5,7-dichloro-4-(4-fluorophenoxy)quinoline;quinoxyfen (ISO)

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: U.S. EPA OPPTS Draft Guideline 850.4400

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

Substance ID: TSN100097
Lot number: DECO-97-152-1
Purity: 97.3%

Analytical monitoring:

yes

Details on sampling:

- Sampling: At day 0, samples of newly prepared solutions were removed from the test and control solutions prior to division into the replicate test vessels. On day 3, samples of aged solutions were removed from individually composited replicate solutions of the treatment levels and controls.
- Sample storage conditions before analysis: Day 0 quality control samples which contained organic solvent were refrigerated until day 3 for reanalysis

Vehicle:

yes

Remarks:

Dilution water and dimethylformamide (DMF)

Details on test solutions:

A 460 μg a.i./mL primary stock solution was prepared prior to test initiation by placing 0.01182 g (0.01150 g as active ingredient) of the test substance in a 25-mL volumetric flask and bringing it to volume with dimethylformamide. The resulting stock solution was observed to be clear with a brown tint and no visible undissolved test substance following hand-inversions and shaking. Secondary stock solutions were prepared in dimethylformamide as dilutions of the 460 μg a.i./mL primary stock solution. Nominal test concentrations were prepared from the primary and secondary stock solutions diluting with sterile AAP Medium.
A solvent control solution was prepared by placing 0.10 mL of DMF in a 1000-mL flask and bringing it to volume with 20X AAP medium. Additional untreated 20X AAP medium was used for the control.

Test organisms (species):

Lemna gibba

Details on test organisms:

TEST ORGANISM
- Common name: Duckweed
- Strain: Lemna gibba
- Source: Canadian Phycological Culture Centre (CPCC) at the University of Waterloo, Canada.
- Method of cultivation: Stock cultures were grown in 20X Algal Assay Procedure (AAP) medium

Test type:

static

Water media type:

freshwater

Total exposure duration:

7 d

Test temperature:

23 to 24 °C

pH:

7.6 to 9.1

Nominal and measured concentrations:

Nominal: 2.9, 5.8, 12, 23 and 46 μg a.i./L
Measured: 2.1, 4.2, 9.1, 16 and 35 μg a.i./L

Details on test conditions:

TEST SYSTEM
- Incubation chamber used: yes
- Test vessel: Sterile 270-mL Pyrex glass crystallizing dishes
- Solution renewal: On test day 3 and 5, fronds were transferred to newly prepared test solutions to maintain the solution concentrations and replenish nutrients used in plant growth.
- No. of fronds per vessel: 12
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 3
- No. of vessels per vehicle control (replicates): 3

GROWTH MEDIUM
- Standard medium used: yes (20X AAP medium)

OTHER TEST CONDITIONS
- Sterile test conditions: yes
- Adjustment of pH: Yes
- Photoperiod: Continous
- Light intensity and quality: 5200 to 6700 lux (fluorescent bulbs)

EFFECT PARAMETERS MEASURED
- Determination of frond number: On days 3, 5 and at test termination (day 7), fronds were counted and observations were made.
- Determination of biomass: At test termination (day 7), after frond density determinations were complete, the fronds were removed from each vessel, blotted dry and transferred to preweighed aluminum pans. Fronds were dried in an oven at 62 to 64 °C for ten days prior to dry weight determination.

RANGE-FINDING STUDY
- A 7-day preliminary static-renewal exposure was conducted at nominal concentrations of 0.046, 0.46, 4.6 and 46 μg a.i./L, a control and a solvent (DMF) control. Two replicate exposure vessels were established for each concentration and control. Test solutions were renewed on days 3 and 5. All test solutions were clear and colorless with no visible undissolved test substance following solution preparation. Following 7 days of exposure, frond densities in the 0.046, 0.46, 4.6 and 46 μg a.i./L treatment levels averaged 191, 203, 214 and 184 fronds/replicate, respectively. Frond density in the control and the solvent control averaged 211 and 209 fronds/replicate, respectively. Fronds exposed to all treatment levels and controls were observed to be normal.

