Natural and synthetic materials can adversely affect the physical, chemical and biological] properties of soil and seriously affect its productivity are called soil pollutants. Here the pollutants remain in direct contact with soil for longer time.
Soil is getting heavily polluted by toxic materials and dangerous microorganisms, which| enter, through air, water and food chain.
Types of Soil Pollutants are:
1. Agricultural waste
ADVERTISEMENTS:
2. Industrial waste
3. Urban waste
4. Hazardous waste
1. Agricultural Waste
ADVERTISEMENTS:
Agricultural practices pollute the soil to a large extent. Huge quantities of fertilizers, pesticides, herbicides etc. are used to increase the crop yield. Excessive addition of the above chemicals! Increases the problem of soil pollution
(a) Fertilizers
Fertilizers are used to fortify the soil and to increase the rate of productivity. These fertilizers contain pollutants. These cause many undesirable effects on the water quality creating many health hazards.
It has been observed that in India, soil has suffered from pollution because of two practices: (i) excessive use of fertilizers and growth regulation agents in agriculture, and (ii) improper disposal of urban waste on land.
ADVERTISEMENTS:
Thus the soil is becoming increasingly polluted with toxic chemicals and heavy metals, which reach the food chain, surface water (through runoff or ground water through infiltration), and ultimately be ingested by man.
In cultivated lands, ions of N, P, and K are commonly present in the sub optimal amounts, because of being the chief constituents of commercial fertilizers. Although in nature soil fertility is not continually reduced through the annual removal of material from the area, nutrient deficiency is definitely a factor of considerable importance under certain conditions.
Nutrient deficiency may arise through the action of natural vegetation upon a soil originally more fertile or due to over-cropping and more irrigatorial frequency, as water may carry some nutrients through runoff process. Nitrogen, which is also an essential constituent of the soil, exists in both organic and inorganic forms.
Effects
ADVERTISEMENTS:
(i) Potassium fertilizers in soil decrease vitamin c and carotene in vegetables and fruits.
(ii) Excessive accumulation of nitrates can impose problem of diarrhoea and cyanosis in children.
(iii) Excessive use of chemical fertilizers may reduce the ability of plants to fix nitrogen.
(iv) Excessive nitrates and phosphates will result in Eutrophication.
ADVERTISEMENTS:
(v) If nitrates conc. is increased above 90 pppm in drinking water it leads to jaundice, (b) Pesticides
Pesticides include herbicides, fungicides and rodenticides. Pesticides, which are applied to the crops, are retained in the soil in considerable quantities. Pesticides may enter into the food chain and pose serious health hazards.
A man employs pesticide as purposeful environmental contaminates in order to improve the environmental quality for himself and his domestic animals and plants. In agricultural practices, pesticides and insecticides are used to protect or increase the yield of crops. But its use above the prescribed doses adversely affects soil fertility and phytotoxicity. It also causes groundwater pollution through seepage. Fertilizers such as nitrogenous, phosphorus and potassium also contribute to soil pollution.
The unwise use of pesticides and insecticides on croplands also contributes to soil pollution. When certain pesticide is sprayed over a cultivated land, a part of its residue goes into the soil contaminating plant leaves, roots, and fruits. Table 11:9. shows that organ chlorine type of pesticides remain in soil for many years posing serious problems to human health.
ADVERTISEMENTS:
Albrin remains for 1-6 years and is harmful to soil. Similarly DDT lasts for 4-10 years, which after chemical reactions becomes more toxic to human beings through soil and plants. The rate of degradation of pesticides in the soil is a function of its chemical properties and formulation applied. It has been found through various studies that the wide range of soil microorganisms accomplishes its degradation in soil.
Increase in chloride content is also caused due to excessive use of pesticides. Persistence rate of pesticide depends upon soil type, soil moisture content, temperature, uptake by plants, leaching by plants and wind erosion. Therefore, it is very difficult to generalize about soil persistence of pesticide, which is higher in percentage in soil having more organic matter content, while it is lower in sandy soil.
Effects
(i) Excessive usage of pesticides will create resistance in the pests.
(ii) Pesticides like aldrin, DDT etc. seep gradually through soil into groundwater.
(iii) Organophosphate pesticides cause extreme muscular weakness and dizziness.
(iv) Arsenic pesticides make the soil permanently infertile.
2. Industrial Waste
Disposal of industrial waste is the major reason for soil pollution. These wastes are mail discharged from paper and pulp industries, electrical and atomic power plants, mining and smelting operations etc. Industrial waste mainly consists of organic compounds Nitrogen (N), Phosphorous (P) and Potassium (K). Nitrogen fertilizers are highly soluble, nutrient release is rapid and in mo soils absorption is limited.
Phosphorous and potassium fertilizers are relatively low solubility and the released are often strongly absorbed along with inorganic components and non-biodegradable materials. These pollutants affect the chemical and biological properties of soil.
Effect
(i) Industrial wastes consist of a variety of chemicals, which are extremely toxic to living beings.
(ii) Metallic contaminants (Hg, Zn, Cal) destroy bacteria and beneficial microorganisms in the soil.
(iii) Some of the wastes contain pathogenic bacteria. Example: Anthrax bacilli in tannery wastes.
3. Urban Wastes
Urban wastes comprise both commercial and domestic wastes. All urban wastes are commonly referred as refuse. This solid waste contains garbage and rubbish materials like plastics, glasses, metallic can etc. These wastes are not degraded easily.
Effects
(i) Sewage is the good medium for the growth of pathogenic bacteria, viruses etc.
(ii) Solid wastes result in offensive smell and cause clogging of groundwater filters.
(iii) Suspended matter in sewage can blanket the soil thereby interfering with the soil moisture.
(iv) The use of polluted groundwater containing human excreta, sewage sludge decreases soil fertility by killing microorganisms.
4. Hazardous Wastes
Hazardous waste means a waste or combination of wastes, which because of quantity or concentration can cause serious illness and irreversible hazards to the humans. These mainly include radioactive wastes, biomedical wastes and non-radioactive industrial wastes.
Effects
(i) Radiation affects the soil fertility.
(ii) These radiations kill plant species.
(iii) Radioactive radiations also bring genetic changes through mutation and cause death of many organisms.
(iv) When food-containing radio nuclides are taken by man, some of them concentrate in specific body organs and cause undesirable diseases.