Dioxins in Eggs

German authorities have blocked meat and eggs sales from some 4,700 farms across the country after it was revealed that chickens and pigs had eaten feed contaminated with dangerous levels of dioxins.

What are dioxins and why are they dangerous?

According to the World Health Organization, dioxins are a group of highly toxic, chemically-related compounds.

Dioxins can occur through natural processes but they are mainly the by-products of industrial processes including smelting, chlorine bleaching of paper pulp and the manufacturing of some herbicides and pesticides.

Dioxins are found throughout the world in the environment. The highest levels of these compounds are found in some soils, sediments and food, especially dairy products, meat, fish and shellfish.

The higher in the animal food chain, the higher the concentration - and danger - of dioxins.

Once dioxins have entered the human body, they endure a long time because of their chemical stability and their ability to be absorbed by fat tissue, where they are then stored.

They can cause reproductive and developmental problems, damage the immune system, interfere with hormones and cause cancer.

How did the dioxins enter the food chain in Germany?

According to the European Union, the incident began when fatty acids meant to be used for industrial processes - from a biodiesel company - were mixed with vegetable feed fat, used to make food for animals.

The contaminated feed was distributed to several farms in Germany, and consumed by pigs and hens whose meat and eggs now have levels of dioxins higher that those allowed under EU law. Most of the affected farms are pig farms in Germany's Lower Saxony region.

Some of the eggs were sent to a processing plant in the Netherlands, and a 14-tonne consignment of pasteurised egg has been sent on to the UK, where it may have entered the food chain.

EU authorities say they were first informed about the incident by Germany on 27 December 2010. But the first message only referred to one consignment - 26 tonnes - of contaminated feed. By 3 January 2011, German officials realised that the contamination was much bigger - a total of nine consignments - delivered to 25 feed manufacturers.

However, the state agriculture ministry in Schleswig-Holstein says the dioxin alert began even earlier. It says the company where the contaminated oils originated - Harles und Jentzsch - carried out a test in March 2010, which revealed that dioxin levels were twice the permitted level. The company is alleged not to have informed the authorities of this.

However, some test results released later by the ministry showed the fat of the feed contained 77 times the approved amount of dioxin.

Why is the rest of Europe worried?

Europe's food production and processing systems are highly integrated, meaning that tracing which food products have been contaminated, and where, can be complex.

Because of this, the EU says that the best way to prevent human exposure is to strictly control industrial processes to limit the formation of dioxins.

The EU has warned that eggs from farms affected by dioxins have entered the UK in processed products destined for human consumption. The eggs had been sent to the Netherlands for processing and then on to the UK in liquid form where, the BBC has learnt, they have been used by two manufacturers of cakes and quiches.

But this isn't the first time there has been a dioxin-related food scare in Europe, is it?

No, there have been several. In Italy, for example, in early 2008, worries about the levels of dioxins in the buffalo milk used to make some mozzarella cheese led Japan and South Korea to cancel orders. There were allegations that waste incineration in the region around Naples might have led to the higher levels of the carcinogens in the cheese.

Later that same year, all pork products made in the Irish Republic were recalled after it was discovered that some pork contained more than 200 times the acceptable level of dioxins. The pigs were thought to have eaten contaminated feed. A few months later, some 7,000 cattle on 10 Northern Ireland farms were culled because because of fears of dioxin contamination.

How dangerous are the levels of dioxins found?

Authorities in Germany are emphasising that they have closed the farms and blocked sales as a precautionary measure and that all meat, poultry and eggs are safe to eat.

The EU has said that although the eggs found on affected farms in Germany had five times the legal limit of the chemical, consumers would have to eat vast quantities of eggs, or processed products made with these eggs, in order for the dioxins to pose a risk to human health.