German authorities said on Friday the highly-poisonous chemical dioxin had been found above permitted levels in eggs from two more German farms following its discovery in eggs from three other farms in early April.

Dioxin has been discovered on two poultry farms in the northern German state of Lower Saxony, the state Agriculture ministry said in a statement.

The two farms have been sealed off and the eggs they produced recalled, the ministry said. The source of the contamination was unknown and being investigated.

It cannot be ruled out that eggs with high dioxin content have been sold for consumption but the eggs presented no immediate threat to health, the state ministry said.

Dioxin was also discovered in three farms in the central German state of North Rhine Westphalia in early April. The source of the North Rhine Westphalia contamination is still unknown.

In January 2011, an EU-wide health alert started when German officials said animal feed tainted with 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.

Dioxin presents a danger to health if consumed over long periods but small doses are not harmful.