Course description

Introduction Soil pollution or contamination is largely caused by the presence of man-made chemicals or other alteration in the natural soil environment. This type of contamination typically arises from the failure caused by intensification of agriculture, irrigation methods, application of chemical fertilizers, pesticides, herbicides, insecticides, percolation of contaminated surface water to subsurface strata, oil and fuel dumping, disposal of coal ash, leaching of wastes from landfills or direct discharge of industrial wastes to the soil, and corrosion of underground storage tanks (including piping used to transmit the contents). This chapter focuses attention on the importance of soil as natural resources, soil and land pollution, the classification and description of major soil pollutants, factors causing soil pollution, health and environmental impacts, and management. Soil The soil is the upper most layer of the Earth crust- a thin cover over the land- has formed over thousands of years through natural processes, and the process is still continuing. The soil is an important natural resource for which there is no substitute. The soil consists of a mixture of minerals, organic material, living organisms, air and water, that together support plant growth (See Chapter 5), and is composed of two layers: the top soil and subsoil. The top soil being rich in organic matters and other plant nutrients is highly productive. Agricultural production is very much dependent on the quality of the top soil. Several factors that contribute to the formation of soil from the parent material includes the mechanical weathering of rocks due to temperature changes and abrasion, wind, moving water, glaciers, and chemical weathering activities. Climate and time are also important determinants in the development of soils. In extremely dry or cold climates soils develop very slowly, while in humid and warm climates soils develop more rapidly. Under ideal climatic conditions, soft parent material may develop into 1 cm of soil within 15 years. Under poor climatic conditions, a hard parent material may require hundreds of years to develop into soil. It is important that we should preserve the natural fertility of the soil as well as its other properties. Human activities have already led to deterioration in the condition of soil in many ways. Deterioration of soil quality will bring disaster to different species of flora and fauna through its links along the food chain. This chapter >>>>> Soil Pollution The soil pollution may be defined as the presence of materials in the soil which are harmful to the living beings when they cross their threshold concentration levels. In other words, it is the presence of toxic chemicals (pollutants or contaminants) in soil high enough in quantity (concentrations) and duration to be of risk to human health and/or ecosystem. Further, even when the levels of contaminants in soil are not at risk, soil pollution may occur simply due to the fact that the levels of the contaminants in soil exceed the levels that are naturally present in soil. Land Pollution: Land pollution is a kind of land degradation. Land is polluted when large quantities of wastes from different sources are dumped on it. A land is polluted when the action of external factors leads to a deterioration of the quality of land (soil) by the removal of its useful chemical properties. Alternatively, it can be the accumulation of noxious substances that are harmful to the flora and fauna using it. So, any dynamics that is brought about by different agents, resulting in a negative qualitative change in the physical characteristics of land or the chemical constituents of the soil may be termed as land degradation. Soil Erosion is another form of land degradation (Chapter 5) which can be defined as the movement of surface litter and topsoil from one place to another. While erosion is a natural process, often caused by wind and flowing water, it is greatly accelerated by anthropogenic activities such as farming, construction, deforestation, overgrazing by livestock, and burning of vegetative cover. The loss of the topsoil makes a soil devoid of essential nutrients or less fertile and reduces its water-holding capacity. The topsoil, which is eroded, also contributes to water pollution by clogging lakes and increasing the turbidity of the water, ultimately leading to the loss of aquatic life. For one inch of topsoil to be formed it normally requires 200-1000 years, depending upon the climate and soil type. Thus, if the topsoil erodes faster than it is formed, the soil becomes a non-renewable resource. Factors Causing Soil Pollution Soil Pollution/land degradation is mainly the consequences of urbanization and industrialization, but modern agricultural practices are also responsible for it to a great extent (Chapter 5). The United States alone produces more than 18 million tons