Reference substance (positive control):

no

Key result

Duration:

7 d

Dose descriptor:

NOEC

Effect conc.:

35 µg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

act. ingr.

Basis for effect:

other: frond density, growth rate and frond dry weight (biomass)

Key result

Duration:

7 d

Dose descriptor:

other: EC50 and LOEC

Effect conc.:

> 35 µg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

act. ingr.

Basis for effect:

other: frond density, growth rate and frond dry weight (biomass)

Duration:

7 d

Dose descriptor:

EC5

Effect conc.:

7.9 µg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

act. ingr.

Basis for effect:

other: Frond density

Remarks on result:

other: 95% Confidence Limits: 2.2-16 μg a.i./L

Duration:

7 d

Dose descriptor:

EC5

Effect conc.:

> 35 µg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

act. ingr.

Basis for effect:

growth rate

Duration:

7 d

Dose descriptor:

EC5

Effect conc.:

< 2.1 µg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

act. ingr.

Basis for effect:

other: dry weight

Duration:

7 d

Dose descriptor:

EC90

Effect conc.:

> 35 µg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

act. ingr.

Basis for effect:

other: frond density, growth rate and frond dry weight (biomass)

Reported statistics and error estimates:

A t-test was conducted on the frond density, growth rate and dry weight biomass data to compare the results of the solvent control to the negative (blank) control.
The data were first checked for normality using Shapiro-Wilks' Test and for homogeneity of variance using Bartlett's Test. If the data sets passed the tests for homogeneity and normality, then Dunnett’s Test was used to determine the NOEC and LOEC. If the data did not pass the tests for homogeneity and normality, then Kruskal-Wallis’ Test was used to determine the NOEC. All statistical determinations were made at the 95% level of certainty, except in the case of Shapiro-Wilks' and Bartlett's Tests, where the 99% level of certainty was applied.

Validity criteria fulfilled:

yes

Conclusions:

Lemna gibba 7-day NOEC: 35 μg a.i./L (frond density, growth rate and frond dry weight (biomass))
Lemna gibba 7-day LOEC and EC50: >35 μg a.i./L (frond density, growth rate and frond dry weight (biomass))

Executive summary:

The purpose of this study was to determine the effects of the test substance on the growth of the duckweed, Lemna gibba per the general requirements of the U.S. EPA OPPTS Draft Guideline 850.4400. The nominal test concentrations chosen for the definitive study were 2.9, 5.8, 12, 23 and 46 μg a.i./L corresponding to the measured concentrations of 2.1, 4.2, 9.1, 16 and 35 μg a.i./L respectively. Three replicate exposure vessels were established for each concentration and control. Test solutions were renewed on days 3 and 5.

At test termination, fronds exposed to all treatment levels tested, the control and the solvent control were observed to be normal. The 7-day NOEC and LOEC were determined to be 35 and >35 μg a.i./L, respectively for frond density, growth rate and frond dry weight (biomass). Since no concentration tested resulted in ≥ 50% reduction, the 7-day EC50 value was empirically estimated to be >35 μg a.i./L for frond density, growth rate and frond dry weight (biomass).

Description of key information

7-day E_rC₅₀ (Lemna gibba): > 35 µg/L (the highest dose tested); U.S. EPA OPPTS Draft Guideline 850.4400; Reliability = 1

7-day NOEC (Lemna gibba): > 35 µg/L (the highest dose tested); U.S. EPA OPPTS Draft Guideline 850.4400; Reliability = 1

Key value for chemical safety assessment

EC50 for freshwater plants:

35 µg/L

EC10 or NOEC for freshwater plants:

35 µg/L

Additional information

The E_rC₅₀ and NOEC from the 7-day Lemna gibba test was > 35 µg/L, based on growth rate.