Soil Pollution: Sources, Effects, and Control Measures PDF

Soil pollution Sources of pollutants and mitigation measures Basic Soil Chemistry Soils are composed roughly equally of solid particles, about 90% of which are inorganic in nature and 10% organic matter, and of pore space, about half of which is air and half water. The inorganic particles...

Soil pollution Sources of pollutants and mitigation measures Basic Soil Chemistry Soils are composed roughly equally of solid particles, about 90% of which are inorganic in nature and 10% organic matter, and of pore space, about half of which is air and half water. The inorganic particles are residues of weathered rock; chemically they are mainly silicate minerals. At the atomic level, these minerals consist of polymeric inorganic structures in which the fundamental unit is a silicon atom surrounded tetrahedrally by four oxygen atoms. Soil Composition  Soil types Soil types depends on particle size, factor-of-ten increase in size with each transition of type Sources of Soil pollution. Soil pollution is defined as, “contamination of soil by human and natural activities which may cause harmful effect on living organisms” Cause of Soil pollution: 1. Industrial wastes Inorganic Pollutants 2. Urban wastes Organic wastes 3. Agricultural practices [Pesticides, Salts (fertilizers), etc.] 4. Radioactive pollutants 5. Biological agents Industrial wastes Disposal of Industrial wastes is the major problem for soil pollution Sources: Industrial pollutants are mainly discharged from various origins such as pulp and paper mills, chemical fertilizers, oil refineries, sugar factories, tanneries, textiles, steel, distilleries, fertilizers, pesticides, coal and mineral mining industries, drugs, glass, cement, petroleum and engineering industries etc. Effect: These pollutants affect and alter the chemical and biological properties of soil. As a result, hazardous chemicals can enter into human food chain from the soil or water, disturb the biochemical process and finally lead to serious effects on living organisms. Urban wastes Urban wastes comprise of both commercial and domestic wastes consisting of dried sludge and sewage. All the urban solid wastes are commonly referred to as refuse. Constituents of urban refuse: This refuse consists of garbage and rubbish materials like plastics, glasses, metallic cans, fibres, paper, rubbers, street sweepings, fuel residues, leaves, containers, abandoned vehicles and other discarded manufactured products. Urban domestic wastes though disposed off separately from industrial wastes, can still be dangerous. This happens because they are not easily degraded. Agricultural practices Modern agricultural practices pollute the soil to a large extent. With the advancing agro-technology, huge quantities of fertilizers, pesticides, herbicides and weedicides are added to increase the crop yield. Apart from these farm wastes, manure, slurry, debris, soil erosion containing mostly inorganic chemicals are reported to cause soil pollution  The main insecticide and herbicide groups Pesticide groups Specified pesticide types Insecticides Organochlorines DDT, Aldrin, Heptachlor carbamates Herbicides Phenoxyacetic acids 2, 4-D, 2, 4, 5-T Toluidines Trifluralin Triazines Atrazine, Simazine Phenylureas Fenuron Bipyridyls Diquat, Paraquat Glycines Glyphosate Persistent organic pollutants (POPs) Chemical substances Designed use Major concerns Aldrin Pesticide to control soil insects and to Toxic to humans, may be carcinogenic protect wooden structures from Chlordane Broad-spectrum insecticide to protect crops Biomagnification in food webs DDT Widely used insecticide, malaria control Biomagnification in food webs Dieldrin Termite control, crop-pest control Toxic, biomagnification in food webs, high persistence Endrin Insecticide and rodenticide Toxic, especially in aquatic systems Heptachlor General insectivide Toxic, carcinogenic Hexachlorobenzene Fungicide Toxic, carcinogenic MirexTM General insecticide, against ants High aquatic animal toxicity, carcinogenic ToxapheneTM General insecticide High aquatic animal toxicity, carcinogenic PCBs Variety of industrial uses, especially in Toxic, teratogenic, carcinogenic transformers and capacitors Dioxins No known use; by products of incineration Toxic, carcinogenic, reproductive system and paper bleaching effect Furans No known use; by products of incineration, Toxic, especially in aquatic systems PCB production Common range of persistence of a number of pesticides Pesticides Persistence Arsenic Indefinite Chlorinated hydrocarbon insecticides (e.g., DDT, chlordane, 2-5 yr dieldrin) Triazine