of agricultural wastes every year. Some of the agents responsible for this pollution are listed as follows: 1. Anthropogenic activity including: Accidental spills and leaks during storage, transport or use of chemicals (e.g., leaks and spills of gasoline and diesel at gas stations); Industrial wastes involving release of effluents into the soil Manufacturing processes that involve furnaces or other processes resulting in possible dispersion of contaminants in environment; Mining activities involving crushing and processing of raw materials; Construction and building activities Agricultural technology involving the use of herbicides/pesticides/insecticides and chemical fertilizers; Urban wastes involving the dumping of chemicals and toxic substances; Dumping of solid wastes in landfills (which may leak to groundwater reservoir) 2. Natural sources Natural accumulation of contaminants in soil due to imbalances between atmospheric deposition (e.g. volcanic dusts, acid deposition etc.) and leaching away with precipitation water; Leaks from sewer lines into subsurface; Soil Pollutants All soils contain a variety of compounds which are naturally present. They are mainly formed through soil microbial activity and decomposition of organisms (e.g., plants and animals). In addition, various compounds get into soil from the atmosphere (with precipitation water, as well as by wind activity or other types of soil disturbances) and from surface water bodies and shallow groundwater flowing through the soil. When the amounts of soil contaminants exceed natural levels (what is naturally present in various soils) pollution is generated. Soil pollution results from the build up of a large variety of contaminants, toxic compounds, radioactive materials, solvents, salts (e.g., phosphates, carbonates, sulfates, nitrates), chemicals (such as inorganic ions), many organic compounds (such as proteins, DNA, fatty acids, alcohols etc.) and cancer-causing agents. The most common soil pollutants are hydrocarbons, heavy metals (cadmium, lead, chromium, copper, zinc, mercury and arsenic), herbicides, pesticides, oils, tars, PCBs and dioxins. The following are some of the categories of soil pollutants discussed in detail: Sources of Soil Pollution The sources or agents of soil pollution may be divided into the following seven categories: Physical sources Biological agents Chemical and metallic pollutants Radioactive pollutants Urban and industrial sources Air-borne sources Modern agriculture: Chemical fertilizer and biocides Physical Sources: Physical sources of soil pollution are related to soil erosion and consequent soil degradation, caused by both natural and anthropogenic factors. The natural factors of soil erosion include amount and intensity of rainfall, temperature, wind speed, topographic factors, vegetation and soil characteristics. These factors are further accelerated by human activities such as land use changes. In most of the developing countries of the world, particularly in the tropical and sub-tropical regions accelerated rate of soil erosion due to rapid rate of deforestation and faulty agricultural practices has polluted the soil on a large scale, because the top most fertail layer has been washed out. , Biological Agents: A major source of soil pollution is caused by biological agents such as human, animals, birds, and microorganisms. The biological agents are highly responsible for heavy contamination of soils and crops by pathogens. The microorganisms enter the soil from various sources and pollute them. These, in turn, enter the food chains and thus affect human bodies. Pathogenic soil bacteria ( Mycobacterium, Salmonella Typhosa, Leptospira, Tuberculosis etc.) are chronic disease carrier which are transmitted from man to soil or vice-versa causing cholera, typhoid, paratyphoid fever, and dysentery. Flies which breed or get in contact with the contaminated soil become carriers of disease bacteria. Solid wastes mainly constitute animal manures, food processing materials, sewage sludge, municipal wastes, and garbage composts. These organic materials are now being added to soils- the potential sources of contaminants. The leachates of the areas join the aquifers below the surface, posing danger to the ground water. Municipal Solid wastes result in offensive odor and cause clogging of ground water filters. Suspended matter in sewage can blanket the soil, thereby interfering with the soil moisture content. Sewage is an excellent medium for growth of pathogenic bacteria, viruses, and protozoa causing cholera, dysentery and typhoid. Sewage sludge does have numerous faults as these are contaminated with active viruses, bacteria and viable intestinal worm's eggs. In developing countries, intestinal parasites constitute the most serious soil pollution problem. Further, digested sewage sludge as well as heavy application of manures to soils without periodic leaching could cause