Dioxins explained
January 5, 2011
Dioxins are chemical compounds that contain carbon, hydrogen, oxygen and chlorine. They are by-products of chemical reactions, such as waste burning and the manufacture of steel, paint and gasoline. Dioxins also come from natural occurrences, including volcanic eruptions and forest fires. There are about 200 different dioxins, which have no smell or color. Seventeen of them raise concerns from the toxicologist's point of view.
Dioxins have no real use. "Dioxins are not produced with the aim of being used by people. Dioxins are by-products of burning processes and the downside is that some of them are toxic, which is to say, poisonous," said Helmut Schafft of the German Institute for Risk Assessment, a government consumer protection body. Dioxins also are extremely tenacious: They do not dissolve in water, are not biodegradable, and accumulate in fatty substances.
Farm animals in particular take in dioxins through their feed. The animals absorb dioxins in their body fat or excrete the substances through their eggs or milk. Food intake, said Schafft, is the biggest "dioxin donor" for human beings. Some 95 percent of the dioxins in our bodies come from the consumption of fish, meat and milk products. In contrast, dioxin intake through breathing the air is relatively low.
Once dioxins are in the body, they accumulate in body fat. The most toxic dioxin, called 2,3,7,8-TCDD, is present in the body for around seven years before it's fully eliminated. One less toxic, though durable, type of dioxin, called 2,3,4,7,8-pentachlorodibenzofuran, requires 20 years to be eliminated by half.
Dangers of dioxin poisoning
How the substance affects the human body depends on various factors, including the person's age and weight and what type of dioxin he or she has been exposed to. Some dioxins are extremely toxic even in small quantities. But normally the effect to humans is only noticeable when there's been a high level of exposure.
Scientists have studied the long-term effects of exposure in animals. "It can disrupt the reproductive system, the immune system, the nervous system and even the hormonal system," said Schafft. He stressed that some dioxins are also carcinogenic.
In addition to liver damage, metabolic disorders and skin irritation, dioxin exposure can cause a massive weight loss condition known as "wasting syndrome."
The World Health Organization classified 2,3,7,8-TCDD as a cancer-causing substance in 1991. Other types of dioxins are suspected of being carcinogenic as well.
No ban in sight
In spite of the hazards of dioxins, the substances cannot be banned. "For, dioxins always result wherever burning, combustion or large heating processes take place," Schafft said. "They are secondary products that unintentionally come about and end up in the environment."
People in industrialized regions especially, such as central Europe, simply have to deal with the pervasive environmental impact of dioxins, he added. "We toxicologists call it the background damage."
The ongoing scandal in Germany about livestock feed has revived discussion about dioxins. But even Schafft cannot account for how dioxins got into animal feed, which is normally plant-based. "The appropriate authorities in the respective German states are feverishly investigating the question," he said of the current state of affairs.
Author: Hannah Fuchs (srs)
Editor: Nancy Isenson