Dioxin is actually an abbreviation, which refers to two organic compounds with similar structures and properties, including many homologues or isomers. The full names are polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), which are collectively referred to as dioxins in China's environmental standards.
Polychlorinated dibenzo-dioxins consist of two oxygen atoms and two benzene rings substituted by chlorine atoms. Polychlorinated dibenzofurans consist of 1 oxygen atom and two benzene rings substituted by chlorine atoms. Each benzene ring can replace 1~4 chlorine atoms, thus forming a variety of isomers, including 75 isomers of PCDDs and 135 isomers of PCDFs. Therefore, dioxins include 265,438+00 compounds, which are very stable, have a high melting point, are extremely insoluble in water, can be dissolved in most organic solvents, and are colorless and odorless fat-soluble substances, so they are very easy to accumulate in organisms. 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.
2. What are the serious hazards of dioxins to human health?
The biggest harm of dioxins is irreversible "three-cause" toxicity, that is, teratogenicity, carcinogenesis and mutation. May cause fetal death, organ structure destruction and permanent organ damage in early development, or developmental retardation and reproductive defects; It can interfere with the hormone secretion of reproductive system and endocrine system, leading to the decrease of sperm quantity and quality, the interruption of testicular development, permanent sexual dysfunction, gender self-cognition disorder and so on. Causes canceration deformity of female uterus, breast cancer, etc. It may also cause permanent obstacles to children's immune ability, intelligence and sports ability, such as ADHD, dementia and low immune function. According to the latest case reports and animal experiments, the lifetime carcinogenic probability of 2,3,7,8-TCDD can reach1100-12g.
Dioxin is currently recognized as the most toxic environmental hormone. Environmental hormone refers to an exogenous chemical substance that interferes with the normal hormone function of human body. Its structure is similar to endocrine hormone, which can cause endocrine disorder, also known as environmental hormone or endocrine disruptor. Environmental hormones enter the human body or wild animals through environmental media and food chain, interfere with their endocrine system and reproductive function system, and affect the survival and reproduction of future generations.
Dioxin is a persistent organic pollutant (POPs), which persists in the environment and is constantly enriched. Once ingested, organisms are difficult to decompose or excrete, and will spread and accumulate with the food chain. Humans are at the top of the food chain and the last gathering place of this pollution.
The impact of dioxins on people can be described as "tuning". General pollutants will have obvious harmful effects (i.e. action threshold) only when they reach a certain dose, but the action threshold of dioxins has not been studied so far. As long as it is an "ultra-micro" dose, it may cause harm, and the harm to infants is more obvious and irreversible.
Another feature of dioxin hazards is its long-term nature and concealment. There is a long latent process before obvious symptoms appear, which may affect human offspring. Therefore, some scientists even worry about whether human evolution will be terminated by such substances.
3. What is the current situation of dioxin pollution in China?
Although China lacks convincing data on dioxin pollution, according to foreign experience and limited data, dioxins have been detected in human blood, breast milk and lake sediments in China. Although the concentration level is low, it also shows the existence of dioxins in our environment. The production of chlorine-containing pesticides, wood preservatives and herbicides, especially the snail control drug (sodium pentachlorophenol) used to treat schistosomiasis in China, will produce dioxin by-products, and their production and use will make dioxins enter the environment unconsciously. Sodium pentachlorophenol, as the preferred chemical for snail control, has been used in China for decades, and the annual spraying amount is about 6000 tons, which will inevitably lead to the deposition of dioxins in the spraying area. Therefore, China has the potential of dioxin pollution. In addition, among the 47 categories of hazardous wastes listed in the National Hazardous Waste List released on October 4th, 1998/kloc-0, at least 13 is directly related to dioxins or may be generated during the treatment. For example, H04 pesticide waste, H05 wood preservative waste, HW 10 PCB-containing waste, HW 18 incineration residue, HW43 PCB-containing furan waste and HW44 PCB-containing dioxin waste. Therefore, it is of great significance to investigate and control dioxin pollution in the next few years or even more than ten years.
According to the investigation results of the sources of dioxins in the air in developed countries such as the United States and Japan, dioxin emissions from incineration facilities account for a large proportion. In recent years, the production and treatment of solid waste and medical waste in China have been increasing. Centralized incineration facilities have been established or prepared in various places. In 20001year, the State Environmental Protection Administration organized a sampling survey on the pollutant discharge status of domestic waste treatment facilities in 47 key cities across the country. The treatment scale of 329 garbage treatment facilities investigated is 179348 tons/day, accounting for about 55% of the national domestic garbage removal1180,000 tons, and only 3.3% of the garbage is in 20 incinerators. The over-standard rate of dioxin in flue gas of waste incineration plant is 57. 1%, and some backward waste incineration facilities exceed the standard by more than 99 times. Most of the waste incinerators that exceed the standard are small incinerators, and the furnace type is relatively backward. However, considering the low rate of garbage incineration in China, the total dioxin pollution caused by garbage incineration is not very serious at this stage. According to the data we have, it is estimated that the dioxin emitted into the air by garbage incineration in China is about 72g TEQ/a, which is far lower than the kg emission level in the United States and Japan. Of course, garbage incineration is in the ascendant in China, and its development momentum is rapid, so it should be paid enough attention to control the possible secondary pollution to an acceptable level.
