Environmental Pollution Chemistry PDF

Unit-3 Environmental Pollution Air pollution-Sources and effects of pollutants, primary and secondary pollutants, control measures. Acid rain: Impacts on human communities and agriculture. Green-house effect: Definition, causes and consequences. Depletion of oz...

Unit-3 Environmental Pollution Air pollution-Sources and effects of pollutants, primary and secondary pollutants, control measures. Acid rain: Impacts on human communities and agriculture. Green-house effect: Definition, causes and consequences. Depletion of ozone layer: CFC, destruction of ozone layer by CFC, consequences, the effect of ozone modification, Photochemical smog, Bhopal gas tragedy. Water pollution-Water characteristics, water quality (WHO standard), natural water pollutants their origin and effects: oxygen demanding wastes, pathogens, nutrients, salts, heavy metals, pesticides, volatile organic compounds. River/lake/ground water pollution: DO, BOD, COD, TOC, oil & grease, pH and eutrophication. Thermal pollution- Cause, effects and control measures. Solid waste management- Causes, effects and control measures of urban and industrial wastes. 1 Nuclear hazards- Causes, effects and control measures. By: Dr. Shradha Gandhi Pollution: may be defined as an undesirable change in the physical, chemical or biological characteristics of air, water and land that may be harmful to human life and other animals, living conditions, industrial processes and cultural assets. Pollution can be natural or manmade. Pollutants: The agents that pollute are called pollutants. Pollutants may be physical, chemical or biological substance unintentionally released into the environment which is directly or indirectly harmful to humans and other living organisms. The important pollutants are summarized below: Deposited matter- Soot, smoke, tar or dust and domestic wastes. Gases- CO, nitrogen oxides, sulphur oxides, halogens (chlorine, bromine and iodine). Metals- Lead, zinc, iron and chromium. Industrial pollutants- Benzene, ether, acetic acid etc., and cyanide compounds. Agriculture pollutants- Pesticides, herbicides, fungicides and fertilizers. Photochemical pollutants- Ozone, oxides of nitrogen, aldehydes, ethylene, photochemical smog and proxy acetyl nitrate. Radiation pollutants- Radioactive substances and radioactive fall-outs of the nuclear test. Classification of Pollutants (I) Nature of disposal: On the basis of natural disposal, pollutants are of two types: 1. Non-degradable pollutants: These are the pollutants, which degrade at a very slow pace by the natural biological processes. These are inorganic compounds such as salts (chlorides), metallic oxides waste producing materials and materials like, aluminium cans, mercuric salts and even DDT. These continue to accumulate in the environment. 2. Biodegradable pollutants: These include domestic sewage that easily decomposes under natural 2 processes and can be rapidly decomposed by natural/artificial methods. These cause serious problems when accumulated in large amounts as the pace of deposition exceeds the pace of decomposition of disposal. (II) Nature of form: On the basis of the form in which they persist after their release into the environment, pollutants can be categorized under two types: 1. Primary Pollutants: These include those substances, which are emitted directly from some identifiable sources. This include- a. Sulphur compounds: SO2, SO3, H2S produced by the oxidation of fuel. b. Carbon compounds: Oxides of carbon (CO+CO2) and hydrocarbons. c. Nitrogen compounds: NO2 and NH3. d. Halogen compounds: Hydrogen fluoride (HF) and hydrochloric acid (HCl). e. Particles of different size and substances: These are found suspended in air. The fine particles below the diameter of 100 mm are more abundant and include particles of metals, carbon, tar, pollen, fungi, bacteria, silicates and others. 2. Secondary Pollutants: The secondary pollutants are produced by the combination of primary emitted pollutants in the atmosphere. For eg: In bright sunlight, a photochemical reaction occurs between nitrogen oxides; oxygen and waste hydrocarbons from gasoline that forms peroxy-acetyle nitrate (PAN) and ozone (O3), both of them are toxic components of smog and cause smarting eyes and lung damage. Types of Pollution  Air pollution  Noise pollution  Water pollution  Soil pollution  Thermal pollution  Radiation pollution 3  AIR POLLUTION Definition: A physical, biological or chemical alteration to the air in the atmosphere can be termed as pollution. It occurs when any harmful gases, dust, smoke enters into the atmosphere and makes it difficult for plants, animals and humans to survive as the air becomes dirty. The WHO defines air pollution as the presence of materials in the air in such concentration which are harmful to man and his environment. Sources of Air Pollution There are four main types of air pollution sources: Mobile sources– cars, buses, planes, trucks, and trains Stationary sources– power plants, oil refineries, industrial facilities, and factories Area sources– agricultural areas, cities, and wood burning fire places Natural sources– wind-blown dust, wildfires, and volcanoes 4 Figure 1: Sources of Air Pollution  Harmful Effects Carbon Monoxide (CO) Carbon monoxide (CO) is a colourless, odourless, and poisonous gas Vehicle exhaust contributes roughly 60% of all CO emissions nation wide and up to 95% in cities. Other sources include fuel combustion in industrial processes and natural sources such as wildfires. CO concentrations typically are highest during cold weather because cold temperatures make combustion less complete and cause inversions that trap pollutants low to the ground. Hazards CO enters the bloodstream through the lungs and binds chemically to haemoglobin, the substance in blood that carries oxygen to cells. In this way, CO interferes with the ability of the blood to transport oxygen to organs and tissue throughout the body. This can cause slower reflexes and drowsiness. It can also reduce visual perception and coordination and decrease the ability to learn. Sulphur Dioxide (SO2) SO2 is a colourless, reactive gas produced while burning sulfur containing fuels such as coal and oil, during metal smelting, and by other industrial processes. SO2 emitted to the atmosphere results largely from stationary sources such as coal and oil combustion, steel mills, refineries, pulp and paper mills, nonferrous smelters, power plants, and industrial boilers. Hazards High concentrations of SO2 affect breathing and may aggravate existing respiratory and cardiovascular diseases. Sensitive populations include asthmatics, individuals with bronchitis or emphysema, children, and the elderly. SO2 is also a primary contributor to acid rain, which causes acidification of lakes and streams and 5can damage trees, crops, buildings, and statues. In addition, sulphur compounds in the air contribute to visibility impairment in large parts of the Particulate Matter Particulate matter (PM) is the term for small particles in the air, including dust, dirt, soot, smoke, and liquid droplets. Particles can be suspended in the air for long periods. Some particles are large or dark enough to be seen as soot or smoke. Particles less than 10 micro-meters in diameter are the most significant health concern because they can be inhaled into and accumulate in the respiratory system. Particles less than 2.5 micro-meters in diameter are referred to as fine particles. Sources include all types of combustion (e.g. motor vehicles, power plants, and wood burning) and some industrial processes. Particles with diameters between 2.5 and 10 micro-meters are referred to as coarse. Hazards Coarse particles can aggravate respiratory conditions such as asthma. Adverse health effects have been associated with PM exposure over short periods (such as a day) and extended periods (a year or more). When exposed to PM, people with existing heart or lung diseases such as asthma, chronic obstructive pulmonary disease, congestive heart disease, or ischemic heart disease—are at increased risk of premature death or ailments. When exposed to PM, children and people with existing lung disease may be unable to breathe normally and experience symptoms such as coughing and shortness of breath. Volatile organic compounds (VOCs) VOCs are compounds that have a high vapor pressure and low water solubility. Many VOCs are human-made chemicals used and produced in manufacturing paints, pharmaceuticals, refrigerants, wood preservatives, pesticides, and automotive products. VOCs typically are industrial solvents, such as trichloroethylene; fuel oxygenates, such as methyl tert-butyl ether (MTBE); or by-products produced by chlorination in water treatment, such as chloroform. 