chronic slat hazard to plants within a few years. Chemical and Metallic Pollutants: Today, the most anticipated problem in soil pollution is the contamination of land with toxic chemicals. Solid, liquid and gaseous chemicals from various industries such as paper and pulp, iron and steel, fertilizers, automobiles, dyes, pesticides, tanneries, thermal power plants etc. contain a variety of pollutants e.g. heavy metals, solvents, detergents, plastics, suspended particulates and non-biodegradable chemicals. In Bangladesh, there are a large number of industries around the major cities (e.g. textiles, tanneries, paper and pulp, sugar, paints, dyes, soap and synthetic detergents, drugs, batteries, cement, asbestos, petroleum, rubber, steel, glass, electroplating and metal industries) that pour hazardous effluents in soil creating a disastrous effect on living organisms. If they are not treated at source, give rise to environmental pollution. Indiscriminate dumping of untreated and inadequately treated domestic, industrial and commercial wastes on land is an important source of soil pollution. Fallout of gaseous and particulate air- pollutants from mining, smelting operations, smoke stakes etc. is a major source of soil pollution in nearby areas. Heavy metals contaminate the soil by using chemical fertilizers and polluted water to wet crops. Chemical fertilizers are a source of trace metals (e.g. As, Pb and Cd) which are added to the soil either deliberately or as an impurity. Heavy metals come from iron, steel, power plants and chemical manufacturing plants that recklessly use the Earth as a dumping ground for their refuse. Well documented constituents include mercury, chloride, nitrate, zinc, iron and cadmium which have significant adverse effect on crop productivity. Plants that burn their waste on-site are guilty of releasing heavy metals into the atmosphere, which come to settle in the soil, thus leaving behind lasting effects for years to come. Soluble salts needed by the industries are responsible for crop damage, metallic corrosion and leading to costly cleansing activities. FAO states that 50 percent of the irrigated farms in the world are damaged by soluble salts. Excessive amounts of farm wastes, soil nutrient mining resulting from the uses of inorganic chemicals are also reported to cause soil pollution. Industry is to blame for some of the biggest soil-pollution disasters. Even companies that try to dispose of their waste properly contribute to the problem when faulty landfills and bursting underground bins leach undesirable toxins into the soil. Metallic contaminants in soil are considered to be the destructive poisons and their accumulation in plants are seriously damaging since they affect all living beings through the food chain. Metallic contaminants destroy bacteria and beneficial microorganisms in the soil. The toxic metals, however, may be absorbed by plant grown in contaminated soil. Urban and Industrial Sources: Improper disposal of industrial and urban wastes and irrigation of agricultural fields from polluted urban sewage wastes (near urban and industrial areas) pollute the soil properties by changing their physical and chemical characters. The untreated sewage sludge not only pose serious health hazards but also pollute soil and decrease its fertility. Other waste materials such as used plastic bags, municipal garbage, sludge, dead animals, skins, shoes, cans, wastes from hospital and clinics etc. also cause soil pollution (Chapter 17). Moreover, soil gets enormous amount of liquid industrial wastes each year. The toxic chemical substance of industrial effluents and urban sewage enter the soil and pollute them mostly in the neighborhood of cities and factories. Much of the sulfur dioxide ends up on soil as sulphates which react with soil water to form sulphuric acid. Leads from smelters occur on soil near industrial areas. Eroded sediments can carry huge amount of nitrogen, phosphorus, pesticides, fertilizers and organic matter. Air-born Sources: Air-born sources of soil pollution are, in fact, air pollination which are released into the atmosphere by industries, automobiles, thermal power plants and domestic sources. Gaseous and soil particulate pollutions emitted by factory chimneys and other sources are transported to the areas far away from the sources of the emission by prevailing wind. The fallouts of these pollutants are deposited in the soil which are polluted due to toxic substances. For example, sulphur emitted from the factories causes acid rain which lower the pH of the soil, increasing the acidity of the same. Highly acidic soil are injurious to plant growth. Fallouts of metallic particulate matter from mtal smelters into soils damage their physical and chemical properties. Mining and Soil Pollution: Degradation of soil during mining is unavoidable as vegetation has to be removed and huge quantities of top soil and waste