Abstract: Through the analysis of the origin, form, migration and dispersion of mercury pollution in the atmosphere, soil and water in China, and in combination with the overspend of mercury in various media and its impact on the health of people in the polluted areas, we can understand the current status of mercury pollution in China and its impact on human health.

Keywords: mercury; Pollution; Health damage

Along with the rapid development of industry, which brings huge economic benefits, it also constitutes severe environmental pollution. During the ultra-low emission dust meter, environmental mercury pollution has caused great damage to the health of the population. For example, in the 1950s, the Minamata disease in Minamata Bay, Kyushu, Japan, was the first environmental hazard caused by mercury pollution, which caused great social damage. According to statistics, 5172 people were ill and 730 died of Minamata disease in Japan [1]. In 1972, 459 people died of mercury poisoning in Iraq caused by treating seeds with methyl mercury and ethyl mercury fungicides [1]. Since then, mercury pollution has also occurred in a series of countries around the world, which has aroused widespread concern around the world, and various measures have been taken to prevent and control mercury pollution. Mercury pollution has the characteristics of persistence, mobility, high bioaccumulation, strong toxicity, etc., and mercury in any method in the environment can be converted into highly toxic methyl mercury under certain conditions, thus causing great harm to human health. Together, mercury has the attribute of long-term transboundary pollution, and has been listed as a global pollutant by the United Nations Environment Programme. Besides greenhouse gases, mercury is a chemical substance that has an impact on the global scale, and has become one of the environmental pollutants of global concern. The author introduces the current situation of environmental mercury pollution in China from three aspects: the fundamental nature and use of mercury, the distribution of mercury pollution in China, and the current situation of mercury pollution on human health.

1 Fundamental nature and use of mercury

Mercury is widely distributed in the natural world, such as rocks, soil, plants, rivers, and the atmosphere, but its content is very small, which will not harm human health. It can be called the natural mercury content. Mercury exists in the natural world in the form of metallic mercury, inorganic mercury and organic mercury. Common inorganic mercury mainly includes mercury sulfide, mercury oxide and mercury chloride. Organic mercury in the ultra-low CEMS system mainly includes methyl mercury, ethyl mercury and phenyl mercury. The elemental mercury can easily react with sulfur and generate red HgS, commonly known as cinnabar. Mercury is stable in air and water, does not react with acid (concentrated nitric acid) and alkali, and has excellent thermal conductivity and conductivity. Mercury can form an alloy with almost all metals except iron, which is called amalgam [2]. Metallic mercury and its compounds have a wide range of uses. There are about 80 kinds of industries in the world that need mercury as a raw material for production, which is mainly used in chemical industry, metallurgy, electronics, light industry, medicine, medical equipment and other professions. Mercury can also be used as a protective agent and coolant for nuclear reactors [2]. Mercury and inorganic mercury in the natural world can be transformed into organic mercury under the action of microorganisms, which can enter the human body through the enrichment of the food chain and damage health. Mercury of any method will be toxic to human body, and cannot be differentiated or degraded into non-toxic substances [3], while the toxicity of methyl mercury is strong. However, in the process of being widely used, mercury and its compounds have also polluted the environment to a certain extent due to improper environmental protection measures or accidents.

2. Dispersion of mercury pollution in China

The sources of mercury causing environmental pollution can be divided into two categories: natural emissions and anthropogenic emissions. Natural emissions are mainly caused by volcanic eruptions, geothermal activities, natural weathering, vegetation release, forest fires, etc., while anthropogenic emissions are mainly caused by human activities, including mercury use, mercury impurities contained in substances, and mercury emissions caused by waste treatment [4]. Mercury pollution caused by natural emissions is not about human power, and generally only accounts for 1/4 of the total mercury emissions [5]. Human emission is the primary cause of mercury pollution. China is the third largest mercury producer in the world after Spain and Italy [6], and also a large mercury consumer. Many enterprises are closely related to mercury. The primary source of mercury supply in China is mercury mining [7], especially in Guizhou, where there are many mercury mines. Guizhou Wanshan region is known as the mercury capital of China, and it is a large mercury mining area in Zui. During the mining process, due to the low level of technology, the lack of environmental protection measures and other reasons, the surrounding areas of mercury mines are seriously polluted by mercury. Many scholars have discussed the mercury pollution situation in this region. Ding Zhenhua found in 2002 that the mercury pollution in the mercury mine and its surrounding environment (soil and atmosphere) in Wanshan District, Guizhou Province is relatively severe.