6 VOCs comprise petroleum fuels, hydraulic fluids, paint thinners, and dry cleaning agents. VOCs are common ground-water contaminants. Hazards Eye, nose and throat irritation Headaches, loss of coordination, and nausea Damage to the liver, kidney, and central nervous system Some organics can cause cancer in animals. Some are suspected or known to cause cancer in humans. Nitrogen Dioxide (NO2) NO is a brownish, highly reactive gas in all urban atmospheres. NO can irritate the lungs, cause bronchitis and pneumonia, and lower resistance to respiratory infections. NO contributes to ozone and acid rain formation and may affect terrestrial and aquatic ecosystems. The principal mechanism for forming NO in the atmosphere is oxidizing the primary air pollutant nitric oxide (NO)—nitrogen oxide forms when fuel is burned at high temperatures. Hazards In children and adults with respiratory diseases such as asthma, nitrogen dioxide can cause coughing, wheezing, and shortness of breath. Even short exposures to nitrogen dioxide can affect lung function. In children, short-term exposure can increase the risk of respiratory illness. Animal studies suggest that long-term exposure to nitrogen dioxide may increase susceptibility to respiratory infection and cause permanent lung damage. Ozone (O3) Ozone is a gas that forms in the atmosphere when three oxygen atoms are combined. It is not emitted directly into the air but is created at ground level by a chemical reaction between 7 nitrogen oxides and volatile organic compounds in the presence of sunlight. Ozone can be good or bad, depending on its location in the atmosphere.  Ozone occurs in two layers of the atmosphere. At ground-level or bad ozone is an air pollutant that damages human health, vegetation, and many common materials. The stratospheric, or good ozone layer, extends upward from about 10 to 30 miles and protects life on Earth. Hazards It damages lung tissue, reduces lung function, and sensitizes the lungs to other irritants. Scientific evidence indicates that ambient levels of ozone not only affect people with impaired respiratory systems, such as asthmatics, and healthy adults and children. Exposure to ozone for several hours can significantly reduce lung function and induce respiratory inflammation in normal, healthy people during exercise. Causes of Air Pollution 1. Burning of Fossil Fuels: Sulfur dioxide emitted from the combustion of fossil fuels like coal, petroleum and other factory combustibles is one of the major causes of air pollution. Pollutants emitting from vehicles cause immense amount of pollution. Carbon Monoxide produced by improper or incomplete combustion emitted from vehicles is another major pollutant along with Nitrogen Oxides that is produced from both natural and manmade processes. 2. Agricultural activities: Ammonia is a very common by product from agriculture related activities and is one of the most hazardous gases in the atmosphere. Use of insecticides, pesticides and fertilizers in agricultural activities emit harmful chemicals into the air and cause water pollution. 3. Exhaust from factories and industries: Manufacturing industries release large amount of carbon monoxide, organic compounds, and chemicals into the air thereby depleting the quality of air. 4. Mining operations: Mining is a process wherein minerals below the earth are extracted using large equipments. During the process dust and chemicals are released in the air causing massive air pollution. 5. Indoor air pollution: Household cleaning products, painting supplies emit toxic chemicals in the air and cause air pollution. 8 6. Suspended Particulate matter: Suspended particulate matter popular by its acronym SPM, is another cause of pollution.  Effect of Air Pollution On Human Health  The main problems are related to Respiratory Track -Asthma, high fever, and other allergic diseases.  Irritation of the eyes, nose and throat. In severe cases, there may be headaches, nausea, and loss of coordination.  Prolonged exposure can cause damage to the nervous system, digestive problems, and in some cases, cause Lung cancer.  It lowers our resistance to colds and pneumonia.  CO has an affinity towards Hb, which cause disturbance in the transportation of Oxygen, impairing our concentration, slowing our reflexes, and making us confused and sleepy.  SO2 in the air leads to diseases of the lung and other lung disorders such as wheezing and shortness of breath.  Chronic respiratory disease, lung cancer, heart disease, and even damage to the brain, nerves, liver, or kidneys. On Plants  Pollutants enter through the stomata.  Destroy chlorophyll and affect photosynthesis.  Cuticle( Wax Layer on Leaves) is lost.  Necrosis – Damage to Leaf Structure.  Chlorosis - Loss/ reduction of Chlorophyll.  Abscission - Dropping of leaf.  Epinasty – Downward curling of Leaf 9 On Animals and Materials  Corrosion of metal surfaces, fading.  SO2 & water form H2S – corrosion and disfigurement of statues made up of limestone or Marble.  Air pollutants mix with rain water and increase the acidity (Acid Rain) of the water body and kill fish.  Ozone causes the crackling of rubber. On Environment  Visibility  Pollutants in the presence of sunlight produce photochemical Smog  Emission of Green House Gases tend to Global Warming  CFCs cause Ozone Depletion What are air toxics? Air toxics are pollutants that are known to cause cancer and serious health problems. They are emitted in small amounts but can have short-term and long-term effects, depending on the level of exposure, causing respiratory and neurological diseases. 10  Control measures of Air Pollution The atmosphere has several built-in self cleaning processes such as dispersion, gravitational settling, flocculation, absorption, rain-washout, etc to cleanse the atmosphere. However, control of contaminants at their source level is a desirable and effective method through preventive or control technologies. 1. Source control: Some measures that can be adopted in this direction are (i) Using unleaded petrol (ii) Using fuels with low sulphur and ash content (iii) Encouraging people to use public transport, walk or use a cycle as opposed to private vehicles (iv) Plant trees along busy streets as they remove particulates, carbon dioxide and absorb noise (v) Industries and waste disposal sites should be situated outside the city preferably on the downwind of the city. (vi) Catalytic converters should be used to help control emissions of carbon monoxide and hydrocarbons 2. Control measures in industrial centers: (i) Emission rates should be restricted to permissible levels by each and every industry (ii) Incorporation of air pollution control equipment in design of plant layout must be made mandatory (iii) Continuous monitoring of the atmosphere for pollutants should be carried out to know the emission levels. 3. Equipment used to control air pollution Air pollution can be reduced by adopting the following approaches. (i) Ensuring sufficient supply of oxygen to the combustion chamber and adequate temperature so that the combustion is complete thereby eliminating much of the smoke consisting of partly burnt ashes and dust. (ii) To use mechanical devices such as scrubbers, cyclones, bag houses and electro-static precipitators in manufacturing processes. The equipment used to remove particulates from the exhaust gases of electric power and industrial plants are shown below. All methods retain hazardous materials that must be disposed 11 safely. Wet scrubber can additionally reduce sulphur dioxide emissions. (iii) The air pollutants collected must be carefully disposed. The factory fumes are dealt with chemical treatment.  