German agricultural officials lifted a sales ban Monday for 3,050 of the farms closed after livestock feed was tainted with dioxin and met with feed producers to find the source of the contamination.

What are dioxins?

Dioxins are a family of toxic chemicals that are released into the air when organic substances — especially plastics, fuels and chemically treated wood — are burned. Incineration of municipal and medical waste is the biggest source in Canada. Some industrial processes such as smelting and the manufacture of some herbicides and pesticides also produce dioxins. Some dioxins are produced naturally from forest fires and volcanic eruptions.

More than 90 per cent of human exposure to dioxins is through food, mainly meat and dairy products, fish and shellfish.

Dioxins have been linked to some cancers. They can also cause health problems affecting the:

  • Liver.
  • Immune system.
  • Endocrine system.
  • Reproductive functions.
  • Development of the nervous system.

They may also cause the skin condition chloracne — the severe form of acne that affected Ukrainian presidential candidate Viktor Yushchenko in 2004 after he was poisoned with dioxin.

Dioxins accumulate in the tissues of living things and don't easily break down. Because of that, they're considered persistent organic pollutants.

"The situation has eased ... but there can't be an all-clear yet," Agriculture Ministry spokesman Holger Eichele said, adding that 1,635 farms were still closed.

Almost 500 dairy farms were also again being allowed to sell their products, and Slovakia has lifted a ban on German farm products, Eichele said.

The scandal broke last week when German investigators found excessive levels of dioxin in eggs and a few samples of chicken meat. As a precaution, authorities froze sales of poultry, pork and eggs from more than 4,700 farms.

South Korea then banned the sale of some German farm products, and supermarkets in Britain stopped selling quiches and cakes made with German eggs.

Dioxins are contaminants that often result from industrial combustion, and exposure to them at high levels is linked to an increased incidence of cancer.

Investigators are probing the German firm Harles & Jentzsch GmbH, which had produced fat used in the tainted feed pellets. Samples of the fat contained more than 70 times the approved amount of dioxin, according to tests published Saturday by the Schleswig-Holstein state agriculture ministry.

Consumer protection pressure group Foodwatch said Monday that its own tests of a contaminated sample found dioxin 164 times over the legally tolerated level.

It concluded that the dioxin must result from pesticide use on crops that were later used to produce the fat and urged the government to force livestock feed producers to check all their ingredients for excessive dioxin levels.

Eichele declined to comment on Foodwatch's report, saying that federal and state authorities were currently examining the origin of the dioxin.

On Sunday, Agriculture Minister Isle Aigner promised tough legal action against those responsible for contaminating the livestock feed.

"The judiciary has to clamp down hard here," she told the newspaper Bild am Sonntag.