Soil

E.7.3 List common organic soil pollutants and their sources
Jun Hoe

By the way, the Wikispace editor is really bad. __ Salinization __

Salinization describes the concentration of soluble salts that accumulate in soil. It is detrimental to the soil because the salt in soils decrease the osmotic potential in water, so plants growing in that soil will not be able to absorb much water. The accumulated salts include sodium, potassium, magnesium and calcium, chloride, sulphate, carbonate and bicarbonate.

These are the factors that affect soil salinity:
 * Humidity
 * Rainfall
 * Farming practices
 * Movement of water table

Water used for irrigating the soil contains salt minerals in them, and when they evaporate into the atmosphere, the salts are left behind. The water then evaporates and leaves the salt behind, which increase the salinity of the soil. The less humid an area, the easier it is for the water to evaporate. Therefore, if the area that the soil is in is not very humid, it results in more of the water to evaporate which leaves behind a greater amount of salt that increases the salinity of the soil. Irrigation that has high salt content drastically worsens the soil.

Rainfall has the same effect. An area with higher precipitation would mean more rainfall. Rainwater contains salts and minerals in it, and with more rainfall, there is going to be a higher amount of salts spread over the soil.

Salinity of soil is also affected by secondary factors. These stem from Man's activities which have a direct or indirect effect to the soil. Poor farming practices are an example of this, when farmers do not drain their soil completely. This problem is prevalent in parts of the Middle East, North China, and Soviet Central Asia, where water is not flushed out properly. In coastal areas, salinization can be associated with the over exploitation of groundwater caused by the demands of growing urbanisation, industry and agriculture. Over extraction of groundwater can lower the normal water table and lead to the intrusion of marine water. Natural disasters in coastal areas, such as tsunamis, can cause severe salinisation problems with several years of low fertility of the affected soil before recovery.


 * Picture showing how salinization stems from moving of water table**

__ Nutrient Depletion __

Through heavy fertilizing and re-using of the same patch of soil, it becomes depleted of the necessary nutrients. Vitally important soil microbes that break down minerals into a form useable by the body are lost. Vitamin and mineral levels are drastically reduced. So in layman terms, the soil is referred to as "used up", like how we are unable to keep on using the same piece of coal to start a fire.

When farmers grow crops onto nutrient-depleted soil, the resultant crops actually do not contain as much nutrition as it is supposed to (theoretical). Therefore, we are actually consuming less amount of nutrients, so the vegetables and fruits that we eat do not necessarily make as healthy as we think they do. Africa faces the greatest problem in nutrient depletion, and below is a picture showing the areas which face this problem.



__ Soil Pollution __

=
Soil pollution comprises the pollution of soils with materials, mostly chemicals, that are out of place or are present at concentrations higher than normal which may have adverse effects on humans or other organisms.======

Some soil pollutants include (but are not limited to):
 * Industrial waste material
 * Man-made chemicals
 * Radioactivity
 * Acidic precipitates

Industrial waste materials and man-made chemicals contain high amounts of heavy metal, and when it is runoff onto soil, it leeches the metal ions and this causes serious soil pollution. If the soil is repeatedly being run over by industrial sewage, it may become so polluted that it will not be able to support plant life. Furthermore, the decomposition of organic materials in soil can release sulfur dioxide and other sulfur compounds, causing acid rain. In addition, some pollutants are not soluble in water, and they contaminate the plant itself. If the pollutant is very concentrated, it would go up the food chain and it might lead up to humans.

 ** How acid rain is formed ** __ ﻿ __ Soil pollution is one of the causes of acid rain, which lead to other problems as well.

__Organic Soil Pollutants__

Commonly found organic soil pollutants include:
 * PCBs
 * Dioxins and furans
 * PAH
 * Brominated flame retardants

PCBs are a group of organic pollutants consisting of two benzene rings with 1-10 chlorine atoms in different positions around these rings. They were manufactured in the early 20th century. Their main applications include hydraulic oils, paint, and sealants. They are also hydrophobic (insoluble in water), so they are able to accumulate in living organisms and then travel the food chain, contaminating the organisms in the chain. PCBs have been proven to cause impaired immune defense, disturbance of the hormone balance, in addition to infertility. PCBs have also been proven to cause cancer.

Dioxins and furans are toxic compounds that consist of benzene rings which degrade very slowly in soil. A varied amount of chlorine atoms are bound to the benzene rings, which gives rise to different dioxin and furan compounds with a varying degree of toxicity. They are produced through the incineration of organic waste, and they are spread by the weather and wind.

Polycyclic aromatic hydrocarbons (PAH) are organic compounds which are common in tar that has been used for centuries to preserve wooden material in buildings and ships. Formation of PAH can also take place by combustion and during fires. PAH are present in fossil fuels such as oil and coal.

Brominated flame retardants consists of a group of organic compounds that contain the element bromine, which is a flame retarding agent. Brominated flame retardants are emitted into air, water and soil from several processes: from industrial production, from product use, from recycling, and from waste management. __﻿__

= =

= = = Bibliography ﻿=

Gergley, T. (2010, - -). Soil Themes. Retrieved 10 10, 2010, from Soil Salinization: http://eusoils.jrc.ec.europa.eu/library/themes/salinization/

Kryzak, A. (2009, - -). Nutrient Depletion in Soil leads to poor health. Retrieved 10 9, 2010, from Nutrient Depletion in Soil leads to poor health: http://ezinearticles.com/?Nutrient-Depletion-in-Soil-Leads-to-Poor-Health&id=314089

NGU. (2007, - -). NGU. Retrieved 10 9, 2010, from Organic Pollutants: http://www.ngu.no/en-gb/hm/Climate-and-environment/Pollution/p/

__ ﻿ __