Abstract: In recent years, with the rapid development of global economy, pollutants containing heavy metals have entered the agricultural ecological environment through various channels, polluting soil and water bodies. This paper discusses the pollution of heavy metals on vegetables and its control methods.
Keywords: heavy metals; Pollution; Research; processing method
1 Vegetables are indispensable food in people's daily life, and the quality of vegetables is directly related to people's health.
Heavy metal pollution is the biggest harm to the quality of vegetables. Heavy metal pollution of vegetables mainly comes from industrial "three wastes", municipal solid waste, sewage and agricultural production itself. According to the way vegetables are polluted, there are the following sources.
Irrigation sewage 1. 1
With the development of urban industry and the acceleration of urbanization, water resources are gradually scarce. Sewage irrigation has become an important part of agricultural irrigation water, and industrial wastewater often contains heavy metals. A large number of untreated industrial wastewater and waste residue are discharged into rivers and lakes, polluting water resources to varying degrees. Vegetable production and yield increase mainly depend on irrigation. Urban industrial and mining areas and suburban vegetable fields have to use a lot of industrial wastewater and domestic sewage to irrigate vegetable fields. Therefore, the main soil heavy metal pollution areas in China are all caused by sewage irrigation.
1.2 industrial waste residue
According to incomplete statistics; Over the years, 75 cities in China have produced 710.572 billion tons of industrial waste residue and tailings, and 78 provinces and cities have counted the industrial waste residue10.980 billion tons. These waste residues not only occupy a large area of land, but also cause more soil pollution. Especially in vegetable fields near urban suburbs and industrial and mining enterprises, heavy metal pollution is becoming more and more serious.
1.3 Agricultural production activities
(1) In agricultural production activities, in order to unilaterally pursue high yield and increase benefits, a large number of unqualified fertilizers containing mercury, cadmium, lead and arsenic are produced. It is directly used as fertilizer without any treatment, which leads to the decrease of soil organic matter and essential nutrients for crops, and the excessive content of heavy metals, thus affecting vegetables; (2) In agricultural production activities, agricultural plastic films and stabilizers used in production all contain heavy metals Cd and As. In the process of using plastic greenhouses and plastic films in large quantities, heavy metal pollution may be caused in the soil, thus causing great harm to the growth, yield and quality of vegetables and other crops.
1.4 Other sources
With the rapid development of automobile industry, heavy metals, toxic and harmful gases, dust and so on. Heavy metals produced by heavy use of leaded gasoline, automobile exhaust emissions and automobile tire wear will pollute crops such as soil and vegetables near traffic trunk lines. There are also Cd in lubricating oil, Cd plating process and other production or discharge processes that discharge waste containing Cd into the soil, causing pollution. In addition, there is microbial pollution.
One of the most direct impacts of heavy metals on human health is the threat to food safety.
Most consumers' food safety concepts are only pesticide residues and food deterioration, and they know little about the problem that heavy metal pollution in soil affects food safety. Moreover, heavy metal pollution has potential, and ordinary consumers can't judge whether agricultural products are polluted by heavy metals from the appearance and avoid it.
(1) Different heavy metals do different harm to human body. Organic mercury is the most harmful to human body. It is not only toxic and can damage the brain, but also relatively stable. Its half-life in human body is as long as 70 days, and it can accumulate toxicity even in a small dose. It can be seen that the harm of heavy metals to human beings is incalculable, so the production of pollution-free vegetables has been paid more and more attention.
(2) At present, the pollution of vegetable fields and vegetables is very serious, and the exposure pollution of heavy metals and nitrates must be paid enough attention. Cadmium, mercury, chromium and arsenic are the heavy metals that soil pollution has great influence on vegetables.
Three methods to control heavy metals in soil
Through experiments on various vegetables, we found the critical concentration of soil when different vegetables exceeded the standard, and controlled the content of heavy metals in vegetables by controlling and controlling the content of heavy metals in soil. Because the main source of heavy metals in vegetables is soil, we can control heavy metals in soil through the following aspects.
3. 1 Prevention and control of soil pollution
Engineering measures can be taken for soil pollution, including: (1) foreign soil method: adding pure land to polluted soil. However, guests should try to choose soil with relatively heavy viscosity or high organic matter content to increase soil capacity and reduce the amount of foreign soil. This method is suitable for shallow-rooted plants and pollutants with poor mobility. (2) Soil replacement method: it is to remove the polluted soil and replace it with new soil; However, for the soil with serious pollution in a small area, the pollutants are radioactive or easy to spread and difficult to decompose, the soil replacement method must be adopted to prevent the scope from expanding and endangering the health of people and livestock.
3.2 Strengthen the treatment and comprehensive utilization of industrial "three wastes"
(1) It is forbidden to use untreated industrial sewage to irrigate farmland. While actively and cautiously promoting sewage irrigation, we must strictly monitor the sewage from irrigated farmland. (2) Reduce the discharge of industrial wastewater and domestic sewage, develop a regional pollution prevention and control system, including making regional water quality management plans, rationally utilizing natural purification capacity, controlling the total discharge of pollutants, adjusting industrial layout, changing product structure, and improving management measures. The industrial layout should be reasonable, change the way of fuel burning, afforest trees, adopt tall chimneys and high-efficiency dust removal equipment, adopt central heating, reduce traffic waste gas pollution, and apply low-toxic and low-residue pesticides. (3) Choose farmland that is not polluted by industrial wastewater, waste residue and waste gas, and establish vegetable production bases in areas far away from urban industrial and mining enterprises, hospitals, domestic garbage, domestic water and other pollution sources.
3.3 Carry out pollution-free treatment of feces, garbage and domestic sewage.
Livestock manure must be composted, the purpose of which is to use the high temperature (70℃) generated in the process of decomposing organic matter by microorganisms to eliminate germs, eggs and viruses, so as not to cause biological pollution to vegetables. In recent years, new fertilizers produced by green food and vegetables, namely bio-fertilizers, include microbial agents and bio-organic fertilizers. After being applied to the soil, slow-release nutrients in the soil can be released for absorption and utilization by vegetables, reducing pesticide residues and heavy metal pollution, which is not only beneficial to improving the quality of vegetables, but also beneficial to protecting the ecological environment.
To improve the awareness of vegetable quality, we must protect the agricultural ecological environment. Water, soil, air and ecology are the resource bases of the environment and food chain on which human beings depend for generations. We must make up our minds, strengthen legislation and attach importance to the comprehensive improvement of agricultural ecological environment. On the one hand, prevent and control the environmental pollution of urban industries and township enterprises; On the other hand, it is necessary to widely publicize the scientific utilization of vegetables, standardized production and technical regulations for the production of pollution-free agricultural products, and improve the quality awareness, agricultural product safety awareness and agricultural product standardization awareness of vegetable farmers and citizens. Develop green food, carry out ecological engineering construction, and protect and improve the agricultural ecological environment.
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