Dioxins enter the body by ingestion, inhalation, and dermal absorption. In humans, the following percentages of total absorption have been reported for various exposure routes: inhalation, 25% to 29%; ingestion of contaminated soil, 20% to 26%; and ingestion of contaminated fish, 50% to 80%. Skin was found to absorb up to 3% of the dioxin in contaminated soil.

The metabolic pathway of TCDD for humans has not been established. TCDD orally administered to animals is metabolized relatively slowly, but once metabolites are formed, they are rapidly excreted in the urine and bile. Metabolism is primarily by hepatic detoxification, with the major metabolites consisting of hydroxylated or methoxylated TCDD derivatives, which are then excreted as glucuronide and sulfate conjugates. Unabsorbed TCDD is excreted through direct elimination in the feces. Because of the lipophilic nature of milk, nursing females decrease their body burden of TCDD through lactation. Dioxins distribute to organs according to lipid content and readily accumulate in body fat. In the general population, the background level of TCDD in adipose tissue may be as high as 20 ppt.

The half-life of TCDD ranges from several hours (on the surface of plants) to 7.1 years (in human serum and adipose tissue). On the soil’s surface, where TCDD undergoes photodegradation when exposed to ultraviolet light, the half-life is 1 to 3 years. Beneath the soil’s surface, the half-life of TCDD can be over 10 years.