One of the most toxic and persistent substances known, dioxin is measured and regulated in picograms. A picogram is 10-12 g. In 1999, the World Health Organization has estimated that the maximum daily intake should not exceed 1 to 4 picograms toxicity equivalents (pgTEQ) per kilogram of body weight. However, there is no such thing as a "safe" dose of dioxin because the chemical accumulates in the body, increasing the risk of cancer and reproductive and nervous system disorders over time. While no health experts expect any immediate toxic reaction, it is not known at what accumulated level any individual might be harmed.
In 1998, the USA, Canada and other countries in western and eastern Europe signed an agreement under the UN Economic Commission for Europe that will result in controls on major sources of dioxins throughout the region.
Her Majesty's Inspectorate of Pollution in the UK has pledged that all waste incineration plants not complying with dioxin safety limits are by December 1996 will be closed down. This threatens the Government's hopes that incineration could provide the answer to the UK's waste disposal problems.
Developing countries have generally done little or nothing to address dioxin releases. One of the most important benefits of an international agreement on persistent organic pollutants is the degree to which it will advance further understanding and action among these countries about the nature and extent of their dioxin problem. Because developed countries have acted, both individually and collectively, the treaty's controls for dioxin must be able to be met by all countries, not just those of the developed world. This is essential if the agreement is both to have broad participation and produce progress in all regions of the world. A critical starting point will be the development of dioxin inventories.
Even more important than add-on technology, which is expensive, the key to preventing dioxin formation is good combustion. This applies whether the source is a highly sophisticated municipal waste combustor or simpler applications including open burning of refuse. In the latter case, there are a number of low-cost, practical techniques available to improve combustion. These range from providing additional combustion air to the process to source separation that removes non- and poorly combustible materials.
The role of chlorine, particularly chlorinated plastics (e.g. PVC) in dioxin formation is not well understood. We know that, beyond a certain point, excess chlorine has no effect on dioxin evolution and that waste streams often contain ample chlorine in the form of salt and other chlorine containing materials. Some data suggest that added PVC increases dioxin, others that there is no detectable change.
Maximum dioxin levels must be set for animal feed as well as food for human consumption.
In closing their borders to Belgian food products in 1999, countries around the world displayed a vigilance that had been growing year by year as dioxin's potency and potential health effects became appreciated.