5,7-dichloro-4-(4-fluorophenoxy)quinoline;quinoxyfen (ISO)

Biodegradation in water: screening tests

Link to relevant study record(s)

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.5 (Degradation: Biochemical Oxygen Demand)

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

Test substance ID: XDE 795
Batch No: TSN100004
Purity: 99.7%

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic (adaptation not specified)

Details on inoculum:

Preliminary test (Bacterial inhibition test): A sample of secondary effluent was obtained on the day of the test from a trickling-filter plant at a sewage treatment works that treats predominantly domestic waste. Inoculum was maintained under aerobic conditions in the laboratory until required, and vacuum-filtered through a Whatman GFC filter paper immediately before use. The filtrate was used as the source of inoculum for the test (1 drop/litre test medium).

Modified Sturm test: A sample of activated sludge was collected on the day before the test from a sewage treatment works that treats predominantly domestic waste, and aerated in the laboratory for approximately four hours. A sample of the mixed liquor was then homogenised in a mechanical blender and allowed to settle for 30 minutes. An aliquot of the supernatant was passed through a Whatman GFC filter paper to remove coarse solids and the filtrate used as the inoculum for the test.

Duration of test (contact time):

28 d

Initial conc.:

10 mg/L

Based on:

test mat.

Initial conc.:

20 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

Parameter followed for biodegradation estimation:

DOC removal

Details on study design:

TEST CONDITIONS
- Composition of medium: Mineral salts medium
- Solubilising agent (type and concentration if used): Dilution water was used to prepare stock and test solutions of mineral salts was tap water that had been softened and treated by reverse osmosis and then purified.
- Conductivity of Dilution water: 18 Megohm/cm
- Test temperature: 17.5°C to 24.0°C.
- pH: 7.56 to 7.61 at the start of the test and from 6.62 to 7.60 at the end.

TEST SYSTEM
- Culturing apparatus: 5 litre vessels, brown glass carboys
- Number of culture flasks/concentration: 1
- Method used to create aerobic conditions: Bacterial inoculum at a concentration of 1% were aerated overnight with air that had been passed through cylinders containing Carbosorb AS followed by twelve one-litre bottles containing 10N sodium hydroxide
- Measuring equipment: A sample (500 ml) was removed from each vessel for the determination of pH and, after passing through a membrane filter (0.2 µM), acidification and sparging with nitrogen, DOC analysis.
- Details of trap for CO2 and volatile organics if used: 0.25N barium hyroxide was used to remove CO2.

BLANK SYSTEM:
Inoculum blank: Inoculum containing Mineral salts medium

Reference substance:

benzoic acid, sodium salt

Remarks:

Concentration: 20 mg/L

Preliminary study:

The five-day bacterial inhibition assay was conducted before the main test to determine whether test substance, at concentrations of 2 and 10 mg/L, inhibited the normal degradative activity of the bacterial inoculum on the reference material, sodium benzoate. The presence of test substance at either test concentration had no significant effect, indicating that it was not inhibitory. Neither was it, itself, readily degradable in this preliminary test.

Key result

Parameter:

% degradation (CO2 evolution)

Value:

3

Sampling time:

28 d

Remarks on result:

other: Not readily biodegradable

Remarks:

For 10 mg/L

Key result

Parameter:

% degradation (CO2 evolution)

Value:

2

Sampling time:

28 d

Remarks on result:

other: Not readily biodegradable

Remarks:

For 20 mg/L

Key result

Parameter:

% degradation (DOC removal)

Value:

14

Sampling time:

28 d

Remarks on result:

other: At the end, DOC concentrations at 10 mg/L (0.8 mg/L) were equivalent to 14% of its theoretical carbon content which indicated that some dissolution of material had taken place during the test.

Key result

Parameter:

% degradation (DOC removal)

Value:

9

Sampling time:

28 d

Remarks on result:

other: At the end, DOC concentrations at 20 mg/L (1.1 mg/L) were equivalent to 9% of its theoretical carbon content which indicated that some dissolution of material had taken place during the test.

Key result

Parameter:

COD

Value:

1.58 other: mgO2/mg

Remarks on result:

other: The mean of six determinations (1.58 mgO2/mg) was 101% of the test substance theoretical oxygen demand.

Remarks:

The results indicate that test substance was completely oxidised under the conditions of the COD test

Key result

Parameter:

BOD5

Value:

0 other: mgO2/mg

Remarks on result:

other: For 2 mg/L concentration

Key result

Parameter:

BOD5

Value:

0 other: mgO2/mg

Remarks on result:

other: For 10 mg/L

Results with reference substance:

- BOD5 of Sodium benzoate (2 mg/L): 0.95 mgO2/mg
- The degradation of sodium benzoate was rapid and had achieved 68% of its TCO2 after nine days and 85% after 28 days. These results confirm that the inoculum was viable and that the test was valid.
- DOC: At the start of the test, the DOC content of the sodium benzoate mixture (11.0 mgC/l) was 94% of the theoretical value (11.7 mgC/l) calculated from its carbon content. DOC analysis at the end of the test showed that benzoate as 97% degraded.

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

Not readily biodegradable

Executive summary:

The test was conducted according to guideline OECD 301B to assess test substance using modified sturm test. The Chemical Oxygen Demand (COD) of test substance was determined by oxidation with an acid-dichromate mixture using a semi-micro procedure. The mean of six determinations (1.58 mgO2/mg) was 101% of its theoretical oxygen demand (1.56 mgO2/mg). These results indicate that the carbon content of the material was completely oxidized under the conditions of the COD test.

In a five-day bacterial inhibition test conducted under the conditions of the Closed Bottle Test (EEC Procedure C6, OECD Method 301D), test substance concentrations of 2 and 10 mg/L did not inhibit degradation of the reference material sodium benzoate (2 mg/L). The test material alone showed no degradation.

In the Modified Sturm test, test substance was added to inoculated mineral salts medium, to give nominal test concentrations of 10 and 20 mg/L. Control vessels contained inoculated mineral salts medium alone, or inoculated mineral salts medium plus sodium benzoate (20 mg/L). Test and control vessels were aerated for 28 days with air that had been treated to remove carbon dioxide (CO2). The CO2 produced by each culture was trapped in a series of drechsel bottles containing barium hydroxide, which were connected to the outlet of each test vessel. The residual barium hydroxide was determined at intervals by titration. The pH of control, reference and test cultures was measured at the start of the test and on Day 27 and the dissolved organic carbon (DOC) content of each at the start and end.

The reference substance sodium benzoate was degraded to 68% of its theoretical carbon dioxide production (TCO2; 2.14 mgCO2/mg) after nine days and 85% after 28 days; DOC analysis indicated that benzoate was 97% degraded. Cumulative CO2 production in the control after 28 days (10.8 mgCO2) was acceptable for this assay system (recommended maximum, 50 mgCO2). These results confirm that the inoculum was viable and that the test was valid.

DOC was not detected in mixtures containing test substance at the start of the test which indicated that the material was not in solution. At the end, measured concentrations indicated that some dissolution had taken place during the test.

Cumulative CO2 production by mixtures containing test substance at 10 and 20 mg/L respectively was equivalent to 3% and 2% of its TCO2 (2.14 mgCO2/mg).

Substances are considered to be readily degradable in this test, if CO2 production is equal to or greater than 60% of the theoretical value within ten days of the level first achieving 10%. The test material cannot therefore considered to be readily degradable.

Description of key information

The test substance reached a maximum mean of 3 and 2% ThCO2 by day 2 when tested at 10 and 20 mg/L; therefore, the substance is considered not readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed