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Dioxins - Toxicological Overview

Key Points

Identity

  • Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzo-p-furans ("dioxins") is a term used to refer to a group of 210 compounds with similar chemical structures
  • Most of these compounds pose no health hazard at the levels commonly found but 17 of them are of more toxicological concern
  • The most toxic dioxin is 2,3,7,8-tetrachlorodibenzo-p -dioxin (TCDD)  and most of the available data refer to this compound

Kinetics and metabolism

  • Dioxins are readily absorbed following ingestion and are also likely to be absorbed following inhalation or dermal exposure
  • Once absorbed they are extensively distributed throughout the body, with particular accumulation in the liver and adipose tissue
  • The metabolism of dioxins is extremely slow, with partial excretion in the faeces as metabolites. They are extremely persistent with the elimination half-life of TCDD being 7 to 12 years, therefore there is potential for accumulation in body tissues

Health effects of acute exposure

  • The characteristic adverse effect following a severe acute exposure to dioxins is chloracne, the onset of which may be delayed several months
  • Acute exposure to dioxins may also cause nausea, vomiting, diarrhoea, hepatic damage and neurological effects

Health effects of chronic exposure

  • The adverse effects of chronic exposure to dioxins are similar to those following acute exposure
  • Chronic exposure to dioxins may also cause liver disease, increased risk of developing diabetes, alterations in thyroid function, impaired immune function, cardiovascular disease, mild neuropathies and developmental effects
  • TCDD is classified by IARC as being carcinogenic to humans

 

Dioxins is a term used to describe a group of 210 closely related compounds with similar chemical structures but varying greatly in their toxicity. They comprise 75 polychlorinated dibenzo-p-dioxins and 135 polychlorinated dibenzofurans. TCDD is the most toxic of the dioxins and is the most extensively studied. Most of the data in this document refer to TCDD.

Exposure to dioxins is most likely to be in the form of a mixture of related dioxin compounds with differing potency. Therefore, a system has been devised to consider the toxicity of a given mixture. The system is referred to as the 'toxic equivalent approach' and is based on weighting the individual compounds present in the mixture compared to the most potent compound (TCDD). This approach is recommended by the World Health Organisation (WHO) and has been endorsed by the Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (COT) [2, 3].

Decontamination and First Aid       Summary of Health Effects

Prepared by J C Wakefield
CHAPD HQ, HPA
2008
Version 1

This document will be reviewed not later than 3 years, or sooner if substantive evidence becomes available.