CHEMICAL DANGERS:THE WORLD Health Organisation (WHO) includes dioxins among a group known as the "dirty dozen", chemicals highly likely to cause health effects if consumed and also extremely persistent once released into the environment.
The Food Safety Authority of Ireland describes the chemical pollutants found in some pig meat samples as dioxin-like PCBs. The term dioxin applies to a very large family of chemicals, all of which are organic chemicals that contain forms of chlorine.
The pig meat scare involves the PCB (polychlorinated biphenyls) form of the dioxin family. PCBs can arise from two main sources, actual manufactured PCBs and PCBs arising as a by-product of a number of industrial processes.
PCBs were manufactured for use as coolants and lubricants in large electrical transformers and capacitors, for inclusion in a variety of plastics, including PVC coatings, and in pesticides. These went out of production in the late 1970s however after medical studies showing that these chemicals posed a significant long-term health risk to the general public.
Dioxins, including PCBs, also arise from smelting, chlorine bleaching processes, pesticide manufacture and other processes. These are known sources for these harmful substances and so all are closely monitored to limit the amount of dioxins escaping from manufacturing activities. The single largest source for dioxin build-up in the environment is waste incineration, forest fires and in particular the burning of household waste in fireplaces and outdoors.
The most important characteristic of the chemical is its persistence in the environment once released. It remains bio-available for long periods before breaking down, which means that it can be ingested by animals. It is fat soluble and so it tends to build up in fat tissues, and is passed up the food chain, causing higher and higher levels of dioxin accumulation.
Up to 90 per cent of human exposure comes through the foods we eat, according to the WHO. PCB accumulates readily in dairy products, meat, fish and shellfish.
There is always a low background level of dioxins and PCBs in our diet, and foods are regularly monitored to ensure they do not exceed the recommended limit of 70 million-millionths of a gram per kg of bodyweight per month.