Pyrasulfotole

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:

16 Aug - 19 Aug 2016

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 (Carbon and Ammonium Oxidation))

Version / remarks:

2010

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

Version / remarks:

2008

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Ministerium fur Arbeit, Integration und Soziales des Landes Nordrhein-Westfalen, Leverkusen, Germany

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: The exposure medium with the reference substance was prepared by adding 8 mL of the synthetic medium, 100 mL of activated sludge and a defined amount of the stock solution to achieve the test concentrations, and was filled up with deionised water to 250 mL and aerated at 20 ± 2°C.
Before use the wet weight/dry weight relationship of the activated sludge was determined by drying 10 mL of sludge suspension. Subsequently, a sludge suspension of 2 g (dry weight)/L was prepared. The pH of this suspension was measured and adjusted to 6-8. 8 mL of the synthetic medium and 100 mL of activated sludge were added to the dissolved test item. The mixture was filled up with deionised water to 250 mL and aerated at 20 ± 2 °C. To determine the heterotrophic oxidation four additional controls and two replicates with the test item concentration 100 mg/L, all containing 1.25 mL of ATU-solution (N-allylthiourea), which equals to a final concentration of 11.6 mg ATU/L, were prepared.
- Eluate: no
- Differential loading: no
- Controls: Control vessels (inoculated sample without test item) were prepared the same way.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Laboratory culture: no
- Name and location of sewage treatment plant where inoculum was collected: aeration tank of a domestic waste water treatment plant (Municipal WWTP Cologne-Stammheim, Germany)
- Method of cultivation: aeration of the activated sludge at 20 ± 2 °C, daily fed with synthetic medium
- Preparation of inoculum for exposure: Sludge was settled and the supernant was decanted. The sludge was centrifuged and the supernant was decanted. A portion of the sludge was dried to obtain a dry weight. The calculated amount of sludge was dissolved in synthetic medium and diluted with deionised water.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Test temperature:

20 ± 2 °C

pH:

6-8

Nominal and measured concentrations:

nominal: control, 100 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Type (delete if not applicable): open
- Material, size, headspace, fill volume: 300 mL glass Erlenmeyer flasks, fill volume: 250 mL, headspace: 50 mL
- Aeration: permanent
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6
- Sludge concentration (weight of dry solids per volume): 800 mg/L suspended solids
- Nutrients provided for bacteria: synhetic sewage feed: For each liter of water - 16.0 g peptone, 11.0 g meat extract , 3.0 g urea, 0.7 g NaCl, 0.4 g CaCl2 x 2H2O , 0.2 g MgSO4 x 7H2O, and 2.8 g K2HPO4
- Nitrification inhibitor used (delete if not applicable): N-allylthiourea

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: deionized water

OTHER TEST CONDITIONS
- Adjustment of pH: pH was adjusted to 7.3 - 7.5
- Details on termination of incubation: The aeration was discontinued and the contents of the flask were transferred to 250 mL BOD bottles for oxygen content measurement.

EFFECT PARAMETERS MEASURED (with observation intervals if applicable): oxygen consumption as a proxy for respiration rate aftere aeration time of 3 h.

TEST CONCENTRATIONS: control and 100 mg/L

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

inhibition of total respiration

Key result

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

inhibition of total respiration

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 100 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

inhibition of total respiration

Details on results:

- Blank controls oxygen uptake rate: 19.264 mg/L-h (with ATU 19.983 mg/L-h)
- Coefficient of variation of oxygen uptake rate in control replicates: 14 %

Results with reference substance (positive control):

- Results with reference substance valid? The EC50 of the reference compound 3,5-Dichlorophenol should be in the range of 2 - 25 mg/L for total respiration. In the present test the EC50 of the reference compound was 20.171 mg/L; thus the test is valid.

Reported statistics and error estimates:

Student-t test for Homogeneous Variances

For details on respiration rates see attachment.

Table 1: Validity criteria for OECD 209

Criterion from the guideline	Outcome	Validity criterion fulfilled
The blank controls (without the test substance or reference substance) oxygen uptake rate should not be less than 20 mg oxygen per one gram of activated sludge (dry weight of suspended solids) in an hour.	The oxygen uptake rate in the blank controls was 24.1 mg oxygen per one gram of activated sludge (dry weight of suspended solids) in an hour.	yes
The coefficient of variation of oxygen uptake rate in control replicates should not be more than 30% at the end of definitive test.	The coefficient of variation of oxygen uptake rate in control replicates was 14% at the end of definitive test.	yes

 

Validity criteria fulfilled:

yes

Remarks:

See Table 1 in "Any other information on results incl. tables".

Description of key information

EC10 (3 h) > 100 mg/L (activated sludge, OECD 209)

Key value for chemical safety assessment

EC50 for microorganisms:

100 mg/L

EC10 or NOEC for microorganisms:

100 mg/L

Additional information

One experimental study was conducted in accordance with OECD Guideline 209 and EU method C.11 under GLP conditions (M-566988-01-1). The activated sludge was exposed to the test item at a limit test item concentration of 100 mg/L. The respiration rate of each mixture was determined after aeration periods of 3 hours (no nitrification set up was performed). The test item showed 1.4% respiration inhibition of activated sludge at a test item concentration of 100 mg/L. The EC50 (3 h) is higher than 100 mg/L. The NOEC (3 h) is equal or higher than 100 mg/L. The effect value relates to a nominal concentration, since no analytical monitoring was performed. No inhibition of the degradation process in sewage treatment plants is expected.