Scientific statement on the health-based guidance values for dioxins and dioxin-like PCBs

Different organisations have undertaken risk assessments of dioxins resulting in the issuance of a range of health-based guidance values. This report examines the approaches taken by the Scientific Committee on Food (SCF), the Joint FAO/WHO Expert Committee on Food Additives (JECFA) and the United States Environmental Protection Agency (US EPA) and how these differing approaches impact on the final derivation of a numerical value. SCF and JECFA concluded that the critical studies for derivation of a health-based guidance value (HBGV) were animal studies, whereas the US EPA selected the human data, as their preference is to use human data where available. SCF and JECFA applied a body burden one-compartment kinetics approach to derive a HBGV from rat data, whereas US EPA applied physiologically based pharmacokinetic modelling of blood levels estimated from epidemiology studies. An uncertainty factor of 3 was applied by SCF and JECFA as the lowest-observed-adverse-effect level (LOAEL) was close to the no-observed-adverse-effect level (NOAEL) (observed in another animal study), as opposed to the US EPA applying their default uncertainty factor of 10 for extrapolation from a LOAEL in the absence of a NOAEL. This resulted in the reference dose set by US EPA being 3-fold lower than the tolerable weekly intake (TWI)/provisional tolerable monthly intake (PMTI). In view of the different approaches used in the most recent assessments undertaken by the authorities, it would appear appropriate to undertake a comprehensive risk assessment on the risks for animal and human health related to the presence of dioxins and dioxin-like polychlorinated biphenyls (dl-PCBs) in feed and food.