α-n-butyl-α-(4-chlorophenyl)-1H-1,2,4-triazole-1-propanenitrile

Short-term toxicity to fish

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to fish

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2003-21-04 to 2003-25-04

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Justification for type of information:

Guideline study performed to GLP with supporting analysis.

Qualifier:

according to guideline

Guideline:

OECD Guideline 203 (Fish, Acute Toxicity Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

0 hours and 96 hours

Vehicle:

yes

Remarks:

acetone

Details on test solutions:

The toxicity test was conducted in 20.8-L glass aquaria, each containing 15 L of test solution. One test aquarium was established for each treatment level and the controls. A 200 mg/mL primary stock solution was prepared by adding 5.2258 g of myclobutanil (4.9959 g) to 25 mL of acetone. This stock solution was observed to be clear and yellow in color following two minutes of sonication. Each solution was mixed for one minute using a laboratory stirrer. Following mixing, the 8.0 and 16 mg/L exposure solutions were clear and colorless and contained a small oily film on the water surface. The remaining exposure solutions were observed to be clear and colorless. In addition, a control aquarium was also established and maintained under the same conditions as the treatment level solutions. The aquarium contained dilution water and no myclobutanil. The definitive test was initiated when rainbow trout were impartially selected and distributed to the test vessels until each test vessel contained 10 rainbow trout. At any given time during the exposure period, the maximum organism loading concentration did not exceed 0.8 g of biomass per liter of test solution.

Test organisms (species):

Oncorhynchus mykiss (previous name: Salmo gairdneri)

Details on test organisms:

Mean total length = 39 mm (range: 34 to 48 mm); N =30
Mean wet weight = 0.61 g (range: 0.36 to 0.98 g); N = 30

Test type:

static

Water media type:

freshwater

Remarks:

well water

Total exposure duration:

96 h

Hardness:

The dilution water consisted of well water with a hardness of 52 mg/L as CaC03 and an alkalinity of 39 mg/Ls as CaC03.

Test temperature:

13 to 14 °C

pH:

7.4 to 7.5

Dissolved oxygen:

81 to 91% saturation

Conductivity:

160 µmhos/cm

Nominal and measured concentrations:

Nominal concentrations: 1.0, 2.0, 4.0, 8.0. 16.0 mg/L
Mean measured concentrations: 0.85, 1.8, 3.0, 2.9 and 6.1 mg a.s./L

Details on test conditions:

Test system:
The toxicity test was conducted in 20.8-L glass aquaria, each containing 15 L of test solution. Exposure levels were monitoring by measuring concentrations of myclobutanil at 0 and 96 hours. Nominal concentrations were 2.0, 4.0, 8.0 and 16 mg/L. Initial measured test concentrations were 0.85, 1.8, 3.0, 3.5 and 2.2 mg/L representing 85, 92, 75, 44 and 14% of the nominal concentration, respectively. Day 4 measured concentrations were 0.84, 1.7, 2.9, 2.4, 9.9 mg/L representing 84, 85, 73, 30, 62 % of nominal concentrations, respectively.

Test dilution water:
The dilution water (well water) used during this study was from the same source as the water used to culture rainbow trout and was characterized as having total hardness and total alkalinity (as CaC03) of 52 mg/L and 39 mg/L, respectively, a pH of 7.8 and a specific conductance of 160 µmhos/cm.

Test conditions:
Each 20.8-L aquarium, constructed entirely of glass and silicone sealant, was impartially placed in a temperature-controlled water bath designed to maintain exposure solution temperatures at 14 ± 1°C. A single aquarium was established for each treatment level and the control. The test area was illuminated with fluorescent bulbs at an intensity of 80 to 100 foot-candles at the water surface. The photoperiod during the test was the same as in the culture area. Sudden transitions from light to dark and vice versa were avoided. Light intensity was measured with a General Electric type 217 light meter.

All aquaria were examined after 0, 2, 3, 6, 24, 48, 72 and 96 hours of exposure as follows: mortalities were recorded and dead fish removed, biological observations, including sublethal effects (e.g., lethargy, loss of equilibrium) of the exposed rainbow trout and observations of the physical characteristics of the test solutions (e.g., presence of precipitate, film on the solution's surface) were made and recorded. Test solution temperature was continuously monitored during the definitive test in the 2.0 mg/L treatment level using a Fisher Scientific minimum-maximum thermometer. Gentle, oil-free aeration was initiated at the 72-hour interval to raise and maintain dissolved oxygen levels at or above 60% of saturation.

Evaluation of test conditions:
The water quality parameters were unaffected by the concentrations of myclobutanil tested and remained within acceptable ranges for the survival of rainbow trout. Daily measurement of the temperature in the test solutions and continuous temperature monitoring established that the exposure solution temperature ranged from 13 to 14°C during the definitive study.

Determination of EC50 and NOEC:
Both the initial measured concentrations and the mean measured concentrations tested and the corresponding immobilization data derived from the definitive toxicity test were used to estimate the median lethal concentrations (EC50) and 95% confidence intervals. The EC50 is defined as the concentration of the test substance in dilution water which caused immobilization of 50% of the test organism population at the stated time interval.

Key result

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

2.3 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

act. ingr.

Basis for effect:

mortality (fish)

Key result

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

1.8 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

act. ingr.

Basis for effect:

mortality (fish)

Details on results:

Following 24 and 96 hours of exposure, 70, 100 and 100% mortality was observed among fished exposed to the 3.0, 2.9 and 6.1 mg/L treatment levels (mean measured concentrations), respectively.
No mortality or sublethal effects were observed in the 0.85 and 1.8 mg/L treatment levels or the controls.

Sublethal observations / clinical signs:

Nominal Concentration mg/L	Initial Measured Concentrations as mg a.s./L (% if nominal)	96-Hour Measured Concentrations as mg a.s./L (% of nominal)	Mean Measured Concentrations as mg. a.s./L (% of nominal)	24-Hours Cummulative % Immobilized	96-Hour Cummulative % Immobilized
Control	<0.10	<.10	0	0	0
Solvent Control	<.10	<.10	0	0	0
1.0	0.85 (85)	3.4 (68)	0.85 (85)	0	0
2.0	1.8 (92)	8.4 (84)	1.8 (88)	0	0
4.0	3.0 (75)	16 (81)	3.0 (74)	70	70
8.0	3.5 (44)	18 (45)	2.9 (37)	100	100
16.0	2.2 (14)	34 (43)	6.1 (38)	100	100

 

Validity criteria fulfilled:

yes

Conclusions:

Based on mean measured concentrations the 96-hour LC50 value for myclobutanil and Oncorhynchus mykiss under static conditions was determined to be 2.3 mg a.s./L, and the NOEC was determined to be 1.8 mg a.s./L.

Executive summary:

The purpose of this study was to determine the toxicity of myclobutanil based on the results (LC₅₀) of a 96-hour static acute toxicity test using rainbow trout (Oncorhynchus mykiss). Based on the initial measured concentrations (0-hour), the 96-hour LC₅₀ value for myclobutanil and Oncorhynchus mykiss was determined to be 2.3 mg/L, with 95% confidence intervals of 1.8 to 2.9 mg/L. The No-Observed-Effect Concentration (NOEC) was determined to be 1.8 mg/L.

Description of key information

In a GLP-study performed according to OECD TG 203, the LC₅₀-value of of myclobutanil was revealed to be 2.3 mg/L (96-hour). Test organism was Oncorhynchus mykiss.

 

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Dose descriptor:

LC50

Effect concentration:

2.3 mg/L