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Description of key information

The acute dermal and oral toxicity of the test substance SMBT (50%) is very low, indicated by LD50 values greater than 2000 mg/kg bw. The acute oral LD50 value in rats is 2100 mg/kg bw (Bayer AG 1978) and the dermal LD50 value in rabbits is greater than 7940 mg/kg bw for SMBT (50%) (Monsanto Co. 1974).

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion
Dose descriptor:
LD50
Value:
2 100 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 SMBT was evaluated in 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 male Wistar rats undiluted SMBT solution (50%) was administered by gavage to male Wistar rats at doses of 0.5, 1.0, 2.0, 3.1, 3.5, 4.0, and 5.0 ml/kg bw (ca. 400, 800, 1600, 2480, 2800, 3200, 4000 mg/kg bw). A 14-day observation period followed administration. The oral LD50 calculated was 2.63 ml/kg bw (ca. 2100 mg/kg bw). Mortality occurred at 800 mg/kg bw and higher (1/10, 2/10, 4/10, 8/10, 8/10, 10/10 at 800, 1600, 2480, 2800, 3200, 4000 mg/kg bw, respectively). Clinical signs were observed and included sedation, difficulties in respiration and myoclonus.

In another acute toxicity study with rats, a LD50 value of 4350 mg/kg bw was calculated (Monsanto Co. 1974). Male and female Sprague Dawley rats (5 animals per dose) were administered once by gavage with the undiluted test substance SMBT (50%) at doses of 2510, 3160, 3980 and 5010 mg/kg bw. A 14-day observation period followed administration. Mortality occurred (one hour to one days after application) in the mid and higher dose groups evaluated (2/5, 2/5, 4/5 at 3160, 3980, 5010 mg/kg bw, respectively). Clinical signs were observed and included reduced appetite and activity (lasting up to one day in survivors), rapidly increasing weakness, tremors, convulsions, collapse, and death. Autopsy of decedent showed hemorrhagic areas of the lungs, liver hyperemia, and acute gastrointestinal inflammation; viscera of surviving animals appeared normal at sacrifice (Monsanto Co. 1974).

In another acceptable documented acute oral toxicity study with Sprague-Dawley rats, an oral LD50 of 9500 mg/kg bw was calculated for SMBT (22%) (Monsanto Co. 1979).

Acute toxicity: dermal

The acute dermal toxicity of SMBT (50%) was evaluated in a limited but acceptable documented acute dermal toxicity study with New Zealand Albino rabbits (Monsanto Co. 1974). One male was treated with 5010 mg/kg and one male and one female with 7940 mg/kg bw undiluted SMBT (50%) for 24 hours. No mortality occurred during the study. Clinical signs observed included reduced appetite and activity (four to seven days). Gross autopsy at study termination revealed no abnormalities in viscera in the treated animals. A dermal LD50 value greater than 7940 mg/kg bw is suggested.

In another dermal toxicity study with rabbits a dermal LD 50 value greater 7940 mg/kg bw was suggested for SMBT solution (22%). One male was treated with 5010 mg/kg and one male and one female with 7940 mg/kg bw undiluted sodium MBT (22%) for 24 hours. No mortality occurred. Clinical signs observed were weight loss for two to four days. Gross autopsy at study termination revealed no abnormalities in viscera in the treated animals.

Justification for classification or non-classification

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