herbicides (e.g., atrazine, simazine) 1-2 yr Benzoic acid herbicides (e.g, amiben, dicamba) 2-12 month Urea herbicides (e.g., monuron, diuron) 2-10 yr Phnexy herbicides (2, 4-D, 2, 4, 5-T) 1-5 month Organophosphate insecticides (e.g., malathion, diazinon) 1-12 wk Carbamate insecticides 1-8 wk Carbamate herbicides (e.g., baran, CIPC 2-8 wk Radioactive pollutants Radioactive substances resulting from explosions of nuclear testing laboratories and industries giving rise to nuclear dust radioactive wastes, penetrate the soil and accumulate giving rise to land/soil pollution. Example: 1. Radio nuclides of Radium, Thorium, Uranium, isotopes of Potassium (K-40) and Carbon (C-14) are commonly found in soil, rock, water and air. 2. Explosion of hydrogen weapons and cosmic radiations include neutron, proton reactions by which Nitrogen (N-15) produces C-14. This C-14 participates in Carbon metabolism of plants which is then into animals and human beings. 3. Radioactive waste contains several radio nuclides such as Strontium90, Iodine129, Cesium-137 and isotopes of Iron which are most injurious. Strontium get deposited in bones and tissues instead of calcium. 4. Nuclear reactors produce waste containing Ruthenium-106, Iodine-131, Barium140, Cesium-144 and Lanthanum- 140 along with primary nuclides Sr-90 with a half life 28 years and Cs-137 with a half life 30 years. Rain water carries Sr-90 and Cs-137 to be deposited on the soil where they are held firmly with the soil particles by electrostatic forces. All the radio nuclides deposited on the soil emit gamma radiations. Biological agents Soil gets a large amount of human, animal and bird excreta which constitute a major source of land pollution by biological agents. Example: Heavy application of manures and digested sludge can cause serious damage to plants within a few years Green House Impact Continuing declines in soil moisture can increase the need for irrigation in agriculture and lead to smaller yields and even desertification. Affect soils, leading to changes in soil erosion, organic carbon, nutrients and alkalinity. Decreasing soil carbon due to climate change also has implications for accounting of carbon emissions from the land, which is an important Acid Rain Control measures of soil pollution 1. Soil erosion can be controlled by a variety of forestry and farm practices. Example: § Planting trees on barren slopes § Contour cultivation and strip cropping may be practiced instead of shifting cultivation § Reducing deforestation and substituting chemical manures by animal wastes also helps arrest soil erosion in the long term Control measures of soil pollution… 2. Proper dumping of unwanted materials: Excess wastes by man and animals pose a disposal problem. Open dumping is the most commonly practiced technique. Nowadays, controlled tipping is followed for solid waste disposal. The surface so obtained is used for housing or sports field. 3. Production of natural fertilizers: Bio-pesticides should be used in place of toxic chemical pesticides. Organic fertilizers should be used in place of synthesized chemical fertilizers. Ex: Organic wastes in animal dung may be used to prepare compost manure instead of throwing them wastefully and polluting the soil. Control measures of soil pollution… 4. Proper hygienic condition: People should be trained regarding sanitary habits. Example: Lavatories should be equipped with quick and effective disposal methods. 5. Public awareness: Informal and formal public awareness programs should be imparted to educate people on health hazards by environmental education. Example: Mass media, Educational institutions and voluntary agencies can achieve this. Control measures of soil pollution… 6. Recycling and Reuse of wastes: To minimize soil pollution, the wastes such as paper, plastics, metals, glasses, organics, petroleum products and industrial effluents etc should be recycled and reused. Ex: Industrial wastes should be properly treated at source. Integrated waste treatment methods should be adopted. 7. Ban on Toxic chemicals: Ban should be imposed on chemicals and pesticides like DDT, BHC, etc. which are fatal to plants and animals. Nuclear explosions and improper disposal of radioactive wastes should be banned. DDT = Dichloro diphenyl trichloroethane. BHC = Benzene hexachloride. 