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EC number: 258-904-8
CAS number: 53988-10-6
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 with methyl-2-mercaptobenzimidazole, zinc salt for dermal toxicity determined a LD50 > 2000 mg/kg bw. At 2000 mg/kg bw none of 10 animals died. Justification for read across of 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione, zinc salt and 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione:The toxicological properties of 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione (CAS n° 53988-10-6) and 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione, zinc salt (CAS n° 61617-00-3) are quite similar in toxicological studies available for both compounds (e.g. acute toxicity, irritation/corrosion, genotoxicity, repeated dose studies). This result is assumed to be an effect of the of 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione anion rather than of the hydronium ion (which is a normal constituent of body fluids) or zinc cation, which is an essential element in humans. Therefore a read across between 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione (CAS n° 53988-10-6) and its sodium salt (CAS n° 75045-07-7) and 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione, zinc salt (CAS n° 61617-00-3) is justified.
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).
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.
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.
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-mercaptotobenzimidazole,
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.
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 4, H 302) is justified. In an acute dermal toxicity study,
none of 10 animals died at 2000 mg/kg bw. Therefore a classification is
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