Acid Rain  Normal rainwater is always slightly acidic because CO2 is present in the atmosphere & get dissolved in the form of carbonic acid.  Normal acidity of rainwater is 5.6 H2O(l) + CO2(g) H2CO3(aq)  Because of SO2 & NO2 gases as pollutants in the atmosphere.  The pH of rain is further lowered to 2.4 & this type of precipitation is called ACID RAIN.  Acid rain is the combination of H2SO4, HNO3, and HCl.  Formation of Sulphuric Acid S + O2 SO2 SO2 + 1/2O2 + H2O H2SO4  Formation Of Nitric Acid NO + O3 NO2+O2 NO2 + O3 NO3+O2 NO3 + NO2 N2O5 N2O5 + H2O 2HNO3  Formation of Hydrochloric Acid Dissolved in Water 12 HCl (g) HCl acid (l)  Causes of Acid rain Natural  Volcanic emissions  Biological processes  Lightning Anthropogenic  Industrialization  Motor vehicles, automobile exhaust  Coal-based power plants  Domestic fires  Smelters Adverse Effects of Acid Rain Plants  Effects plants and trees.  Causes yellowing of leaf tissue (chlorosis)  Direct effect on plant growth due to toxification of soil  It takes away soil nutrients causing stunted growth.  Block stomatal pores of leaves.  In the electron transport system, biochemical reactions dominated by pH are affected.  Degradation of plant chlorophyll. Soil  Acid rain damages soil biological and chemically.  Microbes are not able to tolerate low pH and die. 13  The upper fertile layer of soil is affected as essential nutrients are leached away from the soil. Surface Water and Aquatic Animals  Acid rain causes lower pH in surface water that causes damage to fish and aquatic animals.  The biodiversity of water bodies is reduced.  Lakes and rivers are fragile ecosystems where each species depend on the other to survive, if one disappears other too disappears. Human Health:  The aerosol mist of H2SO4 has very serious respiratory effects.  Acidification plays havoc with the human nervous system, respiratory system, and digestive system. Effect on Buildings  Causes extensive damage to buildings, and structural materials of marble, limestone, slate etc. CaCO3 + H2SO4 CaSO4 + H2O + CO2  In Greece and Italy, invaluable stone statues have been partially dissolved by acid rain.  The Taj Mahal in Agra is also suffering due to acid fumes from Mathura refinery. Cure for Acid Rain 1. Decrease Emissions of SOX and NOX. 2. Reduction of use of Conventional Resources 3. Treatment of Industrial Gases before emissions 4. Alternate Energy Resources 5. Considering Nuclear Energy as an option for fuel 14 6. Purification of Polluted Water  Greenhouse Effect The greenhouse effect is a natural process that warms the Earth’s surface. What is green house? The greenhouse effect is a naturally occurring phenomenon that is responsible for the heating of the Earth’s Surface and atmosphere. The greenhouse effect is the process by which radiation from a planet's atmosphere warms its surface to a temperature above what it would be without this atmosphere. A Greenhouse (also called a Glasshouse) is a building where plants are grown. It has glass walls and a glass roof. People grow vegetables, flowers, and other plants in them. A greenhouse stays warm inside even during the cold season. Greenhouses also protect plants from weather phenomena such as snowstorms or duct forms. In tropical countries, greenhouses are used by commercial plant growers to protect flowering and ornamental plants from harsh weather conditions and insect attacks. 15  How does greenhouse works? Greenhouses allow sunlight to enter but prevent heat from escaping. The transparent covering of the greenhouse allows visible light to enter without obstruction. It warms the inside of the greenhouse as energy is absorbed by the plants, soil and other things inside the building. Air warmed by the heat inside is retained in the building by the roof and walls. The transparent covering also prevents the heat from leaving by reflecting the energy into the walls and preventing outside winds from carrying it away. If the greenhouse effect is natural, that keeps our Earth’s climate regular and comfortable. The man-made greenhouse effect enhances the natural greenhouse effect (made from burning fossil fuels, petroleum, coal, and natural gas). If the greenhouse effect is too strong, Earth gets warmer and warmer. Too much carbon dioxide and other greenhouse gases in air can make the greenhouse effect stronger, which would result to global warming. 16 Green House Gases  Water vapor (H2O) is the gaseous phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice.  Carbon dioxide (CO2) is naturally produced when people and animals breathe. Plants take in and use CO2 to produce their food. When food is oxidized in the cells, CO 2 is given off as a waste product. It is also returned to the air as a product of combustion and decomposition.  Methane (CH4) is emitted by natural sources such as wetlands, as well as human activities such as leakage from natural gas systems and raising livestock.  Ozone (O3) is created by sunlight acting on oxides of nitrogen and volatile organic compounds in the air.  Nitrous oxides are naturally present in the atmosphere as part of the nitrogen cycle and have a variety of natural sources. Human activities such as agriculture, fossil fuel combustion, wastewater management, and industrial processes are increasing the amount of nitrous oxide in the atmosphere. Consequences ofcause Rising temperatures the water Greenhouse of the oceanseffect along with the sea to increase.  Increasing temperatures melt ice as it starts to flow into the seas of Antarctic and Greenland.  Sea levels rise by 20-40 cm causing floods in areas with low coast areas e.g. Bangladesh and Netherland.  Flood in many areas case a danger for living things. 17 Control of Greenhouse effect 18  Ozone Layer Depletion  O3 is produced continuously by reacting molecular oxygen O 2 with an oxygen atom.  Oxygen atoms are generated by the dissociation of molecular oxygen in the presence of UV radiation of the sun UV 2O O2 242 nm O2 + O O3  O3 formed in the stratosphere distributes itself and forms a layer  O3 further absorbs UV radiation and dissociates into molecular oxygen and atomic oxygen UV O2 + O O3 320 nm  Ozone is continuously created and destroyed by the sun’s radiation, this results in equilibrium concentration of ozone. 242 nm O2 + O O3 19 320 nm  Causes of Ozone Layer Depletion 1. Chlorofluorocarbons (CFCs)  CFCs are the leading cause of ozone layer depletion.  Releasing of solvents, spray aerosols, refrigerators, air-conditioners, etc.  The molecules of CFCs in the stratosphere are broken down by ultraviolet radiations and release chlorine atoms. These atoms react with ozone and destroy it. 2. Nitrogenous Compounds Nitrogenous compounds such as NO2, NO, N2O are highly responsible for the depletion of the ozone layer. 3. Natural Causes  Specific natural processes like sunspots deplete the ozone layer.  It does not cause more than 1-2% of the ozone layer depletion.  The volcanic eruptions are also responsible for the depletion of the ozone layer. 20  Effects of Ozone Layer Depletion The depletion of the ozone layer has harmful effects on humans, animals, and the environment. Effects on Human Health  Humans will be directly exposed to the sun’s harmful ultraviolet radiations due to the depletion of the ozone layer.  This might result in serious health issues among humans, such as skin diseases, cancer, sunburns, cataracts, quick aging, and a weakened immune system. Effects on Animals  Direct exposure to ultraviolet radiations leads to skin and eye cancer in animals. Effects on the Environment  Intense ultraviolet rays may lead to minimal plant growth, flowering, and photosynthesis.  The forests also have to bear the harmful effects of the ultraviolet rays. Effects on Marine Life  Planktons are greatly affected by the exposure to harmful ultraviolet rays.  