All You Need To Know About Dioxins
South African Food Review - April 2011
By Susan Featherstone
In December last year, German authorities informed the European Commission's Rapid Alert System for Food and Feed (RASFF) that a batch of fatty acids, produced by a biodiesel company for technical purposes, got mixed with fat for the production of animal feed. Though it contained higher levels of dioxins than allowed for feed by EU law, it was delivered to a feed manufacturing company and used to make compound feeds for poultry and pigs. The high levels of dioxins were picked up in in-house checks by the feed producer.
Investigations showed that 25 different manufacturers of animal feed had received the dioxin-contaminated fat since 12 November 2010 and that the feed was widely distributed, but mainly in Germany. After testing, some 100 000 eggs had to be destroyed, 4 700 farms were closed and banned from selling their products pending the results of product testing. To date, most of these have been cleared. Investigations are ongoing.
Germany's action plan for the future includes new restrictions that ensure that producers do not make fats for industrial uses and for animal feed on the same site. Furthermore, makers of animal feed will be subject to tougher regulations and more frequent inspections, and penalties will be harsher.
Products made with liquid egg from some of the suspect German farms have been quarantined in the United Kingdom, and are subject to further investigation. The UK Food Safety Authority has taken the view that the amounts detected in the products tested thus far do not pose a direct threat to public health if inadvertently consumed and there is little danger of long-term exposure. South African authorities have been alerted, and as far as is known, no contaminated products have come into our country.
What are dioxins and why the concern?
The term dioxin usually refers to a group of persistent organic pollutants that share a similar chemical structure (polychlorinated dibenzodioxins (PCDDs). The word dioxin formally refers to the central dioxygenated ring, which is stabilised by the two flanking benzene rings (Figure 1). Polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) are often called 'dioxin-like' as they behave in a similar way and are often included in the same set of safety limits.
 The main concern with dioxins is that they accumulate in fatty tissue in the body and are very persistent. Exposure to relatively low levels of dioxins over long periods can contribute to reproductive and developmental problems and damage the immune system of humans and animals. They are thought to interfere with hormones and also cause cancer. Exposure to high levels of dioxins results in a skin disease called chloracne; a condition where acne-like lesions occur mainly on the face and upper body. Other effects of exposure to large amounts of dioxins include skin rashes, skin discoloration, excessive body hair, and mild liver damage.
Dioxins are not manufactured intentionally, but are formed as by-products of ordinary human activities,such as metal smelting, the manufacture of herbicides and pesticides and in the bleaching of paper , and also in combustion processes such as commercial or municipal waste incineration, burning of chlorine-containing substances such as polyvinyl chloride (PVC) and fuels such as wood, coal, diesel or oil, and even household fires. Dioxins can also be formed as a result of natural processes such as forest fires and volcanic eruptions. Cigarette smoke contains small amounts of dioxins. The uncontrolled burning of residential waste is thought to be a major source of dioxins to the environment.
When released into the air, dioxins may be transported long distances and eventually settle in minute amounts on plants, where they are taken up by animals. When dioxins are released into water, they tend to settle into sediments. Here they can be ingested by fish and other aquatic organisms. Dioxins are extremely persistent and decompose very slowly in the environment. They become concentrated in the food chain so that animals have higher concentrations than plants, water, soil, or sediments. Within animals, dioxins tend to accumulate in fat.
Foods high in animal fat, such as milk, meat, fish and eggs (and foods that use these as ingredients) are the main source of dioxins for humans where are stored in fatty tissues and are neither metabolised nor excreted.
There are several hundred different compounds that are dioxins or dioxin-like. Only a few of them are toxic and of those that are, not all have the same degree of toxicity. Dioxins are most often found in mixtures rather than as single compounds in the environment. The most toxic dioxin is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). A method has been established for comparing the toxicity of different types of dioxins to the toxicity of TCDD. These toxicity-weighted concentrations are then summed to give a single value, which is expressed as a Toxic Equivalent (TEQ). The system of Toxic Equivalency Factors (TEFs) that is used by a number of countries is that set by the World Health Organization (WHO), and the resulting overall concentrations are referred to as WHO-TEQs.
The limits for dioxins in foods
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 given in Table 1.
Table 1
Dioxin limits in food
| Foodstuff | WHO-TEQ/kg fat basis in nanograms |
Meat | 1-3 |
Liver | 6 |
Fish | 4 |
Eggs | 3 |
Milk and milk products | 3 |
Fats and oils depending on type | 0,75-3 |
(Sourced from http://www.foodnavigator.com)
In November 2001 The WHO set a provisional recommendation for tolerable monthly intake (PTMI) for dioxins of 70 picogram / kg body weight per month. This level is the amount of dioxins that can be ingested over a lifetime without detectable health effects (Table 2).
Table 2
Measurement equivalents
| Value | Symbol | Name |
| 1 | g | gram |
| 10-1 | dg | decigram |
| 10-2 | cg | centrigram |
| 10-3 | mg | milligram |
| 10-6 | µg | microgram |
| 10-9 | ng | nanogram |
| 10-12 | pg | picogram |
Low levels of dioxins are believed to exist ubiquitously. There is currently no way of removing dioxins from our bodies, so the best way to ensure that we do not consume amounts that will be detrimental to our health is by reducing the amount in the environment. Many countries have been actively working over the past 30 years on reducing the amounts of dioxin emission from industrial sources. In the USA, the current quantifiable levels have been reduced by more than 90% since 1987. In the United Kingdom, where intake has been measured since 1982, intake has been reduced by 85%.
Although dioxins are environmental contaminants, most dioxin exposure occurs through diet, with over 95% coming through ingestion of animal fats. A long-term strategy to reduce the body's burden includes trimming fat from meat, consuming low-fat dairy products and ensuring a balanced diet that includes adequate intake of fruits, vegetables and cereals. This will help to avoid excessive exposure to one of the source s of dioxins.
For more information, please contact Owen Frisby of FACS at (012) 346 2091
F.A.C.S. Scientific Director. 2011.
|
