Fluocortolone

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

Study period:

Sep - Oct 1991

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Draft report

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 B (Ready Biodegradability: CO2 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 well-operated municipal sewage treatment plant (Kläranlage Berlin-Ruhleben, Germany)
- Storage conditions: Upon arrival at the laboratory, the activated sludge was aerated and stirred for 3 hours, then homogenised for two minutes in a blender and stirred for about 1.5 hours. After settling for 30 minutes, 30 mL were taken from the supernatant for each test vessel and given to one litre of test solution. The storage length was at a maximum of 24 h.

Duration of test (contact time):

28 d

Initial conc.:

10 mg/L

Based on:

DOC

Initial conc.:

20 mg/L

Based on:

DOC

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

Three CO2-absorber bottles, filled with 100 ml 0.025 N Ba(OH)2 each, were connected in series to the exit air-pipe of each test bottle. The amount of CO2 produced was determined by titration of the remaining Ba(OH)2 with 0.05 N standardised HCl. Periodically (for a maximum of 3 days out of the first 11 days, and every 3 to 5 days within the rest of the test period) the CO2 -absorber nearest to the test bottles was removed for the titration. The remaining two absorbers were each moved one place closer to the test vessel, and a new absorber bottle filled with fresh Ba (OH)2 was placed at the far end
of the series. In the case of any BaCO3 precipitating in the second absorber vessel also, titrations of two Ba(OH)2 bottles were performed. Subsequently, two fresh absorbers were added.

The test began when the test compounds or the reference substance respectively, were added and the CO2 -absorbers were connected to the test vessels (day 1). TOC-analysis of the reference stock solution was carried out in order to check whether the measured concentration agreed with the nominal on the basis of organic carbon content. The carbon analysis was performed by injecting 20 μL of the solution into the TOC-carbon analyzer (Shimadzu TOC 500).

I. Addition of the inoculum and preparation of the reference and test compound solutions:
- 30 mL of the inoculum from the activated sludge were added to the nutrient solutions in each of the test vessels
- These mixtures were aerated with C02-free air for 24 hours to purge the system of carbon dioxide before test and reference compounds were added. C02free air was obtained by bubbling filtered air through 10 N KOH
- A stock solution of the reference substance was prepared by dissolving 1 g sodium acetate in 1000 mL demineralized H20
- 60 mL of this stock solution were added to the reference test bottle
- The test material was rubbed well in 2-3 mL water and added directly in amounts of 30 mg and 60 mg each case
- Then each test vessel was filled up with demineralized water to a volume of 3000 mL
- The concentrations of the reference and the test compounds were 20 mg/L (Reference substance), 10 and 20 mg (test substance)
- One test bottle contained only nutrient reagents and inoculum and served as a blank (control) vessel

II. lncubation conditions:
- The test solutions were incubated and protected from light under aeration with filtered C02-free air (3.0-5.0 L per hour for each test vessel) at a temperature of 21 to 25 °C
- On day 28 the pH of the test solutions ranged from 7.3 to 7.4.

Reference substance:

acetic acid, sodium salt

Remarks:

Merck AG, Batch No. 945 TA 75 69 68

Key result

Parameter:

% degradation (CO2 evolution)

Value:

5

Sampling time:

28 d

Remarks on result:

other: 10 mg/L

Key result

Parameter:

% degradation (CO2 evolution)

Value:

0

Sampling time:

28 d

Remarks on result:

other: 20 mg/L

Details on results:

The test substance was not or only marginally degraded (up to 5% at the lowest concentration).

Results with reference substance:

The reference compound was degraded to more than 60% at day 9.

Validity criteria for the measurement of the biodegradation:

Target condition according to guideline:	Actual condition according to the study:	Validity criteria met:
In order to check the procedure, reference compounds which meet the criteria for ready biodegradability are tested by setting up an appropriate vessel in parallel as part of normal test runs. Suitable compounds are aniline (freshly distilled), sodium acetate and sodium benzoate.	Sodium acetate was used as a reference substance.	Yes
A test is considered valid if the 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% and if the percentage degradation of the reference compound has reached the pass levels by day 14.	The reference substance sodium acetate was degraded to more than 60 % within 9 days (approximately 7 days after the start of the degradation process}. The produced C02 of the blank (control) (49.8 mg) in the normal test period was within the limit set by the OECD guideline (50 mg). Hence, the quality criteria of the OECD guideline were fulfilled, i.e. the inoculum was viable and active.	Yes
If in a toxicity test, containing both the test substance and a reference compound, less than 35% degradation (based on total DOC) or less than 25% (based on total ThOD or ThCO2) occurred within 14 days, the test substance can be assumed to be inhibitory. The test series should be repeated, using a lower concentration of test substance (if this can be done without seriously impairing the accuracy of the DOC determination) and/or a higher concentration of inoculum, but not greater than 30 mg solids/l.	Not reported in the study.	Not applicable.

 

Validity criteria fulfilled:

yes

Remarks:

for details please refer to "Any other information on results incl. tables"

Interpretation of results:

under test conditions no biodegradation observed

Conclusions:

For two test concentrations (10 and 20 mg/L) degradation rates between 0 and 5 % were determined within 28 days of incubation. The test substance was not or only marginally degraded (up to 5% at the lowest concentration). The reference compound sodium acetate was degraded to 98 %.

Executive summary:

The study was conducted in agreement with the OECD test guideline no. 301 B. Fluocortolone was incubated in aqueous solutions including nutrients, with microorganisms from a municipal sewage treatment plant for 29 days. The nutrient solutions were made up of phosphates, ammonium sulphate, magnesium sulphate, ferric chloride, ammonium chloride and calcium chloride, and added to the test solution. Additionally, a reference substance sodium acetate was tested according to the same procedure in order to verify the viability and activity of the degrading microorganisms. The test substance was incubated in two concentrations (10 mg/L and 20 mg/L) and the reference substance in a concentration of 20 mg/L. Furthermore, one additional vessel without any test or reference substance was used as blank (control). The biological degradation of the test and reference substance was evaluated by measurement of the CO₂ produced during the test period. CO₂-production was determined on days 3, 4, 7, 9, 11, 15, 18, 23, 28, 29 and calculated as the percentage of total CO₂ that the test material could theoretically have produced, based on carbon composition. For the two test concentrations degradation rates between 0 and 5 % were determined within 28 days of incubation. The reference compound sodium acetate was degraded to 98 %. In accordance with the OECD 301 B fluocortolone is not readily biodegradable under the conditions of the test.

Description of key information

In the study on ready biodegradability for two test concentrations (10 and 20 mg/L) according to OECD 301B degradation rates between 0 and 5 % were determined within 28 days of incubation. The test substance was not or only marginally degraded (up to 5% at the lowest concentration). The reference compound sodium acetate was degraded to 98 % after 28 days of incubation.

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Type of water:

freshwater