These are higher in the aquatic food chain. If the plankton are destroyed, the organisms present in the lower food chain are also affected. 21  Solutions to Ozone Layer Depletion The depletion of the ozone layer is a severe issue, and various programs have been launched by the government of various countries to prevent it. However, steps should be taken at the individual level as well to prevent the depletion of the ozone layer. 1. Avoid Using Pesticides Natural methods should be implemented to get rid of pests and weeds instead of using chemicals. One can use eco-friendly chemicals to remove the pests or weeds manually. 2. Minimize the Use of Vehicles The vehicles emit many greenhouse gases , leading to global warming and ozone depletion. Therefore, the use of cars should be minimized as much as possible. 3. Use Eco-friendly Cleaning Products Most cleaning products have chlorine and bromine-releasing chemicals that enter the atmosphere and affect the ozone layer. These should be substituted with natural products to protect the environment. 4. Use of Nitrous Oxide should be Prohibited The government should take action and prohibit the use of harmful nitrous oxide that adversely affects the ozone layer. People should be aware of the harmful effects of nitrous oxide and the products emitting the gas so that its use is minimized individually. 22  Photochemical Smog First observed in Los Angles, 1943 Does not involve Smoke + Fog. Smog is a name that is incorrectly or unsuitably applied here. Occurs in summer or sunny day Contains- NOx, O3, hydrocarbons, PAN Source-gasoline, combustion. Chemically it has oxidizing character. Mainly cause eye irritation. 23  Photochemical Smog o Also known as “Los Angeles smog,” occurs most prominently in urban areas with large numbers of automobiles. o It requires neither smoke nor fog. This smog originates in the NOx and hydrocarbon vapors emitted by automobiles and other sources, which undergo photochemical reactions in the lower atmosphere. o It is visible as a brown haze and is most prominent during the morning and afternoon, especially in densely populated, warm cities. o This type of smog has four main requirements: oxygen (O 2), nitrogen oxides (NOx), hydrocarbons, and ultraviolet light (UV). o The most significant contributor is automobiles, while coal-fired power plants and others also produce the necessary pollutants to facilitate their production. Due to its abundance in areas of warmer temperatures, photochemical smog is most common in the summer. Photochemical smog—a mixture of ozone, nitric acid, aldehydes, peroxy acyl nitrates (PANs), and other secondary pollutants. 24 Aldehydes 25  Peroxyacyl nitrates (PAN) PAN is produced in the atmosphere when oxidized volatile organic compounds combine with NO 2. PANs can remain in the atmosphere for about three months after formation under cold conditions (-20°C and lower). However, in warmer areas, PANs persist only for a few hours. Effects of Photochemical Smog When combined with hydrocarbons, the chemicals contained within it form molecules that cause eye irritation. Radicals in the air interfere with the nitrogen cycle by preventing the destruction of ground-level ozone. Reduced visibility, respiratory and lung problems High levels of smog also trigger asthma attacks. Some plants, such as tobacco, tomato, and spinach, are highly responsive to ozone so photochemical smog 26 can destroy these sensitive crops, trees, and other vegetation. Ozone causes necrotic (dead) patterns on the upper surfaces of the leaves of trees. It corrode metals, rubber, and painted surfaces.  Bhopal Gas Tragedy Also referred to as the Bhopal disaster, it was a gas leak incident on the night of 2–3 December 1984 at the Union Carbide India Limited (UCIL) pesticide/insecticide plant in Bhopal, Madhya Pradesh (India). It is considered among the world's worst industrial disasters. About 45 tons of the dangerous gas methyl isocyanate escaped from an insecticide plant that the Indian subsidiary of the American firm Union Carbide Corporation owned. The gas drifted over the densely populated neighborhoods around the plant, killing thousands immediately and creating a panic as tens of thousands of others attempted to flee Bhopal. The final death toll was estimated to be between 15,000 and 20,000. Some half a million survivors suffered respiratory problems, eye irritation or blindness, and other maladies resulting from exposure to the toxic gas. Background The UCIL factory was built in 1969 to produce the pesticide Sevin (UCC's brand name for carbaryl) using methyl isocyanate (MIC) as an intermediate. An MIC production plant was added to the UCIL site in 1979. The chemical process employed in the Bhopal plant had methylamine reacting with phosgene to form MIC, which was then reacted with 1-naphthol to form the final product, 27 carbaryl. What is Methyl Isocyanate (MIC)? Methyl Isocyanate is a colorless liquid used for making pesticides. MIC is safe when maintained properly. The chemical is highly reactive to heat (boiling point: 39 oC). When exposed to water, the compounds in MIC react, causing a heat reaction.  The Bhopal UCIL facility housed three underground 68,000-litre liquid MIC storage tanks.  UCC safety regulations specified that no one tank should be filled more than 50% (here, 30 tons) with liquid MIC. Each tank was pressurized with inert nitrogen gas.  This pressurization allowed liquid MIC to be pumped out of each tank as needed and kept impurities out of the tanks. The introduction of water into the tank subsequently resulted in a runaway exothermic reaction, which was accelerated by contaminants, high ambient temperatures, and various other factors, such as the presence of iron from corroding non-stainless steel pipelines 28 By early December 1984, most of the plant's MIC-related safety systems were malfunctioning, and many valves and lines were in poor condition. The pressure in the tank (E610), although initially nominal at 2 psi at 10:30 p.m., reached 10 psi by 11 p.m. Two different senior refinery employees assumed the reading was an instrumentation malfunction. By 11:30 p.m., workers in the MIC area were feeling the effects of minor exposure to MIC gas and began to look for a leak. One was found by 11:45 p.m. and reported to the MIC supervisor on duty. The decision was made to address the problem after a 12:15 a.m. tea break, and in the meantime, employees were instructed to continue looking for leaks. MIC area employees discussed the incident during the holiday. Five minutes after the tea break ended at 12:40 a.m., the reaction in tank E610 reached a critical state at an alarming speed. Temperatures in the tank were off the scale, maxed out beyond 25 °C (77 °F), and the pressure in the tank was indicated at 40 psi (275.8 kPa). One employee witnessed a concrete slab above tank E610 crack as the emergency relief valve burst open, and pressure in the tank continued to increase to 55 psi (379.2 kPa); even though atmospheric venting of toxic MIC gas had already begun. Direct atmospheric venting should have been prevented or at least partially mitigated by at least three safety devices that were malfunctioning, not in use, and insufficiently sized. 29 On commission with press agency Rapho, Photographer Pablo Bartholomew took an iconic color photograph of a burial of the December 4, Bhopal gas disaster girl. The photo became symbolic of the suffering of victims of the Bhopal disaster, and Bartholomew went on to win the 1984 World Press Photo of the Year. 30 Safety Precautions/Maintenance A refrigeration system meant to cool tanks containing liquid MIC shut down in January 1982, and whose freon had been removed in June 1984. Since the MIC storage system assumed refrigeration, its high-temperature alarm, set to sound at 11 °C (52 °F), had long since been disconnected, and tank storage temperatures ranged between 15 °C and 40 °C. A flare tower, to burn the MIC gas as it escaped, which had a connecting pipe removed for maintenance and was improperly sized to neutralize a leak of the size produced by the tank. A vent gas scrubber, which had been deactivated at the time and was in 'standby' mode, and similarly had insufficient caustic soda (NaOH). 