Methomyl

Toxicity to aquatic plants other than algae

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic plants other than algae

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 221 (Lemna sp. Growth Inhibition Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPPTS 850.4400 (Aquatic Plant Toxicity Test using Lemna spp. Tiers I & II))

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

Methomyl technical
DPX-X1179-571
Purity: 99.4%

Analytical monitoring:

yes

Details on sampling:

Samples of the freshly prepared batch test solutions were collected at test initiation and day 4, and samples of old test solution pooled from all replicates were collected on day 4 and at test termination to measure concentrations of the active substance. For the new solutions, samples were collected from each test concentration and control solution prior to distribution into test chambers. For the old solutions, the biological replicates from each respective test concentration and control solution were pooled and then sampled, and the single abiotic replicate was also sampled. All samples (8.0 mL) were collected in glass scintillation vials containing 2.0 mL of methanol. Two sets of samples were collected at each interval. One set was processed immediately for analysis. The second set was stored refrigerated for potential future analysis.

Vehicle:

yes

Remarks:

medium

Details on test solutions:

A primary stock solution was prepared on day 0 by dissolving 0.1006 g of methomyl (DPX-X1179-571) in 20X AAP medium to a total volume of 1000 mL, for a nominal concentration of 100 milligrams active substance per liter (mg a.s./L), based on a reported purity of 99.4%. The 100 mg a.s./L primary stock was placed in an ultrasonic water bath for five minutes and inverted at least twenty times to mix. Test solutions were then prepared by proportionally diluting the primary stock with 20X AAP medium to achieve the nominal concentrations of 6.3, 13, 25, and 50 mg a.s./L. The test solutions were inverted at least twenty times to mix. On day 4, the test solutions were prepared in exactly the same manner as on day 0. On both days, the 6.3, 13, 25, 50 and 100 mg a.s./L test solutions appeared clear and colorless and otherwise unremarkable at the time of preparation. The blank control solution consisted of 20X AAP medium without test substance added. On day 4, plants were transferred from the old solutions to the new solutions with a sterile inoculating loop.

Test organisms (species):

Lemna gibba

Details on test organisms:

TEST ORGANISM
- Common name: freshwater, floating vascular plant
- Strain: Lemna gibba G3
- Source (laboratory, culture collection): original samples were obtained from United States Department of Agriculture and have been maintained at Wildlife International, Easton, Maryland

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

7 d

Test temperature:

24±2°C

pH:

7.7-9.1

Nominal and measured concentrations:

Nominal: 0, 6.3, 13, 25, 50, and 100 mg/L
Measured: 0, 6.2, 13, 25, 51, and 100 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: sterilized 250 mL glass beakers
- Type: covered with a disposable petri dish to permit gas exchange
Each replicate, excluding the abiotic control, was initiated with 4 plants totaling 12 fronds. Plants were transferred from the culture to the test chambers using a sterile inoculating loop. On day 4 plants were transferred to test chambers containing freshly prepared solutions using a sterile inoculating loop.
- No. of vessels per concentration (replicates): 4
- No. of vessels per control (replicates): 8

GROWTH MEDIUM
- Standard medium used: yes/no
- Detailed composition if non-standard medium was used:



TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: well water
- Total organic carbon: < 4.8 µg/L
- Particulate matter: not reported
- Metals: < 35 mg/L
- Pesticides: < 4.8 µg/L
- Chlorine: not reported
- Alkalinity:not reported
- Ca/mg ratio: 34.9/13.4
- Conductivity:not reported

OTHER TEST CONDITIONS
- Sterile test conditions: yes
- Photoperiod: 24
- Light intensity and quality: 6500±650 lux

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
Fronds were enumerated on test days 0, 3, 5 and test termination from the four replicates included in each treatment group and the eight replicates included in the blank control. Frond count yield, biomass yield, and their corresponding growth rates were determined after 7 days from the each of the replicates.

Reference substance (positive control):

no

Key result

Duration:

7 d

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Basis for effect:

frond number

Key result

Duration:

7 d

Dose descriptor:

NOEC

Effect conc.:

51 mg/L

Nominal / measured:

nominal

Basis for effect:

frond number

Key result

Duration:

7 d

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Basis for effect:

other: frond count growth rate

Key result

Duration:

7 d

Dose descriptor:

NOEC

Effect conc.:

51 mg/L

Nominal / measured:

nominal

Basis for effect:

other: frond count growth rate

Key result

Duration:

7 d

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Basis for effect:

biomass

Key result

Duration:

7 d

Dose descriptor:

NOEC

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Basis for effect:

biomass

Key result

Duration:

7 d

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Basis for effect:

other: biomass growth rate

Key result

Duration:

7 d

Dose descriptor:

NOEC

Effect conc.:

51 mg/L

Nominal / measured:

nominal

Basis for effect:

other: biomass growth rate

Details on results:

Lemna gibba G3 was exposed to five time-weighted, mean, measured concentrations of methomyl ranging from 6.2 to 100 mg a.s./L and evaluated for effects on frond count yield, frond count growth rate, biomass yield and biomass growth rate. Dunnett’s test indicated that for frond count yield and growth rate and biomass growth rate, the 100 mg a.s./L treatment group means were significantly reduced (p < 0.05) when compared to the blank control group means. Consequently, the 7-day NOEC and LOEC were determined to be 51 and 100 mg a.s./L, respectively, based on the mean frond count yield, frond count growth rate and mean biomass growth rate.

