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

Endpoint summary

Description of key information

Acute toxicity studies performed via oral, dermal and inhalation route are available. The studies were performed according to OECD/EC guidelines and GLP principles. This data indicate that myclobutanil is of low acute toxicity via the dermal and inhalation route. The substance was shown to have adverse effects when administered via the oral route.  

Key value for chemical safety assessment

Acute toxicity: via oral route

Link to relevant study records

Reference

Endpoint:

acute toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

24-June-2005 to 29-September-2005

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.1100 (Acute Oral Toxicity)

Version / remarks:

2002

Deviations:

no

Qualifier:

according to guideline

Guideline:

OECD Guideline 425 (Acute Oral Toxicity: Up-and-Down Procedure)

Version / remarks:

2001

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test type:

up-and-down procedure

Limit test:

yes

Species:

rat

Strain:

Fischer 344

Sex:

female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Raleigh, NC
- Females nulliparous and non-pregnant: yes
- Age at study initiation: Young adult (9-10 weeks)
- Weight at study initiation: 112-127 grams
- Fasting period before study: yes, Overnight
- Housing: The animals were singly housed in suspended stainless steel caging with mesh floors which conform to the size recommendations in the most recent Guide for the Care and Use of Laboratory Animals DHEW (NIH). Litter paper was placed beneath the cage and was changed at least three times per week.
- Diet: Purina Certified Rodent Diet, ad libitum (except o/n before dosing)
- Water: Filtered tap water was supplied ad libitum by an automatic water dispensing system
- Acclimation period: 6-16 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 19-22ºC
- Humidity (%): 66-70%
- Photoperiod (hrs dark / hrs light): 12-hour light/dark cycle

Route of administration:

oral: gavage

Vehicle:

CMC (carboxymethyl cellulose)

Remarks:

1.5% w/w solution in distilled water

Details on oral exposure:

An initial limit dose of 5,000 mg/kg was administered to one healthy female rat by oral gavage. Due to mortality in this animal, the study proceeded to the Main Test. Using the default starting level of 175 mg/kg bw and following the Up and Down procedure, eight additional females were dosed at levels of 550, 1,750, or 5,000 mg/kg bw.

Doses:

175 mg/kg bw, 550 mg/kg bw, 1,750 mg/kg bw and 5,000 mg/kg bw.

No. of animals per sex per dose:

175 mg/kg bw (1 animal), 550 mg/kg bw (1 animal), 1,750 mg/kg bw (3 animals) and 5,000 mg/kg bw (4 animals)

Control animals:

no

Details on study design:

- Duration of observation period following administration: 14 days
- Frequency of observations and weighing: The animals were observed for mortality, signs of gross toxicity, and behavioral changes for the first several hours post-dosing and at least once daily thereafter.
- Necropsy of survivors performed: yes
- Other examinations performed: The external surface of the body and all orifices, tissues, and organs of the thoracic and abdominal cavities were examined.

Statistics:

The Acute Oral Toxicity (Guideline 425) Statistical Program (Weststat, version 1.0, May 2001) was
used for all data analyses including: dose progression selections, stopping criteria determinations
and/or LD50 and confidence limit calculations.

Key result

Sex:

female

Dose descriptor:

LD50

Effect level:

> 1 750 - < 5 000 mg/kg bw

Based on:

test mat.

Mortality:

All animals that were administered 5,000 mg/kg bw dose level of the test substance died within one day. No mortality occurred in the other dose groups.

Clinical signs:

other: 175 mg/kg (1 animal) and 550 mg/kg (1 animal) Dose Levels: There were no signs of adverse clinical signs. 1,750 mg/kg Dose Level (3 animals): Clinical signs observed for two animals included ano-genital staining and/or hypoactivity. However, the animals r

Gross pathology:

No gross abnormalities were noted for any of the animals when necropsied at the conclusion of the 14-day observation period, except the four rats that were administered the highest dose level (5,000 mg/kg). Gross necropsy of these four rats revealed discoloration of the intestines.

Results are provided in Table 1 below.

Interpretation of results:

Category 4 based on GHS criteria

Conclusions:

Under the conditions of this study, the acute oral LD50 of Myclobutanil was found to exceed 1750
mg/kg of body weight in female rats, and was lower than 5000 mg/kg bw/day.

