What is Soil Pollution- Definition, Causes, Consequences and Restored Process


What is Soil Pollution- Definition, Causes, Consequences and Restored Process

What is the importance of land as a Natural Resource?

Our Land is a very important resource. We need land for building homes, agriculture, farming, industries, transportation etc. When we use land carefully, then it can be a renewable resource. Trees and grasses grow on land, Their roots bind the soil. If forests are cut or grasses are overgrazed, then the land becomes a wasteland. If we use excess irrigation, then it causes waterlogging and the salinity of the soil. Then, the crops cannot grow on that soil.

When industrial wastes, nuclear wastes and other toxic materials are dumped on land, then, it becomes a non-renewable resource. 

The land area of the earth, about 140 million sq km, occupies less than a third of the surface. Yet, it is vital for our existence since it is land that:

  • Preserves terrestrial biodiversity and the genetic pool,
  • Regulates the water and carbon cycles,
  • Becomes a dump for solid and liquid waste, 
  • Acts as the store of basic resources like groundwater, minerals, and fossil fuels, and
  • Forms the basis for human settlement and transport activities.

What is the Importance of Soil?

Soil is a complex mixture of rock particles, minerals, organic matter, water, air, and billions of microorganisms. Soil forms when rocks break down into particles due to physical, chemical, and biological processes.

Soil is the foundation for agriculture and the medium in which nearly all food-producing plants grow. In fact, it is estimated that 95% of our food is directly or indirectly produced on our soil. The weathering of the earth’s crust over the centuries forms soil that supports the variety of microscopic and macroscopic life forms. The process of soil formation is a very complex one involving a number of physical, chemical and biological transformations. The topmost layer of soil is comparatively richer in nutrients and supports maximum life forms. This layer is composed of minerals of various sizes and organic matter along with pore space filled with air and water.

Soil also supports other vegetation that is cultivated for animal feed, fibre, fuel, and medicinal products.

Healthy soil supplies the essential nutrients, water, oxygen, and root support that plants need to grow and flourish. A shortage of any one of the 15 nutrients required for plant growth can limit crop yield.

Soils on earth also:

  • Support our planet’s biodiversity and host a quarter of the total
  • Store and filter water, improving our resilience to floods and droughts.
  • Serve as a buffer to protect delicate plant roots from drastic fluctuations in temperature.

Soil, however, is a finite resource, meaning its loss and degradation is not recoverable within a human lifespan. Thus, its preservation is essential for food security and our sustainable future. 

Our soils are in danger because of expanding cities, deforestation, unsustainable land use and management practices, pollution, overgrazing, and climate change. The current rate of soil degradation threatens the capacity to meet the needs of future generations. The promotion of sustainable soil and land management is central to ensuring a productive food system, improved rural livelihood, and a healthy environment. 

Soil Pollution 

Population of the whole world is increasing at a very fast rate. Therefore, the demand for food is also increasing. More agriculture is needed to produce more crops. Farmland is used more or more to increase crop productivity. This is degrading the farmlands. Land degradation is increasing at a rate of 5 to 7 million hectares per year worldwide. If soil is more used for farming, then it increases soil erosion. If more irrigation is used, then it causes waterlogging and the salinity of the soil. Then, it decreases the fertility of the soil and hence decreases crop production. Chemical fertilizers make the soil poisonous and the land becomes degraded.

Land degradation occurs not only due to agricultural practices but also due to growing of urban areas and industries. Forests are cut to get land for cities and industries. This degrades the land and also has harmful effects on the environment.

When the structure and composition of the soil are destroyed due to any reason, then it causes a gradual loss of soil fertility. This harms crop production. Different plant species cannot grow on such soil. This is called desertification of soil. It decreases the production of crops. It causes a loss in biodiversity

Causes of Soil Pollution -  

Soil gets polluted in a number of ways. The major reasons for soil pollution are:

1. Acidification:

Acidification has a number of natural and anthropogenic causes. The principal natural causes are long-term leaching and microbial respiration.

