The following HTML text is provided to enhance online
readability. Many aspects of typography translate only awkwardly to HTML.
Please use the page image
as the authoritative form to ensure accuracy.
Environmental Medicine: Integrating a Missing Element into Medical Education
(2) Would you consider the patient described in the case study at increased risk from dioxin exposure? Explain.
❑ Dioxins and furans accumulate in adipose tissue.
❑ In animals, the major routes of absorbed TCDD elimination are through lactation and excretion of urine and bile.
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.
Items in cart [0]
