic acid reference substance within 14 days).

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

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