Dioxins are a group of relatively stable lipophilic organic substances. They are formed in small amounts during the combustion of organic materials and also in the manufacture of certain chemicals. They may be present in foods and feeds at low but measurable values and in highly variable amounts, and they have been associated with a number of possible negative biological effects.
Dioxins are classified as contaminants and regulated under Commission Regulations (EC) No 1881/2006, No 1883/2006 and No 152/2009 for food. Animal feed and additives are regulated under the ‘feed additives’ Commission Regulation (EC) No 1831/2003 and ‘undesirable substances in products intended for animal feed’ Commission Directive 2006/13/EC.
The purpose of this document is to provide an overview on dioxins, their formation and occurrence in foods and feeds, public health significance, legislation, methods of detection and industry good practices.
Further background and information can be found in the references.
They are a group (several hundred halogenated aromatic compounds) of closely related chemical structures, namely polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and some structurally related polychlorinated biphenyls (PCBs). Some 419 types have been identified of which approximately 30 are considered to have significant toxicity.
Dioxins are environmental contaminants resulting from natural and industrial processes. In nature they can result from volcanic eruptions and large-scale forest fires. In industry they are formed in small amounts by various combustion processes as well as being by-products of some chemical manufacturing procedures. They can persist for a long time in the environment because of their chemical and thermal stability (USFDA, 2010).
They may be transported over considerable distances when dispersed into the air, which is the primary pathway into the environment and ultimately the food chain. Dispersal in water is initially more local i.e. settlement in sediments from where they can eventually enter the food chain.
Dioxins in the food chain are of concern because of a number of perceived adverse health effects. Elevated population exposures to dioxins have caused chloracne (a skin condition), possible mild liver damage, decreased sperm production and sperm abnormalities (Faqi et al., 1998) and, where exposure has been prolonged, a suggestion of increased cancer risk (COC, 2001). Accidental high exposures are not typical of normal dietary exposures.
When dioxins enter the food chain there is a tendency for them ultimately to accumulate at the top of the chain i.e. in animals. As they are lipophilic by nature they will concentrate in the fat tissues of animals and subsequently by ingestion in those of humans (Fries, 1995). A comprehensive survey of supermarket products in the USA (Schecter et al., 1997) during the 1990s established that meats (0.32–0.38 Toxic Equivalent Quantities (TEQ)), eggs (0.34 TEQ), fish (0.47–1.43 TEQ), dairy products (0.12–1.07 TEQ) and animal fats tended to have the highest dioxin concentrations. Concentrations in vegetables, fruits and grains were much lower (0.07 TEQ). TEQs of dioxins are explained later in this document.
In all instances reported levels were low, highly variable (Eduljee and Gair, 1996) and not thought to be of public health significance at the time. However, risk assessments carried out by the European Commisson’s Scientific Committee on Food (SCF) in 2000 and 2001 indicated that a proportion of the European population was exposed through their diet to levels of dioxins and dioxin-like PCBs that exceeded the suggested tolerable intake, although this level was set very conservatively (SCF, 2000; 2001). This led to European Commission action aimed at monitoring and reducing the presence of dioxins, furans and PCBs in food and feed (Commission Recommendations 2006/794/EC and 2006/88/EC).
There is a natural dioxin background at all times in the environment, albeit a very low one – a combination of natural sources and man-made activities. Concerns are focusing upon levels in food animals at the top of the supply chain.
Dioxins are formed, in small amounts, during high-temperature combustion of organic matter in the presence of a source of chlorine. This can be man-made e.g. commercial/waste incineration, burning of fuels e.g. wood, coal, oil or can come from natural sources (as mentioned above). Manufacture of certain chlorinated chemicals and the use of chlorine gas itself (in industrial processes) have also all been suggested as possible sources of small amounts of dioxins on occasion. Some of these compounds are highly toxic to living organisms, others considerably less so.
Better awareness of what contributes to dioxin levels, improved recognition of the changes required to reduce emissions from various industrial processes, and implementation of these changes are contributing to lower environmental levels of dioxins worldwide (USFDA, 2010).
Commission Regulation EC No 178/2002 sets out the general principles of food law. It states that the presence of any contaminants at a level which would lead to the food not being safe for consumption fails to meet the above Regulation and therefore cannot be sold in the market place.
