What types of Pollution are there

what types of pollution are in the ocean, types of pollution and their causes and prevention, what types of pollution cause global warming what types of pollution cause acid rain
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Dr.LeonBurns,New Zealand,Researcher
Published Date:21-07-2017
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MODULE - 4 Pollution Environment and Health 27 Notes POLLUTION You have already learnt about the environment and its components in the earlier lessons. You have also studied the importance of maintaining a life-supporting environment. However, the environment has undergone many changes over the period of time. Population explosion in recent times has resulted in a number of environmental problems. The population of India has crossed the figure of 2 billion and the world population is estimated to have touched the 7 billion mark. To meet the demands of food, housing and energy, environmental resources are being exploited at a fast pace. Over-exploitation of resources and human activities have resulted in many environmental problems, such as deforestation, destruction of wild life, air, water, land and noise pollution, diminishing fossil fuels (oil, coal and natural gas), concentration of pesticides in alarming proportions in the bodies of organisms, and depletion of ozone layer and global warming. In this lesson, you will learn about various kinds of environmental polluton, their causes effects and control. OBJECTIVES After completing this lesson, you will be able to : z define pollution; z list various types of pollution and mention their sources; z describe effects of air, water and soil pollution on flora and fauna; z describe methods of control of air, water and soil pollution; z describe methods of nuclear and solid waste management z describe the causes and effects of sound pollution; z describe the causes and effects of radiation pollution; z discuss rates of entry and translocation of pollutants in the human body. 27.1 POLLUTION We perform a number of daily activities such as bathing and washing of clothes with soaps and detergents. By doing so we add some chemical residue to water and 212 BIOLOGYPollution MODULE - 4 Environment and Health change its quality. This water may mix with the water in ponds and rivers due to ignorance and carelessness. Cooking of food by using firewood may release smoke in the air. Agricultural activities may dump fertilizers and pesticides in the environment. The addition of unwanted substances in a concentration that has an adverse effect on organisms and environment, is called pollution. An undesirable change in the physical, chemical and biological characteristics of the environment especially air, water and land that may adversely affect Notes human population and the wild life, industrial processes, cultural assets (building and monuments), is called pollution. The agents that pollute the environment or cause pollution are called pollutants. 27.2 TYPES OF POLLUTION Depending upon the area or the part of environment affected, pollution may be of the following types : z Air pollution z Water pollution z Land pollution z Noise pollution 27.2.1 Air pollution We all breathe in air, we can feel, and even smell the air and say whether it is fresh or stale. The pollution in air may not be noticed until we see smoke coming out from some source. All human activities from cooking at home to activities in highly mechanized industries contribute to air pollution. 27.2.1a Sources of air pollution The sources of air pollution can he divided into two categories (i) natural, and (ii) human-made (i) Natural sources (i) Ash from burning volcanoes, dust from storm, forest fires (ii) Pollen grains from flowers in air are natural sources of pollution (ii) Anthropogenic (human-made) sources (i) Power stations using coal or crude oil release CO in air 2 (ii) Also furnaces using coal, cattle dung cakes, firewood, kerosene, etc. (iii) Steam engines used in railways, steamers, motor vehicles, etc. give out CO . 2 (iv) So do Motor and internal combustion engines which run on petrol, diesel, kerosene. etc. 213 BIOLOGYMODULE - 4 Pollution Environment and Health (v) Vegetable oils, kerosene, and coal as household fuels (vi) Sewers and domestic drains emanating foul gases (vii) Pesticide residues in air Major air pollutants Some major air pollutants are discussed here. Notes zzzzz Carbon dioxide Carbon dioxide is one of the major gases which contributes towards air pollution. It is mainly produced during the combustion of fuel in factories, power stations, household etc. The increasing CO in the atmosphere is likely to have the following 2 effects: (i) A rise in atmospheric temperature or global warming due to greenhouse effect. Also causes climate change. (ii) Reduced productivity of the marine ecosystem. This is due to the fact that water in the oceans would be more acidic due to increased concentration of CO in the air, which dissolves in the water. 2 (iii) Due to Global warming, the increased surface temperature would cause melting of continental and mountain glaciers and thus would cause flooding of coastal areas of some countries. zzz Sulphur dioxide zz It is produced by the burning of coal in powerhouses and automobiles (car, trucks etc.). It causes chlorosis and necrosis of plants, irritation in eyes and injury to the respiratory tract (asthma, bronchitis) in humans responsible for discoloration and deterioration of buildings. High concentration of sulphur dioxide in the atmosphere dissolves in rain drops to form sulphuric acid which causes acid rain. zzzzz Carbon monoxide Carbon monoxide is produced as a result of incomplete combustion of fossil fuels like coal, petroleum and wood charcoal. Automobiles using diesel and petroleum are the major sources of carbon monoxide which gets added to the atmosphere. Carbon monoxide is more dangerous than carbon dioxide. It is a poisonous gas which causes respiratory problems. When it reaches the blood stream, it replaces oxygen due to its high affinity for haemoglobin. It also causes giddiness, headache and interferes with normal function of the heart. zzzzz Fluorides Upon heating„ rocks, soils and minerals that contain fluorides, give out hydrogen fluoride gas. This is an extremely toxic gas, which causes serious injury to livestock and cattle. zzzzz Oxides of nitrogen A few oxides of nitrogen, such as nitric oxide (NO), nitrous oxide (N O) and 