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abstract:
Nowadays, the most serious environmental problem is soil pollution. Among soil pollution, heavy metal pollution is the most harmful and widely distributed, which has greatly damaged the ecological environment, endangered people's health and even seriously threatened the sustainable development of China. Under the advocacy of green development concept, people gradually realize the importance of soil environmental protection and pollution prevention and restoration. Based on a brief analysis of the present situation, causes and harm of heavy metal pollution in China, this paper summarizes some countermeasures to prevent and control soil pollution in combination with the basic measures to control soil pollution in various parts of the country.
Key words:
Soil pollution; Harm; Prevention and control countermeasures;
1. Present situation and causes of heavy metal pollution in soil
1. 1, Status of soil pollution in China.
Soil is an indispensable living resource for human beings. Humans get enough material wealth from the soil to recuperate. Without land, it is difficult for human beings to survive. People lack sufficient awareness of protecting soil environmental resources in daily life, which leads to increasingly serious soil pollution. In recent years, with the rapid development of industry and agriculture in China, the pollution degree of soil environment is getting higher and higher, and the content and types of pollutants are also increasing. Heavy metal pollution in soil has seriously affected people's lives and threatened everyone's life safety. Soil heavy metal pollution refers to the pollution caused by the invasion of metals or their compounds with specific gravity greater than 5. At present, about 45 kinds of heavy metal elements have been found, including cadmium (Cd), nickel (Ni), chromium (Cr), manganese (Mn), arsenic (As), mercury (Hg) and zinc (Zn). The cultivated land polluted by heavy metals such as arsenic, cadmium, lead and chromium accounts for about 1/5 of the total cultivated land area in China. According to the survey data of 20 16 of the monitoring system of the Ministry of Agriculture of China, due to the pollution of heavy metals in soil, China's grain production is reduced by more than 10,000 tons per year. According to the statistical data of sewage irrigation areas in agriculture and rural areas, there are about 654.38+0.4 million hm2 sewage irrigation areas in China, and 64.8% of the land area is polluted by heavy metals. Heavy metal pollutants in sewage make plants in soil suffer secondary pollution. Organisms absorb these toxic and harmful substances, such as mercury, lead, zinc, cadmium, copper and other metal elements, and enter the human body through food chains and other channels, laying a huge hidden danger to human health, even damaging human physiological organs and seriously affecting health.
1.2, causes of heavy metal pollution in soil of China.
There are many reasons for soil heavy metal pollution, including excessive use of chemical fertilizers and pesticides, industrial and domestic pollution, traffic pollution and so on. Fertilizers and pesticides are important agricultural means of production, and pesticides play a vital role in the prevention and control of crop diseases and insect pests in agricultural production. However, due to the lack of correct and scientific guidance on selecting pesticide varieties and application methods, the soil ecosystem has been destroyed. Chemical fertilizer can greatly increase the yield of crops. In order to pursue high yield, farmers use too much chemical fertilizer for a long time, which leads to soil acidification and hardening, which not only reduces soil fertility, but also seriously damages the quality of soil cultivated land. Long-term use of chemical fertilizers and pesticides has caused serious cumulative pollution of heavy metals in soil and crops. Industrial and domestic pollution refers to industrial and domestic sewage and garbage, which contains a lot of toxic and harmful substances such as heavy metals and organic substances. Untreated industrial sewage directly irrigates farmland, causing serious pollution of some farmland and destroying soil ecological environment. Any industry that uses heavy metals and materials containing heavy metals as raw materials will cause heavy metal pollution if it discharges waste liquid, waste residue and wastewater that have not been strictly treated in the production process.
2. Harm of heavy metal pollution in soil
Soil can provide basic nutrients for plant growth. When the heavy metals in the soil exceed the standard, it will affect the absorption of nitrogen and phosphorus by plants, change the form of potassium, thus affecting the growth of plants and causing changes in plant physiological characteristics. High concentration of heavy metals will cause insufficient nutrition in plants and reduce the effectiveness of enzymes. Some crops can be rich in heavy metals, resulting in excessive heavy metals in crops, and some even gradually transform into more toxic methyl compounds, which accumulate in the human body at harmful concentrations through the food chain, seriously endangering human health. Excessive intake of heavy metals will cause diseases such as decreased immunity and respiratory disorders. Lead can damage children's central nervous system, cause children's mental and behavioral disorders, and also do harm to adults' nervous, digestive and cardiovascular systems. Excessive intake of cadmium will increase the probability of fracture and reduce bone density, which is harmful to the kidney, liver, lung, bone, blood and immune system of human body. Lead and mercury can cause fetal abortion, malformation and death by affecting human pregnancy. Arsenic can cause hepatosplenomegaly and ascites, inhibit children's intellectual development, and also cause Blackfoot disease, diabetes, nephropathy, cerebrovascular disease and other diseases. Excessive accumulation of copper in human body will lead to copper poisoning, metabolic disorder and severe acute renal failure. It is difficult to effectively control heavy metal pollution in soil, air pollution and water pollution. Many kinds of heavy metals accumulated in soil will cause serious harm to soil environment, animals, plants and microorganisms.
3, the prevention and control measures of soil heavy metal pollution
3. 1, formulate management and supervision regulations.
Facing the increasingly serious soil heavy metal pollution, policies and regulations should be established and improved to ensure the smooth progress of soil pollution prevention and remediation. In 20 16, the Action Plan for Prevention and Control of Soil Pollution was issued, and in 20 18, the Law on Prevention and Control of Soil Pollution in People's Republic of China (PRC) was passed. The two laws and regulations focus on improving the quality of soil environment, strictly prevent and control heavy metal pollution in industrial and mining enterprises and agricultural production and life, and formulate and accountability legal standards for soil pollution. The prevention and control of soil pollution should adhere to the principles of giving priority to prevention, giving priority to protection, strictly controlling new pollution and treating by stages, and form a soil pollution prevention and control system led by the government, responsible by enterprises, with public participation and social supervision. Protecting soil quality and preventing soil pollution is the unshirkable responsibility of every citizen and organization.
