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Definition

An LD₅₀ or 50% Lethal Dose value is the amount of a solid or liquid material that it takes to kill 50% of test animals (for example, mice or rats) in one dose. It is also called the median lethal dose.

This is closely related to the LD_Lo value which is the lowest dosage reported to have killed animals or humans.

LC₅₀ (50% lethal concentration) is a related term used for gases, dusts, vapors, mists etc.

Additional Info

The dose may be administered orally (by mouth), injection into various parts of the body (intraperitoneally or intravenously), or dermally (application to the skin). The value is usually reported along with the administration method.

Both LD₅₀ and LD_Lo values state the animal used in the test. This is important because animal toxicity studies do not necessarily extrapolate (extend) to humans. For example, dioxins (of Love Canal, Times Beach, Sveso and Agent Orange fame) are highly toxic to guinea pigs and ducklings at extremely low levels, but have never been unambiguously linked to a single human death even at very high levels of acute (short term) exposure; note, however they are listed by IARC as "known human carcinogens". However, it is best to err on the safe side when evaluating animal toxicity studies and assume that most chemicals that are toxic to animals are toxic to humans.

Typical units for LD₅₀ values are milligrams or grams of material per kilogram of body weight (mg/kg or g/kg, recall that 1 kg = 2.2 pounds).

SDS Relevance

LC₅₀ and LD₅₀ values, if known, will be found on Section 11 (toxicological information) of a material's Safety Data Sheet. However, the Hazard Communication Standard does not require any testing when an SDS is created, so just because this data is missing or "not known" does not mean that the material is "safe". If no toxicity information is available, treat the material as potentially hazardous!

Never be exposed to an LD₅₀ dose of a hazardous chemical -- by definition, there is a 50% chance this will kill you…and if you survive you're not going to be in good shape.

Of greater practical use than LC₅₀ and LD₅₀ is the OSHA permissible exposure level (PEL) (if the material has one). This is a more realistic determination of the maximum safe exposure to a material and is usually based on the known effects of the chemical on humans rather than laboratory animals.

Further Reading

• The U.S. EPA's Ag 101 entry on LD50.
• The Canadian Centre for Occupational Health and Safety's What is an LD50 and LC50 is quite readable.
• A Review of the LD50 and Its Current Role in Hazard Communication from ACS Chem. Health Saf. 2021, 28(1), 25-33 (institutional access required).
• Comparing LD₅₀/LC₅₀ Machine Learning Models for Multiple Species from ACS Chem. Health Saf. 2023.
• The National Institutes of Health's Intragency Research Animal Committee's 1993 Recommendation on LD50 testing (36kB PDF file) was to replace the classical LD₅₀ method involving ~100 animals with a modified approach.
• Acute oral toxicity, a research article in Environ Health Perspect. 1998 April; 106(Suppl 2): 497-503.
• Visit the Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM) for the development, review, and validation of alternative toxicological testing methods.
• Try your hand at Toxic Trivia here at ILPI.

See also: intraperitoneal, intravenous, LC₅₀, mus (mouse), PEL, STEL, TLV.

Additional definitions from Google and OneLook.

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Disclaimer: The information contained herein is believed to be true and accurate, however ILPI makes no guarantees concerning the veracity of any statement. Use of any information on this page is at the reader's own risk. ILPI strongly encourages the reader to consult the appropriate local, state and federal agencies concerning the matters discussed herein.