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LD50

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Definition

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An LD_Lo or Lowest Lethal Dose value is the lowest amount of a solid or liquid material reported to have caused the death of animals or humans. The exposure may be acute or chronic. This is also called the lowest dosage causing death, lowest detected lethal dose, and lethal dose low.

LD_Lo is closely related to the LD₅₀ value which is the dosage which kills half of the test animals under controlled conditions.

LC_Lo (lowest 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 LD_Lo 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

Never be exposed to an LD_Lo dose of a hazardous chemical - by definition, there is a resonable chance of dying!

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!

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

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• What is a LD50 and LC50? at the Canadian Centre for Occupational Health and Safety.
• Visit the Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM) for the development, review, and validation of alternative toxicological testing methods.
• The U.S. EPA's Ag 101 entry on LD50.
• Dose-Response Relationships In Toxicology from Oregon State's EXTOXNET.
• Advances in acute toxicity testing: strengths, weaknesses and regulatory acceptance from Interdiscip Toxicol 2018, 11(1) pp 5-12.
• Alternative Methods for the Median Lethal Dose (LD50) Test: The Up-and-Down Procedure for Acute Oral Toxicity from ILAR Journal 2002, 43(4), pp 233-243.
• Comparing LD₅₀/LC₅₀ Machine Learning Models for Multiple Species from ACS Chem. Health Saf. 2023.
• Acute oral toxicity, a research article in Environ Health Perspect. 1998 April; 106(Suppl 2): 497-503.
• 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.