4. What is the development level of dioxin pollution detection and prevention research in China at present? The gap with foreign countries?
The monitoring and research of dioxins in China started late. From 65438 to 0996, Wuhan Institute of Water Sciences, Chinese Academy of Sciences established the first research laboratory for detection of dioxin-like substances in aquatic organisms in China. In recent years, China Academy of Sciences, disease control, commodity inspection and other systems began to set up dioxin analysis laboratories to carry out some scientific research projects or engage in commodity inspection, disease control and other fields. However, the supervisory monitoring of industrial enterprises' pollution sources and the investigation and research of dioxins in the environment were less carried out. On 1999, the State Environmental Protection Administration promulgated the Pollution Control Standard for Hazardous Waste Incineration and the Pollution Control Standard for Domestic Waste Incineration, which stipulated the dioxin emission limits for domestic waste and hazardous waste incineration and took the first step to control dioxin pollution according to law. Subsequently, the National Environmental Analysis and Testing Center established a supporting laboratory to carry out dioxin monitoring and research in incineration facilities, and obtained a lot of basic data and research results. At present, the State Environmental Protection Administration (SEPA) is upgrading its laboratories, building SEPA dioxin laboratories, and plans to establish seven environmental dioxin monitoring centers nationwide.
Generally speaking, there is a big gap between China's dioxin monitoring capacity and foreign countries, and there is no systematic investigation and evaluation of dioxin emission sources and pollution status. Dioxin pollution from other sources needs further investigation and study. For example, China is a big chlor-alkali producer. Among the 500 chlor-alkali enterprises in the world, there are nearly 300 in China, and the annual output of caustic soda ranks second in the world from 65438 to 0998. The waste residue from chlor-alkali production may be one of the main sources of dioxins in China. There are also dye chemicals, organochlorine chemicals, pulp bleaching and other industries, all of which are potential sources of dioxin emissions.
5. What is the main research direction of dioxin laboratory of National Environmental Analysis and Testing Center in the future?
(1) Study on sampling and analysis methods of environmental dioxins;
(2) Monitoring and investigating the pollution status and distribution of dioxin in the environment;
(3) Investigation of dioxin emission sources, research on emission control and emission reduction technology;
(4) Study on the toxicity and effects of dioxins;
(5) Research on performance support technology;
(6) International cooperation and exchange;
(7) Training on dioxin analysis technology.
6. What are the difficulties in dioxin detection?
The monitoring, sampling and pretreatment of dioxins are very complicated, belonging to ultra-trace and multi-component analysis, which requires high specificity, selectivity and sensitivity, and it is difficult to effectively separate and quantify by conventional analytical methods. In addition, the standard samples used in the analysis are expensive and complicated to operate. Dioxin directly harms people's health, so the laboratory needs strict protection. Conventional analytical laboratories and ordinary low-resolution mass spectrometry cannot meet the above requirements.
There are many kinds of dioxin isomers, and the toxicity of each isomer is quite different, so the determination method must meet strict requirements:
(1) high sensitivity. Because the dioxin content in environmental samples is generally on the order of ng( 10-9g) or even pg( 10- 12g), the detection limit of this method must reach pg (1pg =10-12g). At present, the absolute detection limit of the best HRGC/HRMS for 2,3,7,8-T4 CDD can reach 20fg (1fg =10-15g), and the detection limit of the method can also reach below 50fg.
(2) High selectivity. In various compounds extracted from monitoring samples, the content of * * interfering components is often several orders of magnitude higher than that of dioxins, and it is impossible to analyze ultra-trace dioxins without a highly selective method;
(3) High specificity. Dioxin itself is a mixture of 2 10 isomers, and the analysis targets are dioxins with 4 ~8 chlorine substituents, and there are also 136 species. Among the dioxin isomers to be detected, all 65,438+07 chlorinated isomers at positions 2, 3, 7 and 8 must be analyzed from 65,438+036 dioxin isomers and quantified separately, so the method is required to be highly specific.
(4) Strict quality assurance measures. Dioxin analysis is different from routine project analysis, and its characteristics such as extremely low concentration, complicated operation and long analysis period require that the analysis method itself must have a set of strict quality assurance measures.