Some of the sources of soil pollutions are discussed below:
1. Industrial wastes:
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There are two kinds of wastes that are generated from industrial activities: unused chemicals and unwanted industrial garbage.
Unused chemicals like fly ash, sludge, plastics and sawdust are some of the chemicals that are discharged from industries.
Unwanted garbage from industrial activities like glass, metals and wood are the other kinds of wastes which industries generate. When these wastes are left on the soil’s surface, they change the chemical composition of the soil. The physical qualities of soil are also altered. Such sources of soil pollution make the soil harmful as well as barren.
i. They spoil the fertility of the soil.
ii. The chemicals released are harmful to living organisms dependent on the soil.
iii. Contamination of the soil is a direct cause of contamination of the crops. As a result harmful chemicals enter the food chain.
2. Agricultural practices:
Sometimes, excessive chemical fertilizers are applied to the crops. Plants absorb what they need and the excess goes into the soil. Animal excreta, debris and crop residues are some other contaminants that result from agricultural practices. These contaminate the soil by changing its physical and chemical properties.
i. Soils that have been spoiled due to excessive use of chemicals and pesticides become barren.
ii. When plant macronutrients like potassium, phosphorus and nitrogen are used excessively, the soil becomes deficient in micronutrients like boron and zinc.
iii. Excess chemicals from agricultural practices harm the survival of a number of friendly m icroorgan isms.
iv. Pesticides that contaminate the soil seep lower down the soil layer and contaminate groundwater that is used for domestic purposes.
3. Biological agents:
Biological agents like bacteria, fungi, virus and protozoans are a major cause of soil pollution. Human and animal excreta, poor sanitary conditions, wastes from hospitals and food joints cause soil pollution because they perpetrate growth of biological agents in the soil.
i. They cause diseases in human beings.
ii. They harm the development and existence of flora and fauna.
iii. They spoil qualities of fruits and vegetables grown in the polluted soil.
4. Mining and smelting:
Mining and smelting activities are lethal causes of soil pollution. Extraction and processing of mineral ores causes harm to the top soil layer. Mining fires destroy lands around the area and mining wastes cause heaps of wastes to be produced if the activity is not checked. Similarly, on one hand, installation of cement factories in the mountainous region weakens the soil strata leading to landslides, and on the other hand, the cement dust that falls on natural vegetation and crops blocks their stomata to cause their eventual death.
i. Mining wastes often cover the top soil, thus spoiling a precious natural resource.
ii. It makes the soil infertile.
iii. It harms the existence of microorganisms thriving on the soil.
iv. Heavy metals that enter the soil enter the food cycle. These metals are particularly absorbed by infants and children.
5. Radioactive pollutants:
Radioactive pollutants arise from nuclear activities like explosion devices, nuclear tests and laboratories, as well as nuclear power plants. Refining of plutonium and thorium as well as fuels for industrial and domestic uses are some other causes of radioactive pollution. Radioactive elements that are released into the air also enter the soil as radionuclide’s with rainwater.
i. The rainwater that passes through the polluted soil picks up radioactive elements. This harms the flora and fauna that thrive on rainwater.
ii. Radioactive elements are absorbed by soil particles, causing harm to soil qualities.
iii. They can cause health problems for human beings.
6. Dispersion of acids and acid rain:
Acids that enter the soil along with heavy metals or acid rain harm soil properties. This polluted soil becomes acidic in nature and becomes unproductive for crops, which require alkaline or neutral soils. Acidic gases like SO2 and NOx when combine with atmospheric moisture form acids and fall on the earth. They cause soil pollution by changing the pH of the soil.
i. Acids harm growth of plants that are sown in these soils.
ii. When acids are present in the soil, they are carried away with flowing water, causing harm to water bodies.
iii. Acid deposition changes the chemical qualities of soil.
7. Urban wastes:
Urban wastes that result in residential areas cause contamination of the soil at places where the wastes are not properly disposed. Wastes like glass, plastic, human excreta, fuel residues, metals and vehicular products are common urban wastes.
Not only does accumulation of these wastes result in poor human health, they also cause pollution of the soil. Urban wastes do not dispose easily, and therefore cause a lot of harm to the soil and its properties. Nonbiodegradable wastes like plastic, metal cans and glass cause great harm to the soil.
i. Urban wastes dirty residential areas, resulting in the growth of insects and pathogens.
ii. They are harmful to human health.