The term “dioxins” is commonly used as a general term designating a group of compounds with a similar chemical structure: dioxins and furans containing chlorine. In total, this group of dioxins consists of 75 polychlorinated dibenzo-p-dioxins (PCDDs) and 135 dibenzofurans (PCDFs). Dioxins occur as mixtures of individual compounds (congeners) with various compositions. The various dioxins (PCDD/Fs) have similar chemical and physical properties, however, the individual congeners have very different degrees of toxicity. The highest toxicity levels are found in congeners with chlorine substitutes in positions 2,3,7, and 8. Therefore, among the 210 potential congeners, only 17 are toxicologically relevant. Polychlorinated biphenyls (PCBs) are also chlorinated hydrocarbons with a chemical structure similar to dioxins. In total, there are 209 different PCB congeners, of which only 12 are toxicologically relevant. These congeners demonstrate a similarly planar structure as well as a comparable biological effect to the 2,3,7,8-substituted dioxins and therefore are also referred to as dioxin-like PCBs (dl-PCBs). Dioxins and dl-PCBs are extremely stable compounds. They accumulate in fat tissue and can only be broken down very slowly. In animal trials, chronic effects were observed such as impairments to reproductive functions, the immune system, nervous system, and hormonal balance.
Dioxins have never been produced on a large scale. They are unwanted byproducts that can be generated during any combustion process (e.g. industrial incineration plants, housefires, forest fires) where chlorine and organic carbon are present. Many dioxins are produced naturally throughout the earth’s history and accumulate in clay and soil. In contrast to dioxins, PCBs were manufactured industrially for various applications. In most countries, however, commercial or industrial applications of PCBs have been illegal since the 1980s.
Since dioxins and PCBs can be present anywhere in the environment, it is impossible to prevent them from entering the food chain. Livestock absorb these contaminants either through the soil or their feed. From there, the compounds accumulate in their fat tissue. Therefore, dioxin intake in humans mainly occurs through the consumption of animal-based food, such as meat, fish, eggs, and milk, as well as products made from those foods. In order to enable the potential risk to be assessed, a parameter was introduced that provides the sum of the PCDD/F congeners as a toxicity equivalent quantity (TEQ). This model for calculation takes into account the content and the toxicity of the individual congeners. The substance that has been classified as bearing the highest potential risk is 2,3,7,8-tetrachlorodibenzodioxin (TCDD). The acute toxicities of the other PCDD/Fs are indicated relative to TCDD. There is a difference between the sum of the TEQs of dioxins (WHO-PCDD/F-TEQ) and the sum of TEQs of dioxins and dl-PCBs (WHO-PCDD/F-PCB-TEQ). In the year 2000, the World Health Organization (WHO) specified a tolerable daily intake (TDI) in the range of 1 to 4 picograms of WHO-PCDD/F-PCB-TEQ per kilogram bodyweight. A year later, in 2001, Scientific Committee on Food (SCF) set a tolerable weekly intake (TWI) of 14 picograms WHO-PCDD/F-PCB-TEQ per kilogram bodyweight. Furthermore, various maximum values for food are provided in the Regulation (EC) No 1881/2006. Not only are there maximum levels for food, but for feed as well. This helps limit the contamination at an earlier point on the food chain. The maximum levels for feed can be found in the feed regulation, which are based on the guideline 2002/32/EC. Furthermore, on a European level, the commission recommendation 2014/663/EU determined action levels in food. When these action levels are exceeded, the source of the contamination should be investigated, and measures should be taken in order to contain or eliminate it. Exceeding the action values does not make the product unmarketable, but it helps recognize and remedy the source of contamination early. The GBA Group can help you test for dioxins and PCBs in food and feed. Please feel free to contact us about this topic.