3R technique in solid waste management- Here 3R implies Reduce, Recycle and Reuse Waste reduction is the best method to be practiced Recycling is a simple phenomenon of reusing the used items from which utilities can still be derived It is important to recycle waste for the conservation of some of our natural resources for the generations to come Solid Waste Management The main objective of solid waste management is to minimize this adverse effect. Solid waste management can be done by the following steps: 1. Collection 2. Storage 3. Transportation 4. Recycling 5. Treatment and 6. Disposal. Collection: the efficient collection of solid waste leads to dumping of waste management. Improper collection of solid waste leads to dumping of waste in the open spaces Storage: The waste bins act as storage points. Cleaning of those waste bins is necessary for avoiding unhygienic condition. Storage facilities are not yet developed in some urban areas Transportation: the solid waste collected from the bins are finally transported to waste disposal site by truck. The frequency of transportation is controlled by municipal authorities and entirely depend on the rate of solid waste formation Disposal: this is the final step in solid waste management. Due to the unorganized solid waste disposal causes environment pollution. Generally solid wastes are disposed off in low land area. Disposal of solid waste can be done by three ways (1)Land fill (2)Incineration and (3)Composting Land fill: In land filling, the solid wastes are compacted and spread in thin layers over a low land area, each layer being uniformly covered by thin layer of soil. The final layer is covered by a final cover of about one meter of earth to prevent solid waste scattering Land filling is a biological method of solid waste degradation and it will produce CO2, CH4, NH3 as renewable source of energy  Landfills Schematic of a hazardous waste landfill  Beneath the hazardous wastes, there must be a double-liner system to stop the flow of liquids, called leachate, from entering the soil and groundwater beneath the site. The upper liner must be a flexible-membrane lining (FML) usually made of sheets of plastic or rubber. The lower liner is usually an FML, but recompacted clay at least 3 feet thick. Leachate that accumulates above each liner is collected in a series of perforated drainage pipes and pumped to the surface for treatment. To help reduce the amount of leachate formed by precipitation seeping into the landfill, a low permeability cap is placed over completed cells. When the landfill is finally closed, a cap that may consist of an FML along with a layer of compacted clay is placed over the entire top with enough slope to assure drainage away from the wastes.  Restrictions and standards for land disposal facilities Banning liquids from landfills Banning underground injection of hazardous waste within a quarter-mile of a drinking water well Requiring more stringent structural and design conditions for landfills and surface impoundments, including two or more liners, leachate collection systems above and between the liners, and groundwater monitoring Requiring cleanup or corrective action if hazardous waste leaks from a facility Requiring information from disposal facilities on pathways of potential human exposure to hazardous substances Anthropogenic sources of methane emissions  Landfills Three classifications for landfills. Class I landfills, or secure landfills, are those designed to handle hazardous wastes Class II landfills, or monofills, handle so-called designated wastes, which are particular types of waste, such as incinerator ash or sewage sludge, that are relatively uniform in characteristics and require special handling; and Class III landfills, or sanitary landfills, are engineered facilities designed to handle municipal solid waste.  Landfills Basic features of a municipal solid waste landfill  Moisture contained in the wastes themselves is rather quickly dissipated, so it is water that percolates through the surface, sides, and bottom that eventually dominates the water balance in the landfill. Leachate collection and treatment is essential to the protection of the local groundwater. Composite liners and leachate collection systems prevent groundwater contamination The composite liner consists of a FML above a layer of compacted clay soil. Leachate is collected with perforated pipes that are situated above the FML A final cover over the completed landfill must be designed to minimize infiltration of water. During waste decomposition, methane gas is formed, so completed landfills need collection and venting systems. Decomposition in Landfills When MSW is deposited in landfills, microbial decomposition breaks down the wastes creating gaseous end products, such as carbon dioxide, methane, and various volatile organic compounds (VOCs), as well liquid leachate. The main focus of environmental engineers has traditionally been on keeping leachate