EXECUTIVE SUMMARY Assessment of the health risk of dioxins: re-evaluation of the Tolerable Daily Intake (TDI)

INTRODUCTION Polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) constitute a group of persistent environmental chemicals. A number of dioxin or furan congeners, as well as some co-planar PCBs have been shown to exert a number of toxic responses similar to those of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most toxic dioxin. These effects include dermal toxicity, immunotoxicity, reproductive effects and teratogenicity, endocrine disruption and carcinogenicity. During the last years the WHO European Centre for Environment and Health (WHO-ECEH) has been coordinating a comprehensive programme in collaboration with the International Programme on Chemical Safety (IPCS) on PCDDs, PCDFs and PCBs, aiming at evaluating the possible health risk, and prevention and control of environmental exposure of the general population to these chemicals. Several WHO meetings in the field of the health risk assessment of dioxins and related compounds have been convened. At a meeting held in Bilthoven, The Netherlands (December 1990), a tolerable daily intake (TDI) of 10 pg/kg b.w. for TCDD was established. Since then new toxicological, epidemiological and mechanistic data have emerged, in particular with respect to neurodevelopmental, reproductive and endocrine effects. Therefore, WHO-ECEH and IPCS jointly organized a consultation on the Assessment of the health risk of dioxins: re-evaluation of the Tolerable Daily Intake (TDI). As a basis for the discussion during the Consultation, working papers were prepared in advance of the meeting on: the health risks for infants, cancer and non-cancer endpoints in humans and animals, mechanistic aspects, toxicokinetics, modeling, exposure, the applicability of the TEQ concept, and risk assessment approaches for dioxins in various countries. The meeting was opened by Dr R.van Leeuwen (WHO-ECEH) who welcomed the participants and presented the objective of this joint ECEH/IPCS meeting: the health risk assessment of dioxins considering both classical risk assessment methodologies and probabilistic risk assessment approaches, with a view to establishing a TDI for dioxins. He stressed the importance of a thorough, scientific evaluation of all available data and underlined the need for transparency in the derivation of a TDI. Dr M. Mercier (Director IPCS) welcomed the participants to WHO Headquarters and expressed his appreciation for the close collaboration between WHO-ECEH and IPCS in this matter. He noted that the risk assessment of dioxins is a global effort rather than just a European endeavour, as could also be seen from the geographical 3 representation of the experts, and he expressed his confidence in the scientific expertise of the participants …