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An LDLo 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.
LDLo is closely related to the LD50 value which is the dosage which kills half of the test animals under controlled conditions.
LCLo (lowest lethal concentration) is a related term used for gases, dusts, vapors, mists etc.
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 LDLo 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 LDLo values are milligrams or grams of material per kilogram of body weight (mg/kg or g/kg, recall that 1 kg = 2.2 pounds).
Never be exposed to an LDLo 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.
See also: intraperitoneal, intravenous, LC50, mus (mouse), PEL, STEL, TLV.
Additional definitions from Google and OneLook.