from contaminating groundwater, but more recently attention has shifted to the global warming implications of keeping potent methane emissions from reaching the atmosphere, capturing those emissions for clean power generation, and the potential for longterm carbon storage in landfills The decomposition of landfill materials can be thought of as a four-stage process. I. Aerobic Phase: When wastes are placed in a landfill, there is enough entrained oxygen to allow aerobic decomposition to take place for the first few days. Oxygen levels drop, and at the end of this phase, anaerobic conditions begin. II. Acid Phase: During this phase, anaerobic conditions prevail, and a two-step process begins. First, hydrolyzing-fermentative organisms produce enzymes that break down complex organics such as cellulose and starch into simpler products that can be fermented into hydrogen, carbon dioxide, fatty acids, and alcohols. In the second step, those products are converted by bacteria, called acetogens, into simpler organic acids, typified by acetic acid. As these acids form, the pH of the leachate drops, which can allow heavy metals to be solubilized. The concentration in the waste rises and small amounts of hydrogen gas are produced. III. Methanogenesis: Another group of microorganisms, called methane formers or methanogens, convert the organic acids into and CO2. The pH begins to return toward more neutral conditions and the release of heavy metals into the leachate declines. This phase can last for months. IV. Methanogenesis, steady: The duration of each phase depends on the availability of moisture and nutrients, but typically on the order of a year or so after a landfill cell is completed the generation rate of and settles down into nearly equal percentages, which is the characteristic of Phase IV. After many years, perhaps several decades, the decomposition process and the rate of production of methane decline significantly. The rate of landfill decomposition is affected by a number of factors, including moisture, available nutrients, pH, and temperature. Equation that describes the complete decomposition of organic materials under anaerobic conditions Waste Incineration Incineration is particularly effective with organic wastes, not only in soils but in other solids, gases, liquids, and slurries (thin mixtures of liquids and solids) and sludges (thick mixtures) as well. Carcinogens, mutagens, and teratogens as well as pathological wastes can all be completely detoxified in a properly operated incinerator.Combustion of solid waste at a temperature range of 900-1200 o C in a specially designed furnace is known as incineration Various types of rotary kiln, air –controlled incinerators have been used for this purpose Volume of the waste an be reduced up to 90% by this process. The completion of combustion in an incinerator depends on following factors : temperature and the amount of oxygen available for combustion  The rotary kiln incinerator unit consists of a slightly inclined, rotating cylinder. Wastes and auxiliary fuel are introduced into the high end of the kiln, and combustion takes place while the cylinder slowly rotates. The rotation helps increase turbulence, which improves combustion efficiency. Partially combusted waste gases are passed to a secondary combustion chamber for further oxidation. The most critical factors that determine combustion completeness are (1) the temperature in the combustion chamber, (2) the length of time that combustion takes place, (3) the amount of turbulence or degree of mixing, and (4) the amount of oxygen available for combustion.  Composting Composting is the term used to describe the aerobic degradation of organic materials under controlled conditions, yielding a marketable soil. It is a natural process that can be carried out with modest human intervention, or it can be carefully controlled to shorten the composting time and space required, and to minimize offensive odors. The stabilized end product of composting is rich in organic matter, which makes it a fine soil conditioner, but the concentrations of key nutrients such as nitrogen, phosphorus, and potassium are typically too low for it to compete with commercial fertilizers.  