Dioxin

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Changed on: 05.07.2017

Dioxins and polychlorinated biphenyls (PCBs) belong to the group of persistent organic pollutants. Due to their high solubility in fat they are hard to break down and therefore build up in humans, animals and the environment. These substances are also taken up via food, as they are found everywhere in the environment. In order to keep a check on the incidence of dioxins and PCBs in food, there is continual monitoring of food in Austria as part of an official control plan.

Dioxins and polychlorinated biphenyls (PCBs) belong to the group of persistent organic pollutants. Due to their high solubility in fat they are hard to break down and therefore build up in humans, animals and the environment. These substances are also taken up via food, as they are found everywhere in the environment. In order to keep a check on the incidence of dioxins and PCBs in food, there is continual monitoring of food in Austria as part of an official control plan.

Origin

Dioxins are formed under particular conditions in combustion processes or as bi-products of the chemical synthesis of various chlorine compounds. These compounds are very persistent and are only degraded with difficulty.

The term PCBs (polychlorinated biphenyls) refers to a group of around 200 substances. They come from insulating fluid in transformers and capacitors, but were also used, amongst other things, as softening agents in plastics, joint sealants etc.

PCBs have been banned worldwide since 2001, but they persist in the environment (soil, sediments, water, atmosphere) for a long time and may subsequently enter the feed production chain and the food chain.
Dioxins occur in very low concentrations. Measurement requires extremely sensitive procedures, such as that provided by gas chromatography with high-resolution mass spectrometry. This is the only way that dioxins and dioxin-like PCBs can be conclusively distinguished from all other substances in the sample.

Toxicity

In humans acute poisoning can lead to chloracne, nausea with vomiting and irritation of the upper respiratory tract, peripheral neuropathy, disorders of the lipid metabolism and liver damage (Nau et al., 2003). Cases of poisoning like this have been reported after chemical accidents, such as in 1976 in Seveso in Italy and occupational exposure of workers in chemical factories.

Negative effects of dioxins and dioxin-like PCBs are mediated through binding to the aryl hydrocarbon receptor (AHR) (Schmid and Bradfield, 1996). Impairment of the immune system, the nervous system, the hormone balance and of reproductive functions have all been observed as chronic effects of dioxins in animal experiments. Chronic exposure to dioxins has led to various types of cancer in animals (WHO, 2002, 2010). Genotoxicity investigations have shown that dioxins have no mutagenic potential. Dioxins and dioxin-like PCBs are consequently assigned to the tumour promoter group. Tumour promoters accelerate the development of tumours from damaged cells, but are not themselves able to trigger tumour formation by damaging DNA (Nau et al., 2003).

All dioxin and dioxin-like PCB congeners are toxic to varying degrees. In order to sum up the toxicity of these various compounds and to facilitate risk assessment and regulatory control, the concept of the toxic equivalency factor (TEF) has been introduced (WHO, 2000). Various toxicity equivalency factors (TEFs) are used to express the equivalency of a given mixture: thus the most toxic dioxin 2,3,7,8-tetrachlordibenzodioxin (2,3,7,8-TCDD), the so-called Seveso dioxin, has a TEF of 1, while a less toxic mixture will have a value of 0.5 for example. All congeners found in an analysis are multiplied by their respective TEFs and are then added together. The results of analysis are expressed as a single quantifiable unit, called the TCDD toxic equivalency (TEQ) (Nau et al., 2003, EK, 2006).

Various bodies have now derived tolerable intake levels for dioxins and dioxin-like PCBs. The World Health Organization (WHO) has set a tolerable daily intake (TDI) of 1 to 4 pg WHO-TEQ per kg and day (WHO, 2000). However, due to the long half-life of dioxins and dioxin-like PCBs, this value has been revised and the tolerable intake level set for a month in order to estimate the health risk. The WHO calculated a provisional tolerable monthly intake (PTMI) of 70 pg WHO-TEQ/kg body weight and month (WHO, 2002).

In its statement of 30 May 2001 the EU’s Scientific Committee on Food, SCF, set a tolerable weekly intake (TWI) of 14 pg WHO-TEQ/kg body weight and month for dioxins and dioxin-like PCBs (SCF, 2001). For someone weighing 70 kg, this yields a weekly tolerable intake of 980 pg WHO-TEQ.

Maximum levels

Maximum levels for dioxins, furans and dioxin-like PCBs are set in Regulation (EC) 1881/2006 setting maximum levels for certain contaminants in foodstuffs.

The calculation and setting of these maximum levels is a complex process that takes into account all relevant toxicological knowledge, the consumption habits of various population groups, all available data on the Incidence in foodstuffs with regional differences and, not least, all technically possible decontamination procedures. Differences between the individual food groups may therefore result. In the case of fish, the maximum level is based on fresh weight, while that of meat and eggs is based on fat content.

Monitoring

Monitoring of the background contamination in foodstuffs has been carried out annually in Austria since 2005. The aim of this pan-European monitoring is to obtain reliable data on the contamination in foodstuffs with these substances and subsequently to implement the measures necessary to reduce the dioxin content in foodstuffs to the lowest achievable level.

Inspections are made, amongst other things, of milk and milk products, eggs, meat and fish, but also baby food. This targeted programme of dioxin inspections of foodstuffs has clearly shown that Austrian foodstuffs are only slightly contaminated in terms of dioxins and PCBs, i.e. the measured levels are well below the applicable maximum limits.

Risk assessment

From 2005 to 2011 foodstuffs from Austrian trade were tested for dioxins and polychlorinated biphenyls (PCBs) at AGES. Dioxins and PCBs are persistent chlorinated chemical compounds which occur throughout the environment. While dioxins are usually produced as unintended bi-products of combustion processes, PCBs were frequently used in industry. Dioxins and PCBs are fat soluble and are stored in animal fat. High intake of dioxins and PCBs can cause toxic effects such as chloracne and cancer in humans.

The highest average concentrations were found in liver samples from terrestrial animals and fish oil capsules as food supplements. All dioxin and dioxin-like PCB levels were well below the European maximum levels. All concentrations of non-dioxin-like PCBs would have have fallen within the new 2012 European maximum levels.

The average exposure to dioxins and PCBs through food falls within the tolerable daily intake level and within the permissible weekly and monthly intake levels for all population groups. Based on the data available, the health risk posed to the Austrian population by the absorption of dioxins and PCBs via food is therefore rated as low.

Links to publications

Rauscher-Gabernig E., Mischek D., Moche W., Prean M., 2013: Dietary intake of dioxins, furans and dioxinlike PCBs in Austria. Food Additives & Contaminants: Part A, 30:1770-1779.

Mihats D., Moche W., Prean M., Rauscher-Gabernig E., 2015: Dietary exposure to non-dioxin-like PCBs of different population groups in Austria. Chemosphere 126, 53–59.


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