rocks are to be shifted to new location. Mining leads to loss of fertile land, grazing, soil erosion from waste dumps, sedimentation or siltation, damage to aquatic life, flora and fauna and soil pollution. Mining leaves a tremendous impact on the surrounding communities. The 2001 West Virginia Geological and Economic Survey found that people living near mines have a 70 percent higher risk of kidney disease, 64 percent higher risk for chronic obstructive pulmonary disease and a 30 percent higher risk of high blood pressure. Radioactive Pollutants: The problem of radioactive wastes dumped into the soil is more complicated, because every radioactive element like radium, uranium, thorium and plutonium can remain active in soil for thousands of years. Since, these wastes are produced in high quantities, can create an extremely difficult health problem. The volatile materials when released into the air become potential contaminant of the environment as these can easily settle on soil. When, rain containing radio-nuclides fall on the soil, its activity is transferred into the soil by adsorption of soil particles. As the radioactivity in the soil is available to plants, it enters the food chain resulting in the possibility of eventual ingestion by humans. A recent report indicates that a large number of induced radio-nuclides as carbon-14, iron 55, manganese-54, cobalt 57 and zinc-65 get concentrated in biological systems and this is proved by their presence in fish. Radiation acutely affects the soil and soil fertility by killing plant species. Modern Agricultural Practices Modern agricultural practices pollute the soil to a great extent. Today, with the aid of modern agro-technology, huge quantities of chemical fertilizers such as nitrogen, herbicides, pesticides, insecticides and other soil conditioning agents are employed to increase the crop production. Over the years, the use of chemical fertilizers and pesticides in crop cultivation in Bangladesh has increased tremendously. On the average about 160,000 tons of chemical fertilizers and 3000 tons of pesticides are used annually (DOE, 1990). Growth in population and scarcity of cultivable land has led to more intensive agriculture and cultivation of HYV of crops to meet the growing need for more food. Pesticides applied to plants can also seep into the ground, leaving lasting effects. Many agricultural lands are now vulnerable to the stress imposed upon them by the intensification of agriculture. Chemical Fertilizers: Today, agricultural practices rely heavily on chemical fertilizers that generally contain a number of plant nutrients i.e. nitrogen, phosphorous and potassium. Any increase in agricultural productivity can hardly be possible without the application of chemical fertilizers. However, their excessive application reduces soil fertility; moisture retention capacity of the soil is further declined and the soil hardens. Rapid population growth and commercialization of agriculture have been responsible for the phenomenal increase in the production and consumption of chemical fertilizers and biocides. Excessive use of chemical fertilizers to boost agricultural production causes alteration in the physical and chemical properties of soil. Effects of Chemical Fertilizers: Synthetic fertilizers though are employed to increase the soil fertility and crop productivity these concentrate the essential nutrients in layer of top soil. However, an excessive and indiscriminate use of synthetic fertilizers may result in a number of undesirable effects. Chemical fertilizers wipe out essential nutrients present in the top soil. The microbes that enrich the soil humas, and initiate plant growth can not survive under the condition of fertilizer enriched soil. Hence, there remains compact soil with poor humas and less soil nutrients, vulnerable to erosion by wind and water. Excessive use of nitrogen fertilizers in cropland leads to accumulation of nitrate in the soil which may contaminate the ground water, and is transferred to human being through plants. Excessive use of chemical fertilizers may enter the water bodies and contribute to “eutrophication” (excessive growth of algae and aquatic plants to undesirable levels). Its excessive use also reduces the ability of plants to fix nitrogen. Potassium fertilizers in soil decrease the valuable nutrient such as ascorbic acid (vitamin C) and carotene in vegetables and fruits. According to an estimate, there is a 25 to 30 percent decline in protein content of secondary crops such as wheat, maize, and gram that are grown on soil fertilized with NPK fertilizers. Moreover, the subtle balance of amino acids with protein molecule is also disrupted, degrading the carbohydrate and protein quality of the food produced. Chemical fertilizers do not have humus to the soil, and thus its ability to hold water will decrease, and the soil will become compacted and less suitable for crop growth. By