In the composting systems, yard wastes are stacked in long, outdoor piles called windows. Their length is determined by the rate of input of new materials, the length of time that materials need for decomposition, and the cross-sectional area of the pile. The composting process is affected by temperature, moisture, pH, nutrient supply, and the availability of oxygen. Bacteria and fungi are the principal players in the decomposition process, but macroorganisms such as rotifers, nematodes, mites, sow-bugs, earthworms, and beetles also play a role by physically breaking down the materials into smaller bits that are easier for microoganisms to attack. Composting piles, called windrows Environmental Impact Assessment (EIA)  Environmental Impact Assessment (EIA) is the assessment of the environmental consequences (positive and negative) of a plan, policy, program, or actual projects prior to the decision to move forward with the proposed action Environmental assessments may be governed by rules of administrative procedure regarding public participation and documentation of decision making, and may be subject to judicial review The International Association for Impact Assessment (IAIA) defines an environmental impact assessment as "the process of identifying, predicting, evaluating and mitigating the biophysical, social, and other relevant effects of development proposals prior to major decisions being taken and commitments made" Environmental Clearance from central government is required for 32 categories of development projects – under industrial sectors: Mining Thermal power plants River valley Infrastructure (road, highways, ports, harbours, and airports) Industries including very small electroplating in foundry units EIA benefits: Protection of Environment Optimum utilization of resources Saves overall time and cost of the project Promotes community participation Helps decision/policy makers to take appropriate decision Lays base for environmentally sound projects. History & Evolution of EIA  Steps in EIA EIA not EIA required required Screening is the First stage of EIA, which determines whether the proposed project requires an EIA and if requires, then the level of assessment required. Its criteria are based upon: Scales of investment Type of development Location of development Project Category ‘A’ : Category ‘B’ : Only Category ‘C’: This Projects in this category difference between category is for projects typically require an EIA. projects in this category that typically do not The project type, scale and those in Category ‘A’ re q u i re a n E I A. T h e s e and location determine is the scale. Larger Power projects are unlikely to this designation. The plants fall under category ‘A’, have adverse environ- potentially significant Medium Sized Power Plants mental impacts. environmental issues projects are in category ‘B’. for these projects may T h e s e p ro j e c t s a r e n o t lead to changes in land- located in environmentally use, as well as changes sensitive area. Mitigation to social, physical, and measures for these projects biological environment. are more easily prescribed. Scoping: This stage identifies key issues and impact that should be further investigated This stage also defines the boundary and the time limit of the study Quantifiable and non quantifiable impact (aesthetic or recreational value) are to be assessed Baseline status of these should be monitored and then the likely changes in these on account of the construction and operation of the proposed project should be predicted AIR Changes in the ambient level and the ground level concentrations due to emissions from point, line and area source Effects on soils, materials, vegetation and human health. NOISE Changes in the ambient level due to noise generated from equipment and movement of vehicles Effects on fauna and human health. WATER Availability to competing users Changes in the quality Sediment transport Ingress of saline water LAND Changes in the land-use and drainage pattern Changes in land quality including effects of waste disposal Changes in shoreline/riverbank and their stability. BIOLOGICAL Deforestation and shrinkage of animal habitat Impact on flor a and faun a due to con taminants /pollutants Impact on rare and endangered species, endemic species and migratory path of animals including birds Impact on breeding and nesting grounds SOCIO-ECONOMIC Impact on the local community including demographic changes Impact on economic status Impact on human health Impact of increased traffic Cont. Feasibility study Prediction and Mitigation Possible alternative should be identified and environmental attributes compared Alternatives for project location & process technologies Alternative of ‘no project’ should also be considered Ranking of alternatives based on the best environmental option for optimum economic benefits to the community at large Mitigation plan for the selected option have to be drawn, and is supplemented with the Environmental Management Plan (EMP) to guide towards, Environmental Improvement (1) (2)