Executive summary:

An acute oral toxicity test (Up and Down Procedure) was conducted with female Fischer 344 rats. Prior to use, the test substance was ground to a powder then mixed with a 1.5% w/w solution of carboxymethylcellulose (CMC) in distilled water to form a 25% w/w suspension. An initial limit dose of 5,000 mg/kg was administered to one healthy female rat by oral gavage. Due to mortality in this animal, the study proceeded to the Main Test. Using the default starting level of 175 mg/kg and following the Up and Down procedure, eight additional females were dosed at levels of 550, 1,750, or 5,000 mg/kg bw. All animals dosed at 5,000 mg/kg bw/day died within one day, no further mortality occurred. No effects on body weight gain were observed in the surviving rats. No clinical signs, abnormal behaviour and gross necropsy findings were noted for rats dosed at 175 and 550 mg/kg bw/day. At 1,750 mg/kg bw clinical signs were observed for two animals including ano-genital staining and/or hypoactivity. The animals recovered by Day 3. No necropsy findings were noted. 

Under the conditions of this study, the acute oral LD50 of the test substance was found to exceed 1750 mg/kg of body weight in female rats, and was lower than 5000 mg/kg bw/day.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LD50

Value:

> 1 750 - < 5 000 mg/kg bw

Quality of whole database:

The available study is reliable (Klimisch 1).

Acute toxicity: via inhalation route

Link to relevant study records

Reference

Endpoint:

acute toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

25-January-2006 to 25-May-2006

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: JMAFF, Acute Inhalation Toxicity Study

Version / remarks:

200

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.1300 (Acute inhalation toxicity)

Version / remarks:

1998

Deviations:

no

Qualifier:

according to guideline

Guideline:

OECD Guideline 403 (Acute Inhalation Toxicity)

Version / remarks:

1981

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test type:

acute toxic class method

Limit test:

yes

Species:

rat

Strain:

Fischer 344/DuCrj

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories Inc. (Raleigh, North Carolina)
- Age at study initiation: 9 weeks
- Housing: Animals were housed one per cage in stainless steel cages
- Diet: LabDiet® Certified Rodent Diet in pelleted form
- Water: Municipal drinking water, ad libitum
- Acclimation period: Animals were acclimated to the nose cones for at least two hours on the day preceding exposure to the test material
- Method of randomization in assigning animals to test and control groups: Before administration of test material began, animals were stratified by body weight and then randomly assigned to treatment groups using a computer program designed to increase the probability of uniform group mean weights and standard deviations at the start of the study

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22°C with a tolerance of ± 1°C (and a maximum permissible excursion of ± 3°C)
- Humidity (%): 40-70%
- Air changes (per hr): Approximately 12-15 times/hour
- Photoperiod (hrs dark / hrs light): 12-hour light/dark photocycle

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

nose only

Vehicle:

air

Mass median aerodynamic diameter (MMAD):

3.5 µm

Analytical verification of test atmosphere concentrations:

yes

Remarks:

The mass concentration of aerosol present in the chamber was determined gravimetrically three times during the exposure period.

Duration of exposure:

4 h

Concentrations:

The resulting time-weighted average concentration was 5.88 mg/L; the nominal concentration was 17.14 mg/L (calculated based on the mass of test material fed into the generation system divided by the total chamber airflow during the exposure period.).

No. of animals per sex per dose:

5

Control animals:

no

Details on study design:

- Duration of observation period following administration: 14 days
- Frequency of observations and weighing: All animals were observed for morbidity and mortality at least twice daily. Animals were weighed and observed for exposure-related effects approximately every 30 minutes during the exposure period. All rats were weighed on test days 2, 4, 8, 11, and 15 during the two-week post-exposure period.
- Necropsy of survivors performed: yes
- Clinical signs including body weight: Detailed clinical observations (DCO) were conducted pre-exposure and daily following the start of treatment.
- Other examinations performed: The necropsy included the examination of the eyes with a microscope slide using fluorescent illumination. Tissues were not saved and no histopathologic examinations were performed.

Statistics:

Means and standard deviations were calculated for descriptive purposes for chamber concentration (mean only), animal body weights, exposure room temperature and chamber temperature, humidity, and airflow.

Key result

Sex:

male/female

Dose descriptor:

LC50

Effect level:

> 5.88 mg/L air

Based on:

test mat.

Exp. duration:

4 h

Remarks on result:

other: tested at the maximum attainable concentration

Mortality:

All animals survived the four-hour exposure to the test material as well as the two week post-exposure period.

Clinical signs:

other: See below.

Body weight:

Mean body weight losses of 7.7% and 9.3% were noted for male and female rats, respectively, on test day 2. Pre-exposure mean body weight values were exceeded on test day 8.

Gross pathology:

There were no treatment-related visible lesions noted in any of the rats exposed to myclobutanil at the test day 15. However, one female rat was found to have decreased body fat at the gross necropsy.