In addition, mercury pollution in Jilin, Shaanxi, Hubei, Liaoning and Chongqing is also serious. Its pollution sources include the production of caustic soda by mercury electrolysis, mining and training of mercury containing ores and gold mines, coal burning, hospitals, battery manufacturing, instrument appearance production, waste burning, chlor alkali industry and other production occupations or parts. They discharge mercury and its compounds into the natural environment by discharging waste water, waste residue, waste gas, etc., which constitutes the pollution of the surrounding air, water, soil, plants, etc., and then enter the human body through multiple ways, causing severe damage to various systems of the human body, especially the nervous system.

2.1 Atmospheric mercury pollution

In addition to natural sources, the sources of atmospheric mercury pollution include coal burning, nonferrous metal exercise, cement industry, domestic waste burning and landfill, oil burning, etc. During this period, nonferrous metal exercise, coal burning, and waste burning are the primary sources of atmospheric mercury pollution. The discussion indicates that the global anthropogenic pollution sources annually discharge 1900-2200t of mercury into the atmosphere, during which 70% of mercury is emitted from coal burning and waste burning [8]. The cooperative discussion between Tsinghua University and Argonne Laboratory in the United States pointed out that in 2003, various emission sources in China discharged 650t of mercury into the atmosphere, during which the atmospheric emissions of nonferrous metal exercise and coal combustion were high, accounting for 52% and 39% of the total emissions respectively [9]. The primary chemical methods of mercury in the atmospheric environment include elemental mercury (Hg0), bivalent mercury (Hg2 -) and particulate mercury (Hgp), among which the share of elemental mercury (Hg0) is large, accounting for more than 90% of the total [10]. The elemental mercury has weak response and low solubility, can exist in the atmosphere for an appropriate long time (about 0.5~1.5 a), participate in the global atmospheric cycle, and carry out large-scale long-distance transportation; Divalent mercury (Hg2+) contains divalent inorganic mercury compounds, methylmercury and dimethylmercury, which are highly water-soluble and easily enter the surface system through dry and wet sedimentation; However, particulate mercury exists in the atmosphere for a short time with low concentration and is easy to settle, and then enters the soil or water body. For example, Feng Xinbin et al. [11] discussed that waste landfills not only discharge gaseous elemental mercury into the atmosphere, but also discharge methyl mercury and dimethyl mercury.

The total gaseous mercury setting value in the Northern Hemisphere is 1.7ng/m3 [12]. The average atmospheric mercury content in Wuhan in 2002 was 15.9ng/m3 [13]. The average atmospheric mercury content in Changbai Mountain area was (3.22 ± 1.78) ng/m3 [14]. The average atmospheric mercury content in Xiamen was 11.037ng/m3 [15], which was higher than the average atmospheric mercury concentration, indicating that the atmosphere in these areas was polluted by mercury.

2.2 Soil mercury pollution

The origin of mercury in soil is multifaceted. In addition to the mercury contained in soil itself, human industrial and agricultural production activities such as atmospheric mercury deposition (dry and wet deposition), sewage irrigation, sludge composting, application of organic mercury pesticides, accumulation or landfill of mercury containing waste are also important sources of soil mercury pollution [16]. For example, Wang Yinggang et al. [17] showed that the dry and wet deposition of mercury containing pollutants in the atmosphere constituted the mercury pollution of Taiyuan soil. Mercury and its compounds in mercury containing waste can enter the soil under the erosion of rainwater and surface runoff, which constitutes soil mercury pollution.

