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Description of key information

The acute inhalation study is the only acute toxicity study available for 2-methylpropane-2-thiol that has been conducted to a recognised test guideline and in compliance with GLP. However, studies that pre-date GLP and the OECD test guidelines are available for the oral and dermal routes.

Oral LD50 (rat): 4729 mg/kg (Fairchild & Stokinger, 1958)

Dermal LD50 (rat): > 2000 mg/kg (Latven, 1976)

inhalation LC50 (rat, 4h, whole body): 94 622 mg/L (26 643 ppm) (Daly, 1986)

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
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
no guideline followed
Principles of method if other than guideline:
Doses were administered by oral gavage and the test substance was undiluted. The animals were observed for 14 days after dose administration. Tissues samples were submitted for pathologic examination after having first been examined grossly and preserved.
GLP compliance:
no
Test type:
standard acute method
Limit test:
no
Species:
rat
Strain:
Wistar
Sex:
male
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: local commercial breeder
- Age at study initiation: no data
- Weight at study initiation: 200 +/- 20 g
- Fasting period before study: no data
- Housing: no data
- Diet (e.g. ad libitum): Rockland Rat Diet
- Water (e.g. ad libitum): tap water
- Acclimation period: at least one week

ENVIRONMENTAL CONDITIONS
- Temperature (°C): no data
- Humidity (%): no data
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): no data
Route of administration:
oral: gavage
Vehicle:
unchanged (no vehicle)
Details on oral exposure:
Doses were administered by oral gavage and the test substance was undiluted.
Doses:
1672, 3344, 6688, and 13375 mg/kg
No. of animals per sex per dose:
5
Control animals:
no
Details on study design:
The animals were observed for 14 days after dose administration. Tissues samples were submitted for pathologic examination after having first been examined grossly and preserved.
Statistics:
The LD50 was calculated by the method of Weil.
Sex:
male
Dose descriptor:
LD50
Effect level:
4 729 mg/kg bw
95% CL:
3 756 - 5 954
Mortality:
1672 mg/kg - no deaths
3344 mg/kg - no deaths
6688 mg/kg - 5/5 dead, 4 dead by 12 hours, additional death at 32 hours
13376 - 5/5 dead by 20 hours
Clinical signs:
other: no data
Gross pathology:
no data
Other findings:
no data
Interpretation of results:
GHS criteria not met
Conclusions:
The LD50 was 4729 mg/kg bw.
Executive summary:

In an acute oral toxicity study (pre-guideline study), Male rats (5/dose; Wistar) were dosed with 2 -methylpropane-2 -thiol (CAS Number 75 -66 -1) at doses of 1672, 3344, 6688, and 13375 mg/kg bw and observed for 14 days. 

Mortality was 0, 0, 5, and 5 of the 5 animals per group, respectively. No other data (e.g. signs of toxicity) were reported. The LD50 was 4729 mg/kg bw. The substance is not classified according to Regulation (EC) No 1272/2008.

This study received a Klimisch Score of 2 and was classified as reliable with restrictions because it is an older study but there was sufficient detail provided to assess the acute oral toxicity of 2 -methylpropane-2-thiol.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
LD50
Value:
4 729 mg/kg bw
Quality of whole database:
Reliable with restrictions (Klimisch score of 2)

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
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
EPA OPP 81-3 (Acute inhalation toxicity)
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 403 (Acute Inhalation Toxicity)
GLP compliance:
yes
Test type:
standard acute method
Limit test:
no
Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories, Inc., USA
- Age at study initiation: 7-9 weeks for males, 9-10 weeks for females
- Weight at study initiation: 202-306 g for males, 192-215 for females
- Housing: doubly-housed the singly in suspended stainless steel wire mesh cage
- Diet (e.g. ad libitum): Purina Rodent Laboratory chow #5001
- Water (e.g. ad libitum): tap water
- Acclimation period: 7-15 days

ENVIRONMENTAL CONDITIONS
- Temperature (°F): 67-76
- Humidity (%): 30-70
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12/12
Route of administration:
inhalation: vapour
Type of inhalation exposure:
whole body
Vehicle:
other: unchanged (no vehicle)
Details on inhalation exposure:
- Chamber Operation:
The Plexiglas® exposure chamber had a total volume of 100 liters. The chamber was operated dynamically at an initial airflow rate of 25 liters per minute (lpm). This flow rate was calculated to provide one complete air change at least every 4.0 minutes and a 99% equilibrium time of 18.4 minutes. For Groups I, II, IV-VI, the 100 liter Plexiglas® eposure chamber was contained inside a 1 m3 glass and stainless steel exposure chamber, under slightly negative pressure.