decreasing the soil’s porosity, inorganic fertilizers also lower the oxygen content of soil. Management: Excessive use of chemical fertilizers must be discouraged and use of manure and humas should be encouraged along with organic farming. Three basic types of organic fertilizers are animal manure, green manure and compost. Animal manure improves soil structure, adds organic nitrogen, and stimulates beneficial soil bacteria and fungi. Green manure is fresh vegetables plowed into the soil to increase the organic matter and humas available to the next crop. Compost is a rich natural fertilizer and soil conditioner that improves the ability of soil to retain moisture and nutrients. Crop field should be planted with leguminous species during seasons when the land is left fallow. This will certainly reduce dependence on chemical fertilizer. Pesticides Hybrid varieties of crops have higher yields but they are less pest resistant, the use of pesticides is a compulsion. However, excessive use of pesticides (e.g. DDT, aldrin, endrin etc.) is a major cause of environmental degradation. Pesticides not only kill pests that destroy crops but also kill useful soil microorganisms (useful bacteria), hampering biological nutrient replenishment system of the soil- reducing its fertility. Pesticides first kill germs and unwanted plants and then contaminate the soil and reach the plants through their roots. These toxic elements are ultimately transferred to human bodies and thus kill people through several fatal diseases. Some of these pesticides persist in the environment for a long time, and tend to accumulate in the bodies of organisms including man at levels far greater found in the environment. The concentration keeps increasing along the food chain- a process known as biological magnification. Some pesticides may get absorbed by soil particles which may contaminate root crops grown in soils. These chemical agents may contain several toxic metals like lead, arsenic, cadmium, mercury and cobalt etc.; when applied to a cropland is more likely to accumulate on the soil permanently thereby introducing these chemical components into growing crops. Effects of Pesticides: Pesticides may be broadly categorized into three groups: Organochlorines (e.g. DDT- dicloran diphenyl trichloroethane, aldrin, endrin, dieldrin, chlordane etc); organophosphorus (e.g. malathion, parathion, diazinon etc.) and carbamates (e.g. carbaryl), carbofuran etc.). Organochlorines are neurotoxicants and damage the nervous system of organisms exposed to this these. DDT for example, is carcinogenic, biologically magnified, accumulates in the fatty body tissues, and moves along the food chain in ever increasing concentration (DDT was the first synthetic insecticide, originally formulated in 1873 by a German scientist, later rediscovered by Paul Hermann Muller of Switzerland in 1939, Nobel prize 1948). Initially DDT had been identified as a powerful insecticide without precedent. No one realize that it could cause massive harm to the environment and human health until Carson sounded the alarm). Organophosphates and carbamates exert their influence of toxicity by inactivating vital enzymes in the bodies of organisms exposed to these chemicals. Like pesticides, herbicides are chemicals used in controlling weeds that grow on croplands. But the deadly poison dioxin occurs as a contaminant in certain herbicides e.g. trichlorophenol- carcinogenic and may give rise to birth defects. It is striking to note that many of the harmful pesticides have been banned in more developed countries such as the USA, but are still being exported to LDCs regardless of their harmful effects on human health and ecology. World-wide, about 2.5 million tons of such pesticides are used yearly- 0.45 kg- 1 pound, for each person. Cultivation of four crops- corn, cotton, wheat and soybeans- use about 70 percent of the insecticides and 80 percent of the herbicides applied to crops in the United States. According to WHO and UNEP, as many as 25 million agricultural workers in LDCs are seriously poisoned by pesticides each year. Soil gets sufficient quantities of pesticides as an inevitable result of their application to food crops. Among the adverse effects to be considered are the absorption of pesticides by the soil, leaching of the pesticides into aquifers, ill effects of pesticides on soil microbes and possible production of relatively more toxic products. People in contact with pesticides, such as farmers, farm workers, and agriculturalists are more prone to be poisoned by these chemicals. Their excessive absorption leads to accumulation in the body culminating in complexities such as damage liver, kidney causing malfunctioning, excess of amino acid in blood and urine, cancer and deformation of brain tissues. Long lasting effects of herbicides, insecticides and chlorinated pesticides are visible in animals and man where they affect the