Dioxins and dioxin-like polychlorinated biphenyls
Dioxins and dioxin-like polychlorinated biphenyls
Dioxins is a collective term for similar chlorinated hydrocarbon compounds (congeners), which includes 75 polychlorinated dibenzo-p-dioxins (PCDDs) and 135 polychlorinated dibenzofurans (PCDFs).
Polychlorinated biphenyls (PCBs) are a group of substances consisting of 209 congeners that differ in the number and position of chlorine atoms on the biphenyl and exhibit different toxic properties. 12 congeners have a similar structure to dioxins and have the same toxic effects, so they are referred to as dioxin-like PCBs (dl-PCBs). The remaining compounds have different properties than dioxins and are called non-dioxin-like PCBs (ndl-PCBs).
PCDDs, PCDFs and PCBs always occur in a mixture of different compositions.
Dioxins are formed as by-products in combustion processes and in the synthesis of chlorine-containing compounds and are not produced intentionally. PCBs, on the other hand, were produced as technical mixtures until the 1980s and had many industrial uses. They were used as non-flammable liquids in transformers and capacitors and as plasticizers in plastics and sealants. Their use has been banned since 2001. But PCBs are also unintentionally formed and released during combustion and synthesis processes.
Dioxins and PCBs are difficult to degrade, are transported long distances by wind and rain, and remain in the environment for many years. Due to their high fat solubility, they accumulate in the fatty tissue of living organisms and bioaccumulate along the food chain. That is, when farm animals ingest feed contaminated with dioxins, dioxins are stored and accumulated in their fatty tissues. Therefore, they are mainly found in food of animal origin such as milk, eggs, meat and fish and products thereof.
In humans, acute poisoning can lead to chloracne, nausea with vomiting and irritation of the upper respiratory tract, peripheral neuropathies (diseases of the peripheral nervous system), disorders of lipid metabolism, and liver damage (Nau et al., 2003). Such poisonings have been reported in chemical accidents, as in Seveso, Italy, in 1976, or in occupational exposures in chemical factories. The occurrence of chloracne in adults is observed from a single dioxin dose of 1,000,000 pg WHO-TEQ/kg (for explanation, see the technical information) body weight.
Lower sperm concentrations in males have been identified as a consequence of higher exposure already in the womb and after birth. An association between high exposure to dioxins in fathers and a shift in sex ratio in offspring with a lower number of boys relative to girls was observed. Exposure to dioxins in childhood resulted in lower enamel mineralization and enamel defects.
Evidence for other adverse effects in humans is not yet fully established. But there is evidence that there may be a link to type 2 diabetes and obesity, increased mortality from cardiovascular disease, effects on the immune system, nervous system, and female reproductive ability.
Impairments of the immune system, nervous system, hormonal balance, and reproductive functions have been observed as chronic effects of dioxins in animal studies. Various cancers have been observed in animals exposed to dioxins over a prolonged period of time. Genotoxicity studies have shown that dioxins have no mutagenic potential. Due to this fact, dioxins and dioxin-like PCBs are assigned to the group of tumor promoters, i.e. they accelerate the development of tumors from pre-damaged cells, but are not themselves able to trigger tumor development through DNA damage. In rodents, tumors occurred in various organs, such as skin, ovaries and liver. Reduced sperm production, delayed onset of puberty, and changes in bones were noted.
Situation in Austria
Maximum levels for dioxins and dl-PCBs are set for various food groups in the European Union in Regulation (EC) No. 1881/2006 setting maximum levels for certain contaminants in foodstuffs. In addition to the maximum levels, action levels are set for certain foods according to Commission Recommendation 2013/711/EU on the reduction of the presence of dioxins, furans and PCBs in feed and food, as amended by Commission Recommendation 2014/663/EU. Action levels are concentrations of dioxins and dl-PCBs that indicate elevated levels of contamination in food. These action levels are slightly below the maximum levels and are intended to encourage food producers to identify and remove any sources of contamination.
As part of an annual priority action, continuous monitoring of background levels of dioxins and dl-PCB in foodstuffs is carried out in Austria. The aim of this Europe-wide monitoring is to obtain reliable data on the contamination of food with these substances and subsequently to take the necessary measures to reduce the levels of dioxins in food to the lowest achievable level.
The focus is on animal-based, high-fat foods such as milk, eggs, meat and fish and products made from them, but also on baby food and occasionally on plant-based foods. The focus actions on dioxin control in food clearly show that Austrian foodstuffs are only slightly contaminated with regard to dioxins and dl-PCB, i.e. the levels are well below the applicable limits.
The average intake levels for dioxins and dl-PCB in Austria were estimated to be 0.77 pg WHO-TEQ/kg body weight and day for children, 0.75 pg WHO-TEQ/kg body weight and day for women and 0.61 pg WHO-TEQ/kg body weight and day for men. Milk and dairy products were the main contributors to total intake, followed by fish and fish products for children and women, and meat, poultry, game, and offal for men.
Between 2012 and 2020, 251 samples of food produced in Austria were taken from direct marketers and at the slaughterhouse and analyzed for dioxins and PCBs. Samples of animal foods included meat and meat products, sheep liver, muscle meat from fish, milk and milk products such as yogurt, cream, cheese and butter, chicken eggs and fats from beef and pork, and honey. From the group of plant foods, vegetable oils and fats, oilseeds, nuts, vegetables and herbs were examined.
Of the 251 samples, the action levels and maximum levels for dioxins and dl-PCB were met in 248 samples (>98%). In one sample of pork bacon with a concentration for the sum of dioxins of 1.87 pg WHO-TEQ/g fat, the maximum level for dioxins of 1.0 pg WHO-TEQ/g fat was exceeded and therefore subsequently also the maximum level for the sum of dioxins and dl-PCB of 1.25 pg WHO-TEQ/g fat. The action level for dl-PCB in beef of 1.75 pg WHO-TEQ/g fat was exceeded in one sample of veal and one sample of beef.
Dioxins and dl-PCBs always exist as mixtures of individual compounds, so-called congeners. These are similar to each other in terms of their function, structure, origin or other properties, but are not necessarily identical. Each congener of dioxins and dioxin-like PCBs is toxic to a different degree. In order to sum up the toxicity of these different compounds and to facilitate risk assessments and control measures, the World Health Organization (WHO) introduced the concept of Toxicity Equivalence Factors (TEFs). The most toxic dioxin 2,3,7,8-tetrachlorodibenzodioxin (2,3,7,8-TCDD), known as the Seveso dioxin, has a TEF of 1, while a less toxic one, for example, has 0.5. All congeners found in the analysis are multiplied by their respective TEFs and then added together. This sum is called the toxicity equivalent (TEQ) relative to the most toxic dioxin.
In November 2018, the European Food Safety Authority (EFSA) derived a new tolerable weekly intake (TWI) for dioxins and dioxin-like PCBs. This comprehensive risk assessment is based on current scientific studies and evidence. In doing so, the TWI was lowered from 14 pg WHO-TEQ/kg body weight per week to 2 pg WHO-TEQ/kg body weight per week. No adverse effects on humans are expected at a lifetime intake of dioxins and dioxin-like PCBs at a level of 2 pg WHO-TEQ/kg body weight and week.
Final Report Project POPMON - Identification of relevant persistent organic pollutants and potentially contaminated regions as a basis for risk-based food monitoring in Austria.
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.
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.
Last updated: 02.02.2023