Here is a compilation of notes on Soil Pollution. After reading these notes you will learn about: 1. Definition of Soil Pollution 2. Causes of Soil Pollution or Soil Degradation 3. Effects 4. Control.
Note # 1. Definition of Soil Pollution:
Soil is the thin layer of organic and inorganic materials that covers the Earth’s rocky surface. The organic portion, which is derived from the decayed remains of plants and animals, is concentrated in the dark uppermost topsoil.
The inorganic portion made up of rock fragments, was formed over thousands of years by physical and chemical weathering of bedrock. Productive soils are necessary for agriculture to supply the world with sufficient food.
Soil pollution is defined as persistent of toxic compounds, chemicals, salts, radioactive materials, or disease causing agents, which have adverse effects on plant growth and animal health.
Soil becomes polluted by:
i. Seepage from a landfill.
ii. Discharge of industrial waste into the soil.
iii. Percolation of contaminated water into the soil.
iv. Rupture of underground storage tanks.
v. Excess application of pesticides, herbicides or fertilizer.
vi. Solid waste seepage.
vii. Chemicals like petroleum hydrocarbons, heavy metals, pesticides and solvents.
Note # 2. Causes of Soil Pollution or Soil Degradation:
A soil pollutant is any factor which deteriorates the quality, texture and mineral content of the soil or which disturbs the biological balance of the organisms in the soil. Pollution in soil has adverse effect on plant growth.
Mainly soil pollution is caused by the presence of man-made chemicals application of pesticides, percolation of contaminated surface water to subsurface strata, oil and fuel dumping, leaching of wastes from landfills or direct discharge of industrial wastes to the soil.
The most common chemicals involved are petroleum hydrocarbons, solvents, pesticides, lead and other heavy metals. Occurrence of this phenomenon is correlated with the degree of industrialization and intensities of chemical usage.
The main causes of soil pollution are described below in details:
(i) Haphazard use of Fertilizer:
Soil nutrients are vital for plant growth and development. Plants obtain carbon, hydrogen and oxygen from air and water. All other necessary nutrients like nitrogen, phosphorus, potassium, calcium, magnesium, sulfur and more must be obtained from the soil.
Farmers generally use fertilizers to correct soil deficiencies. Fertilizers contaminate the soil with impurities, which come from the raw materials used for their manufacture. Mixed fertilizers often contain ammonium nitrate (NH4NO3), phosphorus as P2O5, and potassium as K2O.
For instance, As, Pb and Cd present in traces in rock phosphate mineral get transferred to super phosphate fertilizer. Since the metals are not degradable, their accumulation in the soil above their toxic levels due to excessive use of phosphate fertilizers becomes an indestructible poison for crops.
Fertilizers are very valuable, as they replace the soil nutrients used up by plants. The three primary soil nutrients often in short supply are potassium, phosphorous and nitrogen (NPK) compounds. These are commonly referred to as macronutrients. Certain other elements like boron, zinc and manganese are necessary in extremely small amounts and are known as micronutrients.
When crops are harvested, a large amount of macronutrients and a small amount of micronutrients are removed with the crops. If the same crop is grown again, depleted levels of the nutrients can result in decreased yields. These necessary nutrients can be returned to the soil through the application of fertilizers.
The over use of NPK fertilizers reduce quantity of vegetables and crops grown on soil over the years. It also reduces the protein content of wheat, maize, grams, etc., grown on that soil. The carbohydrate quality of such crops also gets degraded. Excess potassium content in soil decreases vitamin C and carotene content in vegetables and fruits.
The vegetables and fruits grown on over- fertilized soil are more prone to attacks by insects and disease.
Approximately 25% of the world’s crop yield is estimated to be directly attributed to the use of chemical fertilizers. The use of chemical fertilizers has increased significantly over the last few decades and is expected to rise even higher.
