Germany’s problem with dioxins in eggs has shown no signs of going away, with news that another farm has tested positive for contamination.

The dioxins were discovered during routine tests on a 1,000-hen free-range farm in the northern state of Lower Saxony, which has since been sealed off and is prohibited from selling eggs while investigations continue.

German officials said they were unable to say at this stage how widely eggs from the farm had been sold, but stressed the eggs presented no immediate danger to human health.

This is the ninth German farm to have hit the news because of dioxin contamination since April.

Investigators are initially testing whether the contamination could have sprung from feed used on the farm, but recent egg contamination cases in Lower Saxony and the neighbouring state of North-Rhine Westphalia have been associated with ground contamination and – in one case – were traced back to a piece of polystyrene which was pecked at by hens.

In January 2011, German eggs hit the news when dioxin-contaminated feed was fed to hens and pigs, prompting wide-ranging recalls.