Registration Dossier

Administrative data

Description of key information

The acute dermal and oral toxicity of the test substance MBT is very low, indicated by oral LD50 values greater than 2000 mg/kg. The acute oral LD50 value in rats is = 2830 mg/kg bw (Monsanto Co. 1973, 1974) and the dermal LD50 value in rabbits is greater than 7940 mg/kg bw (Monsanto Co. 1973, 1974).

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion
Dose descriptor:
LD50
Value:
3 800 mg/kg bw

Acute toxicity: via dermal route

Endpoint conclusion
Dose descriptor:
LD50
Value:
7 940 mg/kg bw

Additional information

Acute toxicity: oral

The acute oral toxicity of MBT was evaluated in several acute oral toxicity studies in rats. Although the study results are reliable the test design of the studies does not comply with the current guidelines. In an acceptable documented study with Sprague-Dawley Albino rats a 20 % solution-suspension of MBT (THIOTAX powder) in corn oil was administered by gavage to 4 groups of 5 (mixed males and females) rats at doses of 3160, 3980, 5010 and 6310 mg/kg bw. A 14-day observation period followed administration. The acute oral LD50 for MBT for male and female rats was calculated to be 3800 mg/kg bw. Signs of intoxication noted were reduced appetite and activity (one to three days) in survivors and increased weakness, collapse and death in decedents. Autopsy of decedents showed lung hyperemia, slight liver discoloration, and gastrointestinal inflammation, whereas viscera of surviving animals appeared normal at sacrifice (Monsanto Co. 1975).

In another acceptable documented acute oral toxicity study with Sprague-Dawley rats, an oral LD50 of 2830 mg/kg bw was stated. The test substance MBT (THIOTAX MBT) was suspended in corn oil and were orally administered to four groups of 5 rats (mixed males and females) at doses of 2000, 2510, 3160 and 3980 mg/kg bw. The clinical signs observed were reduced appetite and activity (two to four days in survivors), and increased weakness, collapse, and death in decedents. Gross autopsy of decedents revealed hemorrhagic lungs, liver hyperemia, and acute gastrointestinal inflammation, whereas viscera of surviving animals appeared normal at sacrifice (Monsanto Co. 1974).

Moreover, the acute oral toxicity of different MBT batches received from different suppliers was tested in male Wistar rats. The LD50 values determined ranged from 7300 mg/kg bw to 9400 mg/kg bw (CIVO TNO 1977).

Acute toxicity: dermal

The acute dermal toxicity of MBT (THIOTAX powder) was evaluated in an acceptable documented acute dermal toxicity study with New Zealand Albino rabbits. Male and female rabbits (one to two animals per dose) were treated for 24 hours with a 40 % test substance suspension in corn oil at doses of 5010 and 7940 mg/kg bw. No mortality occurred. The dermal LD50 for MBT was greater than 7940 mg/kg bw. Clinical signs observed included reduced appetite and activity for 1 to 2 days. Viscera of animals appeared normal at sacrifice (Monsanto Co. 1975).

The findings from the above mentioned study were confirmed in an additional experiment with MBT (THIOTAX MBT) in New Zealand Albino rabbits, where a dermal LD50 greater than 7940 mg/kg was obtained (Monsanto Co. 1974).

Justification for classification or non-classification

No classification is required according to the classification criteria 67/548/EWG and regulation no. 1272/2008 (GHS).