highly toxic

Chemical substance that has (1) an orally-administered median lethal dose (lethal dose 50 or LD50) of 50 milligrams (or less) per kilogram of body weight of albino rats, each weighing between 200 and 300 grams; or (2) LD50 of 200 milligrams (or less) per kilogram of body weight when administered by continuous bare skin contact for 24 hours (or less if death occurs within 24 hours) to albino rabbits, each weighing between two and three kilograms; or (3) a median lethal concentration (lethal concentration 50 or LC50) in air of 200 parts per million by volume (or less) of gas or vapor, or two-milligrams per liter or less of dust, fume, or mist, when administered by continuous inhalation for one-hour (or less if death occurs within one-hour) to albino rats, each weighing between 200 and 300 grams.