31 Water Pollution 32  Water is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, the main constituent of Earth's hydrosphere and the fluids of all known living organisms. It is vital for all known life forms, even though it provides no calories or organic nutrients. Its chemical formula is H2O, meaning each molecule contains one oxygen and two hydrogen atoms, connected by covalent bonds. Existing in gaseous, liquid, and solid states What is pure water? Low dissolved gases, solids, suspended solids, biological life 33 Characteristics of water There are many characteristics of water depending on different variables. Here, are ten essential features of water described below in brief. 1. Water will bond to itself: Cohesion is where substances of the same makeup are attracted to each other. Water will stick to water. 2. Water can store heat efficiently: Water retains heat longer than many other substances because it takes longer to heat. The heat from our bodies is removed when we sweat; sweat is water leaving our bodies. 3. Water will bond to other substances: Adhesion is when substances are attracted to substances of different make-up. Water will connect to other substances, such as when water drops stick to a window. 4. Neutral pH of water: When something is neutral, it has a pH of 7. When an acid is dissolved in pure or neutral water, hydrogen ions are formed. When a base is dissolved in pure water, hydroxide ions are formed. 5. Water is polar: Polarity is when the water molecules have an uneven distribution of their charge. There are negatively charged molecules and then there are positively charged molecules and these are not in balance. They are attracted to ions or charged molecules and other polar molecules. 6. Water density: The density of water changes depending on which state the water is in. Water that is frozen, or ice, is less dense than when in liquid form. That is the reason why ice floats. 7. Surface tension: At the water’s surface, molecules will link together to form a film. This keeps the water strong from being easily broken. Surface tension allows things to be able to float instead of sink. 8. Decreased freezing point due to increased salinity: Water has to be colder and colder before it will genuinely freeze when there are many dissolved substances within it. This is because there are many more 34 molecules to bond. These molecules interfere with the water molecules’ ability to bond together for freezing. 9. Non-polar substances cannot dissolve in water: Since water is classified as polar, it does not mix with anything that is non-polar. Oil is non-polar, and when water is mixed with oil, the molecules separate, leaving the oil molecules clinging to each other and the water molecules doing the same. 10. Freezing point of water: Water can freeze at 32 degrees Fahrenheit or 0 degrees Celsius. Water boils at 212 degrees Fahrenheit or 100 degrees Celsius. Physical Characteristics of Water Physical characteristics of water (temperature, color, taste, odor, etc.) are determined by senses of touch, sight, smell, and taste. For example, temperature by touch, color, floating debris, turbidity, suspended solids by presence, and taste and odor by smell. 1. Temperature:- Water temperature affects some of water's essential physical properties and characteristics: thermal capacity, density, specific weight, viscosity, surface tension, specific conductivity, salinity and solubility of dissolved gases, etc. Chemical and biological reaction rates increase with increasing temperature. Reaction rates are usually assumed to double for an increase in temperature of 10°C. The temperature of water in streams and rivers throughout the world varies from 0 to 35 °C. 2. Color:- Color in water is primarily a concern of water quality for aesthetic reasons. Colored water appears unfit to drink, even though the water may be perfectly safe for public use. On the other hand, color can indicate the presence of organic substances, such as algae or humic compounds. More recently, color has been used to quantitatively assess the presence of potentially hazardous or toxic organic materials in water. 3. Taste and Odour:- Taste and odor are human perceptions of water quality. Human perception of taste includes sour (hydrochloric acid), salty (sodium chloride), sweet (sucrose), and bitter (caffeine). Relatively simple compounds produce sour and salty tastes. However, sweet and bitter tastes are produced by more 35 complex organic compounds. Humans detect many more tips of odor than tastes. Organic materials discharged directly to water, such as falling leaves, runoff, etc., are sources of taste and odor-producing compounds released during biodegradation. 4. Turbidity:- Turbidity is a measure of the light-transmitting properties of water and is comprised of suspended and colloidal material. It is essential for health and aesthetic reasons. Chemical Characteristics of Water The chemical characteristics of natural water reflect the soils and rocks with which the water has been in contact. In addition, agricultural and urban runoff and municipal and industrial treated wastewater impact the water quality. Microbial and chemical transformations also affect the chemical characteristics of water. 1. Inorganic Minerals:- Runoff causes erosion and weathering of geological formations, rocks, and soils as the runoff travels to the surface water bodies. During this contact period with rocks and soils, the water dissolves inorganic minerals entering the natural waters. Inorganic compounds may dissociate, to varying degrees, to cations and anions. (a) Major Cations:- Major cations found in natural water include calcium (Ca2+), magnesium (Mg2+),sodium (Na+) and potassium (K+). Calcium (Ca2+), is the most prevalent cation in water and the second inorganic ion to bicarbonate in most surface water. Other constituents in natural water in a concentration of 1 mg/L or higher include Al, B, Fe, Mn, K, etc. (b) Major Anions Major anions include chloride, sulfate, carbonate, bicarbonate, fluoride, and nitrate. HCO 3-is the principal anion found in natural water. These ions are very important in the carbonate system, which provides a buffer capacity to natural moisture and is responsible in a great measure for the alkalinity of water. One source of 36 HCO3-in natural water is the dissociation of carbonic acid (H 2CO3)formed when CO2from the atmosphere or animals (e.g., fish) and bacterial respiration dissolves in water. In addition to bicarbonates (HCO 3-) anions such as chlorides (Cl-), sulfates (SO 2-), and nitrates (NO3-) are commonly found in natural water. 2. pH and Alkalinity:- Alkalinity is defined as the capacity of natural water to neutralize acid added to it. Total alkalinity includes Hydroxide alkalinity [OH -], Bicarbonate alkalinity [HCO3-], and Carbonate alkalinity [CO32-]. If the pH and total alkalinity are measured, the concentration of the various alkalinity components can be calculated. 3. Acidity:- Acidity is the "quantitative capacity of aqueous media to react with hydroxyl ions.” Acidity indicates the corrosiveness of acidic water on steel, concrete, and other materials. 4. Microbiological Characteristics:- The principal groups of microorganisms in natural water include microorganisms, plants and animals. Many bacteria, viruses, and protozoa are causative organisms for some of the more virulent diseases transmitted to humans directly through water and indirectly through contaminated food. Sources of water pollution Point and Non-point Pollution Sources 1. Pollution originating from a single, identifiable source, such as a discharge pipe from a factory or sewage plant, is called point-source pollution. Example: Factories and sewage treatment plants are two common types of point sources. Factories, including oil refineries, pulp and paper mills, and chemical, electronics, and automobile manufacturers, typically discharge one or more pollutants in their discharged waters (called effluents). Some factories discharge their effluents directly into a water body. Others treat it themselves before it is released, and others send their wastes to sewage treatment plants. Sewage treatment plants treat human feces and send the treated effluent to a stream 37 or river. 