Methyl (R)-2-(4-(3-chloro-5-trifluoromethyl-2-pyridyloxy)phenoxy)propionate

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:

other: EPA Pesticide Assessment Guidelines, Subdivision J, Section 122-2 and 123-3

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: draft OECD Guideline for Testing of Chemicals 'Duckweed, Static Growth Inhibition Test'

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

Haloxyfop-R methyl ester
Lot #: RMM 2055
Purity: 96.8%

Analytical monitoring:

yes

Details on sampling:

- Concentrations: 55667, 556.67 mg/L

Vehicle:

yes

Remarks:

Sterile nutrient medium

Details on test solutions:

A 200 mg sample of the test substance was dispersed into 2 litres of fresh sterile nutrient medium and the solution stirred for approximately 24 hours using a magnetic stirrer to give a saturated stock solution. The solution was filtered using Whatmans 0.45 µm pore filter paper and measured volumes made up to 1 L with nutrient medium, to give dilutions of 1, 3.2, 10, 32 and 100% saturated solution. The mean measured concentration of the saturated solution was determined to be 7.022 mg/L (ester plus acid as ester equivalents).

Test organisms (species):

Lemna minor

Details on test organisms:

TEST ORGANISM
- Common name: Common duckweed
- Source: Laboratory culture originating from specimens obtained from Blades Biological, Edenbridge, Kent, UK

ACCLIMATION
- Acclimation period: At least 7 days

Test type:

semi-static

Water media type:

other: Aqueous medium

Limit test:

no

Total exposure duration:

14 d

Post exposure observation period:

After 14 days exposure, five groups of three fronds were taken from control, solvent control, 32 and 100 mg/L vessels (those concentrations exhibiting approximately greater than 50% inhibition of growth) and placed in fresh untreated medium. Plants were re-transferred to fresh medium on days 2 and 4 of the re-culturing phase.

Test temperature:

24 ± 1°C

pH:

3.8-6.7 (controls: 3.7-6.7)

Nominal and measured concentrations:

Nominal: 0.070, 0.22, 0.70, 2.2, 7.0 mg/L
Measured: 0.054, 0.16, 0.61, 2.5, 7.0 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: Conical flasks
- Type: Closed
- Material, size, headspace, fill volume: Conical flasks (500 ml), containing 200 ml of test or control culture
- Type of cover: Foam bungs
- No. of fronds per colony: 15
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 3

GROWTH MEDIUM
- Standard medium used: Yes

OTHER TEST CONDITIONS
- Photoperiod: Continuous illumination
- Light intensity: 4200 to 5880 lux

Key result

Duration:

14 d

Dose descriptor:

EC50

Effect conc.:

3.1 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

other: ester equivalent

Remarks on result:

other: 95% CI: 1.1-8.9 mg/L

Key result

Duration:

14 d

Dose descriptor:

NOEC

Effect conc.:

0.054 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

other: ester equivalent

Details on results:

All test and control cultures were inspected after 14 days exposure. All plants in the control, 0.054, 0.16, 0.61 and 2.5 mg/L groups appeared in good health. In the 7.0 mg/L test group the plants appeared to exhibit shorter roots and chlorosis.

Following re-culturing in untreated medium, exposure to test substance was found to have had a phytostatic effect on frond production of Lemna minor at the highest concentration tested (7.0 mg/L measured) based on increases in frond number.

Analysis of variance of the fresh weights of fronds in the control and test concentration groups showed no significant difference (p=0.92) after the exposure phase. Direct comparison between test culture means and control means showed no significant difference between groups.

Evidence for a difference in mean fresh weights after the recovery phase (p=0.01) had no obvious concentration-relationship.

Validity criteria fulfilled:

yes

Conclusions:

14-day EC50 (Lemna minor): 3.1 mg/L (frond number)
14-day NOEC (Lemna minor): 0.054 mg/L (frond number)

Executive summary:

A study was carried out to assess the inhibitory effect of the test substance on the growth of the aquatic higher plant Lemna minor, under semi-static conditions.

The study was conducted following the general recommendations of the EPA Pesticide Assessment Guidelines, Subdivision J, Section 122-2 and 123-3 and the draft OECD Guideline for Testing of Chemicals 'Duckweed, Static Growth Inhibition Test'.

Lemna plants were exposed to a range of solutions of test substance in aqueous medium plus an untreated control. A saturated solution in aqueous medium was prepared by stirring overnight. This saturated solution. was filtered and the filtrate used to prepare nominal exposure solutions of 1.0, 3.2, 10, 32 and 100% saturated solution. Test media were renewed every two to three days.

Test vessels were held in a controlled environment between 23 and 25°C and continuously illuminated for 14 days. This was followed by a re-culturing period when a number of surviving plants from control, 1, 32 and 100% treatments were placed in untreated media and held under similar conditions for a further seven days. Growth was monitored by counting the number of fronds in each vessel every two to three days.

Results of the chemical analysis are expressed as the sum concentrations of test substance and its hydrolysis product haloxyfop-R (as ester equivalents). Results of the chemical analysis of the test samples ranged from 33 to 158% of the target concentrations in fresh samples and 49 to 134% in expired samples. The overall mean percent of target dilutions ranged from 70.3 to 109.4% over the exposure period giving a mean measured concentration test series of control, 0.0544, 0.158, 0.605, 2.454 and 7.022 mg/L. No difference was noted between the mean measured concentration of test substance in the "100% saturated solution" test media samples with and without Lemna, indicating that the presence of plants had no effect on the stability of the exposure media. It was noted that the analysis of day 0 fresh samples provided poor results, subsequently the method of analysis was revised for all following samples.

The following EC50 value (with 95% confidence interval) based on mean measured concentrations of the active substance were derived from the data:

EC50 (14 days): 3.1 mg/L (95% confidence interval: 1.1 to 8.9 mg/L)

"No-observed effect concentration": 0.054 mg/L

Following re-culturing in untreated medium, test substance was found not to be phytotoxic to Lemna minor at any exposure level tested. Reduced frond production at the highest test level (7.0 mg/L, measured) during the exposure phase was therefore a phytostatic effect.

Description of key information

14-day EC50 (Lemna minor): 3.1 mg/L (frond number); EPA Pesticide Assessment Guidelines, Subdivision J, Section 122-2 and 123-3 ; according to draft OECD Guideline for Testing of Chemicals ‘Duckweed, Static Growth Inhibition Test’; Reliability = 1

14-day NOEC (Lemna minor): 0.054 mg/L (frond number); EPA Pesticide Assessment Guidelines, Subdivision J, Section 122-2 and 123-3 ; according to draft OECD Guideline for Testing of Chemicals ‘Duckweed, Static Growth Inhibition Test’; Reliability = 1

Key value for chemical safety assessment

EC50 for freshwater plants:

3.1 mg/L

EC10 or NOEC for freshwater plants:

0.054 mg/L