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

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

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

Qualifier:

according to guideline

Guideline:

other: Commission Regulation 440, Activated Sludge Respiration Inhibition Test, May 2008

Deviations:

no

Qualifier:

according to guideline

Guideline:

ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

Lot No.: DECO-104-116
TSN100010
Purity: 98.2%

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Activated sludge, microorganisms from a domestic waste water treatment plant was supplied by the municipal sewage treatment plant Bensheim, Germany.

Test type:

static

Limit test:

yes

Total exposure duration:

3 h

Test temperature:

20°C ± 2°C

pH:

6.4

Nominal and measured concentrations:

100 mg quinoxyfen/L (Nominal)

Details on test conditions:

TEST SYSTEM
- Test vessel: Glass flasks of approximately 1 litre volume and Karlsruher flasks of 300 mL volume
- Aeration: Compressed air (1.017 litre per minute)
- Controls: Six controls (pure water, synthetic sewage feed and inoculum, but without addition of the test item) were tested in parallel.
- Replicates: 6 controls, 3 replicates for positive control, 3 replicates for test item
- Preparation of test flasks: For each replicate a test solution with a final volume of 500 mL was tested per treatment in a glass flask. 16 mL synthetic sewage feed and an adequate amount of the test item or an adequate volume of the stock solution of the reference item were filled up with pure water to 250 mL before the start of the test.
At the start of the test 250 mL activated sludge inoculum with a sludge concentration of 3.0 g/L suspended solids was added, first to two controls, then to the test solutions of the reference item in increasing concentrations, to further two controls, then to the test item and finally to additional two controls. During the 3 hour aeration period the flasks were stirred on a magnetic stirrer to maintain sludge flocs in suspension.

TEST MEDIUM / WATER PARAMETERS
The activated sludge used for this study was used as collected, but coarse particles were removed by settling for a short period (15 minutes) and then the upper layer decanted. During holding prior to use the sludge was fed with 50 mL synthetic sewage feed (see below) per litre and kept aerated at room temperature overnight.

An aliquot of the final sludge suspension was weighed, dried and the ratio of wet sludge to its dry weight determined. Based on the sludge dry matter, calculated amounts of wet sludge were suspended in pure water to yield a concentration equivalent to 3 g/L on dry weight basis. This level gives a concentration of 1.5 g/L suspended solids in the test medium. The pH of the activated sludge inoculum was 6.4 and therefore no adjustment necessary.

EFFECT PARAMETERS MEASURED:

Measurement of Respiration Rate: For the measurement of the respiration rate a well-mixed sample of each test medium was poured into a Karlsruher flask after exactly 3 hours incubation time. The oxygen concentration was then measured with an oxygen electrode and recorded for about ten minutes. During measurement, the samples were continuously stirred on a magnetic stirrer. The oxygen consumption (in mg O2 L-1 minute-1) was determined over a time period of 10 minutes from the most linear part of the respiration curve in the range between 8.3 and 1.4 mg O2/L for total respiration. In case of low oxygen consumption, the values over a period smaller than 10 minutes were used.

Measurement of pH, Dissolved Oxygen and Water Temperature: The dissolved oxygen concentrations were determined at the start and at the end of the incubation period in at least one replicate of all test concentrations and controls. The pH-value was determined at the start and at the end in at least one replicate of the test concentrations and controls. The water temperature was measured in one control medium at the start and the end of the incubation period.

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Details on results:

At a nominal test concentration of 100 mg quinoxyfen/L less than 10% inhibition was observed after three hours of incubation. The mean inhibition was 3.7% at three replicates of 100 mg quinoxyfen /L.
The respiration rate of the activated sludge to quinoxyfen at the rate of 100 mg/L was not statistically significant reduced when compared to the control (two-sample t-test).
The mean respiration rates of the activated sludge treated with the test item at a concentration of 100 mg/L differed by less than 10% from control.

Results with reference substance (positive control):

In comparison to the controls the respiration rate of the activated sludge was moderately inhibited by 30.3% at the lowest nominal concentration of 1 mg/L. At the nominal concentrations of 4 and 16 mg reference item/L, the respiration rate was inhibited by 30.3% and 73.3%, respectively.

The oxygen uptake in the blank controls was 27.0 mg/g/h and therefore clearly above 20 mg oxygen/g of activated sludge (dry weight of suspended solids) in an hour. The respiration rates of the six controls differed not more than 30%. The value was 2.8% for the total respiration. The validity criterion was fulfilled.

Validity criteria fulfilled:

yes

Conclusions:

Quinoxyfen at the rate of 100 mg/L had no toxic effects on respiration activity of activated sludge. Therefore it can be assumed that the NOEC is above 100 mg/L.

Executive summary:

The influence of the test item quinoxyfen on the activity of activated sludge was evaluated by measuring the respiration rate under defined conditions according to OECD guideline 209. The respiration rate (oxygen consumption) of an aerobic activated sludge fed with a standard amount of synthetic sewage feed was measured in the presence of one concentration of the test item after an incubation period of 3 hours.

 

This limit test was performed in compliance with the test guidelines to demonstrate that the test item had no toxic effect on activated sludge up to at least this concentration.

 

Quinoxyfen had no effects on the respiration of activated sludge microorganisms. In comparison to the inoculum controls, the respiration rate of the activated sludge was inhibited by 3.7%. Therefore, quinoxyfen at the rate of 100 mg/L was not reduced significantly when compared to the control (two-sample t-test). The oxygen uptake in the blank controls was 27.0 mg/g/h and therefore clearly above 20 mg oxygen/g of activated sludge (dry weight of suspended solids) in an hour. The respiration rates of the six controls differed not more than 30%. The value was 2.8% for the total respiration. The validity criterion was fulfilled. The positive control 3,5-Dichlorophenol was tested in the same way as the test item. The 3-hour EC₅₀was found to be 6.1 mg/L thus being in the range of 2 - 25 mg/L recommended by the test guidelines. The result confirms the suitability of the activated sludge used.

 

Quinoxyfen at the rate of 100 mg/L had no toxic effects on respiration activity of activated sludge. Therefore it can be assumed that the NOEC is above 100 mg/L.

Description of key information

NOEC (activated sludge) > 100 mg/L (limit dose); OECD Guideline 209: Reliability = 1

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

100 mg/L