tissues of and interferes the metabolic activities of man by destabilizing the enzyme functions in the body. Pesticides retained in soil concentrates in crops, vegetables, cereals and fruits in such an extent that they are seldom useable. These are potent pollutants of the soil and affect soil texture and functions of the ecosystems. DDT, endrin, dieldrin and PCBs accumulate in soil and enter human bodies through plant. In a sprayed crop field, pesticides (DDT and other chlorinated hydro carbons) contaminated soil may be carried away by wind erosion to other areas. Some of these pesticides such as DDT persist in the environment for a long time and tend to accumulate in the bodies of organisms at level far greater than found in the environment. The concentration keeps on increasing along the food chain. This is known as biological magnification. DDT accumulates in the fatty tissues of organisms; it moves along the food chain in ever increasing concentration as it is retained in the body tissues. Management: Integrated Pest Management (IPM)- a better way to control pests by using different biological and physical methods- could be used as a means to an end. In this method, pests are controlled biologically by other organisms. For example bacterial pathogens may be used against specific insects; frog farming in crop lands, insect traps, introducing pest resistant plants and crop rotation are other effective pest control. It is the indigenous species that should be used for controlling the pests. Foreign species introduced into a new environment may cause ecological disasters. Irrigation Problems: All over the world, irrigation is practiced in one from or another to increase agricultural productivity. Today, roughly 18 percent of the world’s cropland irrigated by various methods produces about one-third of the world’s food. Even though irrigated land has the capacity to produce crop yields that are two to three times greater than those from rain fed agricultural systems, irrigation has downside too. Although irrigation facilities are expected to increase agricultural production, these may turn out to be the major cause of soil degradation on which it is practiced. Effects of Salinization: Poorly managed irrigation systems have potentials to destroy soil fertility through salinization- the accumulation of salts. Irrigation water some time contains dissolved salts. In dry season, much of the water in this saline solution evaporates, leaving its salts (such as sodium chloride) in the topsoil. The accumulation of these salts stunts crop growth, lower yields, and eventually kills crop plants, and ruins the land. According to an estimate, severe salinization has reduced crop yields on 10 percent of the world’s irrigated cropland and another 30 percent has been moderately salinized. However, in the coastal areas of Bangladesh, soil salinity from irrigation happens in a somewhat different way. Saline water from the sea percolates into the underground aquifer. Salt water being denser lies at the bottom of the freshwater in the aquifer. If there is an over withdrawal of groundwater, then salt water infiltrates into the well- cone of depression- and reaches the surface contaminating the soil of the croplands and increasing its salinity. Effects of Waterlogging: Further, farmers often apply large amount of irrigation water to leach salts deeper into the soil. However, without adequate drainage, water accumulates underground, gradually rising the water table and creates a temporary stagnant situation called waterlogging. Saline water then envelops the roots of plants and kills them. At least one-tenth of all irrigated land worldwide suffers from waterlooging, and the problem is getting worse. Continuous waterlogging will mean an absence of oxygen in the soil, as air spaces between the soil particles will be replaced by water. Prolonged submersion in water will also leach out micronutrients and organic matters in the soil, resulting in the loss of soil fertility. Waterlogged soil environment is the breeding ground for different types of pests and disease causing microbes and animals. Since soil is the base for life, human induced soil degradation must be slowed and replace with soil rebuilding and conservation practices. Management: In order to avoid salinization and waterlogging, irrigation scheme should be managed properly. Over-extraction of groundwater should be prevented, methods involving more economic use of irrigation water should be adopted, and loss of water from drainage through evaporation should be minimized. Provisions should be made for good drainage so that water recedes after the flood. Salt tolerant species of vegetation may be planted as an adaptation process to deal with salinization. Planting crop varieties that need less irrigation water should be encouraged. Salts can be flashed out of soil by applying much more irrigation water than is needed for crop