After mercury and its compounds enter the soil environment, they can exist in the soil for a long time, be absorbed by plants and enter the food chain cycle, be released into the air in gaseous form, and enter the water cycle system through precipitation or runoff washing under the physical and chemical effects of adsorption, exchange, dissolution, precipitation, redox, biochemistry, etc. through different methods. According to the form of mercury, it can be divided into three forms: metal mercury, organically bound mercury and inorganic bound mercury. The content of metal mercury is very low, but it can be directly absorbed by plant roots or leaves. In addition, soluble organic matter (DOM), humus, iron oxide and clay mineral deposits contained in soil have certain adsorption effect on Hg2+[18], which can form bound mercury. Cl - has a strong affinity for Hg2+and can form easily soluble inorganic compounds (HgCl2), which can be transported biologically through plant absorption and enter the food chain, causing damage to human body. Plants have different mercury absorption capacities, which are shown as follows: conifers>deciduous plants>rice>corn>sorghum>wheat>leaf vegetables>root vegetables [19]. And the mercury content in different parts of plants is also different. It is generally believed that when mercury in plants is absorbed by soil, the underground part is higher than the aboveground part [20]; When mercury in plants is absorbed by the atmosphere, the aboveground part is higher than the underground part. Zhang Zhongsheng et al. [21] discussed that mercury content is gradually enriched in the process of the food chain of soil plant, plant plant herbivorous insects, and plant plant carnivorous insects. Generally, inorganic mercury is contained in plants and organic mercury is contained in animals. The mercury content in different soils is different. The VOCs online monitoring system includes pH value, temperature, organic matter, soil components, etc. Li Yonghua et al. [22] pointed out that the content of total mercury and various forms of mercury in soil increased with the increase of soil pH value. In addition, the study shows that the trend of soil mercury pollution in China is: industrial areas>residential areas>scenic areas>rural areas [23]. The first level specification of China's soil environmental quality specification (GB15618-1995) is 0.15 mg/kg. The mercury content of farmland soil in a gold mine area is 0.21 ～ 20.3 mg/kg, with an average of 2.23 mg/kg24. The mercury content of Huludao City soil is 0.055 ～ 14.575 mg/kg, with an average of 1.435 mg/kg [25]. The mercury content of Guilin soil is 0.076 ～ 2.336 mg/kg, with an average of 0.288 mg/kg [26]. The mercury content of Taiyuan soil is 0.043 ～ 0.297 mg/kg [17], both higher than 0.15 mg/kg, but with less pollution, It is attributed to slight mercury pollution. However, the scale of soil mercury content in Wanshan mining area is 24.31~347.52mg/kg [27], much higher than 0.15mg/kg, indicating that the soil mercury pollution in Guizhou Wanshan mercury mining area is severe.

2.3 Mercury pollution of water body

The origin of mercury pollution in water body includes the exchange of water and air, the mercury and its compounds in the soil under the action of rain washing into the aquatic ecosystem with water flow, and the discharge of mercury containing industrial wastewater. Mercury pollution of water bodies in China is mainly caused by the discharge of industrial wastewater. Many mercury related occupations, such as mining, chemical industry, chemical fiber, fertilizer, pesticide, metallurgy, electroplating, appearance, pigment and other industries, will discharge mercury containing wastewater, thus entering the water cycle system. In the 1960s and 1980s, the mercury poisoning in the Songhua River basin in China was caused by the acetaldehyde production wastewater with high concentration of mercury discharged by chemical enterprises. People suffer from mercury poisoning by drinking water polluted by mercury and its compounds or eating contaminated water and plants.

