Dioxin is one of the most toxic substances known to man: 10 milligrams alone is a fatal dosage. Such high concentrations of dioxin are, thankfully, seldom. Even though the product we know is an  extremely diluted by-product, lower concentrations of dioxin can still be dangerous.  The first symptoms of dioxin poisoning  only become noticeable after a few weeks. In humans this can cause skin rashes (chloracne) and neurological complaints, such as lethargy or depression. Weight loss is another symptom.  In particular, the thyroid and the liver can be affected. Dioxin also influences genetic material, which can lead to cancer and reduced fertility, amongst others.
In certain cases, dioxin contamination in animal fodder has caused high mortality in chickens. In Belgium, the far too tardy reaction to this problem resulted in the dismissal of 2 responsible Ministers and withdrawal of all meat and poultry products from the market.
The source of dioxin contamination may be found both at home and abroad. Dioxin finds its way into human´s  food via fall-out in the meadows which is emitted by refuse incinerators and via imported animal fodder that is fed to animals in factory farming. Human bodies absorb it via meat, milk and eggs and pass it on through breastfeeding.
Dioxin returns to the environment via animal excretions.
According to Molecular Nutrition and Food Research, the highest risk of contamination is run by people who themselves keep chickens on a small scale, and eat their eggs, or by regular clients of small industries. 'If the norms for intake are not made more flexible, more large regions in Western Europe will become too contaminated  to allow for permanent free range  chickens`, says Hoogenboom, researcher at the Dutch research center Wageningen University (WUR).

Earlier contaminations

In  the Seventies and Eighties, dioxin gained notoriety in the form of air pollution. It is emitted through  incineration of certain synthetics (PCBs), in particular refuse incineration. In The Netherlands, the resulting fall-out lands mostly in the meadows and is subsequently  absorbed by the  grazing livestock. Normal incineration does not break down dioxin. This is one explanation for the presence of dioxin in such high concentrations on the Diemerzeedijk, in The Netherlands. Another explanation - and there is probably some truth in both of them - is the Dutch pharmaceutical concern Philips/Duphar, which produced weed killers in a nearby factory in the period 1955 - 1963. In another dump used by this concern, leaking containers were dug up in 1980, which appeared to contain high concentrations of dioxin. 
Dioxin is probably best known from the Italian Seveso disaster in 1976. But that was only one in a series of scandals involving dioxin, which occurred throughout the world at that time. Other incidents were:
In April 1998, The Belgian Minister of Agriculture temporarily prohibited the use of citric pulp in animal fodder after high concentrations of dioxin had been found in it in Germany. In April 1999, residual oil mixed with animal fodder was found to be the actual source.
An independent French environmental bureau (CNIID) raised alarm about unacceptably high concentrations of the cancerous matter dioxin in beef and veal. (source: the Dutch Newspaper Telegraaf, 26 May 1998). France has a total of 300 refuse incinerators, the highest number  of all EU member states.
The CNIID urged the French Government to close the active refuse incinerators. Three refuse incinerators in Northern France were closed in February, following a far too high emission of dioxin. The milk yielded on nearby dairy farms was declared unfit for consumption. Sale of beef and veal in this region, was, however, not stopped.