growth. Heavily salinized soil can also be renewed by taking the land out of production for two to five years Effects of Soil Pollution Health Effects: Contaminated soil directly affects human health through direct contact with soil or via inhalation of soil contaminants which have vaporized. Soil pollution may affect all of us as well as plants and animals. The soil pollution effects may vary based on age, general health status and other factors. The children are usually more susceptible. Health consequences from exposure to soil contamination vary greatly depending on pollutant type, pathway of attack and vulnerability of the exposed population. Chronic exposure to chromium, lead and other metals, petroleum, solvents, and many pesticide and herbicide formulations can be carcinogenic, can cause congenital disorders, or can cause other chronic health conditions. Industrial or man-made concentrations of naturally-occurring substances, such as nitrate and ammonia associated with livestock manure from agricultural operations, have also been identified as health hazards in soil and groundwater. Chronic exposure to benzene at sufficient concentrations is known to be associated with higher incidence of leukemia. Mercury is known to induce higher incidences of kidney damage, some irreversible. PCBs are linked to liver toxicity. Many chlorinated solvents induce liver changes, kidney changes and depression of the central nervous system. There is an entire spectrum of further health effects such as headache, nausea, fatigue, eye irritation and skin rash for the above cited and other chemicals. At sufficient dosages a large number of soil contaminants can cause death by exposure via direct contact, inhalation or ingestion of contaminants in groundwater contaminated through soil Environmental Effects: Not unexpectedly, soil contaminants can have significant deleterious consequences for ecosystems. There are radical soil chemistry changes which can arise from the presence of many hazardous chemicals even at low concentration of the contaminant species. These changes can manifest in the alteration of metabolism of endemic microorganisms and arthropods resident in a given soil environment. The result can be virtual eradication of some of the primary food chain, which in turn could have major consequences for predator or consumer species. Effects also occur to agricultural lands which have certain types of soil contamination. Contaminants typically alter plant metabolism, most commonly to reduce crop yields. This has a secondary effect upon soil conservation, since the languishing crops cannot shield the Earth's soil mantle from erosion phenomena. Some of these chemical contaminants have long half-lives and in other cases derivative chemicals are formed from decay of primary soil contaminants. The immense and sustained growth of the People's Republic of China since the 1970s has exacted a price from the land in increased soil pollution. The State Environmental Protection Administration believes it to be a threat to the environment, to food safety and to sustainable agriculture. According to an estimate, 150 million mi (100,000 square kilometers) of China’s cultivated land have been polluted, with contaminated water being used to irrigate a further 32.5 million mi (21,670 square kilometers) and another 2 million mi (1,300 square kilometers) covered or destroyed by solid waste. An estimated 12 million tones of grain are contaminated by heavy metals every year, causing direct losses of 20 billion yuan (US$2.57 billion). Management Some of the options and measures to arrest further land degradation in Bangladesh and improve the existing situation are as follows: Policy- National land use policy: Long-term vision through people’s participation should be ensured. Land zoning will help sustainable land management and its development for different uses; Appropriate cropping patterns: Balanced cropping patterns through diversification, improvement of organic component of soil through green manure, organic farming and sustainable agricultural production; Research- Assessment and monitoring: Survey of the present state of land degradation and extent of its severity will help to identify future course of actions required for addressing the issues; Restoration of degraded lands: Improvement of soil quality, development of salt tolerant varieties, and soil conservation should be undertaken; Watershed management: Catchment based watershed management to arrest erosion in the hill slopes and improve siltation in the floodplain should be encouraged; Extension- Balanced used of chemical fertilizers to improve soil quality, increase crop production and restrict land degradation; and Mass awareness and motivation: Improvement of soil quality through controlling soil pollution, increase crop production protect land from further degradation.

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