Ethanethiol

Endpoint summary

Description of key information

Key acute oral, dermal, and inhalation toxicity studies were identified. 
• The oral LD50 was 682 mg/kg bw in male rats (Fairchild, 1958)
• The acute dermal LD0 was >2000 mg/kg bw in rabbits (Fairchild, 1958)
• The acute inhalation LC50 was 11.23 mg/L (11230 mg/m3) in rats (Latven, 1977)

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:

No data

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: This study is classified as reliable with restrictions because it was well conducted and documented and generally follows OECD Guideline 420.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 420 (Acute Oral Toxicity - Fixed Dose Method)

Deviations:

yes

Remarks:

maximum dose exceeded guideline recommended dose; animal fasting was not reported; animals were not weighed; pathology and clinical observations were generalized across dose levels of all chemicals tested

GLP compliance:

no

Test type:

fixed dose procedure

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
- Weight at study initiation: 180 to 220 grams
- Diet (e.g. ad libitum): Rockland Rat Diet ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: one week

Route of administration:

oral: gavage

Vehicle:

unchanged (no vehicle)

Details on oral exposure:

VEHICLE : No vehicle used

MAXIMUM DOSE VOLUME APPLIED: 3360 mg/kg bw

CLASS METHOD (if applicable)
- Rationale for the selection of the starting dose: doses were at geometric progression ( factor 1.26 to 2.0)

Doses:

210, 420, 840, 1680, and 3360 mg/kg bw

No. of animals per sex per dose:

5

Control animals:

no

Details on study design:

- Duration of observation period following administration: 15 days
- Frequency of observations and weighing: Observed on days 1, 2, 3, 5, 10, and 15 no weighing was conducted
- Necropsy of survivors performed: yes
- Other examinations performed: pathology

Statistics:

LD50 calculated by the method of Weil (Weil, C.S.: Tables for Convenient Calculation of Median-Effective Dose (LD50 or ED50) and Instruction in Their Use. Biometrics, 8: 249-304 (1954).)

Preliminary study:

No data reported

Sex:

male

Dose descriptor:

LD50

Effect level:

682 mg/kg bw

95% CL:

517 - 900

Mortality:

Mortality occurred in all animals by 7 hours of administration for the 3360 mg/kg dose and day 5 for the 1680 mg/kg dose. Four of the five animals died in the 840 mg/kg dose level; and no mortality occurred at the 420 and 210 dose levels.

Clinical signs:

Toxicity signs included sedative action, and maximal sublethal doses resulted in deep comatose sleep for approximately 48 hours. Diarrhea was also pronounced for the highest doses.

Body weight:

No data reported

Gross pathology:

Gross pathology generally did not show significant gross or microscopic tissue changes. All animals that survived near lethal doses and were sacrificed within 20 days post-treatment, frequently showed pathologic changes which, although inconsistent, were indicative of liver and kidney damage. Microscopic examination revealed occasional marked changes in the kidneys of rats which included: degeneration with swelling and some necrosis of the tubular epithelium, thickening of Bowman’s capsule, and hyaline deposition in glomerular tufts. More often only minor lesions with varying degrees of cloudy swelling of the tubules and hyaline casts in the lumina were present. In general, liver changes were characterized by lymphocytic infiltration, occasional necrotic foci with small hemorrhages, and varying degrees of fatty degeneration. Only rarely did tissue studies show significant pathologic conditions as the result of relatively small doses of the chemical.

Other findings:

No data reported

 Toxicity Data for Rats Following Single Oral Dose of Ethanethiol

Dose (mg/kg)	Cumulative Mortality following Administration for the Day
	1	2	3	5	10	15
210	0/5	0/5	0/5	0/5	0/5	0/5
420	0/5	0/5	0/5	0/5	0/5	0/5
840	2/5	2/5	2/5	2/5	3/5 (7^th)	4/5 (11^th)
1680	4/5	4/5	4/5	5/5
3360	5/5 (all dead 4 to 7 hrs)
LD50(mg/kg)	1034					682
Confidence Limits	667-1603					517-900

 

Interpretation of results:

Toxicity Category IV

Remarks:

Migrated information Criteria used for interpretation of results: EU

Conclusions:

In an acute oral toxicity study, groups of Wistar male rats (5/sex) were given a single oral dose of ethanethiol undiluted at doses of 210, 420, 840, 1680, or 3360 mg/kg bw and observed for 15 days (Fairchild & Stokinger, 1958). The oral LD50 was determined to be 682 mg/kg bw in males. This study is classified as Toxicity Category IV by EU classification.

