Medical Correspondent Dr Muiris Houstonexplains why dioxins in food are a source of concern when it comes to human health
What are dioxins?
They are a group of chlorinated chemicals formed naturally by forest fires and also by industrial processes such as waste incineration.
Some polychlorinated biphenyls (PCBs) are classified as dioxin-like and are also toxic. Although now banned, PCBs were manufactured for almost 50 years for use as insulating fluids in electrical transformers.
The most toxic dioxin is tetrachlorodibenzo-p-dioxin or TCDD.
Why are dioxins toxic?
The main reason is their ability to remain in the body fat of humans and animals for a long time.
Most chemicals are broken down by the liver and kidneys and are excreted quite rapidly; however, the dioxins have half-lives that vary from 3.7 years to 50 years. A half-life is the time it takes one half of the dose of a substance to leave the body.
In what way do they affect humans?
There are two ways that dioxins are harmful to humans: following an acute exposure to high levels of the chemical such as happened in Seveso, Italy in 1976; and the more subtle effects of chronic exposure, which because of dioxins' long half-life, means the toxic chemical can build up slowly in our fat tissue.
What are the effects of an acute exposure to dioxins?
The most striking effect of a large acute exposure is the development of skin lesions called chloracne. The Ukrainian politician Victor Yuschenko developed these disfiguring facial lesions after he was poisoned with dioxin some years ago.
The chemical cloud that released several kilograms of TCDD into the densely populated area of Seveso, north of Milan in 1976 also caused chloracne in some local residents.
A 25-year follow-up study of almost 300,000 residents in the area confirmed a link between high dioxin exposure and certain cancers, such as Hodgkin's lymphoma. This major study also suggested a link between dioxin and chronic obstructive lung disease and also with the development of diabetes in women.
How might a low-grade chronic exposure to contaminated pork products affect my health?
At a practical level, the risk to the health of any individual who has consumed dioxin contaminated pork products is very low.
But there is a theoretical risk, which is why the public health authorities made the decision to remove all of these products from supermarkets and shops.
After dioxins have been absorbed into the body from the small intestine, they are distributed via blood around the body. But the chemicals have a natural affinity for fatty tissue, where, because of their long half-life, they accumulate. Continual exposure from contaminated food could lead in the long term to a high total amount of dioxin in the body.
This body burden of dioxin is unlikely to be added to significantly by a few exposures that exceeded the accepted dietary limit by a hundred fold.
Dioxins' effects on health are more closely related to the concentration built up in fat tissue than to the daily doses of the chemical. Research has shown a link between dioxin exposure and an increased risk of liver cancer and some blood system cancers. There is also a theoretical risk to children exposed to dioxin in their mother's womb. Reports have linked dioxin to thyroid problems and possible learning difficulties. Dioxin exposure has also been linked to damage to the immune and neurological systems.
Do I need to see my doctor if I think I have consumed contaminated pork products?
No. There is no need to attend your GP or go to the emergency department of your local hospital. No treatment is required for the small exposures involved. Nor is there a need to have blood tests or other medical investigations carried out.