There is considerable public, scientific and regulatory concern over the possible adverse health effects of chronic exposure to trace levels of persistent organic pollutants. The class of compounds made up of the polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF), often collectively known as dioxins, has received widespread attention and attracted a great deal of research, following the accidental release of the most toxic of these (2,3,7,8 TCDD) at Seveso in 1976.
Dioxins, and dioxin-like compounds which may have similar effects, are found in all environmental compartments, are persistent and, being fat soluble, tend to accumulate in higher animals, including humans. Their resistance to degradation and semi-volatility means that they may be transported over long distances and give rise to trans-national exchanges of pollutants. In addition, dioxins released into the environment many years ago continue to contribute to contemporary exposure.
Dioxins have never been intentionally manufactured but can be released into the environment from a number of different sources; including chemicals manufacturing, combustion processes, metallurgical processes, paper and pulp processing. Although there are 210 congeners of PCDD/PCDF, only the 17 which have chlorine substitution in at least all of the 2,3,7,8 positions are of concern, owing to their toxicity, stability and persistence in the environment. In order to simplify the handling of data on the individual compounds, a system of toxic equivalency factors (TEFs) is used to derive an equivalent concentration of the most toxic dioxin (2,3,7,8 TCDD). This enables the toxicity of complex mixtures to be expressed as a single number - the toxic equivalent or TEQ.
Previous studies have shown that the principal route to exposure of the general human population is through ingestion of food which carries trace levels of dioxins. In view of this, experts have derived acceptable or tolerable daily intakes (TDIs), designed to ensure that the human population is not exposed to levels of dioxin that could give rise to adverse effects.
Due to the complexity of studying the effects of trace doses of a mixture of chemicals, there is considerable scientific debate about the acceptable level of exposure to dioxins. There is uncertainty about the mechanism of action of the compounds, in relation to causing a range of physical effects in humans and animals, and the alternative interpretations of the available data have led to significant differences in the recommended tolerable dose - notably between the United States Environmental Protection Agency (US EPA) and the World Health Organisation (WHO). In 1990, a WHO (Europe) review group recommended that a daily intake of not more than 10 pg 2,3,7,8 TCDD /kg body weight would give an acceptable level of protection for human health. Whereas, the US EPA advocated a daily intake of less than 0.006 pg TCDD/kg body weight.
In 1998, the WHO European Centre for Environment and Health (WHO-ECEH) and the International Programme on Chemical Safety (IPCS) convened a group of international experts, in order to perform a health risk assessment of dioxin-like compounds. This was based on the most up-to-date knowledge and information regarding critical effects (including developmental, reproductive, hormonal, immune system and neurobehavioural effects), dose-response relationships and quantitative risk extrapolation. A TDI of 1-4 pg TEQ/kg body weight (including dioxin-like PCBs) was recommended. The US EPA has yet to complete its own reassessment.
Over the past two decades the European Commission has implemented wide ranging legislation aimed at directly or indirectly reducing or controlling the release of dioxins into the environment, with the objective of reducing human exposure and protecting human health. However, the recent WHO re-evaluation of the toxicology of dioxins has suggested that additional measures might be required, at the Community level, to further reduce human exposure to an acceptable level, within an appropriate timescale. However, such action can only be formulated on the basis of a detailed knowledge and understanding of the effectiveness of existing legislation, any continuing risk to human health and ecosystems, and an appreciation of the additional control measures already being implemented by individual Member States.
It is the objective of this study to provide information and recommendations, which will act as a sound basis for the formulation of future policy to reduce exposure to dioxins, in order to further protect the population and ecosystems of the European Union.