There are a wide range of sources of soil pollution. These sources might be point sources or diffuse sources. The following are the main sources of soil pollution: Agriculture sources, industrial sources, urban sources, incidental sources, and atmospheric sources. Let’s look at each of them in detail.
Sources of soil pollution
1. Agriculture sources
Pollutants from agriculture sources include fertilizer, pesticides, and manure.
In the last few years, the use of chemical fertilizers in agriculture has been increasing. The reason for high fertilizer consumption is that they increase crop productivity and efficiency. Chemical fertilizers contain heavy metals like Hg,As, Cd, Pb. Also chemical fertilizers contain radionuclide like 238U and 232Th. Excessive use of fertilizers leads to accumulation of heavy metals in soil and plants. Later these fertilizers enter the food chain and affect the agro-ecosystem.
The use of pesticides has been increasing since the last few decades. Pesticides are used for destroying harmful organisms and undesired plants. Pesticides are classified in three categories: 1. Insecticides: These are chemical compounds used to kill insects
2. Herbicides: They are chemicals used to suppress the growth of undesired plants 3. Fungicides: They are chemicals used to kill or suppress the growth of fungus.
Based on the chemical structure, pesticides include organophosphorus, organochlorine, nitrogen-benzene, phenols, metallo-organic, and other compounds. Most of the percentage of pesticides enter the soil and cause soil pollution.
Less than 1% of an applied pesticide reaches the targeted insect and the rest is depleted in soil, water, and air. eventually they enter the food chain and affect non-targeted species such as humans, flora and fauna.
2. Urban source of soil pollution
The urban industrial waste, domestic waste, and expensive use of cars and heavy-duty vehicles leads to top soil contamination. Urban waste and substances are always dumped in soil, resulting in physical and chemical degradation of soil. Municipal waste is always disposed on land, resulting in soil and underground water pollution and also leads to concentration of heavy metals. The disposal of sewage sludge on land, allows heavy metal to accumulate in soil which later enters into the food chain through crops. Apart from this, sewage contain organic pollutants such as PCDDs (polychloro dibenzo-p-dioxin) and PAHs (polycyclic aromatic hydrocarbons), which are toxic compounds.
Emission from power generation plants is also one of the urban sources of soil pollution. A coal-fired station emits pollutants such as polycyclic aromatic hydrocarbons, COx, NOx, and SOx. These pollutants enter into soil either as wet deposition or dry deposition.
3. Atmospheric sources
Due to burning of fossil fuels sulfur dioxide, nitrogen oxide, and ammonia are entered in the atmosphere. These acid-forming pollutants fall on the earth which is called acid deposition. Acid rain removes the minerals and nutrition from soil. Also acid deposition leaches aluminium from soil and increases the pH of soil.
Heavy atmospheric pollutants are transferred by wind from one place to another, and pollute the soil of that region.
4. Incidental sources
The incidental sources include industrial accidents, poisonous gases, and agriculture spillage.