Prometryn

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 Dec 1997 to 19 Dec 1997

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:

Paris 1984

Deviations:

yes

Remarks:

Instead of a centrifuged sludge a settled sludge was used

Qualifier:

according to guideline

Guideline:

other: EEC L133s 118-122

Version / remarks:

30 May 1988

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

200.3 mg test substance were mixed with 800 mL water (20 minutes ultrasonic, 1 hour stirring) and made up to 1000 mL with water. This stock solution was strongly stirred by a magnet stirrer. The stock solution was freshly prepared at the start of the test.

Test organisms (species):

activated sludge

Details on inoculum:

TEST ORGANISMS
Activated sludge collected from the sewage treatment plant on December 18, 1997. The pH after collection was 7.3. The preparation was carried out according to the method described in the guideline. The sludge was separated from the aqueous layer by settling instead of centrifugation. The pH of the sludge before use was 7.7. The sludge concentration in the test bottles was 1.52 g suspended solids/L.

JUSTIFICATION OF SPECIES
Activated sludge is obtained from a sewage work treating predominantly domestic sewage. Results obtained with activated sludge from works treating industrial waste waters may be atypical.

ORIGIN AND ACCLIMATION
On return to the laboratory, the sludge was washed three times by settling for a short period, e.g. 15-30 minutes, decanting the upper layer and adding the same amount of water as the decanted water. The sludge was kept aerated for use during the day.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Hardness:

Not reported

Test temperature:

20 ± 2°C

pH:

7.8 - 8.0

Dissolved oxygen:

Not reported

Salinity:

Not reported

Conductivity:

Not reported

Nominal and measured concentrations:

- Nominal concentration: 100.0, 32.0, 10.0, 3.2 and 1.0 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: 250 mL BOD flasks with gas inlet
- Aeration: Yes
- No. of vessels per test substance concentration:1
- No. of vessels per control: 2
- No. of vessels per reference substance concentration: 1
- Sludge concentration: 1.52 g suspended solids/L
- Nutrients provided for bacteria: According to OECD 209 guideline

TEST MEDIUM / WATER PARAMETERS
- Dilution water: Dechlorinated drinking water
- Oxygen consumption per hour in mg/Liter was measured and recorded

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorphenol

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:

NOEC

Effect conc.:

100 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

inhibition of total respiration

Details on results:

No significant inhibition effects were observed after 3 hours exposure. Based on the nominal concentrations, the EC20-, EC50- and EC80 of the test substance were graphically determined to be over 100 mg/L. Therefore, the NOEC is determined as 100 mg/L. See Table 1 in "Any other information in results incl. tables" for an overview of the results.

Results with reference substance (positive control):

Based on the nominal concentrations, the EC50 of the reference substance was graphically determined to be 10 mg/L.

Table 1. Consumption rate and inhibitory effects of the test substance and reference

Samples	Con. (mg/L)	Consumption rate (mg/L/h)	Inhibition (%)	pH*
Blank 1	0.0	51.7	-1	7.8
Blank 2	0.0	50.8	1	7.9
Reference 1	32.0	9.0	83	7.9
Reference 2	10.0	19.8	61	7.9
Reference 3	3.2	47.6	7	8.0
Test con. 1	100.0	47.6	7	7.9
Test con. 2	32.0	48.4	6	7.8
Test con. 3	10.0	50.0	3	7.9
Test con. 4	3.2	50.0	3	8.0
Test con. 5	1.0	50.8	1	7.9

* The pH was measured after 3h aeration.

Validity criteria fulfilled:

yes

Remarks:

See validation criteria in the "Any other information on the materials and methods incl. tables"

Conclusions:

After the incubation period of three hours, the test substance had ≤ 7% inhibition on the respiration rate of activated sludge at concentrations up to and including 100 mg/L, the highest concentration tested. Based on the findings, the 3-hour EC20, EC50 and EC80 were ≥100 mg/L. Therefore, the NOEC was determined to be 100 mg/L.

Executive summary:

The inhibitory effects of the test substance on the respiration of aerobic wastewater bacteria were studied according to OECD guideline No. 209 and in compliance with GLP at a temperature of 20 ± 2 °C. The test organisms (activated sludge from a municipal sewage treatment plant) were exposed to nominal concentrations of 1.0, 3.2, 10.0, 32.0 and 100 mg/L of the test substance. The calculated amounts of the test substance to produce the desired test concentrations were mixed with 114 mL dechlorinated tap water, 6.4 mL nutrient solution and 80 mL of the activated sludge in 250 mL BOD flasks and aerated immediately. Two separate blank controls without test substance and three flasks with 3,5-dichlorophenol as a positive control substance at concentrations of 3.2, 10 and 32 mg/L were additionally included in the study.

After the incubation period of three hours, oxygen consumption was determined in all flasks: the test substance produced ≤7% inhibition on the respiration rate of activated sludge at concentrations up to and including 100 mg/L in comparison with no and 1% inhibition in the blank controls. The 3-hour NOEC for the test substance was determined to be 100 mg/L. The 3-hour EC50 of the positive control substance was determined graphically as 10 mg/L, which is within the acceptable toxicity range for the positive control substance, demonstrating the suitability of the test system.

Description of key information

3-h NOEC = 100 mg/L, Activated sludge, inhibition of total respiration, OECD TG 209, Grade 1998

3-h EC50 ≥ 100 mg/L, Activated sludge, inhibition of total respiration, OECD TG 209, Grade 1998

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

100 mg/L

Additional information

The inhibitory effects of the test substance on the respiration of aerobic wastewater bacteria were studied according to OECD guideline No. 209 and in compliance with GLP at a temperature of 20 ± 2 °C. The test organisms (activated sludge from a municipal sewage treatment plant) were exposed to nominal concentrations of 1.0, 3.2, 10.0, 32.0 and 100 mg/L of the test substance. The calculated amounts of the test substance to produce the desired test concentrations were mixed with 114 mL dechlorinated tap water, 6.4 mL nutrient solution and 80 mL of the activated sludge in 250 mL BOD flasks and aerated immediately. Two separate blank controls without test substance and three flasks with 3,5-dichlorophenol as a positive control substance at concentrations of 3.2, 10 and 32 mg/L were additionally included in the study.

After the incubation period of three hours, oxygen consumption was determined in all flasks: the test substance produced ≤7% inhibition on the respiration rate of activated sludge at concentrations up to and including 100 mg/L in comparison with no and 1% inhibition in the blank controls. The 3-hour NOEC for the test substance was determined to be 100 mg/L. The 3-hour EC50 of the positive control substance was determined graphically as 10 mg/L, which is within the acceptable toxicity range for the positive control substance, demonstrating the suitability of the test system.