The acute toxicity and mutagenic potential of 3-methyl-2-benzothiazolinone hydrazone

3-Methyl-2-benzothiazolinone hydrazone (MBTH), widely used in analytical laboratories, was investigated for potential handling hazards. Tested as the hydrochloride, it was found to be of moderately high acute peroral toxicity with LD50 values in rabbits of 177 mg/kg (males) and 268 mg/kg (females), and in the rat 308 mg/kg (males) and 149 mg/kg (females). The major signs of toxicity, seen at peroral doses of 125 mg/kg and above, were convulsions. Although of low acute lethal percutaneous toxicity in rats (LD50 greater than 16 g/kg), rabbits were more sensitive with one of five males dying at an applied dose of 16 g/kg, and females having an LD50 of 12.3 g/kg; convulsions were seen in rabbits having applied cutaneous doses of 4 g/kg and above. There was no evidence for cutaneous inflammation after a 4 hour occluded contact with MBTH in rabbits, although following 24 hour occlusive contact in the acute percutaneous toxicity study there was erythema, edema, desquamation and, in a few animals, local necrosis. Ocular studies in rabbits indicated that, depending on the degree of contamination, MBTH produced mild to moderate eye irritation. In keeping with its low vapor pressure, there were no adverse effects from a 6 hour exposure of rats to an atmosphere saturated with any vapor produced from solid MBTH at ambient temperature. MBTH was positive in an Ames bacterial mutagenicity assay, particularly in the absence of metabolic activation. These studies indicate MBTH to be of moderately high acute peroral toxicity, of moderate percutaneous toxicity, a mild primary skin irritant, a mild to moderate eye irritant, and produced mutations in Salmonella. There is a need for skin and eye protection, and avoidance of swallowing, when handling MBTH.