Methomyl

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 Directive 87/302/EEC: "Activated Sludge Respiration Inhibition Test", Official Journal of the European Communities No. L 133/118-122, dated May 30, 1988

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

Methomyl technical
DPX-X1179-512
Purity: 100%

Analytical monitoring:

no

Vehicle:

yes

Remarks:

tap water

Details on test solutions:

A stock solution of nominal 1 g/L was prepared by dissolving 200 mg test item into 200 mL test water by intense stirring for 10 minutes and ultrasonic treatment for 15 minutes.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Laboratory culture: activated sludge, micro organisms from a domestic waste water treatment plant.
- Name and location of sewage treatment plant where inoculum was collected: supplied by the sewage plant Groß-Zimmern, Germany
The sludge was washed by centrifugation and the supernatant liquid phase was decanted. The solid material was resuspended in tap water and again centrifuged. The latter procedure was repeated twice. An aliquot of the final sludge suspension was weighed, dried and the ratio of wet sludge (g) to its dry weight (g) determined. Based on this ratio, calculated aliquots of washed sludge suspension, corresponding to 4 g dry material per litre, were made up with tap water. To this mixture, 50 mL synthetic sewage feed (see 3.3) per litre was added daily, starting two days prior to use, and the sludge was kept at room temperature under continuous aeration until use. Immediately before use, the dry weight of the activated sludge was determined, and adjusted to 4 g/L with tap water again. The pH of the activated sludge was determined to be pH 7.9.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

pH:

7.7-9.0

Nominal and measured concentrations:

Nominal: 0, 1.0, 3.2, 10.0, 32.0, and 100.0 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: glass flasks of approximately 1 litre volume and Karlsruher flasks of 250 mL volume
- Aeration: with compressed air (approximately 0.6 litre per minute); air flow rate was determined manually
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 1

EFFECT PARAMETERS MEASURED :
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, and was not further aerated. The oxygen concentration was measured with an oxygen electrode, and was 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 from the most linear part of the respiration curve in the range between approximately 6.5 and 2.5 mg O2/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

Basis for effect:

other: inhibition of respiration rate

Details on results:

In comparison to the inoculum controls the respiration rate of the activated sludge was inhibited by 4.2 % at the lowest test concentration of 1.0 mg Methomyl (DPX-X1179) Technical/L. At the test concentrations of 3.2 and 10 mg test item/L inhibition rates of 11.5 % and 4.2 % were determined. Inhibition rates increased up to 13.7 % and 23.9 % at the two highest test concentrations of 32 and 100 mg/L. From the determined inhibition rates, the 3-hour EC 20 was calculated to be 86.7 mg test item/L. The 3-hour EC 50 was > 100 mg test item/L.

Results with reference substance (positive control):

The 3-hour EC 50 for the positive control 3,5-dichlorophenol, which was tested in the same way as the test item, was found to be 13.2 mg/L and is within the range of 5 - 30 mg/L recommended by the test guidelines; thus, confirming suitability of the activated sludge.

Flask	Treatment	Concentration (mg/L)	Oxygen Consumption (mg O2/L min)	Inhibition (%)	pH		Oxygen concentration (mg O2/L)
					start	end	start	end
1	Control	-	0.444	-	7.9	9.0	7.0	6.9
10	Control	-	0.459	-	7.9	8.9	7.0	7.3
Mean			0.452
% deviation			3.3
5	Test item	100.0	0.344	23.9	7.7	8.5	7.0	7.0
6	Test item	32.0	0.390	13.7	7.7	8.6	6.8	6.5
7	Test item	10.0	0.433	4.2	7.8	8.8	6.9	6.7
8	Test item	3.2	0.400	11.5	7.9	8.8	7.1	6.7
9	Test item	1.0	0.433	4.2	7.9	8.9	7.0	6.6

Validity criteria fulfilled:

yes

Conclusions:

3-hr EC50 > 100 mg/L

Executive summary:

The influence of the test item Methomyl (DPX-X1179) Technical on the activity of activated sludge was evaluated by measuring the respiration rate under defined conditions. The respiration rate (oxygen consumption) of an aerobic activated sludge fed with a standard amount of synthetic sewage was measured in the presence of various concentrations of the test item after an incubation period of 3 hours. Test concentrations: 100.0, 32.0, 10.0, 3.2 and 1.0 mg Methomyl (DPX-X1179) Technical/L; 32.0, 10.0 and 3.2 mg 3,5-dichlorophenol/L and two inoculum controls.

 

In comparison to the inoculum controls the respiration rate of the activated sludge was inhibited by 4.2 % at the lowest test concentration of 1.0 mg Methomyl (DPX-X1179) Technical/L. At the test concentrations of 3.2 and 10 mg test item/L inhibition rates of 11.5 % and 4.2 % were determined. Inhibition rates increased up to 13.7 % and 23.9 % at the two highest test concentrations of 32 and 100 mg/L. From the determined inhibition rates, the 3-hour EC 20 was calculated to be 86.7 mg test item/L. The 3-hour EC 50 was > 100 mg test item/L.

 

The 3-hour EC 50 for the positive control 3,5-dichlorophenol, which was tested in the same way as the test item, was found to be 13.2 mg/L and is within the range of 5 - 30 mg/L recommended by the test guidelines; thus, confirming suitability of the activated sludge.

 

The 3-hour EC 20 of Methomyl (DPX-X1179) Technical was determined to be 86.7 mg/L The 3-hour EC 50 was higher than 100 mg test item/L.

Description of key information

Duration/Value Type	Species	Value	Guideline	Reliability
3-hr EC50	Activated sludge	> 100 mg/L	OECD 209, Commission Directive 87/302/EEC	1

Key value for chemical safety assessment

EC50 for microorganisms:

100 mg/L