Executive summary:

In an acute oral toxicity study, groups of Wistar male rats (5/sex) were given a single oral dose of ethanethiol undiluted at doses of 210, 420, 840, 1680, or 3360 mg/kg bw and observed for 15 days (Fairchild & Stokinger, 1958). 

 

Toxicity signs included sedative action, and maximal sublethal doses resulted in deep comatose sleep for approximately 48 hours. Diarrhea was also pronounced for the highest doses. Gross pathology generally did not show significant gross or microscopic tissue changes. Survivors of near lethal doses showed changes which, although inconsistent, were indicative of liver and kidney damage. Body weights were not measured. The oral LD₅₀ was determined to be 682 mg/kg bw in males. This study is classified as Toxicity Category IV by EU classification.

 

This study received a Klimisch score of 2 and is classified as reliable with restrictions because it was well conducted and documented and generally follows OECD Guideline 420.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LD50

Value:

682 mg/kg bw

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:

Not reported

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: This study is classified as reliable with restrictions because it was well conducted and documented. The study was conducted prior to adoption of GLP guidelines.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

no guideline followed

Principles of method if other than guideline:

This study is pre-guideline but the methods used are considered deemed appropriate as utilized in the report.

GLP compliance:

no

Test type:

acute toxic class method

Species:

rat

Strain:

Wistar

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: at least 1 week

Route of administration:

inhalation: vapour

Type of inhalation exposure:

not specified

Vehicle:

other: compressed air and compressed nitrogen

Details on inhalation exposure:

The generation of thiol vapors was accomplished by either of two methods: (1) bubbling a stream of nitrogen gas (to prevent possible oxidation to sulfide) through a midget fritted-glass bubbler, which contained the liquid thiol, or (2) by passage of nitrogen into a borosilicate glass nebulizer which contained the thiol.

The bubbler was modified by adding an upright side-arm delivery tube with a 10/30 ground joint distal end into which a separatory funnel was inserted. The funnel served as a reservoir for the thiol being vaporized.

Each of the described methods was used interchangeably, but with some of the lower boiling point thios the bubbler proved more manageable and gave more uniform chamber concentrations than the nebulizer.

Duration of exposure:

>= 4 h

Remarks on duration:

Only studied one sex, males

Concentrations:

6.61, 8.00, 9.08, 11.28, 12.28, 12.37, 12.98, 13.02 mg/L (2600, 3150, 3573, 4438, 4832, 4868, 5100, 5125 ppm)

No. of animals per sex per dose:

5 males per dose

Control animals:

not specified

Details on study design:

- Duration of observation period following administration: 15 days
- Necropsy of survivors performed: yes

Statistics:

LC50 values by inhalation were calculated by the method of Miller and Tainter, using logarithmic-probit graph paper.

Sex:

male

Dose descriptor:

LC50

Effect level:

11.23 mg/L air

Exp. duration:

4 h

Remarks on result:

other: (11, 230 mg/m3)

Mortality:

Mortality was first observed at dose levels of 11.28 mg/L (4438 ppm), and were higher at higher dosage levels. The cumulative results are presented in the data table below.

Clinical signs:

other: Rats showed signs of intoxication from exposure. Maximal sublethal and lethal concentrations of thiol induced charateristic symptoms of toxicity, such as increased respiration and restlessness, incoordinated movements and staggering gait, muscular weaknes

Toxicity data on four hour inhalation exposure to vapor thiols

Cumulative Mortality During and After Exposure
	0-4 Hrs	24 Hrs	48 Hrs	15 Days
Analyzed conc. (mg/L)
6.61 (2600 ppm)	0/5	0/5	0/5	0/5
8.00 (3150 ppm)	0/5	0/5	0/5	0/5
9.08 (3573 ppm)	0/5	0/5	0/5	0/5
11.28 (4438 ppm)	0/5	0/5	1/5	1/5
12.28 (4832 ppm)	1/6	3/6	3/6	4/6
12.37 (4868 ppm)	1/5	2/5	2/5	2/5
12.98 (5100 ppm)	2/5	5/5
13.02 (5125 ppm)	2/6	2/6	2/6	2/6

Interpretation of results:

Toxicity Category IV

Remarks:

Migrated information Criteria used for interpretation of results: EU

Conclusions:

Toxicity classification based on single 4-hour exposures shows ethanethiol to be slightly toxic (Fairchild & Stokinger, 1958).