In addition to the general principles of food law for specific contaminants, additional specific Regulations apply as outlined below:-
- Council Regulation EEC No 315/93
- Commission Regulation EC No 1881/2006
- Commission Regulation EC No 1883/2006
- Commission Regulation EC No 152/2009
In the UK, the Contaminants in Food (England) Regulations 2010 (SI No 2228), and similar instruments in Wales, Scotland and Northern Ireland, lay out provisions for enforcement and execution.
Commission Regulation EC No 1881/2006 sets out the maximum allowable limits of dioxins and PCBs for certain food products deemed of risk (including meats and meat products, liver, fish and fishery products, milk and dairy products, some animal fats and vegetable oils). These limits apply to the edible foodstuffs.
Animal feed and additives are regulated under ‘the undesirable substances in products intended for animal feed’ Commission Directive 2006/13/EC and ‘feed additives’ Commission Regulation EC No 1831/2003.
In England, the Feeding Stuffs (England) Regulations 2005 (SI No 3281) and the Feeding Stuffs (England) (Amendment) Regulations 2006 (SI No 2808) lay out provisions for enforcement and execution. Similar provisions exist for Northern Ireland, Scotland and Wales.
Dioxins are usually measured as Toxicity Equivalent Quantities (TEQs) or parts per trillion (ppt) of toxicity equivalents. Toxicity equivalents are the sum of the quantity of the individual congeners (chemical types) of the dioxin and related families of compounds multiplied by the respective toxicity equivalent factors (TEF) for each congener. This somewhat complicated means of assessment is necessary because of the wide variation in the relative toxicity of individual dioxins to humans (EC No 1881/2006).
Most analytical procedures for dioxins in foods and feeds use sophisticated techniques (EC No 1883/2006; EC No 152/2009) such as gas chromatography/mass spectrometry (GCMS), coupled with extensive cleanup/concentration, for the required detection limits to be achieved (Alonso et al., 2011). Such measurements are not cheap or routine and these services are likely to be offered only by the larger public and commercial laboratories.
There have been instances of contamination in past years, usually of feed ingredients, that subsequently led to elevated levels of dioxins in some food products for a short time before corrective action was taken. Hence it is important to ensure that feed streams are fully taken into account in the HACCP plan.
For food and feed production a risk assessment of the incoming raw materials is a good starting point, combined with an understanding of how dioxins may concentrate or develop in the process. In cases where dioxins can concentrate and/or form, validation and verification must be included in the HACCP plan for those product and process streams at risk.
A nationwide survey of dioxins in foodstuffs in the USA in the late 1990s detected elevated levels of dioxins in some samples of poultry meats (USFDA, 2010). Animal feed was implicated as the likely source of contamination due to incorporation of ball clay (an anti-caking agent) in the production of the feeds. Control centred upon initially changing certain production practices to minimise the issue and subsequently in providing appropriate general advice to the feed industry regarding suitable monitoring to prevent repetition.
A programme of dioxin monitoring in foods in Germany in the 1990s initially showed a gradual decline which was followed by a gradual increase in certain products namely milk, butter and meats. Investigation implicated contaminated citrus pulp (a feed ingredient for ruminants) being supplied from South America. Once again changes in production practices of the feed material eliminated the issue. This particular incident affected other European countries, as well as Germany, which highlighted the international aspect of the situation as well as emphasising the need for analysing large numbers of food samples for dioxins regularly in order to detect shifts in trends including seasonal variations (Malisch, 2000).
An outbreak of illness in poultry in Belgium in 1999 was traced to animal feed contaminated with dioxins in recycled fat used in its manufacture. Farms in France, Holland and Spain had also used the contaminated material for their livestock. Products from poultry and pigs were affected but not those from cattle (Bernard et al., 1999). Farms were quarantined and contaminated products destroyed. More than 30 countries temporarily banned certain food imports from Belgium until the issue was resolved (Ekperigin, 2000).
Ireland experienced trouble with elevated dioxin levels in some pork products in 2008. Again, contaminated animal feed was implicated. The cause of the contamination was thought to be fuel oil used in the drying of the affected feed (USFDA, 2012).
In all these cases issues were initially raised by the finding of elevated dioxin levels in food products during routine random testing (USFDA, 2010; 2012).