(ii) Indiscriminate use of Pesticides, Insecticides and Herbicides:
In addition to fertilizers, a large amount of pesticides (chemicals used to kill or control populations of unwanted fungi, animals or plants often called pests) are also used to ensure a good yield. Pesticides can be subdivided into several categories, based on the kinds of organisms they are used to control.
Insecticides are used to control insect populations, while fungicides are used to control unwanted fungal growth. Mice and rats are killed by rodenticides, while plant pests are controlled by herbicides. The first widespread insecticide use began at the end of World War-IT and included DDT (dichlorodiphenyltrichloroethane) and gammaxene.
Insects soon became resistant to DDT and as the chemical did not decompose readily, it persisted in the environment. Since it was soluble in fat rather than water, it biomagnified up the food chain and disrupted calcium metabolism in birds, causing eggshells to be thin and fragile.
As a result, large birds of prey such as the brown pelican, ospreys, falcons and eagles became endangered. DDT has been now banned in most western countries. Ironically many of them including USA still produce DDT for export to other developing nations whose needs outweigh the problems caused by it.
The most important pesticides are DDT, BHC, chlorinated hydrocarbons, organophosphates, aldrin, malathion, dieldrin, furodan, etc. The remnants of such pesticides may get adsorbed by the soil particles, which then contaminate root crops grown in that soil. The consumption of such crops causes the pesticides remnants to enter human biological systems, affecting them adversely.
An infamous herbicide used as a defoliant in the Vietnam War called Agent Orange (dioxin), was eventually banned. It had caused cancer, skin conditions and infertility in soldiers.
Pesticides not only bring toxic effect on human and animals but also decrease the fertility of the soil. Some of the pesticides are quite stable and their bio- degradation may take weeks and even months.
For example, DDT, one of the first synthetic organic insecticides to be used, was thought to be the perfect insecticide. During the first ten years of its use (1942-1952), DDT is estimated to have saved about five million lives primarily because of its use to control disease-carrying mosquitoes.
However, after a period of use, many mosquitoes and insects became tolerant to DDT, thus making it lose its effectiveness. In temperate regions, DDT has a half-life (the amount of time required for half of the chemical to decompose) of 10-15 years. This means that if 100 kg of DDT were to be sprayed over an area, 50 kg would still be present in the area 10-15 years later.
The half-life of DDT varies according to the soil type, temperature, kind of soil organisms present, and other factors. In tropical parts of the world, the half-life may be as short as 6 months. Persistent pesticides become attached to small soil particles which are easily moved by wind and water to different parts thus affecting soils elsewhere.
Persistent pesticides may also accumulate in the bodies of animals, and over a period of time increase in concentration if the animal is unable to flush them out of its system, thus leading to the phenomenon called bioaccumulation. When an affected animals is eaten by another carnivore, these pesticides are further concentrated in the body of the carnivore.
This phenomenon of acquiring increasing levels of a substance in the bodies of higher trophic level organisms is known as ‘bio-magnification’. This process, especially in the case of insecticides like DDT, has been proved to be disastrous.
(iii) Dumping of Solid Wastes:
In general, solid waste includes garbage, domestic refuse and discarded solid materials such as those from commercial, industrial and agricultural operations. They contain a large amounts of paper, cardboards, plastics, glass, old construction material, packaging material and toxic or otherwise hazardous substances.
a. Waste dumps:
Land gets dumping of industrial wastes, municipal wastes, medicals or hospital wastes. Industrial solid wastes and sludge are the major sources of soil pollution by toxic organic and inorganic chemical compounds and heavy metals.
The fall-out from industrial emissions, for example the fly ash emitted by thermal power plants, can pollute surrounding lands. We must keep in mind that the particulates of the industrial emissions from the tall chimney always come back to the earth surface sooner or later.