Executive summary:

In an acute toxicity inhalation study, five male rats (Wistar derived) per dose were subjected to the inhalation of ethanethiol vapors at concentrations of 6.61, 8.00, 9.08, 11.28, 12.28, 12.37, 12.98, or 13.02 mg/L (2600, 3150, 3573, 4438, 4832, 4868, 5100, 5125 ppm) (Fairchild & Stokinger, 1958). The generation of thiol vapors was accomplished by either of two methods: (1) bubbling a stream of nitrogen gas through a midget fritted-glass bubbler, which contained the liquid thiol, or (2) by passage of nitrogen into a borosilicate glass nebulizer which contained the thiol.

Toxicity data showed that rats were susceptible to the thiol and mortality was observed at all dose levels greater than and equal to 11.28 mg/L (4438 ppm). Rats exhibited signs of intoxication, and maximal sublethal and lethal concentrations of thiols induced characteristic symptoms of toxicity (ie increased respiration and restlessness, incoordinated movement and staggering gait, muscular weakness, partial skeletal muscle paralysis, light to severe cyosis, and tolerance of prone position. The LC₅₀ was determined to be 12.38 (4870 ppm) mg/L at 24 hours, 11.6 mg/L (4565 ppm) at 48 hours, and 11.23 mg/L (4420 ppm) at 15 days after the exposure period.

This study received a Klimisch score of 2 and is classified as reliable with restrictions because it was well conducted and documented. The study was conducted prior to adoption of GLP guidelines.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LC50

Value:

11 230 mg/m³

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:

1977

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: This study is classified as reliable without restriction because it was conducted according to or similar to now existing guidelines.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 402 (Acute Dermal Toxicity)

Deviations:

yes

Remarks:

Observation period was only 7 days rather than the recommended 14 day duration.

GLP compliance:

no

Test type:

standard acute method

Limit test:

no

Species:

rat

Strain:

not specified

Sex:

male

Type of coverage:

occlusive

Vehicle:

other: none

Duration of exposure:

24 hours

Doses:

2000 mg/kg

No. of animals per sex per dose:

10

Control animals:

not specified

Sex:

male

Dose descriptor:

LD50

Effect level:

> 2 000 mg/kg bw

Initial skin contact evoked a severe pain reaction which coincided with a slight darkening in the color of the skin, none of the treated animals showed any toxic symptoms and all gained body weight during the subsequent period of observation. None of animals died following the test substance administration

Interpretation of results:

not classified

Remarks:

Migrated information Criteria used for interpretation of results: EU

Conclusions:

The acute dermal LD50 was determined to be >2000 mg/kg bw (Latven, 1977).

Executive summary:

In a key acute dermal toxicity study, 10 male albino WBS/W rats were dermally administered ethanethiol (ethyl mercaptan) at doses of 2000 mg/kg bw (Latven, 1977). The test material was applied to clipped trunks under an impervious sleeve for a period of 24 hours and the animals were subsequently observed for 7 days.

There was no mortality observed through the study period but initial skin contact with the test material produced a mild pain reaction that was accompanied by dark discolouration of the skin. There were no other treatment-related effects observed through the study. The acute dermal LD₅₀was determined to be >2000 mg/kg bw.

This study received a Klimisch score of 2 and is classified as reliable with restrictions because it adheres closely to OECD guideline but does not follow GLP.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

LD50

Value:

2 000 mg/kg bw

Additional information

Key data are available to evaluate the acute oral, dermal, and inhalation toxicity potential of ethanethiol.

Acute Oral Toxicity

 

One key study in the rat was identified to evaluate the acute oral toxicity potential of ethanethiol.

 

In a key acute oral toxicity study (Fairchild and Stokinger, 1958; Klimisch score = 2), male Wistar rats (5/dose) were orally administered (via gavage) ethanethiol (undiluted) at single doses of 210, 420, 840, 1680, or 3360 mg/kg bw. The animals were subsequently observed for a period of 15 days. All animals (5/5) in the 1680 and 3360 mg/kg bw test groups died before the end of the study period while mortality was observed in four of five animals in the 840 mg/kg bw by day 15. There was no mortality observed in the 210 and 420 mg/kg bw dose groups. Clinical signs of toxicity included sedative action, deep comatose sleep for 48 hours (maximal sublethal doses), and diarrhea (highest doses). Survivors of near lethal doses showed changes which, although inconsistent, were indicative of liver and kidney damage. The oral LD₅₀ for ethanethiol was determined to be 682 mg/kg bw.

 

Acute Inhalation Toxicity

 

One key study in the rat was identified to evaluate the acute inhalation toxicity potential of ethanethiol.