The main anthropogenic causes of acidification include certain land use practices, such as coniferous afforestation, excessive use of inorganic nitrogen fertilizers, land drainage and acid deposition resulting from urban and industrial pollution. Needleleaf afforestation has been associated with the acidification of soils and surface waters for a number of reasons. First, coniferous trees produce litter that is very acidic in comparison with most broadleaf species. Second, because of their canopy surface area, coniferous trees are able to ‘scavenge’ acid pollutants from the atmosphere, later releasing them into the soil via leaf-fall and stem flow. 

Excessive use of inorganic nitrogen fertilizers in agricultural systems has also been associated with soil acidification, partly through the process of nitrification.

Acidification of soils and associated nutrient leaching also cause damage to trees in forested areas. 

2. Salinisation:- 

Although salinisation occurs naturally in semi-arid and arid environments. It is often exacerbated as a result of human activity. In parts of southwest Australia, for example, the removal of indigenous eucalyptus forests has resulted in extensive salinisation of soils. This has occurred because the deeply-rooted trees have been replaced by shallow-rooted grasses and crops, which are less effective in lowering the groundwater level. Capillary action is most intense, and salinity is greatest in soils where the water table is within about 2m of the surface. Another important cause of soil salinity is poor irrigation practices. Overwatering leads to a rise in the water table which, in turn, causes enhanced capillary action. Similarly, poor maintenance of irrigation channels and canals results in the leakage of water into adjacent agricultural land.

3. Agrochemical Pollution - 

In the last few decades, the use of inorganic fertilizers has increased notably replacing more traditional organic nutrient treatment. Between 1952 and 1985, the global use of fertilizers increased from 14 million tonnes to 125 million tonnes, an increase of almost 900 per cent.

Inorganic fertilizers are used in preference to organic treatments because the nutrients are in a more readily available form and are released rapidly after applications. Organic material releases its nutrients slowly, through decomposition processes only when conditions are suitable (warm and moist), and not necessarily when crops need them.

Fertilizers are applied in a variety of forms - solutions, suspensions, emulsions and solids. The solid forms vary in particle size from fine powder to coarse granules which are either spread evenly over the soil surface or are mechanically placed, by drilling, into the rhizosphere. Generally, the rate of nutrient release decreases with increasing particle size. Fertilizers are based on compounds of plant macronutrients (e.g. nitrogen, phosphorus and potassium) and micronutrients (e.g. zinc, copper, boron and molybdenum). A variety of nutrient combinations are available depending on the nature of the nutrient demand. Increased use of inorganic fertilizers, eventually decreases the soil fertility at a faster rate. It also results in an increase in harmful insect and pest attacks. 

4. Urban and Industrial Pollution - 

Urban and industrial development has been associated with both physical degradation and chemical contamination of soils. Problems of physical degradation include erosion, compaction and structural damage resulting from construction activities and opencast mineral extraction. Similarly, chemical problems result from waste disposal activities, discharge and spillage of liquid effluents and atmospheric emission, including acid deposition.

How Serious Are Waterlogging and Soil Salinity?

When irrigation is not accompanied by proper drainage, waterlogging occurs. This in turn brings salt to the surface, where it collects at the roots of plants or as a thin crust of land surface. Rapid evaporation of groundwater also adds salt to the soil.

Pakistan, Egypt, and the US are some of the countries worst affected by salinization and waterlogging. In Egypt, 90% of all farmland suffers from waterlogging. In India, 12-25% of land is waterlogged or salinized.

What is the Impact of Urbanization and Industrialization on Soil?

More than 50% of the world’s population now lives in urban areas and this figure is expected to go up. Urban areas constantly need more land for settlement, infrastructure, industries, leisure activities, and the like hence increasing pressures on land. More and more agricultural land gets converted into urban colonies. 

We know that solid waste piles up on many urban streets. Outside the city, there are large dumps of waste brought from the city. It is estimated that about 2 million hectares of land have been degraded due to waste disposal and landfills.

Urban agriculture has been expanding globally over the past 25 years. In Sao Paulo in Brazil and Havana in Cuba, for example, urban home gardens have been very successful. While urban agriculture provides locally grown food and helps recycle organic matter, it can also cause pollution of water and soil if chemicals are used. 

Why are plants unable to tolerate saline soil?

