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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:
29-03-2005 to 02-05-2005
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Version / remarks:
1992
Deviations:
no
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): City of Geneva, Peney-Dessous.
- Storage length: collected in the morning to be used on the same day
- Preparation of inoculum for exposure: washed 3 times with mineral medium, centrifuging at 1000g for 10 minutes, discarding the supernatant and resuspending in mineral medium
- Storage conditions: kept aerobic
- Determination of the dry weight of suspended solids: two 50 mL samples of homogenised sludge are used, the water is evaporated on a steam bath and the sludge is subsequently dried at 105-110°C for 2 hours. The residue is weighed.
Duration of test (contact time):
34 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:
Solution A: 8.5g KH2PO4, 21.75g K2HPO4, 33.4g Na2HPO4.2H2O and 0.5g NH4Cl dissolved in water and made up to 1 L.
Solution B: 27.5g CaCl2 dissolved in water and made up to 1 L.
Solution C: 22.5g MgSO4.7H2O dissolved in water and made up to 1 L.
Solution D: 0.25 g FeCl3.6H2O and one drop HCl conc. dissolved in water and made up to 1 L.
Medium: 50 mL Solution A + 2000 mL deionised water + 5 mL each of solutions B, C and D, and making up to 5 L. Adjustment of the pH to 7.4 +/- 0.2 with phosphoric acid or potassium hydroxide.
- Test temperature: 22°C

TEST SYSTEM
- Culturing apparatus: In Sapromat bottles
- Number of culture flasks/concentration: 2
- Measuring equipment: Sapromat

SAMPLING
- Sampling frequency: daily
- Sampling method: recording of oxygen consumption as measured by Sapromat device

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes
- Toxicity control: yes

Key result
Parameter:
% degradation (O2 consumption)
Value:
81
Sampling time:
28 d
Parameter:
% degradation (O2 consumption)
Value:
84
Sampling time:
34 d

% Degr.

2

7

12

21

28

34

Flask 1

15

53

65

81

85

86

Flask 2

13

42

51

67

77

82

Mean

14

47

58

74

81

84

Degradation with the reference substance sodium benzoate reached >40% after 7 days and > 65% after 14 days. Hence, the activity of the inoculum is verified.

The repeatability validity criterion is fulfilled: not more than 20% difference between replicates.

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
The substance was found mineralize to up to 81% after 28d. Nevertheless, the 10-day window is not met, and hence the substance is concluded to be not readily biodegradable according to OECD criteria.
Executive summary:

The ready biodegradability of the test item was determined by the Manometric Respirometry test according to OECD Guideline 301F and GLP. The substance was found to reach 81% of biodegradation after 28 days. The 10 - day window was not met: 14% degradation on day 2; 58% degradation on day 12. The toxicity control (biodegradation of test item + reference substance) showed that the test item is not toxic towards the microorganisms at the tested concentration (100 mg/L). As a consequence, the test shows that the substance is not readily biodegradable according to OECD criteria.

Description of key information

81% after 28 days (10 -day window was not met) (OECD 301 F)

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable but failing 10-day window

Additional information

The ready biodegradability of the test item was determined by the Manometric Respirometry test according to OECD Guideline 301F and GLP. The substance was found to reach 81% of biodegradation after 28 days. The 10 - day window was not met: 14% degradation on day 2; 58% degradation on day 12. The toxicity control (biodegradation of test item + reference substance) showed that the test item is not toxic towards the microorganisms at the tested concentration (100 mg/L). As a consequence, the test shows that the substance is not readily biodegradable according to OECD criteria.