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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
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)
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): A sample of activated sludge was collected from on of the return lines at Burley Menston sewage treatment works (Yorkshire Water), a treatment works whose waste-water catchment is predominantly domestic.
- Storage conditions: On arrival in the laboratory the sample was aerated by means of a compressed air supply delivered through a diffuser block.
- Preparation of inoculum for exposure: The suspended solids concentration was determined by filtering a 25 mL subsample through a pre-weighed glass microfibre filter (Whatman GF/C). The filter and retained solids were then dried at a nominal 105°C, re-weighed and the contribution made by the sludge solids determined by difference.
- Pretreatment: Not pretreated with the test substance.
- Concentration of sludge: 30 mg/L
Duration of test (contact time):
28 d
Initial conc.:
15 mg/L
Based on:
TOC
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: The test was conducted in synthetic mineral salts medium based on distilled water as per the OECD guideline.
- Additional substrate: None
- Solubilising agent (type and concentration if used): None
- Test temperature: In the range 20 to 22°C.
- pH:
Control Day 0, 7.69 to 7.72 and Day 28, 7.58 to 7.63.
Test substance Day 28, 7.77 to 7.83
Reference substance Day 0, 7.70 to 7.71, and Day 28 7.95 to 7.97.
Toxicity control: Day 28, 8.24.
The pH in the test substance and toxicity control vessels were not assessed on Day 0 as the addition of pH probes into the medium may have removed test substance from the vessels.

- pH adjusted: No
- Aeration of dilution water: Yes.
- Suspended solids concentration: The final suspended solids concentration in all vessels was nominally 10 mg/L.
- Continuous darkness: Yes

TEST SYSTEM
- Culturing apparatus: Not specified but assumed to be standard BOD bottles.
- Number of culture flasks/concentration: Two replicates for the test substance, control and reference control. One for the toxicity control.
- Method used to create aerobic conditions: Vessels purged with air
- Test performed in open system: No
- Details of trap for CO2 and volatile organics if used: Nominally CO2 free control air fed from cylinders. As an added precaution, the flow passed through a column packed with Carbosorb AS, a self indicating, artificial silicate CO2 absorber.
- Dosing the test substance: The test substance was weighed onto PTFE discs and added together with the weighing supports to the two test vessels and toxicity control.

SAMPLING
- Sampling frequency: Days 2, 4, 6, 8, 10, 14, 19, 24 and 28.
- Sampling method: Scrubbers were detached at appropriate intervals and their contents titrated with acid to determine the quantity of CO2 purged from the respective test vessels.
- Sterility check if applicable: Not applicable
- Sample storage before analysis: Determined soon after scrubbers detached.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes (2 replicates)
- Abiotic sterile control: No
- Toxicity control: Yes (1 replicate)

STATISTICAL METHODS: Not required.
Reference substance:
benzoic acid, sodium salt
Preliminary study:
Not a guideline requirement
Test performance:
Validity criteria:
- The reference compound satisfied the requirements for classification as readily biodegradable by Day 14. The percentage degradation exceeded 60% of theoretical within ten days of first reaching 10% and the individual percentage degradation data recorded in the duplicate reference vessels lay within 20% of one another throughout the study.

- CO2 blank generation: Total mean blank CO2 production in this study was 38.83 mg/3L, indicating that respiration of the inoculum had not been of sufficient magnitude to cause interference with test results. The guideline states blanks should not exceed 120 mg/3L of medium.
Parameter:
% degradation (CO2 evolution)
Value:
1
Sampling time:
28 d
Details on results:
Degradation at the end of the study failed to reach the 60% 'pass' level and accordingly the substance was not considered to be readily biodegradable
Results with reference substance:
Measured CO2 production exceeded the 'pass' level at 60% of theoretical within 14 days and within the ten day window.

Biodegradation as percentage of theoretical CO2 yield:

Days

Test substance

Reference substance

Rep. 1

Rep. 2

Tox control

Rep. 1

Rep. 2

2

0

0

14

21

21

4

0

0

39

45

44

6

0

0

57

60

59

8

1

1

69

69

68

10

1

1

74

73

73

14

1

1

79

77

77

19

1

1

83

81

82

24

1

1

86

85

86

28

1

1

91

90

90

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
In accordance with the OECD 301B guideline, no significant production of CO2 was registered at the applied concentration of the test substance over the 28 day test period. Therefore, the substance is not considered to be readily biodegradable.

Description of key information

In an OECD guideline, GLP study only minimal degradation was observed. Accordingly the substance would not be considered readily biodegradable.

Key value for chemical safety assessment

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

Additional information