The toxic chemical dioxin has been found on a ninth farm Germany, authorities have confirmed.

The discovery marks the ninth in the space of four months, all within the north-west region of the country.

The poisonous chemical was found during routine checks at a large poultry unit near Aurich.

Eggs from the farm have been recalled and the farm is now under quarantine pending an investigation into the source of contamination.

Dioxins are a group of chemicals commonly formed as by-products from chemical processes such as waste incineration. They can have adverse effects on humans if they consumed at high levels over long periods of time

Tighter safety regulations and feed checks have been in place throughout the country, following a dioxin health scare last year.

More than 5,000 farms were temporarily shut down after German feed company Harles and jentzsch was found to have produced feed contaminated with high levels of dioxin.

The contamination was caused by a fat by-product of biofuel manufacture.

But investigators ruled out this as a possible source of transmission in this year’s case. Instead, they believe the series of outbreaks has been caused by hens roaming on fields that have been contaminated with construction materials.