2. Pollution that does not originate from a single source, or point, is called nonpoint-source pollution. Liquid, solid, and airborne discharges from point sources as well as pollutants from nonpoint sources may go either into surface water or into the ground. (Airborne pollutants can be assimilated into rainwater and can affect water quality: acid rain is an example.) The ability for these pollutants to reach surface water or groundwater is enhanced by the amount of water available from precipitation (rain) or irrigation. Example: Excess fertilizers, herbicides, and insecticides from agricultural lands and residential areas Oil, grease, and toxic chemicals from urban runoff and energy production Sediment from improperly managed construction sites, crop and forest lands, and eroding stream banks Salt from irrigation practices and acid drainage from abandoned mines Bacteria and nutrients from livestock, pet wastes, and faulty septic systems Water quality (WHO Standard) Good water quality is essential to human health, social and economic development, and the ecosystem. However, as populations grow and natural environments become degraded, ensuring sufficient and safe water supplies for everyone is increasingly challenging. A significant part of the solution is to produce less pollution and improve how we manage wastewater. Water must be carefully managed during every part of the water cycle: from freshwater abstraction, pre- treatment, distribution, use, collection, and post-treatment to the use of treated wastewater and its ultimate return to the environment, ready to be abstracted to start the cycle again. 38 39  Water pollutants, their origin and Effects 1. Oxygen-demanding materials/wastes 2. Pathogens/ disease causing agents 3. Nutrients 4. Salts 5. Heavy metals 6. Pesticides 7. Volatile organic compounds/ Organic compounds 1. Oxygen-demanding materials/wastes Most surface water in contact with the atmosphere has a small amount of dissolved oxygen (5-10 mg/L), which is needed by aquatic organisms for cellular respiration. Bacteria decompose dead organic matter and remove dissolved oxygen (O 2) according to the following reaction: Organic matter + O2 CO2 + H2O Too much decaying organic matter in water is a pollutant because it removes oxygen from water, which can kill fish, shellfish, and aquatic insects. The amount of oxygen used by aerobic (in the presence of oxygen) bacterial decomposition of organic matter is called biochemical oxygen demand (BOD). The primary source of dead organic matter in many natural waters is sewage; grass and leaves are smaller sources. An unpolluted water body with respect to BOD is a turbulent river that flows through a natural forest. Turbulence continually brings water in contact with the atmosphere where the O 2 content is restored. The dissolved oxygen content in such a river ranges from 10 to 14 ppm O 2. A polluted water body with respect to oxygen is a stagnant deep lake in an urban setting with a combined sewer system. 40 This system favors a high input of dead organic carbon from sewage overflows and limited chance for water circulation and contact with the atmosphere. Biochemical oxygen demand (BOD) is the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at a certain temperature over a specific time period.  The term also refers to a chemical procedure for determining this amount. This is not a precise quantitative test, although it is widely used to indicate the organic quality of water.  The BOD value is most commonly expressed in milligrams of oxygen consumed per litre of the sample during 5 days of incubation at 20 °C and is often used as a robust surrogate of the degree of organic pollution of water. Chemical oxygen demand (COD) is an indicative measure of the amount of oxygen that can be consumed by reactions in a measured solution.  It is commonly expressed in mass of oxygen consumed over volume of solution which in SI units is milligrams per litre (mg/L).  A COD test can be used to easily quantify the amount of organics in water. The most common application of COD is in quantifying the amount of oxidizable pollutants found in surface water (e.g. lakes and rivers) or wastewater. COD is useful in terms of water quality by providing a metric to determine the effect an effluent will have on the receiving body, much like biochemical oxygen demand (BOD). Eutrophication: Excessive plant nutrients, particularly nitrogen (N) and phosphorous (P), are pollutants closely related to oxygen-demanding waste. Aquatic plants require about 15 nutrients for growth, most of which are plentiful in water. N and P are called limiting nutrients, however, because they usually are present in water at low concentrations and therefore restrict the total amount of plant growth. This explains why N and P are major ingredients in most fertilizer. High concentrations of N and P from human sources (mostly agricultural and urban runoff including fertilizer, sewage, and phosphorus-based detergent) can cause cultural eutrophication, which leads to the rapid growth of aquatic producers, particularly algae. 41  Eutrophication is an enrichment of water by nutrient salts that causes structural changes to the ecosystem such as: increased production of algae and aquatic plants, depletion of fish species, general deterioration of water quality and other effects that reduce and preclude use.  Thick mats of floating algae or rooted plants lead to a form of water pollution that damages the ecosystem by clogging fish gills and blocking sunlight. A small percentage of algal species produce toxins that can kill animals, including humans. Exponential growths of these algae are called harmful algal blooms.  When the prolific algal layer dies, it becomes oxygen-demanding waste, which can create very low O 2 concentrations in the water (< 2 ppm O2), a condition called hypoxia. This results in a dead zone because it causes death from asphyxiation to organisms that are unable to leave that environment. 42 2. Pathogens Pathogens are disease-causing microorganisms, e.g., viruses, bacteria, parasitic worms, and protozoa, which cause a variety of intestinal diseases such as dysentery, typhoid fever, and cholera. Pathogens are the major cause of the water pollution crisis. Unfortunately nearly a billion people around the world are exposed to waterborne pathogen pollution daily and around 1.5 million children mainly in underdeveloped countries die every year of waterborne diseases from pathogens. Pathogens enter water primarily from human and animal fecal waste due to inadequate sewage treatment. In many underdeveloped countries, sewage is discharged into local waters either untreated or after only rudimentary treatment. In developed countries untreated sewage discharge can occur from overflows of combined sewer systems, poorly managed livestock factory farms, and leaky or broken sewage collection systems. Water with pathogens can be remediated by adding chlorine or ozone, by boiling, or by treating the sewage in the first place. 3. Oil spills: These are another kind of organic pollution. Oil spills can result from supertanker accidents such as the Exxon Valdez in 1989, which spilled 10 million gallons of oil into the rich ecosystem of coastal Alaska and killed massive numbers of animals. The largest marine oil spill was the Deepwater Horizon disaster, which began with a natural gas explosion at an oil well 65 km offshore of Louisiana and flowed for 3 months in 2010, releasing an estimated 200 million gallons of oil. The worst oil spill ever occurred during the Persian Gulf war of 1991, when Iraq deliberately dumped approximately 200 million gallons of oil in offshore Kuwait and set more than 700 oil well fires that released enormous clouds of smoke and acid rain for over nine months. 