Dioxins: WHO's tolerable daily intake (TDI) revisited

Area of Science:

• Environmental Health
• Toxicology
• Risk Assessment

Background:

• The World Health Organization (WHO) previously set a tolerable daily intake (TDI) for TCDD in 1990.
• New toxicological and epidemiological data, particularly on neurodevelopmental and endocrine effects, necessitated a re-evaluation.
• A WHO consultation convened in May 1998 to reassess health risks and the TDI for dioxins.

Purpose of the Study:

• To re-evaluate the tolerable daily intake (TDI) for dioxins based on updated scientific evidence.
• To assess the health risks of dioxin-like compounds, focusing on sensitive endpoints like hormonal, reproductive, and developmental effects.
• To establish a revised TDI expressed as toxic equivalency (TEQ).

Main Methods:

• Discussion of health risks across various endpoints in humans and animals.
• Consideration of mechanistic aspects, kinetics, modeling, and exposure.
• Focus on sensitive adverse effects (hormonal, reproductive, developmental) from low-dose animal studies.
• Estimation of human daily intakes corresponding to animal effect levels.
• Application of a composite uncertainty factor to derive the TDI.

Main Results:

• Estimated human daily intakes associated with adverse effects in animals ranged from 14-37 pg/kg body weight.
• A composite uncertainty factor of 10 was recommended for deriving the TDI.
• A revised TDI range of 1-4 pg TEQs/kg body weight was established.

Conclusions:

• The re-evaluation led to a significantly lower TDI for dioxins compared to the 1990 guideline.
• The revised TDI accounts for new data on sensitive endpoints and incorporates uncertainty factors.
• The findings provide updated guidance for managing health risks associated with dioxin exposure.