What are dioxins?
Dioxins refers to a group of toxic chemical compounds that share certain chemical structures and biological characteristics. Dioxins are called persistent organic pollutants (POPs), meaning they take a long time to break down once they are in the environment. The word dioxin formally refers to the central dioxygenated ring (Figure 1), which is stabilised by the two flanking benzene rings (Figure 2). Polychlorinated dibenzofurans (PCDFs), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated biphenyls (PCBs) are often called ‘dioxin-like’ as some of them behave in a similar way and are often included in the same set of safety limits (1).
Figure 1: 1,4 dioxin (Dioxins and dioxin-like compounds. Wikipedia)
Figure 2: Polychlorinated dibenzo-r-dioxins (Dioxins and dioxin-like compounds. Wikipedia)
Dioxins are not natural substances but were widely manufactured and used in the past. Once it was realised that they had harmful side effects, the manufacture of dioxins was prohibited (under the Stockholm Convention on Persistent Organic Pollutants), but unfortunately there are still significant amounts that still get released into the environment as biproducts of other manufacturing or chemical processes: 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.
What does dioxin look like?
Pure dioxin looks like white crystalline needles. In the environment, however, it generally is dispersed and attached to soil and dust particles and is invisible to the eye.
Should we be concerned about Dioxins?
Some dioxins are highly toxic and can cause cancer, reproductive and developmental problems, damage to the immune system, and can interfere with hormones.
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.
What can consumers do to reduce their risk of exposure?
A balanced diet (including adequate amounts of fruits, vegetables and cereals) will help to avoid excessive exposure from a single source. Trimming fat from meat and consuming low fat dairy products may decrease the exposure to dioxin compounds if there is a risk of the animals having been exposed. This is a long-term strategy to reduce overall body burdens and is probably most relevant for girls and young women to reduce exposure of developing foetuses during pregnancy and when breastfeeding infants.
Ongoing research and monitoring of dioxins in food and the environment
In 2001, the Joint Food and Agriculture Organization of the United Nations (FAO)/WHO Expert Committee on Food Additives (JECFA) performed an updated comprehensive risk assessment of PCDDs, PCDFs, and “dioxin-like” PCBs. The experts established a provisional tolerable monthly intake (PTMI) of 70 picogram/kg per month. This level is the amount of dioxins that can be ingested over lifetime without detectable health effects.1
In December 2006, maximum limits for dioxins were set by the European Commission in Commission Regulation (EC) No 1881/2006 for maximum levels for certain contaminants in foodstuffs.
This document is available on-line at www.eur-lex.europa.eu.
Low levels of dioxins are believed to exist ubiquitously. As a result of the low water solubility, elimination of dioxins in humans and animals is very slow, as the kidneys are not able to secrete them in urine. Metabolism in humans is extremely slow and this results in biological half-lives of several years for all dioxins. 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. In most countries there is now strict control of industrial processes to reduce formation of dioxins as far as possible. The Codex Alimentarius Commission adopted a Code of Practice for Source Directed Measures to Reduce Contamination of Foods with Chemicals (CAC/RCP 49-2001) in 2001. In 2006 a Code of Practice for the Prevention and Reduction of Dioxin and Dioxin-like PCB Contamination in Food and Feeds (CAC/RCP 62-2006) was adopted.
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 sources of dioxins.
There have been and are still ongoing extensive studies of the amounts of dioxin and related substances in the environment, in our food and in humans. The good news is that the levels have been monitored, they have been shown to have dropped significantly over the past two to three decades (2, 3). In the United States of America, 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%.
- WHO (updated Oct 2016), Dioxins and their effects on Human Health: who.int
- Update of the monitoring of levels of dioxins and PCBs in food and feed, European Food Safety Authority EFSA Journal: EFSA Journal 2012;10(7):2832 [82 pp.].
- EPA, 2023. EPA’s Learn About Dioxins. Available online: www.epa.gov.
Prepared for FACS by SFe (2023).