Radioactive tests from nuclear testing laboratories and nuclear power plants and the radioactive fall-out from the nuclear explosions also contaminate the soil. Radioactive materials thrive in the soil for long periods because they usually have a long half-life. Stroncium-90, for example, has a half-life of 28 years, and the half-life of Caesium-137 is 30 years.
b. Municipal wastes:
Municipal wastes mainly include domestic and kitchen wastes, market wastes, hospital wastes, livestock and poultry wastes, slaughterhouse wastes, waste metals, glass and ceramic wastes, etc. Non-biodegradable materials like used polyethylene, carry bags, waste plastic sheets and bottles etc. persist in soil for long periods.
Hospital wastes contain organic materials, chemicals, metal needles, plastic and glass bottles, vials, etc. Dumping of domestic sewage and hospital organic wastes contaminate the environment with a variety of pathogens that can seriously affect human health.
The portion of solid waste that is hazardous such as oils, battery metals, heavy metals from smelting industries and organic solvents are the ones we have to pay particular attention to. These can in the long run, get deposited to the soils of the surrounding area and pollute them by altering their chemical and biological properties.
More than 90% of hazardous waste is produced by chemical, petroleum and metal-related industries and small businesses such as dry cleaners and gas stations contribute as well. Toxic chemicals leached into the soil underneath homes, causing an unusually large number of birth defects, cancers and respiratory, nervous and kidney diseases.
Soil erosion occurs when the weathered soil particles are dislodged and carried away by wind or water. Deforestation, agricultural development, temperature extremes, precipitation including acid rain, and human activities contribute to this erosion. Humans speed up this process by construction, mining, cutting of timber, over cropping and overgrazing. It results in floods and cause soil erosion.
Forests and grasslands are an excellent binding material that keeps the soil intact and healthy. They support many habitats and ecosystems, which provide innumerable feeding pathways or food chains to all species. Their loss would threaten food chains and the survival of many species.
During the past few years quite a lot of vast green land has been converted into deserts. The precious rain forest habitats of South America, tropical Asia and Africa are coming under pressure of population growth and development.
Soil erosion occurs when the worn out particles are dislodged and passed away by wind or water. Deforestation, agricultural development, and human actions add to this erosion.
Forests hold up many habitats and ecosystems, which make available immeasurable feeding pathways or food chains to all species. During the past few years quite a lot of vast green land has been converted into deserts. Deforestation is slowly destroying the most dynamic flora and fauna areas.
Note # 3. Effects of Soil Pollution:
Land pollution effects will be and still are at the edge of being fatal! Below mentioned are the major effects of soil pollution and how it affects all living things…
(i) Effects on Agriculture:
Everything that we consume in order to live is originated from agriculture … Soil being the beginning of a healthy agriculture.
The major effects of soil pollution on agriculture are:
i. Loss of nutrients in the soil
ii. Soil erosion
iii. Less fertile land for vegetation
iv. Reduction in crop yield and
v. Reduction in nitrogen fixation.
(ii) Effects on Ecosystem:
Contamination of soil will definitely have adverse effects on the ecosystem which are as follows:
i. Ecological imbalance
ii. Permanent change in the chemical properties of soil
iii. Alteration in the metabolism of endemic microorganisms resulting in eradication of the primary food chain which is interred related with the existence of each and every organism in the world, including humans! and
iv. Bad health in all consumers. It is already evident that due to consumption of DDT effected crops, the egg shells of hens have become weak.
(iii) Effects on Human:
Below mentioned are some such effects of soil pollution, which are visible at some places.
i. Pollution in drinking water
ii. Contamination in vegetation due to presence of chemicals
iii. Problems of waste management
iv. Polluted environment with harmful gases to breathe in and foul smells and
v. Health issues
(iv) Long Term Effects of Soil Pollution:
Soil that has been contaminated should no longer be used to grow food, because the chemicals can leech into the food and harm people who eat it.
If contaminated soil is used to grow food, the land will usually produce lower yields than it would if it were not contaminated. This, in turn, can cause even more harm because a lack of plants on the soil will cause more erosion, spreading the contaminants onto land that might not have been tainted before.
