Discuss the Various Sources of Soil Pollution.
chemistry , environmental chemistry
Soil has been used as a dumping ground for most of the waste products—domestic, human, animal, industrial and agricultural. Every year the solid wastes dumped into the soils are increasing at an alarming rate all over the world. Huge amount of a number of hazardous chemicals and several thousand tons of wastes are ultimately dumped on the land. These are leached by municipal and industrial wastes and are responsible for pollution of ground water . The problem of soil pollution is compounded by the use of agrochemicals (e.g. fertilizers, pesticides, fungicides, bactericides, insecticides, etc). Besides these, the soil is polluted by deadly pathogenic compounds.
The soil pollution differ from air and water pollution in the sense that the pollutant in soil remain in direct contact with soil for relatively longer periods. In fact, the soil has been heavily polluted as a result of industrial revolution and green revolution. The humans are basically responsible for the pollution of land.
The main sources of soil pollution are
- Industrial Pollution
- Urban and Domestic Wastes
- Radioactive Pollutants
- Plastic and Polymers
- Chemicals and Metallic Pollutants
- Biological Agents
- Acid Rain
The major cause of soil or land pollution are the wastes, by-products generated from various industries. These wastes are discharged from various textile industries, paper and pulp industries, leather and tanning industry, petrochemical industry, food processing industry, soap and detergent industries dairy farms and metal processing industries etc.
It is believed that in these industries 50 per cent of the raw materials become a part of the waste products. These pollute not only the land or soil but they also pollute water bodies.
Urban and Domestic Wastes:
The urban and domestic wastes together are referred to a municipal wastes. They constitute garbage, and waste materials like plastics, glass, metallic containers, fibers, papers and a number of discarded products. It is estimated that in UK and India about 4,00,000 tonnes of solid waste is produced daily. The situation is so alarming that the land fills sites used for more than 25 years cannot take any more refuse.
A sizable portion of urban and domestic wastes are not biodegradable and so are very harmful. For example, certain items like paints, varnishes, oils etc. create the worst type of soil pollution problems. The leaches from the dumping sites and sewage along with industrial effluents are extremely harmful and dangerous and pollute even the ground water. These leaches contain poisonous gases along with partially decomposed materials from food remains, toxic chemicals and pathogenic bacteria which can be very harmful and may cause various diseases.
Radioactive wastes (nuclear wastes) are any solid, liquid or gaseous waste materials that contains radio nuclides. These wastes are produced in the mining and processing of radioactive ores, the normal mining of nuclear power stations and other reactors; the manufacture of nuclear weapons; and in hospitals and research laboratories. Radioactive pollutants may be highly dangerous to all living matter because they may contain radionuclides having half-fifes of many thousands of years, their disposal has to be controlled with great stringency.
Agrochemicals are the chemicals used in farming, especially for killing insects or for making plants grow better. They are also used in agriculture to increase the yields. They include fertilizers and pesticides.
Polymers and Plastic Pollutants:
To a certain extent, some of the polymers can be recycled. This technology has been successfully used for polyvinyl chloride containers and also for recycling of polymers, e.g. polyester, polyethylene, terephthalate, etc.
Some of the polymers can be converted into monomers, which can be converted back into polymers. The best option is to make polymers which are biodegradable.
Chemical and Metallic Pollutants:
Metals are one of the pollutants which can neither be degraded nor metabolized and so these remains in the environment for an extremely long time. These metals pollute all the components of the environment, viz., atmosphere, land and aquatic systems.
The chemical and metallic pollutants result from a large number of industries including textiles, pesticides, dyes, soap, synthetic detergents, tanneries, drugs, batteries, cement, asbestos, rubber, petroleum, paper and pulp, glass, steel, electroplating and metal extraction processing industries.
A number of toxic metals such as arsenic, cadmium, chromium, copper, lead, mercury and selenium are added to the soil in one form of the other. Synthetic chemicals and fertilizers are a source of trace metals which are added to the soil.
Soil and crops are contaminated by biological agents. These biological agents occur naturally in contaminated soil or are discharged into the soil by excreta of birds, animals and humans. Also, municipal wastes including domestic wastes and garbage are responsible for the discharging of biological agents into the soil.
Air contains pollutants like SO2 and NO2 SO2 present in the air undergoes catalytic and photolytic oxidation to form SO3, which reacts with moisture present in the atmosphere to form H2SO4.
SO2 + O2 → SO3
SO3 + H2O → H2SO4
Also, NO2 present in the atmosphere reacts with rain water or moisture in presence of O2or O3 and produce HNO3
4NO2 + 2H2O + O2 → 4HNO3
2NO2 + H2O + O3 → 4HNO3 + O2
H2SO4 and HNO3 formed (as stated above) come down the atmosphere in the form of acid rain. This damages the crops and plants. Also the soil becomes acidic, which is harmful for subsequent crops.