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Administrative data

Description of key information

In 2 valid oral toxicity studies with 2-mercaptomethylbenzimidazole a LD50 = 340 mg/kg bw (rat, male) (Loeser) and a LD50 = 330 mg/kg bw (rat, male/female) (Saitoh) was found. In an acute oral toxicity study with the corresponding zinc salt (2-mercaptomethylbenzimidazole, zinc salt CAS no 61617-00-3) a LD50 = 390 mg/kg bw was determined.
Acute inhalative toxicity was tested with methyl-2-mercaptobenzimidazole, zinc salt in male and female Sprague-Dawley rats. Rats were exposed nose only for 4 hours at room temperature to a concentration of 0 and 2120 mg/m³. No mortality was observed.
A valid study for dermal toxicity determined a LD50 > 2000 mg/kg bw. At 2000 mg/kg bw none of 10 animals died.

Key value for chemical safety assessment

Acute toxicity: via oral route

Link to relevant study records
Reference
Endpoint:
acute toxicity: oral
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: well documented and scientifically acceptable
Principles of method if other than guideline:
Seven groups of 10 young adult male Wistar rats (160 -180 g) were dosed at 200, 300, 350, 380, 400, 450, or 500 mg/kg bw Vulkanox MB 2 (CAS 53988-10-6) in Lutrol. The animals were observed for mortality, body weights and clinical signs through day 14
GLP compliance:
no
Test type:
standard acute method
Species:
rat
Strain:
Wistar
Sex:
male
Route of administration:
oral: gavage
Vehicle:
polyethylene glycol
Doses:
200, 300, 350, 380, 400, 450, or 500 mg/kg bw
No. of animals per sex per dose:
10
Control animals:
no
Sex:
male
Dose descriptor:
LD50
Effect level:
340 mg/kg bw
Based on:
test mat.

Corresponding mortality was 0, 20, 70, 70, 80, 80 and 100% respectively. Sedation was the only clinical sign. Deaths occured on days 1 to 4. The acute oral LD50 for male rats is 340 mg/kg bw (95% confidence interval: 300 - 370 mg/kg bw).

Interpretation of results:
harmful
Remarks:
Migrated information
Executive summary:

Seven groups of 10 young adult male Wistar rats (160 -180 g) were dosed at 1 200, 300, 350, 380, 400, 450, or 500 mg/kg bw Vulkanox MB 2 (CAS 53988-10-6) in Lutrol. The animals were observed for mortality, body weights and clinical signs through day 14.

Corresponding mortality was 0, 20, 70, 70, 80, 80 and 100% respectively. Sedation was the only clinical sign. Deaths occured on days 1 to 4. The acute oral LD50 for male rats is 340 mg/kg bw (95% confidence interval: 300 - 370 mg/kg bw).

Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
LD50
Value:
340 mg/kg bw
Quality of whole database:
scientifically acceptable and sufficient documented

Acute toxicity: via inhalation route

Link to relevant study records
Reference
Endpoint:
acute toxicity: inhalation
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
other information
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
other: secondary literature - U.S. Environmental Protection Agency, Hazard characterisation document sponsored Chemical: 2H-Benzimidazole-2-thione, 1,3-dihydro-, 4(or 5)-methyl-,zinc salt
Qualifier:
according to guideline
Guideline:
OECD Guideline 403 (Acute Inhalation Toxicity)
Principles of method if other than guideline:
Sprague-Dawley rats (5 per dose) were exposed nose-only to 0 or 2.12 mg/l of an aerosol of methyl-2-mercaptobenzimidazole, zinc salt for 4 hours
GLP compliance:
yes
Test type:
standard acute method
Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Route of administration:
inhalation: aerosol
Type of inhalation exposure:
nose only
Vehicle:
not specified
Duration of exposure:
4 h
Concentrations:
0 or 2.12 mg/l
No. of animals per sex per dose:
10 male/female animals
Control animals:
yes
Sex:
male/female
Dose descriptor:
discriminating conc.
Effect level:
2.12 mg/L air
Based on:
test mat.
Exp. duration:
4 h

There was no fatalities

Endpoint conclusion
Dose descriptor:
discriminating conc.
Value:
2 120 mg/m³
Quality of whole database:
cited from secondary literature - no access, cited owing to all available data requirement

Acute toxicity: via dermal route

Link to relevant study records
Reference
Endpoint:
acute toxicity: dermal
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
other information
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
other: secondary literature - U.S. Environmental Protection Agency, Hazard characterisation document sponsored Chemical: 2H-Benzimidazole-2-thione, 1,3-dihydro-, 4(or 5)-methyl-,zinc salt
Qualifier:
according to guideline
Guideline:
OECD Guideline 402 (Acute Dermal Toxicity)
Principles of method if other than guideline:
Test material was moistened with arachis oil and applied to an area of shorn skin. All test animals received a single dermal exposure of 2,000 mg/kg b.w. The test material was held in place by surgical gauze and self-adhesive bandage. The semi-occlusive wrap was removed after 24 hours and the excess material was wiped from the test animal.
Animals were examined for mortality, systemic toxicity, signs of dermal irritation, weight gain and necropsy.
GLP compliance:
yes
Test type:
standard acute method
Limit test:
yes
Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Type of coverage:
semiocclusive
Vehicle:
arachis oil
Duration of exposure:
24 hours
Doses:
2000 mg/kg bw
No. of animals per sex per dose:
10 male/female animals
Control animals:
not required
Sex:
male/female
Dose descriptor:
LD50
Effect level:
> 2 000 mg/kg bw
Based on:
test mat.
Interpretation of results:
practically nontoxic
Remarks:
Migrated information
Executive summary:

Test material was moistened with arachis oil and applied to an area of shorn skin. All test animals received a single dermal exposure of 2,000 mg/kg b.w. The test material was held in place by surgical gauze and self-adhesive bandage. The semi-occlusive wrap was removed after 24 hours and the excess material was wiped from the test animal.

LD50 > 2000 mg/kg bw. There were no deaths, no signs of systemic toxicity, no signs of dermal irritation and all animals showed expected weight gain. No abnormalities were noted at necropsy.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
discriminating dose
Value:
2 000 mg/kg bw
Quality of whole database:
cited from secondary literature - no access, cited owing to all available data requirement

Additional information

In 3 valid acute oral toxicity studies a LD50 > 330 mg/kg bw for male (and female) rats was found

In a study on rats with 2120 mg/m³ methyl 2-mercaptotobentimidazole, zinc salt (nose-only exposure) for 4 hours. No mortality was observed.

Ten male/female animals rats were exposed in an acute dermal toxicity study semicoocusively to methyl 2-mercaptotobentimidazole, zinc salt) for 24 hours. None of the rats died.


Justification for selection of acute toxicity – oral endpoint
key study used (LD50 of other studies were in the same range)

Justification for selection of acute toxicity – inhalation endpoint
only available data

Justification for selection of acute toxicity – dermal endpoint
only available data

Justification for classification or non-classification

The acute oral toxicity studies revealed a LD50 > 340 mg/kg bw. In the acute inhalation study and a LC50 > 2.12 mg/l was determined.

Therefore a classification as Xn; R20/22 (GHS: Acute Tox 4, H 332; Acute Tox 3, H 301) is justified. In an acute dermal toxicity study,

none of 10 animals died at 2000 mg/kg bw. Therefore a classification is not necessary.