Water always moves from an area of higher concentration to one of lower concentration. Normally, plants have a lower concentration than the surrounding soil and water flows into the plants. Saline soil, however, has often a lower concentration of water than plants. Consequently, water starts flowing out of the plant into the soil. 

Consequences of Soil Pollution 

Soil pollution causes huge disturbances in the ecological balance and health of living organisms at an alarming rate. Some of the effects of soil pollution are: 

  • Reduced soil fertility causes a decrease in agricultural yield. 
  • Reduced nutrients in the soil 
  • Reduced nitrogen fixation. 
  • Increased soil erosion.
  • Imbalance in the flora and fauna of the soil.
  • An increase in soil salinity makes it unfit for cultivation.
  • Creation of toxic dust. 
  • Foul odour due to industrial chemicals and gases.
  • Alteration in soil structure can lead to the death of organisms in it. 

How can Soil Contamination be restored? 

There are many ways of removing pollutants from the soil.

  • Dilution is one of them. It involves running large quantities of water through the soil to leach out the pollutants. This works only if the soil has good drainage properties. Even then, disposing of the water carrying the pollutants poses a problem. The method also requires lots of water.
  • Bioremediation is another way of removing pollutants from the soil. It is often used to describe a variety of quite different microbial processes that occur in natural ecosystems, such as mineralization, detoxification, cometabolism, or activation. It can be defined as the breakdown of organic compounds in nature by the action of microorganisms, such as bacteria, actinomycetes and fungi. 
Since bioremediation uses naturally occurring microorganisms to transfer harmful substances to non-toxic compounds, its role in restoring the contaminated soils to their original health and thus serving the environment from pollution is highly significant. Some of the more common genera involved in the bioremediation of oil products include Nocardia, Pseudomonas, Acetobacter, Flavobacterium, Micrococcus, Anthro-Bacter and Corynebacterium. 

  • Reducing the use of chemical fertilizers and pesticides in the soil. Chemical fertilizers and pesticides should be replaced by organic fertilizers and pesticides.  
  • Recycling paper, plastics and other materials. 
  • Ban on use of plastic bags, which are a major cause of population.
  • Avoiding deforestation and promoting forestation.
  • Suitable and safe disposal of wastes including nuclear wastes.
  • Encouraging social and agroforestry programs. 
  • Undertaking many pollution awareness programs. 

Frequently Asked Questions -

Question: What is the Soil Pollution?

Answer - Soil Pollution is any physical or chemical change in the soil conditions that may adversely affect the growth of plants and other organisms living in or on it.

Acid rain and excessive use of chemical fertilizers result in the soil becoming unable to hold nutrients. This, in turn, allows toxic pesticides or atmospheric fallout to seep rapidly into groundwater or runoff into rivers and coastal waters. Some of the persistent pollutants remain in the soil and degrade it. 

Question: What are the major causes of soil pollution?

Answer - Soil gets polluted mainly due to the following causes 

  • Soil erosion:- This decreases the fertility of the soil and its water-holding capacity. Excess farming, deforestation, overgrazing, construction activities etc. cause soil erosion.
  • Excess salts and water (salinization) pollute the soil.
  • Excess use of fertilizers, insecticides and pesticides.
  • Solid waste adds harmful chemicals and other materials to the soil. This also causes soil pollution. 

 Question: What is Deforestation?

 Answer - It is defined as the long-term reduction of the tree canopy cover for the conversion of forest to another land use. 

Question: What is Desertification?

Answer - It is defined as the deterioration of land in arid, semi-arid and dry sub-humid regions (also called drylands) of the world due to climatic variations and human activities. 

Question: What is Bioremediation? 

Answer - It is the reduction in concentration or clean-up of toxic wastes in the environment using microorganisms like bacteria and fungi. 

Question: What are the benefits of Bioremediation?

Answer - 

  • An ecologically sound, natural process; residues are useful harmless products.  
  • Instead of merely transferring contaminants from one environmental medium to another (e.g. from water to the air or to land)  bioremediation completely eliminates the target chemicals.
  • Bioremediation is far less expensive than other technologies that are often used to clean up hazardous waste. 
  • Bioremediation can often be accomplished where the problem is located. This eliminates the need to transfer large quantities of contaminated waste off-site, and the potential threats to human health and the environment that can arise during such transportation. 

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