First Published: January 9, 2012 | Last Updated:November 22, 2013
Soil pollution occurs when the thin layer of healthy and productive soil, which covers the earth’s surface, is destroyed. Solid waste or rubbish is the most visible form of pollution. Every year, people dispose of billions of tonnes of solid waste.
The solid waste produced in homes, schools, offices and shops is called municipal solid waste. It includes paper, plastic, bottles and cans and our left-over food.
Other waste consists of scrap metal, leftover materials from agricultural processes, and mining wastes known as spoil. Soil pollutants, mainly results from the industrial wastes, urban wastes, radioactive pollutants, agriculture practices, chemical and metallic pollutants, biological agents, mining, objects and soil sediments.
The lignocellulosic biomass generated by agricultural activities is a primary source of solid waste.
In addition, the use of fertilizers and pesticides in agricultural practices can limit the ability of soil organisms to process waste, which he turn makes the soil less productive or in the worst-case scenario, useless or every poisonous.
Some pesticides can remain in the environment for many year and pass from one organism to another. When pesticides are present in a stream, small fish and other organisms build up even larger amounts of pesticides in their flesh and will eventually pass them on to us through the food chain. There are many other human activities, which can damage soil. The irrigation of soil in dry areas with poor drainage can leave fields flooded. When this standing water evaporates, it leave salt deposits behind, making the soil too salty for growing crops.
Disposal of industrial waste is the major problem responsible for soil pollution. These industrial pollutants are mainly discharged from pulp and paper mills chemical industries, oil refineries, sugar factories, tanneries, textiles, steel, metal processing industries, drugs, glass, cement, petroleum and engineering industries.
Mining operations can leave soil polluted with toxic heavy metals. Many scientists believe acid rain can also reduce soil fertility. In surface mining and strip mining top soil and sub-soil is removed. This leaves deep salt in the earth.
The uncontrolled mine fires may also destroy the productivity of certain land areas permanently. Soil damage and environmental degradation during surface mining is inevitable as vegetation has to he removed and huge quantities of top soil and waste rocks are to be shifted to a new location, mining leads to loss of grazing and fertile land, soil erosion from waste dumps, sedimentation or silting, danger to aquatic life, flora and fauna as well as water and soil pollution.
This waste comprises both commercial and domestic wastes consisting of dried sludge of sewage. All the urban solid wastes are commonly referred to as refuse.
Solid wastes and refuse, particularly in urban area contribute to soil pollution. This refuse contains garbage and rubbish materials like plastics, glasses, metallic cans, fibres, rubbles, trash from the streets, fuel residues, leaves containers, abandoned vehicles and other discarded manufactured products.
Municipal waste is largely categorized into three type; waste that can be incinerated (generally called “combustible waste”) waste that is treated by non-incineration intermediate treatment measures (generally called “incombustibles”) and materials that directly go to recycling or re-use procedures through separate collection or voluntary group collection.
The waste generated from agriculture, municipal and commercial activities are putrid solid waste and is known as garbage. There are four broad categories of garbage.
Organic waste : kitchen waste, vegetables, flowers, leaves and fruits.
Toxic waste ; old medicines, paints, chemicals, bulbs, spray cans, fertilizer and pesticide containers, batteries and so on.
Recyclable ; paper, glass, metals and plastics.
Resistant objects; large resistant objects such as cans, plastic, tyres, polythenes, metallic junk, glasses or even old cars, refrigerators, washing machines destroys the beauty of landscape. In india, most of this is purchased by hawkers and resold. In industrialized countries, used vehicles are creating a serious threat to environment.
Soil sediments refer to the depositions of trace elements or metals such as Hg,As, Sb, Cd, Ni, Co, Mo, Cu and Cr.
The process of sedimentation is a comprehensive natural geomorphologic process, which operates through the chain of erosion of soils, transportation of sediments (eroded material) and deposition of thee eroded material in different paths of water bodies.
Sediments thus consist of soil and mineral particles washed away from land by storms and floodwaters, from geological process of denudation, which is both inevitable and universal. Eroded soil becomes a serious pollutant because of the absorbed chemicals that it carries to the particles surface.
In Shifting cultivation, plots of land are cultivated temporarily, then abandoned. This system often involves clearing of a piece of land followed by several years of wood harvesting or farming, until the soil loses fertility. Once the land becomes inadequate for crop production, it is left to be reclaimed by natural vegetation, or sometimes converted to a different long-term cyclical farming practice. Slash-and-burn is one element of their farming cycle. Land clearing without any burning is also used.
The major characteristic of Shifting Cultivation is that the cultivated or cropped area is shifted regularly to allow soil properties to recover under conditions of natural successive stages of re-growth. It is known as Jhum Cultivation in India and Ladang in Malaysia.
The longer a field is cropped, the greater the loss of soil organic matter, the reduction in the cation-exchange-capacity and in nitrogen and phosphorus, the greater the increase in acidity, the more likely soil porosity and infiltration capacity is reduced and the greater the loss of seeds of naturally occurring plant species from soil seed banks.
The indiscriminate destruction of forest for shifting cultivation has also reduced the forest cover. Shifting or jumping cultivation is mainly practiced by the tribal communities for raising food.