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.
The industrial use of pesticides and fertilizers, poorly managed landfills and sewage, the mining of oil and fuels and other mineral extractions as well as drainage of contaminated surface water into the soil have left vast areas of land depleted and useless or even hazardous for cultivation or living. The contamination of our soils is almost entirely human-made: petroleum hydrocarbons, solvents, nitrates, heavy metals, hormones, antibiotics, ammonia, seepage from landfills, discharge of industrial waste, percolation of contaminated water into the soil, rupture of aquifers, excess application of pesticides, herbicides and fertilizers.
The pollution happens when chemicals such as pesticides and artificial fertilizers are applied to the earth, which absorbs it readily. Also through the natural evaporation process, contaminants can be transported via rainfall over long distances. As the world becomes more industrialized, the long term effects of soil pollution are becoming more apparent, globally. Estimates suggest that in China alone more than 150 million miles of farm- and green land is contaminated.
Combustion of brown coal emission factors along with exploration extraction of petroleum and its many uses has contaminated our earth from the polar caps all the way to the equator. The concern over soil contamination is rising to the surface of international attention again as more people are looking back into biological farming for the fear of health risks from toxins in the earth and the groundwater underlying the soil. As floods become more frequent and bacteria and other toxins from sewage plants, landfills and pesticide treated fields are washed abroad vast areas, the need for final disposal and clean elimination become important issues again.
The contaminated soil can affect human health in a number of ways, either by direct contact of the polluted areas or through consumption of agricultural products such as fruits, vegetables and grains that were cultivated on the infested areas, or through the consumption of meat and dairy from the animals grazing on this land. Also groundwater aquifers, used as drinking water recourses, are often affected as the contaminants are flushed into the reservoirs by the natural course after rainfall. Health consequences can vary, depending on the kind of pollutants in the soil, starting from developmental problems in children exposed to lead, different types of cancer, kidney and liver damage and problems with the central nervous system from chromium and other ingredients found in fertilizers and pesticides.
The long term effects of soil pollution are vast and oftentimes noticeable only after many years when it comes to the environment itself. Soil is its own ecosystem. Contaminated soil will usually produce lower yields of plant growth than untouched soil. This will in return cause even more harm because a lack of plants on the soil will cause more erosion, spreading the contaminants even further. Some pollutants can also change the makeup of the soil, which in turn will attract new types of microorganisms that will colonize. When certain organisms start dying off, the fauna, higher up in the food chain, will have to move or even become extinct and so could change entire ecosystems.