They are persistent environmental pollutants (POPs) and tend to accumulate in biota. Dioxin-like compounds such as polychorinated biphenyls (PCBs) and polychlorinated dibenzofurans (PCDFs) show similar properties. This group of chemicals, also known as polyhalogenated aromatic hydrocarbons (PHAHs), display a wide variety of toxic effects in mammals, birds, and fish. Among the toxic effects observed as a result of exposure to PHAHs are immunotoxicity, carcinogenicity, metabolic changes, and even death.

New EU-wide legislation implemented in July 2002, set limit values for dioxins and dioxin-like materials in feed and foodstuffs with the aim of reducing dioxins intake to European populations. Stakeholders at all levels of the food chains have an obligation to make sure that materials going into the food supply - from farm to fork - do not exceed these limits. Materials not meeting these limits are not allowed to be used or are classified as unfit for human consumption. Traditional analytical techniques for dioxins are too expensive and time consuming for food and feed screening. BioDetection Systems' Chemically Activated Luciferase Expression or CALUX?1/SUP> reporter gene bioassay offers a practical technology for monitoring compliance with the new limit values.

    These highly toxic materials are very potent and believed to have significant toxicological effect at very low doses. The units of exposure are usually measured in picogrammes (pg) per kilogramme bodyweight. One picogramme or "pg" is one millionth of one millionth of a gramme or 0.0000000000001 grammes.

A human Tolerable Monthly Intake (TMI) of 70 pg/kg bodyweight/month was established by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) at its fifty-seventh meeting (Rome, 5-14 June 2001) and which builds on the Tolerable Daily Intake (TDI) of 1-4 pg WHO-TEQ/kg body weight, established by the World Health Organisation (WHO) Consultation in 1998.

On 30 May 2001, the Scientific Committee on Food (SCF) of the European Union (EU) adopted an opinion on the Risk Assessment of dioxins and dioxin-like PCBs in food. The SCF established a group Tolerable Weekly Intake (TWI) for dioxins and dioxin-like PCBs of 14 pg Toxic Equivalent (WHO-TEQ) /kg bodyweight which is in line with the JECFA TMI described above.

For these recommended levels, the current dietary exposure to dioxins and dioxin-like PCBs exceeds the Tolerable Weekly Intake (TWI) or the Tolerable Daily Intake (TDI) for a considerable part of the European population.

To respond to this position, the EU has identified a "pressing need" for further action to avoid adverse health effects from dioxins and PCBs, including the reasons that bioaccumulation is continuing along the trophic chain and that the toxicological properties of dioxins and PCBs have previously been underestimated. In order to fulfil this need, the EU has developed a Community Strategy to reduce exposure to these materials and secure better protection of human health and the environment.

The objectives of the EU strategy are to assess the current state of the environment and the ecosystem including the food chains, to reduce human exposure to dioxins and PCBs in the short term, to maintain human exposure at safe levels in the medium to long terms and to reduce environmental effects from dioxins and PCBs.

A key cornerstone of this strategy will be the imminent setting of limit values for dioxins in feedstuffs and foodstuffs. In the initial phase, it currently appears as though the dioxin-like PCBs will not be included as it is thought that not enough is known about the extent of PCBs contamination in the food chains. However, this approach is inconsistent with the JECFA/WHO established tolerable intakes and the toxicological evidence 

available, both of which include the dioxin-like PCBs. The interim solution is to set limits based on the PCDDs and PCDFs (polychlorinated dibenzodioxins and dibenzofurans) only, with a view to including the dioxin-like PCBs no later than the end of 2004 and maybe substantially earlier.

Tables of the proposed limit values for the various feedstuffs and foodstuffs can be found at the EU's Euro-Lex website.

Monitoring compliance with feedstuffs and foodstuffs limit values will entail the undertaking of a large number of analyses.