According to OSHA 29 CFR 1910.1200 App A, toxic is a chemical which falls in any of these three categories: (a) A chemical that has a median lethal dose (LD50) of more than 50 milligramsper kilogram but not more than 500 milligrams per kilogram of body weight when administered orally to albino rats weighing between 200 and 300 gramseach. (b) A chemical that has a median lethal dose (LD50) of more than 200 milligrams per kilogram but not more than 1,000 milligrams per kilogram of body weight when administered by continuous contact for 24 hours (or less if death occurs within 24 hours) with the bare skin of albino rabbits weighing between two and three kilograms each. (c) A chemical that has a median lethal concentration (LC50) in air of more than 200 parts per million but not more than 2,000 parts per million by volume of gas or vapor, or more than two milligrams per liter but not more than 20 milligrams per liter of mist, fume, or dust, when administered by continuousinhalation for one hour (or less if death occurs within one hour) to albino rats weighing between 200 and 300 grams each. Highly toxic is defined by OSHA as: (a) A chemical that has a median lethal dose (LD50) of 50 milligrams or less per kilogram of body weight when administered orally to albino rats weighing between 200 and 300 grams each. (b) A chemical that has a median lethal dose (LD50) of 200 milligrams or less per kilogram of body weight when administered by continuous contact for 24 hours (or less if death occurs within 24 hours) with the bare skin of albino rabbits weighing between two and three kilograms each. (c) A chemical that has a median lethal concentration (LC50) in air of 200 parts per million by volume or less of gas or vapor, or 2 milligrams per liter or less of mist, fume, or dust, when administered by continuous inhalation for one hour (or less if death occurs within one hour) to albino rats weighing between 200 and 300 grams each. Toxicology is the study of the nature, effects, detection, and mitigation of poisons and the treatment or prevention of poisoning. A toxicant is a toxic or poisonous substance. Toxicants may be chemical or physical in nature. Examples include arsenic, benzene, and radiation. A toxin is a highly toxic protein produced by certain plants, animals or pathogenic bacteria. Examples include snake venom and anthrax. All toxins are toxicants, but only those toxicants produced by living organisms are toxins. Substances that are toxic only to specific types of cells or organs are called cytotoxins. MSDS Relevance: MSDS's are required to list is a material is toxic as well as the health effects that can result from exposure. Treat all toxic materials with great respect, especially those that are classified as highly toxic. Avoid their use whenever possible, but if you do you use them take responsible measures to limit their use and minimize hazards. Always wear appropriate personal protective equipment (PPE) such as gloves and respirators and utilize engineering controls such as fume hoods. See also: Antidote, ATSDR, EPCRA, Hazardous, Poison