Soil represents the sojourn of man. It is the place where we live and carry out our lives activities. The food we eat are nurtured by the soil, we build our houses on the soil etc. The activities we carry out on the soil turn out to generate some by-products which often are described as wastes.
Most of these wastes, depending on their nature and characteristics end up deposited on the soil. Therefore the soil turns to become a medium for these wastes which are also described as pollutants.
The pollution of soil has a far reaching implication on public health and the environment. In this unit you are going to learn about the characteristics of the soil as a medium and how it becomes polluted.
Soil media, also called ‘Land’ occupies about 28 per cent of the surface of the earth after water which occupies 72 per cent. The history of soil dates back to billions of years ago perhaps, since the creation of the universe.
It is the comfort station of man as it provides him with the necessary basement to undertake his basic functions of life. The soil is the platform which man builds his house, cites his industries, builds his roads and above all cultivates his crop for food and survival. Therefore the importance of soil to human life cannot be over emphasized.
Soil is a natural body that consists of layers (soil horizon) composed primarily of minerals, which differ from their parent materials in their texture, structure, consistency, and colour, chemical, biological and other physical characteristics.
The result soil is the end product of the influence of the climate (temperature, precipitation), relief (slope), organisms (flora and fauna), parent materials (original minerals), temperature and time. Of all the factors that influence the evolution of soil, water is the most powerful due to its effect on the solution and precipitation on minerals, plant growth, the leaching of minerals from the soil profile, and the transportation and deposition of the materials of which the soil is composed.
Chemical and Colloidal Properties
The chemistry of soil determines the availability of nutrients, the health of microbial populations and its physical properties. In addition, soil chemistry also determines its corrosivity, stability and ability to absorb pollutants and to filter water. It is the surface chemistry of clays and humus colloids that determines soil chemical properties.
The very high specific surface area of colloids gives soil its great ability to hold and release cations in what is referred to as cation exchange.
Cation exchange capacity is the amount of exchangeable cations per unit weight of dry soil and is expressed in terms of milli-quivalents of hydrogen ion per 100 grams of soil.
A colloid is a small insoluble, non-diffusible particle larger than a molecule but small enough to remain suspended in a fluid medium without settling. Most soil contains organic colloid particles as well as the inorganic colloidal particles of clays.
Soil is made up of varieties of mineral resources ranging from silica, metals, nitrates and coal to gases like carbon, oxygen, hydrogen, etc.
As far as pollution is concerned, many things can be introduced into the soil to make it foul for judicious use or having negative impact on environmental health.
Some important soil media subject to pollution include; farmlands, urban environment, the rural areas, estates, schools, markets, homes etc.
Heavy metals on soil from industrial wastes dumps, domestic or commercial use of batteries can be a source of soil pollution.
Physical Properties of Soil
The physical properties of soil, in order of decreasing importance, are texture, structure, density, porosity, consistency, temperature, color, and resistivity. These determine the availability of oxygen in the soil and ability of water to infiltrate and be held in the soil.
The atmosphere of soil is radically different from the atmosphere above. The consumption of oxygen by microbes and plant roots decrease oxygen concentration while their release of carbon dioxide increases carbon dioxide concentration.
Atmospheric carbon dioxide concentration is 0.03 per cent, but in the soil pore space it may range from 10 to 100 times that level. In addition the soil voids are saturated with water vapor.
Adequate porosity is necessary not just to allow the penetration of water but also to allow gases to diffuse in and out. Movement of gases is by diffusion from high concentration to low concentration. Oxygen diffuses in and is consumed and excess levels of carbon dioxide, which can become toxic, diffuse out with other gases as well as water.
Soil pollution results from the build-up of contaminants, toxic compounds, radioactive materials, salts, chemicals and cancer causing agents. The most common soil pollutants are hydrocarbons, heavy metals (cadmium, lead, chromium, copper, zinc, mercury and arsenic) herbicides, pesticides, oils, tars, PCBs and dioxins.
Until 1970s, there was little talk of soil pollution and its devastating effects. In the 1980s, the US superfund was created to set guidelines for the handling of hazardous materials and soil contamination clean up.
In the US alone there are more than 200,000 sites awaiting cleanup, which is very expensive and labor-intensive work. Even a small cleanup project can cost $10, 000 while larger areas require millions of dollars to clean it up for future use.
Causes of Soil Pollution
Following world-war 2 and Vietnam, scientists discover high incidences of mutation, miscarriage, mental defects, cancer and sickness in areas where nuclear warheads had been dropped. Food shortage also alerted officials that something was seriously wrong with the local soil. DDT and dioxin were two of the worst pollutants from war aftermath.
In some cases, agricultural processes cause soil pollution. High level of radionuclide like nitrogen and phosphorus can be found surrounding farm centres containing high pollution densities of livestock. Pesticides applied to plants can also seep into the ground, leaving lasting effects. Heavy metals can arrive in the soil by using polluted water to wet crop and by using mineral fertilizers.
