Biology. Describes the adverse effects resulting from a single exposure to a substance. Additional Info: Human tests for acute toxicity are not performed because of ethical and legal prohibitions. The U.S. Environmental Protection Agency (EPA) describes the following methods for determination of acute toxicity: (1) Animal testing. Animal tests are still used where other laboratory protocols are not available. These tests are combined with other assays (lethality, necroscopy etc.) to minimize the number of animals sacrificed. Evaluation of acute toxicity data should include the relationship, if any, between the exposure of animals to the test substance and the incidence and severity of all abnormalities, including behavioral and clinical abnormalities, the reversibility of observed abnormalities, gross lesions, body weight changes, effects on mortality, and any other toxic effects. (2) Use of data from structurally related substances or mixtures. In order to minimize the need for animal testing for acute effects, the EPA encourages the review of existing acute toxicity information on chemical substances that are structurally related to the agent under investigation. In certain cases it may be possible to obtain enough information to make preliminary hazard evaluations that may reduce the need for further animal testing for acute effects. (3) Chemical properties. For example, if a substance is a strong acid then there is really no need to do skin and eye tests as a corrosive material such as this will obviously cause great harm. (4) In vitro testing (test tube experiments). Animal rights activists advocate such methods whenever possible. While in vitro tools have now become quite powerful, they will never be able to replace completely the need for animal studies, particularly for pharaceutical studies. (5) Limit testing. A single group of animals, typically mice or rats, is given a large dose of the agent. If no lethality is demonstrated, no further testing is pursued and the substance is classified in a hazard category according to the dose used. MSDS Relevance: Acute toxicity helps workers understand the health consequences from a single exposure to a chemical. For example, hydrogen cyanide is a highly toxic substance; acute exposure at relatively low doses can result in death. Acute toxicity differs from chronic toxicity, which describes the adverse health effects from repeated (lower level) exposures to a substance over a longer period (months to years). See: Chronic toxicity, cyanide, LD50, mus (mouse), TLV