To better understand how toxic TCDD is, one needs to understand how it and other toxins are measured. In toxicology, the median lethal dose is identified as LD50 (abbreviation for “lethal dose, 50%”). LC50 is the abbreviation of lethal concentration, 50%. These are used to measure the lethal dose of a toxin, radiation, or pathogen. The value of LD50 for a substance is the dose required to kill half the members of a tested population after a specified amount of time. LD50 figures are often used as a general indicator of a substance’s acute toxicity.
For example: The lethal dose of lead (or LD50) for humans is 450 mg/kg of body weight. Using the EPA’s 1997 carcinogenicity benchmark dose of TCDD as 0.0000156 mg/kg of body weight, TCDD would be approximately 28,846,154 times more toxic than lead.