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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:
10 Jul - 04 Oct 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2017
Report date:
2017

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Qualifier:
according to guideline
Guideline:
EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)
Qualifier:
according to guideline
Guideline:
EPA OPPTS 835.3110 (Ready Biodegradability)
GLP compliance:
yes (incl. QA statement)
Remarks:
The Department of Health of the Government of the United Kingdom

Test material

Constituent 1
Chemical structure
Reference substance name:
Pyridine-2-carboxylic acid
EC Number:
202-719-7
EC Name:
Pyridine-2-carboxylic acid
Cas Number:
98-98-6
Molecular formula:
C6H5NO2
IUPAC Name:
pyridine-2-carboxylic acid

Study design

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): Obtained from aeration stage of the Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK (04 Sep 2017)
- Laboratory culture: no
- Pretreatment: The activated sewage sludge sample was washed twice by settlement and re-suspension in mineral medium.
- Storage conditions: Washed sludge was maintained on continuous aeration in the laboratory at a temperature of approximately 21 °C.
- Storage length: used on the same day of collection
- Suspended solids concentration: 3.0 g/L; Determination of the suspended solids level of the activated sewage sludge was carried out by filtering a sample (100 mL) of the washed activated sewage sludge by suction through pre-weighed GF/A filter paper* using a Buchner funnel. Filtration was then continued for a further 3 minutes after rinsing the filter three successive times with 10 mL of deionized reverse osmosis water. The filter paper was then dried in an oven at approximately 105 °C for at least 1 h and allowed to cool before weighing.
Duration of test (contact time):
28 d
Initial test substance concentrationopen allclose all
Initial conc.:
17.1 mg/L
Based on:
test mat.
Initial conc.:
10 mg/L
Based on:
other: carbon/L
Parameter followed for biodegradation estimation
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: according to guideline
- Test temperature: 22 - 24 °C
- pH: 7.4 - 7.7
- pH adjusted: yes; adjusted to pH 7.4 at the beginning of the study using hydrochloric acid.
- Suspended solids concentration: 30 mg/L
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: 5 L test (filled with 3 L solution)
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: Approximately 24 h prior to addition of the test and reference items the vessels were filled with 2400 mL of mineral medium and 30.0 mL of inoculum and aerated overnight.
- Measuring equipment: The samples were analyzed for IC using either a Tekmar-Dohrmann Apollo 9000 TOC analyzer or a Shimadzu TOC-VCSH TOC analyzer. Samples (50 or 135 μL) were injected into the IC channel of the TOC analyzer. IC analysis occurs by means of the conversion of an aqueous sample to CO2 by orthophosphoric acid or 2 M HCl using zero grade air as the carrier gas. Calibration was by reference solutions of sodium carbonate (Na2CO3). Each analysis was carried out in at least triplicate with 3 replicates being used in the calculation/reported.
- Details of trap for CO2 and volatile organics if used: The CO2 produced by degradation was collected in two 500 mL Dreschel bottles containing 350 mL of 0.05 M NaOH.
- Other: The test vessels were sealed and CO2-free air bubbled through the solution at a rate of 30 to 100 mL/min per vessel and stirred continuously by magnetic stirrer. The CO2-free air was produced by passing compressed air through a glass column containing self-indicating soda lime (Carbosorb®) granules.

SAMPLING
- Sampling frequency and method: Samples (2 mL) were taken from the first CO2 absorber vessels on Days 0, 2, 6, 8, 10, 14, 21, 28 and 29. The second absorber vessels were sampled on Days 0 and 29. On Day 28, 1 mL of concentrated hydrochloric acid was added to each vessel to drive off any inorganic carbonates formed. The vessels were resealed, aerated overnight and the final samples taken from both absorber vessels on Day 29.
- Sample storage before analysis: Samples were analysed immediately.

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes, 2 bottles
- Abiotic sterile control: no
- Toxicity control: yes, 1 bottle
- Reference substance: yes, 2 bottles

STATISTICAL METHODS:
Reference substance
Reference substance:
benzoic acid, sodium salt
Remarks:
(17.1 mg/L)

Results and discussion

Preliminary study:
The results obtained from the samples taken for DOC analysis from the preliminary investigational work indicated that the test item did not adsorb to filter matrices or to activated sewage sludge. Therefore, for the purpose of the study, the samples taken for DOC analysis were filtered to remove the suspended solids present without the loss of any test item.
% Degradation
Parameter:
% degradation (CO2 evolution)
Value:
86
Sampling time:
28 d
Details on results:
The reference substance was degraded to 65% after 14 d. Thus, the test item is not considered to be inhibitory to the inoculum.

BOD5 / COD results

Results with reference substance:
The reference substance was degraded to 71% after 14 d and to 76% after 28 d.

Any other information on results incl. tables

Table 1: Validity criteria for OECD 301B.

Criterion from the guideline

Outcome

Validity criterion fulfilled

Difference of extremes of replicate values of the removal of the test chemical at the plateau, at the end of the test or at the end of the 10-d window, as appropriate, is less than 20%.

< 20%

yes

Percentage degradation of the reference compound has reached the pass levels by day 14.

71% biodegradation after 14 days

yes

The IC content of the test substance suspension in the mineral medium at the beginning of the test must be less than 5% of the TC, and the total CO2 evolution in the inoculum blank at the end of the test should not normally exceed 40 mg/L medium.

CO2 evolution blank: 28.25 mg/L

IC content: 1-2%

yes

Table 2: Percentage degradation after 28 d

Day

% degradation

Reference item

Test item

Toxicity control

0

0

0

0

2

39

4

15

6

40

92

13

8

57

84

27

10

74

80

68

14

71

83

65

21

71

77

70

28

80

87

73

29*

76

86

74

* Day 29 values corrected to include any carry-over of CO2 detected in Absorber 2

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Remarks:
For further details please refer to “Any other information on results incl. tables”.
Interpretation of results:
readily biodegradable

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