Dioxins and PCBs: your questions answered
Tuesday 16 March 2004
Dioxins have never been produced intentionally. They may be formed as unwanted by-products in a variety of industrial and combustion processes, as well as household fires. Most industrial releases of dioxins are strictly controlled under pollution prevention and control regulations.
PCBs have been used since the early 1930s, mainly in electrical equipment. The manufacture and general use of PCBs stopped in the 1970s and is no longer permitted in the UK. The only PCBs remaining in use in the UK are sealed inside some older electrical equipment. However, use of this equipment must be phased out and the PCBs removed and destroyed under UK regulations.
Dioxins and PCBs from these various sources may be released in small quantities to air, water or land.
Dioxins and PCBs have no immediate effect on health, even at the highest levels found in foods. The potential risks to health come from long-term exposure to high levels. They have been shown to cause a wide range of effects, including cancer and damage to the immune and reproductive systems in certain animals, although it appears that people may be less sensitive.
There is very little scope for removal of dioxins and PCBs from foods once they have entered the food chain. It is generally agreed that the best method of preventing dioxins and PCBs from entering the food chain is to control releases of these chemicals to the environment.
What are the current intakes of dioxins and dioxin-like PCBs from the diet and how do they compare to the Tolerable Daily Intake (TDI)?
The estimated average dietary intake by adults in the UK has fallen from 1.8 picograms WHO-TEQ/kg of bodyweight per day to 0.9 pg WHO-TEQ/kg of bodyweight per day between 1997 and 2001, and by around 85% since 1982. The current TDI recommended by the independent Committee on Toxicity, which took effect in November 2001, is 2 pg WHO-TEQ/kg of bodyweight per day.
In July 2002 limits were set by the European Commission (EC) for dioxins in foods that contribute significantly to the total dietary intake of these chemicals. The limits are as follows: meat (1-3 nanograms WHO-TEQ/kilogram fat basis), liver (6 ng WHO-TEQ/kg fat basis), fish (4 ng WHO-TEQ/kg fresh weight), eggs (3 ng WHO-TEQ/kg fat basis), milk and milk products (3 ng WHO-TEQ/kg fat basis), fats and oils depending on type (0.75-3 ng WHO-TEQ/kg fat basis). The EC has also set lower action levels for dioxins in these foods. If these are exceeded work must be carried out to identify and eliminate the source of contamination. These limits and action levels are to be reviewed by December 2004.
Animals and fish take up dioxins and PCBs present in their food and from any soil or sediment they may also take in during feeding. These compounds are not readily lost by the animal or fish but instead pass into its body fat, where they continue to accumulate.
Foods high in animal fat, such as milk, meat, fish and eggs (and their products) are the main source of dioxins and PCBs in the diet. The levels of dioxins and PCBs in any one individual’s diet will vary depending on the amounts and types of foods they eat.
In October 2002 the Government carried out a consultation on future measures that could be taken to further reduce environmental and human exposure. The Department of Environment, Food and Rural Affairs will be producing an action plan to reduce dioxins in the environment and consumer dietary exposure to these chemicals, taking into account responses from the consultation. DEFRA is currently investigating the cost effectiveness of potential measures to achieve these reductions.
The Agency uses food and animal feed surveys to find out more about what foods make the highest contribution of dioxins and PCBs to the diet and to check that controls are adequate; and it carries out dietary surveys to monitor progress and to identify areas where more work is needed.
The Agency also carries out research to gain a better understanding of how dioxins and PCBs enter the food chain in the first place.
Dioxins and dioxin-like PCBs are chemicals that have similar toxic effects but to different degrees. The use of Toxic Equivalency Factors (TEFs) allows concentrations of the less toxic compounds to be expressed as a concentration equivalent to the most toxic dioxin – 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). These toxicity-weighted concentrations are then summed to give a single value, which is expressed as a Toxic Equivalent (TEQ). The system of TEFs used in the UK and a number of other countries is that set by the World Health Organization (WHO), and the resulting overall concentrations are referred to as WHO-TEQs.