Any talk about the introduction of waste incineration here quickly comes around to the subject of dioxins. Thermal waste plants release these highly toxic chemicals, and public fears of the health implications have stymied Government efforts to get municipal incineration up and running.
The BSE crisis has brought the issue to a head, however, with the possibility that the State may have to dispose of 750,000 cattle. Burial would be an unlikely option given the volume of material but also because of strong opposition. A BSE-infected carcass buried near water schemes outside Loughrea, Co Galway, was dug up by concerned local people late last year and dumped at its farm of origin. Exporting carcasses for treatment abroad would also be difficult given that other EU states will be dealing with their own culled animals. Incineration at home is increasingly seen as the only option, but this again brings us back to dioxins.
The term dioxin is used to describe a family of several hundred related chemicals that share both structure and biological effects. They contain varying combinations of chlorine and carbon groups linked by oxygen atoms and all are toxic to some degree. Most toxic of all and the compound that gives its name to the group is 2,3,7,8tetrachlorodibenzo-p-dioxin.
While some dioxins arise naturally from volcanoes and forest fires most are the by-products of human activity. They are formed by incineration, by burning fuels including wood, coal and oil and by certain chemical manufacturing and processing. They can be released in air or water and eventually find their way into the food chain.
Their high level of toxicity is unfortunately matched by an extreme persistence that allows them to survive in the environment for long periods.
Dioxins released decades ago are still causing dioxin exposure to humans today. Even if all incineration and fuel burning stopped the dioxin risk would remain for years to come.
This is why governments around the world are attempting to reduce the output of dioxins. The level of dioxins in the environment has fallen over the past 30 years due to tougher regulations and better technology. Modern incinerators fitted with "scrubbers" can clear most but not all of any dioxin released, but the chemicals are still released by burning fuels and manufacturing.
The chemicals' high toxicity means that even low levels pose a health risk. They are known carcinogens and may cause other health effects such as reduced fertility, impaired development in infants and possible organ damage, according to the US Environmental Protection Agency.
Because dioxins are so widespread in the environment from man-made and natural sources, all of us carry some level of dioxins in our bodies.
Most of the dioxins we encounter, about 95 per cent, are delivered via our food. After release the chemicals remain bio-available for long periods and are gradually taken up by fish and organisms.
As the chemical moves higher up the food chain it concentrates, building up in fatty tissues.
Most of what we absorb comes from eating animal fats in meat and dairy products. Fish can also contain high amounts. This does not mean the foods we eat are dangerous, but it does make avoiding dioxins in the diet very difficult.
More tomorrow