43 4. Nutrients Chemicals that are essential for the growth of living things (N, P, C, S, Ca, P, Fe, Mn, B, Ca, etc.) Nutrients are pollutants when their concentrations are sufficient to allow excessive growth of aquatic plants, particularly algae. The process of nutrient enrichment, leading to excessive growth of algae, is called eutrophication (algal bloom). This phenomenon is particularly important for lakes. Algae eventually die and their decomposition removes DO from water. Algae and decaying organic matter add color, turbidity, odor and objectionable taste to water, making it less attractive as a source for domestic water supply, recreational and other uses. Notice the greenish (sometimes reddish) color of pond, lake, river water, especially during dry season Nutrient Sources Major sources of nitrogen and phosphorus include municipal wastewater discharges municipal wastewater discharges, runoff from animal feedlots, chemical fertilizers and phosphorus based detergents In addition, there are also natural sources that may add nitrogen to the water bodies. Certain bacteria and blue-green algae can directly obtain nitrogen from the atmosphere. These life forms are abundant in lakes and have high biological productivity. Certain form of acid rain can also contribute nitrogen to the lakes. 5. Salts: Water naturally accumulates a variety of dissolved solids and salts as it passes through soils and rocks. Typical cations: Na+ , Ca2+, Mg2+, K+, Typical anions: Cl- , SO4 2- , HCO3 – Effects: Taste, odour Commonly used measures of salinity: TDS (Total Dissolved Solids), Cl- (Chloride), Electrical Conductivity (EC) 44 Freshwater: TDS < 1500 mg/l, Seawater: TDS ~ 30,000 – 34,000 mg/L Agriculture: TDS upto 1500 mg/L can be tolerated by most crops. Concentrations above 2100 mg/L generally unsuitable for irrigation. 6. Heavy Metals: It simply denotes metals that are toxic. Toxic metals include: Al, As, Be, Bi, Cd. Cn, Co, Mn, Hg, Pb, Se etc. Adverse Impacts: Nervous system and kidney damage – creation of mutation and induction of tumour Source: Industrial discharges, natural (e.g. As in groundwater) Often referred to as “Persistent” (inorganic) pollutant (i.e., remain in the environment for long without degradation) Heavy metals of concern in groundwater: - As and Mn 7. Volatile Organic Compounds (VOCs): It is used as solvents in industrial processes. Most commonly found contaminant in groundwater. 5 VOCs are specially toxic and persistent and their presence in drinking water is a cause of special concern. These are: 1. Vinyl Chloride: human carcinogen 2. Tetrachloroethylene: suspected carcinogen 3. Trichloroehtylene: suspected carcinogen 4. 1,2 – Dichloroethane: causes injury to central nervous system, liver and kidneys 5. Carbon Tetrachloride: Very toxic if ingested. A few mL can cause death 45 Thermal Pollution 46 What is thermal pollution? Heavy industries such as power, paper, nuclear, etc, use water as a coolant for the various processes due to its higher heat capacity. These industries take water from the nearby natural water bodies and discharge it back to the natural system after usage. OR Thermal pollution is the direct release or accumulation of unused able heat into the natural water bodies that adversely affect the aquatic organisms and disturbs the ecosystem. But sometimes cold water can cause thermal pollution too. The release of unnatural cold water can also change the local ecosystem and reduce the productivity of water bodies. So what is the problem here? The water acting as coolant exchanges heat with the process fluid and, in turn, becomes hot, then thrown back into the water bodies. When the altered water mixes with the natural water bodies, the effective temperature rises, which leads to a decrease in dissolved oxygen levels. Water temperature influences the biological activity and growth of organisms that live in natural water bodies and a slight increase in temperature can cause difficulty in their survival. Main causes /Sources of Thermal pollution  Heavy Industries  Domestic and Industrial Effluents  Urban Storm water Runoff due to Paved Surface  De-forestation 47  Soil Erosion  Geothermal Activities Effects 1. The dissolved oxygen content of water is decreased as the solubility of oxygen in water is decreased at high temperature. 2. Toxicity of pesticides, detergents and chemicals in the effluents increases with increase in temperature. 3. The composition of flora and fauna changes because the species sensitive to increased temperature due to thermal shock will be replaced by temperature tolerant species. 4. Metabolic activities of aquatic organisms increase at high temperature and require more oxygen, whereas oxygen level falls under thermal pollution. 5. Discharge of heated water near the shores can disturb spawning and can even kill young fishes. 6. Fish migration is affected due to formation of various thermal zones. Control 7. Cooling ponds or reservoirs are the most widely used technique for Substantial temperature reductions. 8. They have large surface areas that can store water for one to two days and are easily constructed nearby various industries. 9. Although cooling ponds are the best and cheapest method, it proves quite inefficient due to improper heat transfer. 48 Spray Ponds The water from condensers is received in spray ponds. Here the water is sprayed through nozzles where fine droplets are formed. Heat from these fine droplets is dissipated to the atmosphere. Cooling Towers 1. Wet cooling tower: Hot water is sprayed over baffles. Cool air entering from sides takes away the heat and cools the water. This cool water can be recycled or discharged. Large amount of water is lost through evaporation and in the vicinity of wet cooling tower extensive fog is formed which is not good for environment and causes damage to vegetation. 2. Dry cooling tower: The heated water flows in a system of pipes. Air is passed over these hot pipes with fans. There is no water loss in this method but installation and operation cost of dry cooling tower is many times higher than wet cooling tower. 49 50 Solid Waste Management 51  Every day, tonnes of solid wastes are disposed off at landfill sites. This waste comes from homes, offices, industries and various other agricultural related activities. These landfill sites produce foul smell if waste is not stored and treated properly.  When hazardous wastes like pesticides, batteries containing lead, cadmium, mercury or zinc, cleaning solvents, radioactive materials, e-waste and plastics are mixed up with paper and other scraps and burnt, they produce gases such as dioxins. These gases are toxic and carcinogenic. These pollute the surrounding air, ground water and can seriously affect the health of humans, wildlife and our environment. Sources 52 Effects of Solid Waste Solid waste can pollute air, water and soil, and leave various environmental impacts, and cause health hazard, due to improper handling and transportation.These adverse effects are seen on health and environment, some of them are as follows: Environmental impacts  Waste products when burnt like plastic and rubber pollute the atmosphere with noxious fumes  Organic solid wastes emits obnoxious odor on their decomposition and make the environment polluted. Health hazards  During handling and transfer of hospital and clinic wastes, disease transmission may take place.  Water and food contamination through flies causes various diseases in humans as dysentery, diarrhea and amoebic dysentery.  Rats dwelling with infectious solid wastes may spread diseases like plague, salmonellosis, trichinosis, endemic typhus etc.  Water supply, if gets contaminated with pathogens present in solid wastes, may result in cholera, jaundice, hepatitis, gastro enteric diseases etc.  Choking of drains and gully pits by the solid wastes results in water logging which facilitates breeding of mosquitoes and results in the spread of diseases like malaria and plague. 