In addition, the pollutants will change the makeup of the soil and the types of microorganisms that will live in it. If certain organisms die off in the area, the larger predator animals will also have to move away or die because they’ve lost their food supply. Thus it’s possible for soil pollution to change whole ecosystems.
Note # 4. Control of Soil Pollution:
There are different types of soil pollution, namely agricultural soil pollution, industrial waste causing soil pollution, urbanization causing soil pollution. These different types of pollution cause the fertility of the soil to reduce and mineral content in the soil to be destroyed. Therefore, measures have to be taken for preventing soil pollution.
(i) Use Bio-Fertilizers:
To increase agricultural yield, most farmers use chemical fertilizers. No doubt that the yield did indeed increase, but at the cost of the soil losing its fertility. To restore the fertility of the soil, the farmers should be encouraged to start using bio-fertilizers. The microorganisms in these fertilizers will help in increasing the fertility of the soil.
(ii) Use Bio-Pesticides and Fungicides:
To avoid soil pollution, it is important, that along with fertilizers, farmers should also use to bio pesticides and fungicides. These products will take a little longer to react, but they do not have adverse effect on the soil.
(iii) Reduce Toxic Waste:
If one has to look at the soil pollution facts, it will be seen that toxic waste has a big role to play in soil pollution. Hence, industrial toxic waste should be treated to reduce its toxicity before it is disposed of. At the same time, responsible methods should be used for disposing off the waste. The best however, is to avoid the use of harmful chemicals unless they are of extreme importance.
(iv) Recycle Waste:
Although a lot of propaganda has been carried out about recycling waste, not many measures have been taken about the same. If each family has to take it upon themselves to recycle waste, the land pollution cause due to land-fills will be reduced considerably. The land so saved can be used constructively for a number of better tasks.
After plastic was invented, people thought it was convenient to opt for plastic containers, bags, etc., which could be disposed of after use. However, plastic is one of the main causes of soil pollution, as it takes a very long time to disintegrate. Therefore, people should consider shifting to reusable containers like glass, cotton bags, etc.
Although paper does disintegrate faster, a lot of trees are cut for producing paper bags. Therefore, it is best to opt for cloth bags. Similarly, instead of using tissue papers in the kitchen, etc., one should opt using cloth napkins, handkerchief, etc. This will go a long way in reducing land-fills.
To prevent soil pollution, deforestation measures have to be undertaken at rapid pace. Soil erosion is caused, when there are no trees to prevent the top layer of the soil from being transported by different agents of nature like water and air. At the same time, measures should be taken to avoid over cropping and over grazing, as it leads to flood and soil erosion and further deterioration of the soil layer.
Control of land loss and soil erosion can be attempted through restoring forest and grass cover to check wastelands, soil erosion and floods. Crop rotation or mixed cropping can improve the fertility of the land.
(viii) Solid Waste Treatment:
Paper methods should be adopted for management of solid waste disposal. Industrial wastes can be treated physically, chemically and biologically until they are less hazardous. Acidic and alkaline wastes should be first neutralized; the insoluble material if biodegradable should be allowed to degrade under controlled conditions before being disposed.
As a lost resort, new areas for storage of hazardous waste should be investigated such as deep well injection and more secure landfills. Burying the waste in locations situated away from residential areas is the simplest and most widely used technique of solid waste management. Environmental and aesthetic considerations must be taken into consideration before selecting the dumping sites.
Incineration of other wastes is expensive and leaves a huge residue and adds to air pollution. Pyrolysis is a process of combustion in absence of oxygen or the material burnt under controlled atmosphere of oxygen. It is an alternative to incineration.
The gas and liquid thus obtained can be used as fuels. Pyrolysis of carbonaceous wastes like firewood, coconut, palm waste, corn combs, cashew shell, rice husk paddy straw and saw dust, yields charcoal along with products like tar, methyl alcohol, acetic acid, acetone and a fuel gas.