Other findings:

Clinical effects noted during the four-hour exposure period were limited to soiling of the haircoat in three male rats and one female rat. In-life observations noted post-exposure included combinations of noisy and/or labored respiration with and without mouth-breathing, decreased resistance to removal, decreased reactivity, decreased feces and urine, perineal, perioral, perinasal, periocular, abdominal and/or extensive body soiling, dehydration and ungroomed appearance. Some of the rats eyes were partially closed due to the physical characteristics of the test material. In addition, one female rat had decreased extensor-thrust response and muscle tone, bilateral palpebral closure, and poor coordination. This female rat was normal by test day 9.
All other rats appeared normal by test day 7.

Interpretation of results:

GHS criteria not met

Conclusions:

Based on these data, the four-hour LC50 of inhaled particulate myclobutanil is greater than 5.88 mg/L (the maximum attainable concentration) for male and female Fischer 344 rats.

Executive summary:

An acute inhalation study was performed with Myclobutanil. Groups of five rats/sex were exposed for four hours, using a nose-only inhalation exposure system, to a time-weighted average chamber concentration of 5.88 mg myclobutanil per liter of air (the maximum attainable concentration). All animals survived the four hour exposure to the test material as well as the two week post-exposure period. Clinical effects noted during the four-hour exposure period were limited to soiling of the haircoat in three male rats and one female rat. In life observations noted post-exposure included combinations of noisy and/or labored respiration with and without mouth-breathing, decreased resistance to removal, decreased reactivity, decreased feces and urine, perineal, perioral, perinasal, periocular, abdominal and/or extensive body soiling, dehydration, and ungroomed appearance. The eyes of some of the rats were partially closed due to the physical characteristics of the test material. In addition, one female rat had decreased extensor-thrust response and muscle tone, bilateral palpebral closure, and poor coordination. This female rat was normal by test day 9. All other rats appeared normal by test day 7. Mean body weight losses of 7.7 and 9.3% were noted for male and female rats, respectively, on test day 2. Pre-exposure mean body weight values were exceeded on test day 8. Based on this data, the four-hour LC50 of inhaled particulate myclobutanil is concluded to exceed the maximum attainable concentration (5.88 mg/L).

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

LC50

Value:

> 5.88 mg/L air

Quality of whole database:

A reliable study is available (Klimisch 1). Testing was done at the maximum attainable concentration.

Acute toxicity: via dermal route

Link to relevant study records

Reference

Endpoint:

acute toxicity: dermal

Type of information:

experimental study

Adequacy of study:

key study

Study period:

24-June-2005 to 29-September-2005

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method B.3 (Acute Toxicity (Dermal))

Version / remarks:

1985

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.1200 (Acute Dermal Toxicity)

Version / remarks:

1998

Deviations:

no

Qualifier:

according to guideline

Guideline:

OECD Guideline 402 (Acute Dermal Toxicity)

Version / remarks:

1992

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test type:

standard acute method

Limit test:

yes

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Received from Charles River Laboratories, Raleigh, NC on July 5, 2005.
- Females (if applicable) nulliparous and non-pregnant: yes
- Age at study initiation: Young adult (9 weeks)
- Weight at study initiation: males 171-182 grams and females 118-124 grams
- Housing: The animals were singly housed in suspended stainless steel caging with mesh floors. Litter paper was placed beneath the cage and was changed at least three times per week.
- Diet: Purina Certified Rodent Diet
- Water: Filtered tap water, ad libitum
- Acclimation period: 6 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 19-22°C
- Humidity (%): 66-70%
- Air changes (per hr): Photoperiod (hrs dark / hrs light): 12-hour light/dark cycle

Type of coverage:

occlusive

Vehicle:

water

Remarks:

distilled

Details on dermal exposure:

TEST SITE
- % coverage: 10%
- Type of wrap if used: Durapore tape

REMOVAL OF TEST SUBSTANCE
- Washing (if done): The test sites were gently cleansed of any residual test substance
- Time after start of exposure: 24 hours after the start of exposure

TEST MATERIAL
- Amount applied: 5000 mg/kg of body weight of the ground test substance.
Prior to application, the test substance was ground in a coffee mill then moistened with distilled water to achieve a dry paste by preparing a 65% w/w mixture.

Duration of exposure:

24 hours

Doses:

5000 mg/kg bw

No. of animals per sex per dose:

5

Control animals:

no

Details on study design:

- Duration of observation period following administration: 14 days
- Frequency of observations and weighing: Individual body weights of the animals were recorded prior to test substance application (initial) and again on Days 7 and 14 (termination). The animals were observed for mortality, signs of gross toxicity, and behavioral changes during the first several hours after application and at least once daily thereafter for 14 days.
- Gross necropsies were performed on all animals. The external surface of the body and all orifices, tissues, and organs of the thoracic and abdominal cavities were examined.

Key result

Sex:

male/female

Dose descriptor:

LD50

Effect level:

> 5 000 mg/kg bw

Based on:

test mat.