Mean Measured Concentration (mg/L)	Day 0 Frond Count	% inhibition	Day 7 Frond Count	% inhibition	Frond Count Yield	% inhibition
0	12±0.0	-	187±26.3	-	175±26.3	-
6.2	12±0.0	-	197±11.7	-6	185±11.7	-6
13	12±0.0	-	187±41.9	0	175±41.9	0
25	12±0.0	-	194±24.3	-4	182±24.3	-4
51	12±0.0	-	176±17.7	6	164±17.7	6
100	12±0.0	-	144±30.3	23	132±30.3	24

 

Mean Measured Concentration (mg/L)	Day 0 Biomass (mg)	% inhibition	Day 7 Biomass (mg)	% inhibition	Biomass Yield	% inhibition
0	2.25±0.0	-	39.3±5.53	-	37.1±5.53	-
6.2	2.25±0.0	-	40.2±1.88	-2	38.0±1.88	-2
13	2.25±0.0	-	39.7±8.07	-1	37.4±8.07	-1
25	2.25±0.0	-	41.0±4.89	-4	38.7±4.89	-4
51	2.25±0.0	-	37.2±4.20	5	34.9±4.20	6
100	2.25±0.0	-	31.7±7.20	19	29.4±7.20	21

 

Mean Measured Concentration (mg/L)	Day 0-7 Frond Count Growth Rate (days^-1)	% inhibition	Day 0-7 Biomass Growth Rate (days^-1)	% inhibition
0	0.391±0.01949	-	0.407±0.01969	-
6.2	0.400±0.008336	-2	0.412±0.00659	-1
13	0.390±0.0330	0	0.408±0.3021	0
25	0.397±0.01794	-1	0.414±0.01663	-2
51	0.383±0.01499	2	0.400±0.01661	2
100	0.353±0.03108	10	0.375±0.3299	8

Validity criteria fulfilled:

yes

Conclusions:

7-day EyC50 (frond count yield) > 100 mg/L
7-day NOEC (frond count yield) = 51 mg/L
0-7-day ErC50 (frond count growth rate) > 100 mg/L
0-7-day NOEC (frond count growth rate) = 51 mg/L
7-day EyC50 (biomass yield) > 100 mg/L
7-day NOEC (biomass yield) > 100 mg/L
0-7-day EyC50 (biomass growth rate) > 100 mg/L
0-7-day NOEC (biomass growth rate) = 51 mg/L

Executive summary:

The acute toxicity of methomyl to duckweed, Lemna gibba G3, under static-renewal conditions was determined in a 7-day exposure test. The test was conducted in accordance with U.S. Environmental Protection Agency (EPA) Series 850 - Ecological Effects Test Guidelines, OCSPP Number 850.4400, which meets the requirements of the OECD 221 guideline.

 

The study was conducted with five concentrations of methomyl, a blank (twenty-strength synthetic algal-assay-procedure nutrient medium, 20X AAP) control and an abiotic (stability) control in an environmental chamber for 7 days at 24 ± 2degC. Four replicates were initiated for each test substance concentration and eight replicates were initiated for the blank control. A single test vessel containing no Lemna gibba G3 was initiated for the abiotic control, included to demonstrate the stability of the test substance in 20X AAP under the test conditions without the presence of the test organism. Fronds were enumerated on test days 0, 3, 5 and test termination from the four replicates included in each treatment group and the eight replicates included in the blank control. Frond count yield, biomass yield, and their corresponding growth rates were determined after 7 days from the each of the replicates.

 

Nominal test concentrations selected were 6.3, 13, 25, 50 and 100 milligrams active substance per liter (mg a.s./L). Measured concentrations of methomyl were determined from samples collected from freshly prepared batch test solutions from each test concentration and control at test initiation, day 4; and from pooled old test solutions on day 4 and at exposure termination (day 7). Measured concentrations of methomyl were determined from the single abiotic replicate on days 4 and 7. At test conclusion, healthy frond counts increased in the blank control by at least a factor of 7 in 7 days.

 

Lemna gibba G3 was exposed to five time-weighted, mean, measured concentrations of methomyl ranging from 6.2 to 100 mg a.s./L and evaluated for effects on frond count yield, frond count growth rate, biomass yield and biomass growth rate. Dunnett’s test indicated that for frond count yield and growth rate and biomass growth rate, the 100 mg a.s./L treatment group means were significantly reduced (p< 0.05) when compared to the blank control group means. Consequently, the 7-day NOEC and LOEC were determined to be 51 and 100 mg a.s./L, respectively, based on the mean frond count yield, frond count growth rate and mean biomass growth rate.

Description of key information

Duration/Value Type	Species	Value	Guideline	Reliability
0-7-day ErC50 (frond count growth rate)	Lemna gibba	> 100 mg/L	OECD 221, EPA OCSPP 850.4400	1
7-day EyC50 (frond count yield, biomass yield, biomass growth rate)	Lemna gibba	> 100 mg/L	OECD 221, EPA OCSPP 850.4400	1
0-7-day NOEC (frond count yield, frond count growth rate, biomass growth rate)	Lemna gibba	51 mg/L	OECD 221, EPA OCSPP 850.4400	1
7-day NOEC (biomass yield)	Lemna gibba	> 100 mg/L	OECD 221, EPA OCSPP 850.4400	1

Key value for chemical safety assessment

EC50 for freshwater plants:

100 mg/L

EC10 or NOEC for freshwater plants:

51 mg/L

Additional information

The 7-day EC50 for Lemna gibba G3 for frond count yield, biomass yield, biomass growth rate, and frond count growth rate was > 100 mg/L. The 7-day NOEC for biomass yield was > 100 mg/L; however, the 7-day NOEC for frond count yield, frond count growth rate, biomass growth rate was 51 mg/L.