The full names of Dioxin are polychlorinated dibenzo-dioxins (PCDDs) and polychlorinated dibenzofuran (PCDFS)-two benzene rings connected by two oxygen atoms and replaced by two chlorine atoms respectively; Polychlorinated dibenzofurans (PCDFs) consist of two benzene rings substituted by chlorine atoms linked by one oxygen atom. Each benzene ring can replace 1 ~ 4 chlorine atoms, thus forming many isomers, including 75 isomers of PCDDs and 135 isomers of PCDFs. Microorganisms and hydrolysis in nature have little influence on the molecular structure of dioxins, so it is difficult to naturally degrade and eliminate dioxins in the environment. It includes 21 compounds. It is very toxic, 13 times as much as cyanide and 9 times as much as arsenic, so it is called "the poison of the century". The International Center for Research on Cancer has listed it as a human first-class carcinogen. Environmental experts say that "dioxins" often exist in the atmosphere, soil and water as tiny particles, and the main pollution sources are chemical metallurgy industry, garbage incineration, paper making and pesticide production. Plastic bags, PVC (polyvinyl chloride) soft glue and other things used in daily life all contain chlorine. When these things are burned, dioxins will be released and suspended in the air.
The toxicity of dioxins varies with the substitution position of chlorine atoms, so the equivalent toxic dose (TEQ) is obtained by multiplying their contents by toxic equivalency factors,TEFs) in the environmental health risk assessment. Among dioxins, 2,3,7,8-tetrachloro-dibenzo-p-dioxins (2,3,7,8-tetrachloro-dibenzo-p-dioxins, 2,3,7,8-tcdd) are the most toxic and have been studied most.
9% of dioxins in the atmospheric environment come from municipal and industrial waste incineration. Lead-containing gasoline, coal, wood after anti-corrosion treatment, petroleum products and various wastes, especially medical wastes, are easy to produce dioxins when the combustion temperature is lower than 3-4℃. The production process of PVC plastics, paper, chlorine and some pesticides, iron and steel smelting, high-temperature chlorine activation of catalysts and other processes can release dioxins into the environment. Dioxins also exist as impurities in some pesticide products such as pentachlorophenol, 2,4,5-T and so on. The formation mechanism of dioxins in the process of municipal industrial waste incineration is still under study. At present, there are three main ways: 1. In the process of incineration of chlorine-containing plastics such as vinyl chloride, the incineration temperature is lower than 8℃, and chlorine-containing garbage is not completely burned, which is easy to generate dioxins. After combustion, chlorobenzene is formed, which becomes the precursor of dioxin synthesis; 2. Other chlorine-containing and carbon-containing substances, such as paper, wood products and food residues, are catalyzed by metal ions such as copper and cobalt to generate dioxins without chlorobenzene. 3. Derived from the process of manufacturing chemicals including pesticides, especially chlorine-based chemicals, such as pesticides, herbicides, wood preservatives, defoliants (used by the US military in Vietnam War), polychlorinated biphenyls and other products.
The concentration of dioxins in the atmosphere is generally low. Compared with rural areas, the atmosphere in cities, industrial areas or areas close to pollution sources contains higher concentrations of dioxins. The amount of dioxins exposed by the general population through respiratory route is very small, that is, it is estimated to be about 1% of the intake through digestive tract, which is about .3pgTEQ(kg? d)。 In some special cases, the amount of dioxins exposed through respiratory route can not be ignored. According to a survey, the dioxin content in the blood of waste incineration employees is 86pgTEQ/L, which is about 4 times that of the normal population. Dioxins discharged into the atmospheric environment can be adsorbed on particles, settled in water and soil, and then enter the human body through the enrichment of food chain. Food is the main source of dioxins in human body. Placenta and lactation can cause dioxin exposure in fetuses and infants. People who have frequent contact are more likely to get cancer.
Dioxin is a highly toxic substance, and one in ten thousand or even one in one hundred million grams of dioxin will bring serious harm to health. Dioxin has not only carcinogenic toxicity, but also reproductive toxicity and genetic toxicity, which directly harms the health and life of future generations. Therefore, dioxin pollution is a major issue related to human survival and must be strictly controlled.
Sun Yat-sen University in Taiwan and Kaohsiung University of Science and Technology are cooperating to find a kind of bacteria that can "eat" toxic dioxins in the soil samples contaminated by dioxins in Anshun Factory in Tainan, which will be the most economical and effective method for remediation of dioxin-contaminated land. Taiwan Province media reported that the Anshun factory of Taiwan Province "China Petrochemical Industry Company" in Annan District of Tainan City was closed in 1982, but the land and rivers nearby were seriously polluted by dioxin and mercury, which was regarded as the most toxic block in the world by environmental groups. High concentration of dioxins will affect human health. The soil contaminated by dioxins in Anshun Factory has been sealed for five or six years, so far there is no effective and economical fundamental remediation method. Kaohsiung Zhengxiu University of Science and Technology has detected hundreds of kinds of bacteria from polluted soil. In the past year, it has cooperated with the Institute of Biochemistry of Sun Yat-sen University to screen out dioxins-based strains from hundreds of strains in soil samples, and found that they "eat quickly". Zhang Jianguoping, director of the Center for Ultra-micro Analytical Research and Technology of the University of Science and Technology, said on the 18th that this kind of bacteria is a "natural nemesis of dioxins". "As long as it is moved into the soil contaminated by dioxins, after a period of time, the bacteria can" eat "dioxins without removing the soil, which will save up to NT$ 1 billion to NT$ 2 billion in remediation funds."
It will be the most cost-effective remediation method if self purification can be used to treat dioxin-contaminated land by bacteria that multiply rapidly in nature. "In the past, environmental testing units and academic units focused on the detection of pollutants, and they were never connected with the microbial community." Zhang Jianguoping said that Zhengxiu and Zhongshan were very excited about this major discovery and described it as "a very exciting discovery". Zhang Jianguoping refused to disclose the name of the bacteria, saying only that "how to catch this kind of bacteria from the soil is a difficult technology". He said that last week, he had cooperated with the Institute of Biochemistry of Sun Yat-sen University to apply for a patent from Taiwan's "Ministry of Economic Affairs", and the research team would also publish the research results in an internationally renowned scientific period for the academic community to share this new discovery.