Fluocortolone

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

29 - 31 Jan 1992

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

no

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

The nutrient solutions were made up of peptone, meat extract, urea, sodium chloride, calcium chloride, magnesium chloride and dipotassium hydrogen phosphate. The test compound was incubated in 4 concentrations 10, 20, 40 and 100 mg/L and the reference substance in three concentrations (10, 17, and 31 mg/L).

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Type: predominantly domestic sewage (content of solid particles: 3.2 g/L)
- Origin: A well-operated municipal sewage treatment plant (Kläranlage Berlin-Ruhleben, Germany),
- Microbial inoculum: Upon arrival at the laboratory, the activated sludge was aerated and stirred for approx. 2 hours and left to settle for approx. 2 hours; 4000 mL were taken from the supernatant and mixed with 4000 mL water and 320 mL nutrient solution; the mixture was aerated and stirred for approx. 18 hours.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

0.5 h

Test temperature:

24.1 - 26.1 °C

Nominal and measured concentrations:

- Test item concentrations (nominal): 10, 20, 40 and 100 mg/L
- Reference substance concentrations (nominal): 10, 17 and 31 mg/L

Details on test conditions:

I. Preparation of the control, reference and test substance solutions
The test vessels were prepared as follows:
- Control: 200 mL of the pre-culture were filled into a 250 mL Erlenmeyer flask. Then 8 mL of the nutrient solution and 42 mL aqua dem. were added
- Test compound: The same mixture as above was prepared. The compound was added directly in amounts of 2.5, 5, 10 and 25 mg. This resulted in an inhomogenous suspension
- Reference substance (3,5-dichlorophenol): 200 mL pre-culture were mixed with 8 ml nutrient solution. 5, 8.5 and 15.5 mL of an aqueous stock solution (500 mg/L) were added and filled up to 250 mL

The test vessels were prepared and incubated at intervals of approx. 7 minutes. Each test concentration of the reference substance and the test compound was incubated in duplicate. For the control, two test vessels were used at the beginning and 3 test vessels at the end of the test series.

II. Measurement of oxygen consumption:
- After the incubation period of 30 minutes approximately 25 mL from the first vessel were introduced into a measuring apparatus by a plastic tube avoiding air bubbles.
- This apparatus consisted of a cylindrical glass container fitted with a polarographic oxygen electrode (Fa. WTW, OXI 92) connected to a recorder
- The test mixture was stirred using a magnetic stirrer; over a period of four minutes the oxygen consumption was measured and recorded
- This determination was repeated for the contents of each vessel at 7-minute intervals, with the result that the incubating time was 30 minutes in each case

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol

Key result

Duration:

0.5 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

The inhibition of respiration varied between 8.7 and 13.6 %, which was not concentration related. Therefore, the inhibition is not considered to be substance related.

Results with reference substance (positive control):

The reference compound showed an EC50 of 10.5 mg/L

Validity criteria for the measurement of the bacterial toxicity:

Target condition according to guideline:	Actual condition according to the study:	Validity criteria met:
In a 2004 international ring test organized by ISO using activated sludge derived from domestic sewage, the EC50 of 3,5-dichlorphenol was found to lie in the range 2 mg/L to 25 mg/L for total respiration. If the EC50 of 3,5-DCP does not lie in the expected range, the test should be repeated with activated sludge from another source.	For 3,5-dichlorophenol an EC50 value of 10.5 mg/L was determined.	Yes
The test should be performed at a temperature within the range 20 ± 2°C.	The test was performed between 24.1 - 26.1 °C	No
The specific oxygen consumption of the controls shall be reported.	The oxygen consumption of the controls is stated.	Yes

 

 

Validity criteria fulfilled:

yes

Remarks:

The temperature criterion in the OECD 209 guideline was not fulfilled, as the test was conducted at a higher temperature than that described. However, all other validity criteria are fulfilled.

Conclusions:

The 30 min-EC50 for activated sludge respiration inhibition of fluocortolone was higher than 100 mg/L. After an aeration of 30 minutes the inhibition of respiration varied between 8.7 and 13.6 %, which was not concentration related. Therefore, the inhibition is not considered to be substance related.

Executive summary:

The study was conducted in accordance with OECD Guideline 209 ‘Activated Sludge, Respiration Inhibition Test, adopted 4. Apr. 1984. The test compound was incubated for 30 minutes as suspensions including nutrients with microorganisms from a municipal sewage treatment plant. The nutrient solutions were made up of peptone, meat extract, urea, sodium chloride, calcium chloride, magnesium chloride and dipotassium hydrogen phosphate. Additionally a reference substance (3,5-dichlorophenol) was tested according to the same procedure in order to verify the sensitivity of the test organisms. The test compound was incubated in 4 concentrations 10, 20, 40 and 100 mg/L and the reference substance in three concentrations (10, 17, and 31 mg/L). The test item and reference compound concentrations were not confirmed by analytical methods, they were based on nominal concentrations. Furthermore, additional vessels without test or reference substance were used as controls. All test concentrations were incubated in duplicate except the control, which was incubated in 5 replicates. As a parameter for the inhibition of the oxygen consumption, the respiration rate of each test vessel was measured in a closed apparatus over a period of 4 minutes after incubation. The reference compound showed an EC50 of 10.5 mg/L, which is in the required range (5-30 mg/L) noted in the guidelines (OECD, ISO, EEC). The control variability did not exceed the required value. The results of the respiration inhibition test with activated sludge demonstrate that the test compound exerted relatively low toxicity on the microorganisms of activated sludge. Since the solubility of the test compound in an aqueous solution was far exceeded - indicated by the inhomogenous turbidity - it can be concluded from the findings that a saturated solution of the test compound had no effects an the microbial population in sewage sludge. The observed inhibition of respiration was probably not due to the test compound, particularly since no clear exposure-effect relationship was observed. This toxicity study is classified as acceptable and satisfies the guideline requirements for the toxicity study to microorganisms.

 

Description of key information

After 30 minutes of exposure the EC50 for activated sludge respiration inhibition was higher than 100 mg/L.

Key value for chemical safety assessment

EC50 for microorganisms:

100 mg/L

Additional information

"Should read: > 100 mg/L"

After an aeration of 30 minutes the inhibition of respiration varied between 8.7 and 13.6 %, which was not concentration related. Therefore, the inhibition is not considered to be substance related.