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LC50

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LD50

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Definition

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An LC_Lo value is the lowest concentration of a material in air reported to have caused the death of animals or humans. The exposure may be acute or chronic. This is also called the lowest concentration causing death, lowest detected lethal concentration, and lethal concentration low.

LC_Lo is closely related to the LC₅₀ value which is the concentration which kills half of the test animals under controlled conditions.

This value applies to vapors, dusts, mists and gases. Solids and liquids use the closely related LD_Lo value for routes other than inhalation.

Additional Info

Both LC₅₀ and LD₅₀ 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 conclusively linked to a single human death even at very high levels of acute (short term) exposure. 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 LC_Lo values are parts per million (ppm) of material in air, micrograms (10^-6 = 0.000001 g) per liter of air and milligrams (10^-3 = 0.001 g) per cubic meter of air (see volume units and mass units).

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 LC_Lo dose of a hazardous chemical -- by definition, there is a resonable chance of dying!

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 has a PC-based and Acute-to-Chronic Estimation (ACE) model and Web-based Interspecies Correlation Estimation model for risk assessment.
• UCI Toxic Gas Fact Sheet and Standard Operating Procedures (Word download) UC Irvine.
• Compressed Gas: Toxic and Hazardous Gas Classifications at UC San Diego.
• Comparing LD₅₀/LC₅₀ Machine Learning Models for Multiple Species from ACS Chem. Health Saf. 2023.
• Measures of Toxicity at SUNY Stony Brook.
• List of highly toxic gases at Wikipedia.
• Try your hand at Toxic Trivia here at ILPI.

See also: LD₅₀, mus (mouse), PEL, STEL, TLV.

Additional definitions from Google and OneLook.