- Exposure Procedure:
Appropriate amounts (milliliters, mls) of the test substance were placed in each of two 500 ml fritted-bottom bubblers for Groups I and II, or each of three 500 ml fritted-bottom bubblers for Groups IV-VI. House-supply air was delivered through a Union Carbide regulator and 3/8" Tygon® tubing to each bubbler via a Nupro metering valve, a Dwyer flowmeter and a Union Carbide pressure gauge. The resultant vapor-laden airstream was directed to a five-neck flask which served as a mixing vessel and a trap. (The trap contained glass wool to facilitate trapping of any aerosol present.) Additional diluted air was delivered to the five-neck flask via a Union Carbide pressure gauge, a Nupro metering valve and a Dwyer flowmeter. This generation system was contained inside a wood and Plexiglas® glove box under slightly negative pressure. The resultant vapor-laden air stream was directd from the five-neck flask into the lm' chamber which contained the 100 liter Plexiglas® exposure chamber, via 1/2" Teflon® tubing.
Control animals (Group III) were exposed to house-supply air only during the four-hour in-chamber period while in a 100 liter Plexiglas® exposure chamber.

- Method of particle size determination:
Measurements for the presence of any particulate in the chamber were made twice during the exposure for Groups I and II and once during exposure for Groups III-VI. In-chamber particle count for all groups was less than five times the background (room air) using the widest channel, therefore the aerosol concentration was considered to be negligible. Measurements were performed using a Royco Model 227 Portable Particle Monitor.
Analytical verification of test atmosphere concentrations:
yes
Remarks:
Samples were taken and using a Miran lA Ambient Air Analyzer and strip chart recorder. The exposure level was determined by comparison of the resultant absorbance to a calibrated response using the same instrumental settings.
Duration of exposure:
4 h
Concentrations:
0, 14400, 19900, 22900, 32400, or 36000 ppm (nominal)
0, 14900, 22400, 27800, 30100, 36100 ppm (analytical)
No. of animals per sex per dose:
5
Control animals:
yes
Details on study design:
In-Life Observations:
Day 1 (Day of Exposure): All animals were observed individually, immediately prior to exposure, as a group at approximately fifteen minute intervals during the first hour of exposure, each half hour for hours 1 through 2, and hourly for the remainder of the exposure period. All survivors were observed individually upon removal from the chamber (half hour after exposure was completed) and four hours post-exposure. Detailed physical observations were recorded at each interval.
Days 2 through 15 (Post-exposure): Detailed observations were recorded for survivors twice daily; viability was assessed twice daily.

Body Weight:
Day 1 (immediately prior to exposure) and on Days 2, 3, 5, 8, 11 and 15 (just prior to sacrifice).

Postmortem:
A complete gross postmortem examination was performed on all animals dying spontaneously during the course of the study as well as those animals surviving to the end of the 14-day post-exposure observation period. The gross postmortem examinations included examination of the nasal passages, trachea, external surface, all orifices, the cranial cavity, carcass, the brain and spinal cord, the thoracic, abdominal and pelvic cavities and their viscera and the cervical tissues and organs.



Statistics:
A calculation of median lethal concentration and 95% confidence limits was performed according to the method of Litchfield and Wilcoxon.
Sex:
male/female
Dose descriptor:
LC50
Effect level:
26 643 ppm
95% CL:
22 733 - 31 227
Exp. duration:
4 h
Remarks on result:
other: = 94622 mg/m3
Mortality:
All deaths occurred during exposure or prior to removal from the chamber (see table below)
Clinical signs:
other: Exposure Period: During exposure, the most commonly noted signs of toxicity were lacrimation, labored breathing, reduced activity and prostration. Several notations of ataxia were made for the 14,900 and 22,400 ppm exposures and observations of tremors we
Body weight:
Weight losses of significant magnitude were noted among survivors on the day following exposure. Recovery of weight occurred over time and by 8 days post-exposure, most animals were in excess of their original body weight. Notable exceptions were two male rats exposed to 27,800 ppm which had still not recovered to their individual weights by termination of the study.
Gross pathology:
A number of animals which died spontaneously had red lungs. This is not considered to be unusual in animals which were not exsanguinated prior to postmortem examination. The toxicological significance of this finding, if any, remains undetermined on the basis of gross examination only. Other postmortem findings, observed grossly, occurred sporadically and were not considered to be related to the test article.
Other findings:
no data

Group

Mean Analytical Concentration (ppm)

Nominal Concentration (ppm)

Amount of Test Material Consumed (grams)