In a key acute toxicity inhalation study (Fairchild and Stokinger, 1958, Klimisch score = 2), five male rats (Wistar derived) per dose were subjected to the inhalation of ethanethiol vapors at concentrations of 6.61, 8.00, 9.08, 11.28, 12.28, 12.37, 12.98, or 13.02 mg/L (2600, 3150, 3573, 4438, 4832, 4868, 5100, 5125 ppm). Toxicity data showed that rats were susceptible to the thiol and mortality was observed at all dose levels greater than and equal to 11.28 mg/L (4438 ppm). Rats exhibited signs of intoxication, and maximal sublethal and lethal concentrations of thiols induced characteristic symptoms of toxicity (ie increased respiration and restlessness, uncoordinated movement and staggering gait, muscular weakness, partial skeletal muscle paralysis, light to severe cyanosis, and tolerance of prone position.TheLC₅₀ was determined to be 12.38 (4870 ppm) mg/L at 24 hours, 11.6 mg/L (4565 ppm) at 48 hours, and 11.23 mg/L (4420 ppm) at 15 days after the exposure period.

In a supporting acute inhalation toxicity study (Collins, 1987; Klimisch score = 2), Sprague-Dawley rats (5/sex) were exposed (head only) to vapours of ethanethiol at concentrations of 0 and 2.52 mg/L for a period of four hours. The animals were subsequently observed for a period of 15 days. Treated animals exhibited transient symptoms of exposure e.g. chromodacryorrhea, nasal secretion and respiratory distress but recovered completely within 24 hours. No treatment-related signs of clinical toxicity or changes in body weight were observed and there were no remarkable findings at necropsy. The acute inhalation LC₅₀ was determined to be >2.52 mg/L (2520 mg/m³).

 

In another supporting acute inhalation toxicity study (Pence, 1983a; Klimisch score = 2), Sprague-Dawley rats (5/sex) were exposed (whole body) to vapours of ethanethiol at concentrations of 0 and 1.93 mg/L for a period of four hours.The animals were subsequently observed for a period of 15 days. No signs of clinical toxicity were observed in the treated animals and necroscopy did not reveal any remarkable findings. An insignificant reduction in mean body weight was noted for female rats on day 4 but this was not considered treatment-related. Based on the lack of effects observed in the study, the acute inhalation LC₅₀ was determined to be >1.93 mg/L (1930 mg/m³).

Supporting data available from studies conducted in mice (Fairchild and Stokinger, 1958; Klimisch score = 2) indicate that the LC₅₀ is 7.04 mg/L (7040 mg/m³) for mice exposed to vapours of ethanethiol for a period of 4 hours.

Acute Dermal Toxicity

 

One key study in the rat was identified to evaluate the acute dermal toxicity potential of ethanethiol.

In a key acute dermal toxicity study (Latven, 1977c; Klimisch score = 2), 10 male albino WBS/W rats were dermally administered ethanethiol (ethyl mercaptan) at doses of 2000 mg/kg bw. The test material was applied to clipped trunks under an impervious sleeve for a period of 24 hours and the animals were subsequently observed for 7 days. There was no mortality observed through the study period but initial skin contact with the test material produced a severe pain reaction that was accompanied by dark discolouration of the skin. There were no other treatment-related effects observed through the study period based on which, the acute dermal LD₅₀ was determined to be >2000 mg/kg bw.

Justification for selection of acute toxicity – oral endpoint
This study is classified as reliable with restrictions because it was well conducted and documented and generally follows OECD Guideline 420.

Justification for selection of acute toxicity – inhalation endpoint
This study is classified as reliable with restrictions because it was well conducted and documented. The study was conducted prior to adoption of GLP guidelines. Two other supporting inhalation studies are available but they did not determine an LC50 as they only tested one dose at which no deaths occurred.

Justification for selection of acute toxicity – dermal endpoint
This study is classified as reliable without restriction because it was conducted according to or similar to now existing guidelines.

Justification for classification or non-classification

Ethanethiol is classified as Acute Category 4 (H302: Harmful if swallowed) for oral toxicity (LD₅₀ = 682 mg/kg bw) according to Regulation (EC) No 1272/2008 (CLP).

Ethanethiol is classified Acute Category 4 (H332: Harmful if inhaled) for acute inhalation toxicity (LC₅₀ = 11.23 mg/L) according to Regulation (EC) No 1272/2008.

Ethanethiol does not meet the criteria for classification for acute dermal toxicity according to Regulation (EC) No 1272/2008 as the as the LD₅₀ values reported for this substance exceed the upper discriminating threshold limits for classification defined in the regulation.