3.2, grasp the source, prevention and control of heavy metal pollution sources in the soil.
To strictly control the pollution sources of heavy metals in soil, we must start from the source, manage them by classification and classification, and strictly control the pollution sources. We must follow the basic principles of putting prevention first and combining prevention with treatment. Strictly control the pollution discharge of industrial and agricultural production and residents' life. Take effective measures to reduce, control and eliminate pollution sources. Vigorously promote clean and non-toxic processes, reduce or eliminate the random discharge of heavy metal pollutants from industrial and mining enterprises, recycle and treat industrial "wastewater, waste liquid and waste residue", strictly control the discharge and concentration of pollutants, and avoid secondary pollution of heavy metals to the soil environment. To control chemical fertilizers and pesticides in agricultural production, it is necessary to enhance farmers' awareness of protecting cultivated land quality and increase publicity and education on soil pollution prevention and control; Law enforcement departments and pesticide monitoring departments regularly monitor pesticide products circulating in the market, prohibit or restrict the use of highly toxic pesticides, and actively promote pesticides with low toxicity, good effect and low residue, such as pyrethrins, nicotine and other natural plant ingredients; Popularizing the Natural Enemy Control Law should not only eliminate the threat of pests and diseases to crops, but also minimize the harm of pesticides to the ecological environment.
4. Do a good job in the prevention and restoration of contaminated soil.
Facing the increasingly severe situation of soil heavy metal pollution in China, we should fully understand the four characteristics of soil heavy metal pollution: irreversibility, arduousness, long periodicity, accumulation, regionality and concealment, and actively take various remediation measures to reduce the degree of soil pollution and create a safe, beautiful and happy ecological environment. In view of the measures taken to control soil heavy metal pollution in various parts of China, there are generally four methods: engineering control measures, chemical control measures, biological control measures and agricultural ecological control measures.
4. 1, engineering control measures
As an authoritative method to control soil heavy metal pollution, engineering control measures can fundamentally solve the problem of heavy metal pollution. However, the implementation of engineering control measures needs a lot of personnel and funds, and it will destroy soil structure and reduce soil fertility. At the same time, it is necessary to deal with the transferred contaminated soil. Engineering treatment generally controls heavy metal pollution in soil through measures such as soil replacement and deep ploughing. The soil pollution in agricultural greenhouses with serious pollution and small area adopts the guest soil method. When unpolluted clean soil moved from other places is added to polluted soil, artificial soil or sandy loam with good texture is mostly used to reduce the concentration of heavy metals in soil topsoil, reduce the toxicity of heavy metals to plant roots and accelerate the speed of soil ecological restoration. Soil replacement method is to transfer polluted soil and replace unpolluted clean soil. This method can quickly repair the damaged soil with obvious effect, but the soil replacement method is time-consuming and laborious, and the cost is high. The soil replacement method can be used for the soil with radioactive pollutants or the soil with serious pollution, such as scenic spots, gardens and scientific research places, which is difficult to decompose and the pollutants are easy to spread. Light pollution and thick topsoil pollution can be reduced by deep ploughing and ploughing, that is, by stirring, ploughing and mixing topsoil.
4.2, chemical control measures
Chemical treatment is to add inhibitors and modifiers to contaminated soil to reduce the bioavailability of heavy metals. Chemical treatment has obvious effect, short cycle and moderate investment, but it cannot guarantee the long-term stability of treatment effect.
4.3, biological control measures
Biotechnology is a new prevention and control measure that is being widely promoted. It can inhibit, reduce and improve the absorption and degradation of pollutants in soil and reduce the toxicity of heavy metals through some unique habits of plants, animals and microorganisms. Phytoremediation technology is a new and potential green and safe remediation technology, which absorbs excessive heavy metals in soil with low investment and maintenance costs, and has the characteristics of high beautification value and less secondary pollution, and is favored by many countries. Microbial remediation refers to a bioremediation technology that makes full use of the microbial metabolic function of naturally occurring or artificially cultured microbial groups with specific functions to degrade them into non-toxic substances or reduce the activity of toxic pollutants under suitable environmental conditions. Microbial remediation is actually biodegradation. It can decompose environmental pollution by using the characteristics of fast reproduction, small size, easy variation and strong adaptability of microbial communities, and can also degrade and transform those "strange" compounds.
4.4, agricultural ecological management measures
The method of agricultural ecological management is to adopt some soil tillage management systems adapted to local conditions in the agricultural production process, plant suitable plant varieties, improve the ecological environment of soil, and reduce or block the harm of heavy metals to human body. Rational planning of agricultural planting areas and planting cash crops or trees, flowers and grass with high heavy metal concentration in areas with serious heavy metal pollution can not only beautify the environment, but also purify the soil; Planting low-enriched heavy metals in basic suitable areas can reduce the accumulation of heavy metals in crops and improve soil quality. The agricultural ecological management method has a long cycle and the effect is not obvious.
5. Concluding remarks
The high content of heavy metals in soil seriously endangers the living environment of human beings and has a negative impact on the whole natural geographical environment. A single remediation technology can't completely repair the soil. It is necessary to focus on phytoremediation, optimize the screening of specific microorganisms, establish related gene banks, cultivate super-strong engineering bacteria, and complement each other with various control measures to completely remove heavy metals from the soil. Do a good job in guiding and publicizing the knowledge of soil environmental protection, improve people's awareness of environmental protection, and promote the healthy development of soil ecology.
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