It is defined as the build-up in soils of persistent toxic compounds, chemicals, salts, radioactive materials, or disease causing agents, which have adverse effects on plant growth and animal health
Soil pollution is also caused by means other than the direct addition of xenobiotic (man-made) chemicals such as agricultural runoff waters, industrial waste materials, acidic precipitates, and radioactive fallout.
Xenobiotics are defined as any foreign chemical substance found within an organism or environmen that is not normally naturally produced by or expected to be present within
Major Causes of Soil Pollution
Agricultural and Industrial
Mining and Dumping
Major Causes :
- Seepage from a landfill - the concentrated liquid consisting of metals, chemicals and organics released due to degradation of solid waste in landfill sometimes gets leached out due to faulty landfill designs.
- Discharge of industrial waste into the soil
- Percolation of contaminated water into the soil - Contaminated industrial waste and sewage often percolate down to water table and soil.
- Rupture of underground storage tanks
- Excess application of pesticides, herbicides or fertilizer - excess fertilizer that plant dont need often stays in soil for many years and becomes a contaminant
- Solid waste seepage - solid waste open dumps release concentrated liquids formed as a by product of degradation process
- Deforestation and Soil erosion
Agricultural Soil Pollution
Crops are often attacked by insects, fungi, bacteria, viruses, rodents and other animals and must compete with weeds for nutrients. To increase yield, fertilizers are also used, to kill unwanted weeds and organisms pesticides are used. The remains of such pesticides used get adsorbed by the soil particles and contaminate root crops grown in that soil. The consumption of such crops causes the pesticides remnants to enter human biological systems, affecting them adversely.
- Reduced soil fertility and increase soil salinity - The use of excess chemicals in soil affects its pH and nutrient uptake capacity thus make it unfertile in long run also the use of fresh water for irrigation leave excess of salts in soil on evaporation causing soil salinity. Saline soil does not support the growth of plants.The organic matter content of soil is also reduced.
- Reduced nitrogen fixation - good bacterias are often killed in soil thus reduce nitrogen fixation.
- Increased erodibility - Soil becomes prone to erosion due to low water holding capacity caused due to decrease in organic matter content.
- Reduce minerals present in soil and thus crop yield
- Imbalance in soil fauna and flora
- Adversely affect soil microbes
- Soil erosion can also cause soil pollution as water holding capacity of soil decreases
Industrial Soil Pollution
Large quantity of solid wastes like unused and rejected chemicals (like sludge, press mud, saw dust, bottles, plastic materials etc.), unwanted industrial wastes generated during manufacturing processes are dumped over on the surface of soil by almost all industries with difference in the degree.
Larger the production base, larger is the generation of wastes. Traditionally, these materials have been dumped around the factory site or around the entire city. Rarely, they are put to recycling or safe conversion
Impacts of Industrial waste on Soil:
- Dangerous chemicals entering underground water
- Ecological imbalance
- Release of pollutant gases
- Increased salinity
- Reduced vegetation
- Heavy metal contamination
Soil Pollution due to Mining Activity
Soil is not just contaminated but also show some mechanical damages due to various activities. Such changes are bad for soil as well as people surviving on it.
Some Major impacts on soil are:
- Land Degradation and Soil Erosion
- Lowering of ground water table and acid mine drainage
- Leaching and contamination from mine spoil - huge holes are dugged in soil and waste is dumped as spoil heaps. This waste consist of poisonous substances which generally leach to soil and ground water table when it comes in contact with rains.
- Depletion of some specific plant species and wild life habitat
Land subsidence by Mining
Land subsidence is often caused due to underground mining and due to heavy earth moving machinery used in mining activity.
Acid Mine Drainage / Acid Rock Drainage - cause soil as well as water pollution
Outflow of acidic water (pH 2-4.5) from metal mines or coal mines. Due to oxidation of pyritic minerals (metal sulfides) found in coal, ore bodies and over burden. It’s a unique pollution as drainage continues even when mining is ceased (90 abondoned mine sites by IBM). Microbes such as Acidithiobacillus ferrooxidans also contribute to Acid mine drainage
Other causes of Soil Pollution
Acid Rain :
All air pollutants and high concentration of SOx and NOx make sulfuric acid and nitric acid and gets added to soil. This changes the pH of soil and also affects soil micro flora and fauna. Soil also losses its nutrient due to high solubility with acidic waste. Acid rain also mobilize the metal bonded with soil thus cause heavy metal contamination.
Leakage of Toxins in soil
Soil pollution by Oil and Petroleum Spills
Health problems by Heavy metals
Heavy metals in Soil directly enters the food chain and thus are a serious concern for health.
Long term exposure to Cadmium is associated with renal dysfunction. Cadmium is biopersistent and once absorbed remains resident for many years. High exposure can lead to obstructive lung diseases and has been linked to lung cancer.Cadmium may also cause bone defects in humans and animals
Chromium can damage the skin and cause ulcers. Long term exposure can cause kidney and liver damage. It can also cause damage to circulatory and nerve tissues
Aluminium toxicity is associated with the development of bone disorders including fractures,osteopenia and osteomalacia
Monomethylmercury causes damage to the brain and the central nervous system while fetal and post-natal exposure have given rise to abortion, congenital malformation and development changes in young children
Exposure to high levels of arsenic can cause death. All types of arsenic exposure can cause kidney and liver damage and in the most severe exposure there is erythrocyte haemolysis
High doses of copper can cause anaemia, liver and kidney damage, and stomach and intestinal irritation
Excessive amounts of nickel can be mildly toxic. Long term exposure can causes decreased body weight, heart and liver damage and skin irritation
Manganese is known to block calcium channels and with chronic exposure results in CNS dopamine depletion. This duplicates almost all of the symptomology of Parkinson’s Disease.
The most common heavy metals found at contaminated sites,such as Pb, Cr, As, Zn, Cd, Cu and Hg. Those metals are important they are capable of decreasing crop production due to the risk of bioaccumilation and biomagnification in the food chain.
The fate and transport of the heavy metal in soil depends significantly on the chemical form and speciation of the metal once in the soil, heavy metals are adsorbed by initial fast reactions, followed by slow adsorption reactions. Therefore redistributed into different chemical forms with varying bioavailability, mobility and toxicity. This distribution is belived to be controlled by reactions of heavy metals in soils such as ion exchange, adsorption and desorption, aqueous complexation, biological immobilization and mobilization, plant uptake, mineral precipitation.
Heavy Metal impact on Seed Germination
Nickel affect amylase, protease and ribonuclease enzyme activity thus retarding seed germination and growth. Affect the digestion and mobilization of food reserves like proteins and carbohydrates in germinating seeds, reducing plant height, root length, fresh and dry weight, chlorophyll content etc
Lead affect the seed morphology and physiology. It inhibits germination, root elongation, seedling development, plant growth, transpiration, chlorophyll production, and water and protein content, causing alterations in chloroplast, inhibition of Calvin cycle etc
Copper cause oxidative stress via generation of reactive oxygen species (ROS) and by decreased catalase (CAT) activity via oxidation of protein structure. Reduce germination rates
Cadmium cause delay in germination, induce membrane damage, impair food reserve mobilization