Industry is to be blamed for some of the biggest soil-pollution disasters. Heavy metals come from iron, steel, power and chemical manufacturing plants that recklessly use the earth as a dumping ground for their refuse.
Plants that burn their waste on one-site are guilty of releasing heavy metals into the atmosphere, which come to settle in the soil, thus leaving behind lasting effects for years to come. Even companies that try to dispose of their waste properly contribute to the problem when faulty landfills and bursting underground bins leach undesirable toxins into the soil. Mining leaves a tremendous impact on the surrounding communities.
Studies show that people living near mines have a 70 per cent higher risk of kidney disease, 64 per cent higher risk for chronic obstructive pulmonary disease and a 30 per cent higher risk of high blood pressure.
Before purchasing land for development or inhabiting, it is important to have a soil test performance to ensure a sound investment. A soil test can reveal the presence of nitrogen, phosphorus, potassium, sulphur, calcium, magnesium, iron, manganese, copper, zinc, boron, molybdenum and aluminum.
It can also analyze soil acidity, electrical conductivity, organic matter, moisture content and identify dangerous soil contaminants like benzene, petroleum hydrocarbons, xylene and toluene. Even if the soil is in fine condition for planting, land owners can use their soil test to make more informed decision regarding fertilizer, and crop growing.
Case Studies of Soil Pollution
In the snowy winter of 1976, chemical waste began to seep above ground in school playground and communities in Niagara Falls New York. The area suffered high incidences of still born births, miscarriages and birth defects.
Officials soon realized that there were over 400 toxic substances in the air, water and soil many of them cancerous. As it turns out, the area has been used as a chemical dumping ground for more than 22,000 tons of toxic waste at the turn of the century, when no one was aware of the hazardous impact it could have decades later.
Another one of the most infamous cases of soil pollution happened in Chernobyl, a small town in Russia. A nuclear power plant exploded in April of 1986, which caused a seven fold increase in birth defects, a marked increase in cancer that was passed down to future generations, livestock death and mutation and tainted agriculture.
It is estimated that 40 per cent of Chernobyl is still uninhabitable due to radiation contamination that is ten times the normal level in some places. Ethiopiais both filled with both air and soil pollution.
The worst area is in Somalia‘s Ayaha valley near Hargeysa. To boost their economy, many farmers began using chemical fertilizers and pesticides to increase productivity without understanding the full ramifications.
Over their war torn years, metal drums holding 14,200 litres of chemicals like fenitrothion, Malathion, diazionon and Durban were punctured. As a result, land pollution has caused widespread famine and sickness.
China is a nation that is developing rapidly, perhaps faster than safety permits. ‘It is estimated that nationwide 12 tons of grain are polluted each year by heavy metals that have found their way into soil‘‘. According to incomplete statistics, about 10 million hectares of arable land in china has been polluted.
Read Also: Natural Sources of Pollution
Impact of Soil Pollution
People living near polluted land have higher incidences of migraine, nausea, fatigue, miscarriage and skin disorders. Long term effects of pollution include cancer, leukaemia, reproductive disorders, kidney and liver damage as well as central nervous system failure. Children often suffer from developmental problems and weakened immune systems.
Chemicals can sometimes absorb into food like lettuce and spinach and be ingested. Other times the pollutants simply kill the plant, which has created widespread crop destruction and famine in other parts of the world. The entire ecosystem changes when materials are added to the soil, as microorganism die off or move away from contaminants.
Predators who feed off the micro-organisms and worms in the polluted soil will also be affected. Researchers found that some species of birds like the peregrine falcon, the brown pelican and the bald eagle prey to DDT poisoning, which caused egg shells of future generation to thin.
Mother birds would arrive home to omelets in their nets, as the thin shells could not support the weight of the incubating offspring. Mortality rates increased, nearly sending the birds to extinction.
If nothing is done to clean up soil pollution, water supplies could become contaminated, threatening the human species. Sudden fires and building structures may corrode and once beautiful regions will turns into cesspools, experts warn.
Prevention of Soil Pollution
Naturally, prevention is the best cure for soil pollution. States can enact tough legislations to stop illegal dumping of wastes. Education and awareness related to actions that promote prevention of soil pollution of any magnitude is imperative. Mining control legislations are also important in the prevention and control strategies.
In summary, soil also called land is an important medium in the environment which is subject to pollution. Varied types of pollutants ranging from hydrocarbons, heavy metals, to herbicides, pesticides etc. can lead to the pollution of soil and subsequent unpleasant impacts. Soil is made up of different properties, chemical, colloidal properties. In the next unit we shall consider another media in the environment.
Soil as a medium is made up of properties which describe its value. Soil pollution occurs through so many events which may be either human or natural. Examples of such human events include war and industrial activities. The example of natural event is volcanic eruption.