Dioxin content of three to six times permitted levels were discovered by routine tests on a farm in the central German state of North Rhine Westphalia, the state agriculture ministry said.
The eggs of two of the four houses contained up to six times above the limit concentration of dioxin-like PCBs (polychlorinated biphenyls). PCBs can be equalled to dioxin, a spokesman of the ministry said.
The farm holds 25,000 organic hens and supplies supermarkets in the area. The farm has been sealed off and is not permitted to sell more eggs, the state ministry said.
How the dioxin came into the eggs is unclear and intensive investigations are underway, the ministry added. Tests had shown no contamination of animal feed at the farm. Although the levels are above legal thresholds, they are still very low in terms of danger to human health.
In January 2011, an EU-wide health alert was issued when German officials said animal feed tainted with highly poisonous dioxin had been fed to hens and pigs, contaminating eggs, poultry meat and pork at the affected farms.
Germany then introduced a series of new measures including tough restrictions on animal feed ingredients.