Mortality

#dead/#exposed

Male

Female

I

36,100

36,000

883.56

5/5

5/5

VI

30,100

32,400

765.21

5/5

5/5

V

27,800

22,900

537.21

0/5

3/5

IV

22,400

19,900

467.90

1/5

0/5

II

14,900

14,400

337.32

0/5

0/5

III

Control

-

0/5

0/5

Interpretation of results:
GHS criteria not met
Conclusions:
In an acute inhalation toxicity study, the LC50s were determined to be 26,643 ppm for combined sexes, 26,799 ppm for males and 25,643 ppm for females.
Executive summary:

In an acute inhalation toxicity study (OECD 403), groups of ten rats (5/sex) were exposed to 2 -methylpropane-2 -thiol (CAS Number 75 -66 -1) at concentrations of 0, 14400, 19900, 22900, 32400, or 36000 ppm for four hours. The animals were observed immediately prior to exposure, at approximately 15 minute intervals during the first hour of exposure, every half hour during 1 and 2 hours and hourly until the completion of the 14-day exposure period. All survivors were observed upon removal from the chamber and hourly for four hours post-exposure. The animals were observed twice daily for mortality and detailed observations were recorded daily through the remainder of the 14 -day post-exposure period. Body weights were recorded on Day 1 (prior to exposure), and on Days 2, 3, 5, 8, 11 and 15 (just prior to sacrifice). A gross necropsy was conducted on all animals dying spontaneously during the course of the study and on all animals that survived to study termination.

 

All animals that died did so either during exposure or prior to removal from the chamber (30 minutes after cessation of compound delivery). Lacrimation, labored breathing, reduced activity and prostration were commonly noted during exposure and up to four hours post-exposure. Several instances of ataxia and tremors were also observed. During the recovery period, secretory and respiratory responses were noted initially but signs decreased in incidence and severity as the recovery period progressed. Body weights were significantly decreased in survivors on the day following exposure but, again, there was general recovery by Day 8 post-exposure. A number of animals, which died spontaneously, had red lungs. This is not considered to be unusual in animals which were not exsanguinated prior to postmortem examination. The toxicological significance of this finding, if any, remains undetermined on the basis of gross examination only. Other postmortem findings, observed grossly, occurred sporadically and were not considered to be related to the test article.

 

The LC50s were determined to be 26,643 ppm for combined sexes, 26,799 ppm for males and 25,643 ppm for females. The substance is not classified according to Regulation (EC) No 1272/2008.

 

This study received a Klimisch Score of 1 and is classified as reliable without restriction because it is a guideline GLP study.

Endpoint conclusion
Dose descriptor:
LC50
Value:
94 622 mg/m³ air
Quality of whole database:
Reliable with restrictions (Klimish score of 2).

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
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
equivalent or similar to guideline
Guideline:
other: FHSA Regulation 1500.40
GLP compliance:
no
Test type:
standard acute method
Limit test:
yes
Species:
rabbit
Strain:
not specified
Sex:
not specified
Details on test animals or test system and environmental conditions:
no data
Type of coverage:
occlusive
Vehicle:
unchanged (no vehicle)
Details on dermal exposure:
Each of six albino rabbits were treated dermally with a single dose of 2000 mg/kg (2.50 ml/kg of the undiluted sample) applied to the hair-clipped skin of the trunk under an occluding prefitted sleeve on each animal. The sleeves were removed 24 hours later.
Duration of exposure:
24 hours
Doses:
2000 mg/kg
No. of animals per sex per dose:
6
Control animals:
no
Details on study design:
The animals were observed for seven days.
Statistics:
not appropriate
Sex:
not specified
Dose descriptor:
LD50
Effect level:
> 2 000 mg/kg bw
Mortality:
None.
Clinical signs:
other: The surface of the treated skin became dry and exfoliation began six days after treatment. None of the animals showed any toxic symptoms.
Gross pathology:
No data
Other findings:
No data
Interpretation of results:
GHS criteria not met
Conclusions:
 There were no effects of treatment observed and the LD50 was > 2000 mg/kg bw.
Executive summary:

In an acute dermal toxicity study (pre-guideline study), six rabbits (sex/strain not specified) were treated dermally with a single dose of 2000 mg/kg bw of 2-methylbutane-2-thiol (CAS Number 75-66-1). Doses were applied to the hair-clipped skin of the trunk under an occluding prefitted sleeve. The sleeves were removed 24 hours later and the animals were then observed for seven days. 

There were no effects of treatment observed and the LD50 was >2000 mg/kg bw.

This study received a Klimisch Score of 2 and is classified as reliable with restriction because the test procedure was in accordance with national standard methods with acceptable restrictions.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
LD50
Value:
2 000 mg/kg bw
Quality of whole database:
Reliable with restrictions (Klimish score of 2).

