Scientists have found that dioxins have two important natural sources - forest fires and the decomposition of chlorophenols. Although dioxins are produced in nature, the main source of dioxin pollution is actually human activities. Dioxins are mainly produced from the incineration process of solid waste or the production process of certain chlorine-containing organic compounds, and enter the soil, water and atmospheric environment through related substances. It can be said that humans are the main culprit in producing dioxin.
Researchers have found that dioxins are produced and released when chlorine-containing feedstocks are present in the combustion process. These processes include waste incineration, such as the incineration of solid waste, iatrogenic and hazardous waste; metallurgical processes, such as high-temperature steelmaking, iron melting, scrap metal recycling; thermal combustion, such as the heating of coal, wood, petroleum products, etc. combustion.
Scientific research has confirmed that municipal waste incineration is one of the largest sources of dioxin emissions into the environment. The U.S. Environmental Protection Agency has conducted an analysis and evaluation of dioxin, and the results show that the dioxin generated during the burning process of garbage accounts for 95% of the total known dioxin generation.
At present, the widely used garbage disposal methods at home and abroad are sanitary landfill, high-temperature composting and incineration. Since landfill processing takes up a lot of land, although sanitary landfilling is a common method, it is by no means a long-term solution. Moreover, landfilling will also pollute the soil and water sources with harmful components in the garbage. High-temperature composting is the best way to treat garbage. As early as the 1980s, my country had begun to apply the "secondary fermentation process" to compost garbage. However, the composting process is relatively complex. It not only requires classification and sorting, but also requires high organic content. Composting still requires a large amount of land. In addition, the fertilizer obtained after composting is not very popular because it is derived from garbage. Although incineration is not the best method, it has the advantages of being harmless, having obvious weight reduction effect, and having waste heat resources to utilize, so it has gradually become the mainstream method of garbage disposal.
In addition to waste incineration producing dioxins, it is also a by-product of industrial processes. Dioxins are derived in industrial production, especially in the process of manufacturing "chlorine-based" chemicals (such as pesticides, herbicides, wood preservatives, defoliants, and polychlorinated biphenyls). According to the "National Survey on Persistent Organic Pollutants in Major Industries", among my country's 17 major industries, there are more than 10,000 companies emitting dioxins, involving steel, recycled non-ferrous metals, waste incineration and other fields. With the rapid economic and social development of our country, the emission of dioxin will also show an increasing trend.
Dioxins emitted from waste incineration and industrial production can drift into the air and enter water and soil. Because dioxin has a stable chemical structure and cannot be biodegraded, it has strong environmental retention. Dioxins are also lipophilic and easily soluble in fat. Therefore, once the human body ingests dioxin-contaminated food and water or inhales dioxin-contaminated air, it is equivalent to removing the dioxin contained in it. All the Ying is "received" into the body. Scientists have found that 90% of the dioxins in the body of ordinary people come from contaminated food.