Industry needs to be vigilant at all times and have sufficiently robust monitoring in place so that emerging issues can be resolved before products reach the market place.
Alonso DE, Binkley J, Siek K. Comprehensive Analysis of Persistent Organic Pollutants in Complex Matrices using GC with High-Performance TOF-MS. Current Trends in Mass Spectrometry. July 2011, 48–53.
Bernard A, Hermans C, Broeckaert F, et al. Food contamination by PCBs and dioxins. Nature. September 1999, 401, 231–232.
COC, Committee on Carcinogenicity in Food, Consumer Products and the Environment. Carcinogenicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin. 2001 (July).
Commission Recommendation 2006/794/EC of 16 November 2006 on the monitoring of background levels of dioxins, dioxin-like PCBs and non-dioxin-like PCBs in foodstuffs.
Commission Recommendation 2006/88/EC of 6 February 2006 concerning the reduction of the presence of dioxins, furans and PCBs in feedingstuffs and foodstuffs.
Commission Regulation (EC) No 178/2002 of 28 January 2002. ‘’Laying down the general principles and requirements of food law, establishing the European Food Safety Authority and laying down procedures in matters of food safety.’’
Commission Regulation (EC) No 1831/2003 of 22 September 2003. On additives for use in animal nutrition.’’
Commission Directive 2006/13/EC of 3 February 2006. ‘’Amending Annexes I and II to Directive 2002/32/EC of the European Parliament and of the Council on undesirable substances in animal feed as regards dioxins and dioxin-like PCBs.
Commission Regulation (EC) No 1881/2006 of 19 December 2006. “Setting maximum levels for certain contaminants in foodstuffs.
Commission Regulation (EC) No 1883/2006 of 19 December 2006. “Laying down methods of sampling and analysis for the official control of levels of dioxins and dioxin-like PCBs in certain foodstuffs.
Commission Regulation (EC) No 152/2009 (Annexe V, letter B) of 27 January 2009. “Laying down the methods of sampling and analysis for the official control of feed.
Council Regulation (EEC) No 315/93 of 8 February 1993. ‘’Laying down Community procedures for contaminants in food
Eduljee GH, Gair AJ. Validation of a methodology for modelling PCDD and PCDF intake via the food chain. Science of the Total Environment. 1996, 187(3), 211–229.
Ekperigin HE. Use of poultry litter or manure as a fertilizer for croplands: impact on animal and public health. FDA Veterinarian Newsletter. 2000 (May/June), 15(3).
European Commission Scientific Committee on Food. Opinion of the SCF on the Risk Assessment of Dioxins and Dioxin-like PCBs in Food, 22 November 2000.
European Commission Scientific Committee on Food. Opinion of the SCF on the Risk Assessment of Dioxins and Dioxin-like PCBs in Food. Update based on new scientific information available since the adoption of the SCF Opinion of 22nd November 2000. Adopted 30 May 2001.
Faqi AS, Dalsenter PR, Merker HJ, Chahoud I. Reproductive toxicity and tissue concentrations of low doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin in male offspring rats exposed throughout pregnancy and lactation. Toxicology and Applied Pharmacology 1998, 150, 383–392.
Fries GF. A review of the significance of animal food products as potential pathways of human exposures to dioxins. Journal of Animal Science. 1995, 73(6), 1629–1650.
Malisch R. Increase of the PCDD/F-contamination of milk, butter and meat samples by use of contaminated citrus pulp. Chemosphere. 2000, 40(9–11), 1041–1053.
Schecter A, Cramer P, Boggess K, et al. Levels of dioxins, dibenzofurans, PCB and DDE congeners in pooled food samples collected in 1995 at supermarkets across the United States. Chemosphere. 1997, 34(5), 1437–1447.
The Contaminants in Food (England) Regulations, 2010, SI No 2228.
The Feeding Stuffs (England) Regulations, 2005, SI No 3281
The Feeding Stuffs (England) (Amendment) Regulations, 2006, SI No 2808.
USFDA, Food and Drug Administration. Food, Questions and Answers about Dioxins. 2010 (May), G1-G12 and F6-F9
USFDA, Food and Drug Administration. Food, Questions and Answers about Dioxins and Food Safety. 2012 (February), section 7.
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