Additional information

Oral toxicity

Male rats (5/dose; Wistar) were dosed with 2-methylpropane-2-thiol (pre-guideline study) at doses of 1672, 3344, 6688, and 13,375 mg/kg bw and followed for 14 days. Mortality was 0, 0, 5, and 5 of the 5 animals per group, respectively. No other data (e.g. signs of toxicity) were reported. The LD50 was 4729 mg/kg bw (Fairchild & Stokinger, 1958).

In a supporting acute oral toxicity study, an LD50 of 8 400 mg/kg bw/day was concluded for 2-methylpropane-2-thiol (Phillips Petroleum Company, 1990).

 

Inhalation toxicity

 

In an OECD 403 study (Daly, 1986), groups of ten rats (five male and five female) were exposed for four hours to various concentrations of 2-methylpropane-2-thiol vapour. The animals were observed immediately prior to exposure, at approximately 15 minute intervals during the first hour of exposure, every half hour during 1 and 2 hours and hourly until the completion of the exposure period. All survivors were observed upon removal from the chamber and hourly for four hours post-exposure. The animals were observed twice daily for mortality and detailed observations were recorded daily through the remainder of the 14 day post-exposure period. Body weights were recorded on Day 1 (prior to exposure), and on Days 2, 3, 5, 8, 11 and 15 (just prior to sacrifice). A gross necropsy was conducted on all animals dying spontaneously during the course of the study and on all animals that survived to study termination. All animals that died did so either during exposure or prior to removal from the chamber (30 minutes after cessation of compound delivery). Lacrimation, laboured breathing, reduced activity and prostration were commonly noted during exposure and up to four hours post-exposure. Several instances of ataxia and tremors were also observed. During the recovery period, secretory and respiratory responses were noted initially but signs decreased in incidence and severity as the recovery period progressed. Body weights were significantly decreased in survivors on the day following exposure but, again, there was general recovery by Day 8 post-exposure. A number of animals, which died spontaneously, had red lungs. This is not considered to be unusual in animals which were not exsanguinated prior to postmortem examination. The toxicological significance of this finding, if any, remains undetermined on the basis of gross examination only. Other postmortem findings, observed grossly, occurred sporadically and were not considered to be related to the test article. The LC50s were determined to be 26,643 ppm (94622 mg/m3) for combined sexes, 26,799 ppm for males and 25,643 ppm for females.

Male Wistar rats (6/group) and male Swiss mice (10/group) were exposed for 4 hours to 2-methylpropane-2-thiol at analytical concentrations of 11520, 15465 and 24495 ppm (Fairchild and Stokinger, 1958). Mortality occurred as follows: 0/6; 0/6 and 4/6 in rats and 0/10, 4/10 and 10/10 in mice, respectively. Maximal sublethal and lethal concentrations induced characteristic symptoms of toxicity, i.e., increased respiration and restlessness, uncoordinated movement and staggering gait, muscular weakness, partial skeletal muscle paralysis beginning in hind limbs, light to severe cyanosis, tolerance of prone position, and mild to heavy sedation. Fatal responses usually followed one of two patterns: (1) animals exposed to maximal lethal concentrations died from respiratory arrest while in or shortly after removal from the chamber, and (2) those animals exposed to minimal lethal concentrations died while in a semiconscious condition of long duration. Animals very often remained in a semi-conscious condition of sedation and lethargy 4 to 6 hours post-exposure before showing signs of recovery. Occasionally a period of deep lethargy of 18 to 28 hours intervened before visible signs of recovery occurred. Irritation to the mucous membranes within approximately 15 minutes after exposure of animals to high concentrations was evidenced by their rubbing of the eyes and nose, eye closure, occasional sneezing, watering of the eyes, and retracting of the head. The 4-hour LC50s were reported to be 22 200 ppm (equivalent to 81 918 mg/m3) in rats and ca. 16500 ppm (equivalent to 60 885 mg/m3) in mice.

Dermal toxicity

Each of six rabbits (sex/strain not specified) was treated dermally with a single dose of 2000 mg/kg bw of 2-methylpropane-2-thiol (pre-guideline study) (Latven, 1976b). Doses were applied to the hairclipped skin of the trunk under an occluding prefitted sleeve. The sleeves were removed 24 hours later and the animals were then observed for seven days. There were no effects of treatment observed and the LD50 was >2000 mg/kg bw (Latven, 1976b).

Justification for classification or non-classification

According to REGULATION (EC) No 1272/2008 and the available acute toxicity data:

Acute oral toxicity:

Not classified: rat/LD50 = 4729 mg/kg

Acute inhalation toxicity:

Not classified: rat/4h/LC50 = 94.622 mg/L

Acute dermal toxicity:

Not classified: rabbit/LD50 > 2000 mg/kg