The water cycle system includes upper water body and base sediment, and the interaction between water body and sediment affects the mercury content of water body. Mercury and its compounds will accumulate in the sludge at the bottom of the water body, convert into methyl mercury under the action of microorganisms, enter the fish through the food chain, and cause mercury poisoning after human consumption. For example, Guizhou Baihua Lake was once polluted by mercury containing wastewater from acetic acid production enterprises using mercury method, but now the average value of total mercury content in the water body is 33.2ng/L, which is lower than the Class III water specification (100ng/g) in China's Environmental Quality Specification for Surface Water (GB3838-2002). The average total mercury content in fish body is 28.0ng/g [28], which is lower than the safety limit of mercury content (300ng/g) in China's regulations on aquatic products and 500ng/g in World Health Organization regulations on edible fish. The impact of mercury pollution on Baihua Lake is no longer significant. Since mercury pollution occurred in the Songhua River basin in the 1970s, through more than 20 years of management such as completely cutting off the pollution source, mercury pollution has not been completely eliminated up to now. The mercury content in river water is 150~380ng/L, higher than the scenery content, and the total mercury content in some fish bodies exceeds China's food hygiene standards [29]. The uniform mercury content in Huangpu River water is 400ng/L, higher than that in Guizhou Baihua Lake and Songhua River [30]. The mercury content of Wuli River in Huludao City is 84~10446ng/L, and the average value is 1395ng/L [31], which is much higher than the Class III water specification of 100ng/g, and the pollution is very serious.

3 Current situation of mercury pollution damage to human health in China

Mercury poisoning caused by environmental mercury pollution is mostly slow mercury poisoning. In the Diagnosis and Treatment Strategy for Heavy Metal Pollution (Trial) released by the Ministry of Health on December 20, 2010, mercury poisoning caused by environmental pollution is divided into slow mild mercury poisoning, slow moderate mercury poisoning, and slow severe mercury poisoning. The symptoms of the nervous system are the main manifestations, and severe cases can lead to death. Now there are statements of mercury poisoning cases caused by environmental mercury pollution in the world. The situation of environmental mercury pollution in China is relatively severe. For example, the Songhua River basin in Jilin Province and the Wanshan region in Guizhou Province have been severely polluted by mercury, which has caused severe damage to the surrounding population. After years of environmental management, the pollution has not been completely eliminated, and the impact on the health of the population still exists. In the mercury pollution incident of Songhua River in the 1970s, there were cases of methyl mercury poisoning. Hair mercury is an important indicator of mercury accumulation in the body to understand the degree of pollution. According to the survey, the average hair mercury content of fishermen along the Songhua River in 1975 was 17.50 μ G/g, the mean value of hair mercury in 1990 was 3.82 μ G/g, the mean value of hair mercury in 2000 was 2.15 μ G/g [32], hair mercury shows a downward trend, but it is still higher than the 1mg/kg hair mercury limit proposed by the United States Environmental Protection Agency, indicating that through more than 20 years of environmental pollution management, the environment has been significantly improved and the damage to human body has been reduced, but there is still mercury accumulation. The average value of mercury content in hair of residents in Guizhou Wanshan Mercury Mine area is 837 μ G/g [33], it can be seen that the mercury pollution in this area is very serious, and the damage to human body is also high. The average hair mercury content of residents in Ningbo City is 1.8mg/kg [34], while the average hair mercury content of residents in Chengdu, Suzhou, Changsha, Shanghai, Hangzhou and other places is higher than 1mg/kg [34], indicating that there is mercury accumulation in the residents and the health risk of exposure to mercury storage.

It can be seen from the above data that many cities in China are now facing the threat of mercury pollution. However, due to the vast territory of China, mercury pollution exists in some regions, but it has not been found or the data has not been published. Therefore, as long as the analysis of mercury pollution in some cities is not representative of the overall situation in China, this paper only analyzes and collects the existing data, so that people can understand the current mercury pollution situation, Pay attention to the harm of environmental mercury pollution to human health, and then take various useful measures to reduce the discharge of mercury pollutants, such as reducing mercury mining, using less mercury containing materials, replacing mercury containing or mercury using products and processes, and strengthening the management of mercury waste.