Mortality:

All animals survived the study period.

Clinical signs:

other: There were no signs of gross toxicity, dermal irritation, adverse clinical signs, or abnormal behavior.

Gross pathology:

No gross abnormalities were noted for any of the animals when necropsied at the conclusion of the 14-day observation period.

Interpretation of results:

GHS criteria not met

Conclusions:

Under the conditions of this study, the single dose acute dermal LD50 of Myclobutanil was greater
than 5,000 mg/kg of body weight in male and female rats.

Executive summary:

An acute dermal toxicity test was conducted with Fischer 344 rats. Five thousand milligrams of ground test substance per kilogram of body weight was mixed with distilled water and applied to the skin of five male and five female healthy rats for 24 hours. All animals survived, gained body weight, and appeared active and healthy during the study. There were no signs of gross toxicity, dermal irritation, adverse clinical signs, or abnormal behavior. No gross abnormalities were noted for any of the animals when necropsied at the conclusion of the 14-day observation period. In conclusion, under the conditions of this study, the single dose acute dermal LD50 of the test substance was greater than 5,000 mg/kg of body weight in male and female rats.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

LD50

Value:

> 5 000 mg/kg bw

Quality of whole database:

A reliable study is available (Klimisch 1).

Additional information

An acute oral toxicity test (Up and Down Procedure) was conducted with female Fischer 344 rats. Prior to use, the test substance was ground to a powder then mixed with a 1.5% w/w solution of carboxymethylcellulose (CMC) in distilled water to form a 25% w/w suspension. An initial limit dose of 5,000 mg/kg was administered to one healthy female rat by oral gavage. Due to mortality in this animal, the study proceeded to the Main Test. Using the default starting level of 175 mg/kg and following the Up and Down procedure, eight additional females were dosed at levels of 550, 1,750, or 5,000 mg/kg bw. All animals dosed at 5,000 mg/kg bw/day died within one day, no further mortality occurred. No effects on body weight gain were observed in the surviving rats. No clinical signs, abnormal behaviour and gross necropsy findings were noted for rats dosed at 175 and 550 mg/kg bw/day. At 1,750 mg/kg bw clinical signs were observed for two animals including ano-genital staining and/or hypoactivity. The animals recovered by Day 3. No necropsy findings were noted. This data indicates that the acute oral LD50 of the test substance exceeds 1750 mg/kg of body weight in female rats, and is lower than 5000 mg/kg bw/day.

 

An acute inhalation study was performed with Myclobutanil. Groups of five rats/sex were exposed for four hours, using a nose-only inhalation exposure system, to a time-weighted average chamber concentration of 5.88 mg myclobutanil per liter of air (the maximum attainable concentration). All animals survived the four hour exposure to the test material as well as the two week post-exposure period. Clinical effects noted during the four-hour exposure period were limited to soiling of the haircoat in three male rats and one female rat. In life observations noted post-exposure included combinations of noisy and/or labored respiration with and without mouth-breathing, decreased resistance to removal, decreased reactivity, decreased feces and urine, perineal, perioral, perinasal, periocular, abdominal and/or extensive body soiling, dehydration, and ungroomed appearance. The eyes of some of the rats were partially closed due to the physical characteristics of the test material. In addition, one female rat had decreased extensor-thrust response and muscle tone, bilateral palpebral closure, and poor coordination. This female rat was normal by test day 9. All other rats appeared normal by test day 7. Mean body weight losses of 7.7 and 9.3% were noted for male and female rats, respectively, on test day 2. Pre-exposure mean body weight values were exceeded on test day 8. Based on this data, the four-hour LC50 of inhaled particulate myclobutanil is concluded to exceed the maximum attainable concentration (5.88 mg/L).

 

An acute dermal toxicity test was conducted with Fischer 344 rats. Five thousand milligrams of ground test substance per kilogram of body weight was mixed with distilled water and applied to the skin of five male and five female healthy rats for 24 hours. All animals survived, gained body weight, and appeared active and healthy during the study. There were no signs of gross toxicity, dermal irritation, adverse clinical signs, or abnormal behavior. No gross abnormalities were noted for any of the animals when necropsied at the conclusion of the 14-day observation period. In conclusion, under the conditions of this study, the single dose acute dermal LD50 of the test substance was greater than 5,000 mg/kg of body weight in male and female rats.

Justification for classification or non-classification

Based on the available data it is concluded that Myclobutanil does not meet classification criteria for acute toxicity via the dermal and inhalation route, Myclobutanil is harmonised classified for oral toxicity (cat. 4) according to the Classification, Labelling and Packaging (CLP) Regulation ((EC) No 1272/2008).