Toxic equivalency factors (TEFs) for dioxins and dioxin-like compounds
Dioxins occur as a complex mixture in the environment and in food. More than 90% of human exposure is through food, mainly meat and dairy products, fish and shellfish. In order to assess the potential health risk of the whole mixture, the concept of toxic equivalence has been applied to this group of structurally and biologically related contaminants. TCDD, the most toxic member of the family, is used as reference compound, and all other dioxins are assigned a toxic potency relative to TCDD, based on experimental studies. These international TEFs have been developed for application in risk assessment and management, and have been adopted formally for regulatory purposes by a number of countries and regional bodies, including Canada, the European Union, Japan and the United States of America.
During the last 15 years, WHO, through the International Programme on Chemical Safety (IPCS), has established and regularly re-evaluated toxic equivalency factors (TEFs) for dioxins and related compounds through expert consultations. WHO-TEF values have been established in 1998 which apply to humans, mammals, birds and fish. The last consultation was held in 2005 to update human and mammalian TEFs. Details on the process and outcome can be found through the links below.