53 Management of Solid Waste: For waste management we stress on 'three R's'-Reduce, reuse and recycle before destruction and safe storage of wastes. (i) Reduction in use of raw materials: Reduction in the use of raw materials will correspondingly decrease the production of waste. Reduced demand for any metallic product will decrease the mining of their metal and cause less production of waste. (ii) Reuse of waste materials: The refillable containers which are discarded after use can be reused. Villagers make casseroles and silos from waste paper and other waste materials. Making rubber rings from the discarded cycle tubes which are used by the newspaper vendors, instead of rubber bands, reduces the waste generation during manufacturing of rubber bands. Because of financial constraints poor people reuse their materials to the maximum. (iii) Recycling of materials: Recycling is the reprocessing of discarded materials into new useful products. (a) Formation of some old type products e.g. old aluminium cans and glass bottles are melted and recast into new cans and bottles. (b) Formation of new products: Preparation of cellulose insulation from paper, preparation of fuel pellets from kitchen waste. Preparation of automobiles and construction materials from steel cans. The process of reducing, reusing and recycling saves money, energy, raw materials, land space and also reduces pollution. Recycling of paper will reduce cutting of trees for making fresh paper. Reuse of metals will reduce mining and melting of ores for recovery of metals from ores and prevent pollution. 54 Method of Solid Waste Disposal Recycling serves to transform the wastes into products of their own genre through industrial processing. Paper, glass, aluminum, and plastics are commonly recycled. It is environmentally friendly to reuse the wastes instead of adding them to nature. Incineration  Incineration features combustion of wastes to transform them into base components, with the generated heat being trapped for deriving energy. Assorted gases and inert ash are common by-products. Pollution is caused by varied degrees dependent on nature of waste combusted and incinerator design. Use of filters can check pollution. It is rather inexpensive to burn wastes and the waste volume is reduced by about 90%. The nutrient rich ash derived out of burning organic wastes can facilitate hydroponic solutions. Hazardous and toxic wastes can be easily be rid of by using this method. The energy extracted can be used for cooking, heating, and supplying power to turbines. However, strict vigilance and due diligence should be exercised to check the accidental leakage of micro level contaminants, such as dioxins from incinerator lines. Composting  It involves decomposition of organic wastes by microbes by allowing the waste to stay accumulated in a pit for a long period of time. The nutrient rich compost can be used as plant manure. However, the process is slow and consumes a significant amount of land. Biological reprocessing tremendously improves the fertility of the soil. Sanitary Landfill A sanitary landfill is a pit with a protected bottom where trash is buried in layers and compressed to make it more solid. The main purpose of sanitary landfills is to ensure waste is safe by reducing the harm from accumulated waste and allowing safe decomposition. The alternative layering of garbage and soil aids in hastening decomposition. Because methane, a toxic gas, is produced from decomposition, it is collected in the landfill to generate electricity instead of being released into the atmosphere. The sanitary landfill also uses a clay liner to isolate the trash from the environment. Besides, it involves well-designed engineering methods to protect the environment from contamination by solid 55or liquid wastes. When the land used as the sanitary landfill is full, impervious clay is used to seal it, and if deemed safe, that area can be used for other purposes. Nuclear Hazards 56  Natural Sources of radiations Cosmic Radiation Terrestrial Radiation Internal Radiation  Man-Made Sources of radiations Production and research of nuclear weapons Mining of radioactive ore Medical waste Nuclear power plants Industrial radiography (X-ray imaging) Production of nuclear Radioactive materials used in this production have high health risks and release a small amount of radioactive pollution. Mining of radioactive Mining these involves crushing and processing of the radioactive ores and this generates radioactive waste which emits alpha particles Medical A number of radioactive isotopes are used in medicine, either for treatment or diagnostics. These can be left to decay over a short period after which they are able to be disposed of as normal waste Nuclear power plants 57 Nuclear power plants under current standards produce little radioactive pollution due to safety precautions that must be adhered to. Accidents at these power plants can cause dangerously high radioactive pollution, such as in the case of Chernobyl, and recently in fukushima of japan. Types of Nuclear Pollution 1) Continuous Pollution: This type of condition exists in uranium mines, nuclear reactors, test labs etc. where the humans are under continuous exposure to radioactive contaminants and protective clothing is required to avoid radiation exposure. 2) Accidental Pollution: This type of condition exists during accidental exposure to radiations by virtue of equipment failure, radiation leak, faulty protective equipment etc. 3) Occasional Pollution: This condition exists during isolated experiment or test of nuclear substance. Contamination by Radioisotopes 1. Radioisotopes may enter the human body either through direct inhalation from air (Rn-222, Xe-133) or through food chain. Radioisotopes are absorbed by soil and then taken up by plants. Humans ingest them by eating contaminated plants or meat of animals. 2. Radioisotopes may also be ingested through aquatic pathway. 3. Many radioisotopes get accumulated in different body parts : 4. K-42 Muscles Co-60 Liver Kr-85 Ovaries I-131 Thyroid 5. Po-210 Spleen Rn-222 Lungs Ra-226 Bones Radioisotopes used in Diagnosis  Tc-99 Most commonly used one. Used in brain, thyroid, liver, bonemarrow, lung, heart and intestinal scanning  I-131 In thyroid function test  Xe-133 In lung imaging  Au-198 In liver disease diagnosis  Y-90 Used in cancer treatment  F-18, Ga-67, In-111, Tl-201 are also used in diagnostic tests. 58  P-32 Used for tracking a plants uptake of fertilizers from the roots to the leaves  Case Study Cherobyl Disaster: Occurred on April 26, 1986 in V.I. Lenin Nuclear power plant in Chernobyl city of Russia. 1000 Ton concrete lid of reactor 4 blew off. More than 175 Mci of radiation released. 100 people died. About 1 lakh people were evacuated. Radiations got absorbed in water, fields, soil etc. Many people were found to have thyroid cancer through milk. Effects of Radiations Ionisation radiations can affect living organisms by causing harmful changes in the body cells and also changes at genetic level. (I) Genetic damage is caused by radiations, which induce mutations in the DNA, thereby affecting genes and chromosomes. The damage is often seen in the offsprings and may be transmitted upto several generations. (II) Somatic damage includes burns, miscarriages, eye cataract and cancer of bone, thyroid, breast, lungs and skin. Many scientists are of the view that due to the body's ability to repair some of the damages, the adverse effects of radiations are observed only beyond a threshold level. However, the other group believes that even a small dose of radiations over a period of time may cause adverse effects. They believe that the permissible limits of ionising radiations should be further reduced. Control 1. Proper maintenance of nuclear plants. 2. Preventive nuclear expenments. 3. Safe Transportation. 4. Ban usage of nuclear weapons. 5. Proper Storage. 6. Minimize use of nuclear elements. 7. Ettraction of radioactive elements from nuclear waste. 8. Laboratory generated nuclear wastes should be disposed off safely and scientifically. 59