Dioxins are mainly by-products of industrial processes, including waste incineration, but can also result from natural processes, such as volcanic eruptions and forest fires. Some of the processes that create Dioxins include smelting, chlorine bleaching of paper pulp and the manufacture of some herbicides and pesticides. When it comes to the release of dioxins into the environment, uncontrolled waste incinerators (solid waste and hospital waste) are often the worst culprits due to incomplete burning.

Dioxin-based waste is not easily disposed of without contaminating the environment and human populations. Such materials need to be treated as hazardous waste and are most quickly destroyed by high temperature incineration in specialized facilities.

Extensive stores of PCB-based [1] waste and industrial oils, many with high levels of PCDF's [2] exist throughout the world. The long-term storage and improper disposal of these materials may result in exposure and contamination of the environment as well as human and animal food supplies.

Quantitatively speaking, the annual global dioxin production is approx. 17,200 kg, which corresponds to about 287 kg-TEQ. TEQ stands for “Toxic Equivalent” which weighs the toxicity of the less toxic compounds as fractions of the toxicity of the most toxic dioxin - TCDD. It been previously calculated (2015) that the total annual emission rate of dioxins into the atmosphere, only 9 kg-TEQ (3%) remains in the air. For the rest, 57% is deposited to land areas (163 kg-TEQ), while the remaining 40% is absorbed by ocean waters (115 kg-TEQ or 354 kg/year).

[1] - Polychlorinated biphenyl, a molecule with a structure similar to dioxin.
[2] - Polychlorinated dibenzofuran, another molecule with structure similar to dioxin.

Main sources of dioxin in each continent:

Europe

The continent of Europe is one of the main producers of dioxins worldwide. The emissions are produced both from industrial activities and nonindustrial burning processes. The ambient concentration varies depending on the climate, residential activities, and the degree of development and social awareness of the inhabitants in the respective countries. Among them, heavily industrialized countries like Germany were the main producers of dioxins until a few years ago (1990s) when stricter legislation and the implementation of more efficient treatment mechanisms led to the decrease of emissions to minimal values. Other industrialized countries like Poland, where less strict legislation is applied, have not shown the same progression.

Asia

As by European countries, combustion activities, metal industries, and waste incineration are the main sources of dioxin emissions in Asia. Concentrations can differ depending on the dioxin-producing process, legislation for the area, and the social awareness of the population. Furthermore, China, as a singular country, has been identified as the largest dioxin emitter in the world. Annual dioxin emission in China from 10 source groups was up to 10.2 kg TEQ in 2004, accounting for about 30% of the total global emissions 14,15. Due to technical difficulties in dioxin monitoring and laboratory analysis, information on dioxin contaminations in food supplies (in China) is limited.

Africa

Dioxin contaminations in Africa are mostly not a result of processes that occur on the continent itself, but rather a result of the airborne travel of Dioxin emissions that originate from Europe, among other sources. Africa is one of the continents that are most influenced by this type of secondary contamination, altering the correlation between the ratio of dioxin accumulation and the ratio of dioxin production per country.

America:

TThe United States is the highest generator of dioxins in both North and South America. According to the study of the National Dioxin Air Monitoring Network (NDAMN), which measured the distribution of atmospheric pollution from 1999 to 2004 in the United States, higher ambient concentrations of airborne dioxins were found in the eastern part of the country.
Furthermore, based on analyses from 1987 to 2000 release of dioxin-like compounds from regulated industrial sources significantly dropped. he annual releases to the U.S. environment over the three reference years were:

14,000 g in 1987,
3,400 g in 1995,
1,400 g in 2000.

Antarctica, Oceania and the seas:

The lowest concentration levels are found in the Antarctic and Oceania, while Europe presents the highest concentrations in soils. On the other hand, the northern parts of the Pacific Ocean, the High Seas, and the Mediterranean Sea show the highest levels of dioxins in water.

Severe contamination events of dioxins:

Agent Orange and the American - Vietnam war

During the War between the US and Vietnam in the 1960’s, thousands of kilometers of land were heavily sprayed with an herbicide called Agent Orange, which was used to clear heavily forested areas. But TCDD was an unintended byproduct of Agent Orange production; thus, the military had unknowingly contaminated all of that land with this toxin. Even today, over 50 years after the event took place, the United States is spending hundreds of millions of dollars to reclaim that land.

Seveso disaster in Italy

An accident at a chemical factory in Seveso, Italy in 1976 resulted in the highest known exposure to TCDD in residential areas. A mixture of toxic chemicals, including TCDD, was released into the air, contaminating an area of about 15 km2 where over 37,000 people lived. Within days, over 3000 animals in the area, including livestock, had perished, with over 80,000 animals being put down in order to prevent the contamination from entering our food chain. In addition, nearly 500 residents received severe skin lesions. In studies on the long-term effects of exposure on the affected population, higher incidences of cancer, nerve damage, cardiovascular and respiratory diseases, and impaired liver function were observed. This event gave rise to numerous scientific studies and standardized industrial safety regulations in Europe.

References:

1. World Health Organization (2016), "Dioxins and their effects on human health".
2. Miguel Dopico & Alberto Gómez (2015), Review of the current state and main sources of dioxins around the world , Journal of the Air & Waste Management Association, 65:9, 1033-1049.
3. Tao Huang , Hong Gao & Jianmin Ma (2016), Trend of cancer risk of Chinese inhabitants to dioxins due to changes in dietary patterns: 1980–2009.
4. Department of Environment and Energy in Australia (2018), "National Dioxins Program in Australia", Australian Government Website.
5. United States Environmental Protection Agency (2018), "Inventory of Dioxin Sources and Environmental Releases".