Soil pollution means that the pollutants generated by human activities enter the soil through various paths. The quantity and speed of the pollutants exceed the soil's containment and purification ability, so that the nature, composition and properties of the soil will change, and the accumulation process of pollutants gradually takes advantage. Soil pollution destroys the natural ecological balance of the soil, and causes the natural function of the soil to be imbalanced and soil quality deteriorates.
What are the main causes of soil pollution?
Pesticides can prevent and control diseases, insects, and weeds. If used properly, they can increase crop yields. However, they are a very harmful soil pollutant. Improper application can cause soil contamination. Only half of the pesticides (powders, liquids, emulsions, etc.) sprayed on crops are partially absorbed by plants or escaped into the atmosphere. Kinds of disinfectants, underground pest fumigants and pesticides, etc. constitute the basic source of pesticides in farmland soil. Crops absorb pesticides from the soil, accumulate in roots, stems, leaves, fruits and seeds, and endanger the health of humans and livestock through food and feed. At present, there are about 50 kinds of chemical pesticides in use. Among them, the main packages are rich in organophosphorus pesticides, organochlorine pesticides, carbamates, phenoxycarboxylic acids, phenols, and amines. In addition, petroleum, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, methane, and harmful microorganisms are also common organic pollutants in the soil. Organophosphorus pesticides account for 70% of pesticides, and 70% of organophosphorus pesticides are highly toxic species, resulting in many pesticide residues and serious soil pollution.
The application of chemical fertilizers is an important measure to increase agricultural production, but unreasonable use can also cause soil pollution. Long-term large-scale use of nitrogen fertilizer will destroy the soil structure, cause soil compaction, deterioration of biological properties, and affect the yield and quality of crops.
The use of heavy metal-rich wastewater for irrigation is an important pathway for heavy metals to enter the soil. Another path is to fall into the soil with atmospheric deposition. The main heavy metals are mercury, copper, zinc, chromium, nickel, cobalt, etc. For example, industrial wastewater from smelting, electroplating, fuel and mercury compounds can cause heavy metal pollution such as cadmium, mercury, chromium and copper; industrial wastewater from petrochemicals, fertilizers and pesticides can cause organic pollution such as phenol, trichloroacetaldehyde and pesticides. Because heavy metals cannot be differentiated by microorganisms, and can be enriched by microorganisms, once the soil is contaminated by heavy metals, its natural purification process and artificial management are very difficult. If the wastewater is used directly for irrigation without necessary treatment, the toxic and harmful substances in the wastewater will be brought to the farmland and pollute the soil.
Radioactive elements are mainly derived from the fallout from atmospheric nuclear experiments, as well as from various exhaust gases, wastewater and sludge emitted during the peaceful use of atomic energy. Radioactive element-rich materials inevitably contaminate the soil with natural sedimentation, rain water and waste accumulation. Once the soil is contaminated by radioactive substances, it is difficult to eliminate itself, and can only decay naturally into stable elements, and eliminate its radioactivity. Radioactive elements can enter the human body through the food chain.
The pathogenic microorganisms in the soil contain, first and foremost, pathogenic bacteria and viruses. They come from human and animal manure and sewage used for irrigation (untreated daily sewage, especially hospital sewage). If people work with soil rich in pathogenic microorganisms or eat vegetables and fruits contaminated by soil, they will be directly harmed.
Industrial waste and municipal waste are solid pollutants of soil. For example, various agricultural plastic films are widely used as greenhouses and mulch, and if they are not well managed and recycled, a large amount of residual film fragments will be scattered in the fields, causing "white pollution" on farmland. Such solid pollutants are not easy to evaporate and volatilize, nor are they easily decomposed by soil microorganisms, which is a kind of pollutant that stays in the soil for a long time.
The harmful gases in the atmosphere are mainly toxic exhaust gases emitted from industries, which have a large pollution surface and can cause serious pollution to the soil. Industrial waste gas pollution is broadly divided into two categories: the first category is gas pollution, such as sulfur dioxide, fluoride, ozone, nitrogen oxides, hydrocarbons, etc.; the second category is aerosol pollution, such as dust, soot and other solid particles and smoke, fog and other liquid particles, which enter the soil through precipitation. The exhaust gas from non-ferrous metal smelters contains heavy metals such as chromium, lead, copper and cadmium, which cause pollution to the nearby soil. factories producing phosphate fertilizer and fluoride can cause dust pollution and fluorine pollution to the nearby soil. SO2, NO and other harmful gases emitted by industries react in the atmosphere and form acid rain, which enters the soil in the form of natural precipitation and causes soil acidification. Metallurgical industry chimney emissions of metal oxide dust, then under the action of gravity in the form of dustfall into the soil, the formation of sewage plants as the center, the radius of 2 to 3 km range of point pollution. The explosion-proof agent tetraethyl lead added in gasoline is discharged with exhaust gas to pollute the soil, and obvious lead pollution zones are often formed on both sides of roads with high traffic frequency.
What are the harms of soil pollution?
Soil pollution has brought about serious consequences.
1、Soil pollution is cutting off the already limited arable land.
2、Soil pollution poses a great threat to people's health. Soil pollution will accumulate pollutants in plant (crop) objects and enrich into human and animal bodies through the food chain, endangering human and animal health and causing cancer and other diseases.
3、 It has a great adverse impact on agricultural development. Soil pollution leads to serious direct economic losses such as decline in soil quality, crop yield and quality.
4、 Soil pollution is also an important cause of other environmental pollution. After the land is polluted, the contaminated topsoil containing high concentrations of heavy metals is easy to enter the atmosphere and water bodies under the action of wind and water forces respectively, leading to atmospheric pollution, surface water pollution, groundwater pollution and ecosystem degradation and other secondary ecological and environmental problems.
5、Pollutants in soil pollution are migratory and retention, and may continue to cause new land pollution.
6、Soil pollution is not conducive to the sustainable development of the rural economy and seriously endangers the interests of future generations.
What are the measures to control soil pollution?