2 nitrogen dioxide (NO ) are produced by natural processes as well as from thermal 2 214 BIOLOGYPollution MODULE - 4 Environment and Health power stations, factories, automobiles and aircrafts (due to burning of coal and petroleum). They reduce the oxygen carrying capacity of blood, may cause eye irritation and skin cancer in human beings. Smog Smog is a mixture of smoke, dust particles and small drops of fog. Smog may cause necrosis and develop a white coating on the leaves (silvering) of plants. In Notes human beings and animals, it may cause asthma and allergies. Aerosol spray propellants Suspended fine particles in the air are known as aerosols. Aerosols contain chlorofluoro carbons (CFCs) and fluorocarbons used in refrigerants and aerosol cans. They cause depletion of the ozone layer. Domestic air pollutants Smoke from cigarettes, biri, cigar and other such objects using burning tobacco, burning of coal, firewood, cow dung cakes, kerosene oil and liquefied gases are major domestic pollutants. The common pollutant gases emitted during the domestic burning of coal, kerosene oil, firewood, cow dung cakes, etc. are carbon monoxide (CO), carbon dioxide (CO ), sulphur dioxide (SO ), etc. The pollution due to these 2 2 pollutants causes suffocation, eye and lung diseases and low visibility. 27.2.1b Effects of air pollution Major effects of air pollution on human health, plants and other animals is given in table 27.1. Table 27.1: Some major air pollutants, their sources and effects Pollutant Source Harmful effect Carbon compounds Automobilez Respiratory problems (CO and CO ) exhaustsz Green house effect global 2 burning of warning and climate change wood and coal Sulphur power plantsz Respiratory problems in humans compounds and refineriesz loss of chlorophyll in plants (chlorosis) (SO and H S) Volcanicz Acid rain 2 2 eruptions Nitrogen Compound Motor vehiclez Irritation in eyes and lungs (NO and N O) exhaust,z Low productivity in plants 2 atmosphericz Acid rain damages material (metals reaction and stone) Hydrocarbons Automobilesz Respiratory problem (benzene, ethylene) and petroleumz Cancer causing properties industries 215 BIOLOGYMODULE - 4 Pollution Environment and Health SPM (Suspended Thermal powerz Poor visibility, breathing problems Particulate matter) plants.z Lead interferes with the development (Any Solid or liquid construction of red blood cells and causes lung particles suspended activities, diseases and cancer in the air, (fly ash, metallurgicalz Smog (smoke+fog) formation leads to dust, lead) processes and poor visibility and aggravates asthma automobiles in patients Fibres Textile andz Lung disorders Notes (Cotton, wool) carpet weaving industries Destruction Ozone Shield Green house effect and Global warming Acid Deposition Photocheminal sinog No HC CO SO CO CH CFC C F Br x 2 2 4 5 xx x Automobile Automobile Automobile Automobile Automobile Fossil fuel Fire extinguisher burring Plastic foam Farms Pesticides Deforestation Fossil fuel burning Deforestation Refrigeration Paints solvents Fig. 27.1 Major effects of air pollution 216 BIOLOGY Nitrogen oxides Hydrocarbons Carbon Monoxide Sulphur Dioxide Carbon dioxide Methane Chlorofluorocarbons HalonsPollution MODULE - 4 Environment and Health 27.2.1c Prevention and control of air pollution There are two types of air pollutants—gaseous and particulate. Methods of controlling gaseous air pollutants (i) Combustion. This technique is used for controlling those air pollutants that are in the form of organic gases or vapours. In this technique, the organic air pollutants are subjected to flame combustion technique (also known as catalytic Notes combustion). In this technique, organic pollutants are converted into less harmful products and water vapour. (ii) Absorption. Absorption is a process in which a substance penetrates into another substance like scrubbers. In this technique, gaseous pollutants are passed through absorbing material like scrubbers. These scrubbers contain a liquid absorbent. This liquid absorbent removes the pollutants present in gaseous effluents. Thus the air coming into scrubber is free from pollutants and it is discharged into atmosphere. (iii) Adsorption. Adsorption is a process in which a substance sticks to the surface of another substance (called absorbent). In this technique, gaseous effluents are passed through porous solid absorbent kept in containers. The gaseous pollutants stick to the surface of the porous material and clean air passes through. The organic and inorganic constituents of gaseous effluents are trapped at the interface of solid adsorbent by physical adsorbent. Methods to control particulate air pollutants The particulate air pollutants such as dust, soot, fly ash etc. can be controlled by using fabric filters, electrostatic precipitators, wet scrubbers and mechanical devices etc. (i) Fabric filters. In this technique, gaseous emission containing dust, soot and fly ash is passed through porous fabric filters made of fabric (cloth) (woven or filled fabric). The particles of pollutants get trapped in this fabric and are collected in the filter and the gases free from the pollutant particles are discharged. (ii) Mechanical devices. There are many mechanical devices that clean the air of pollutants either due to (i) gravity in which the particles settle down by gravitational force; or by (ii) sudden change in the direction of gas flow in which particles separate out due to greater momentum. (iii) Electrostatic precipitators. In this technique, a gas or air stream containing aerosols in the form of dust, mist or fumes, is passed between the two electrodes of the electrostatic precipitator. During this process, the aerosol particles get precipitated on the electrodes. 217 BIOLOGYMODULE - 4 Pollution Environment and Health 27.2.1d Prevention and control of air pollution (i) At domestic level, burning of wood and dung cakes can be replaced by use of cleaner fuel and biogas (formed by the decomposition of animal and plant wastes in a biogas plant). (ii) Automobile pollution can be reduced by : z pooling of transport or use of public transport. Notes z use of unleaded petrol and CNG (Compressed Natural Gas). z regular tuning and servicing of the engines, and z switching off the engine at red lights or when not in use. (iii) Following measures can reduce industrial pollution: z installation of tall chimneys, z installation of devices that do not allow pollutants to be released in the environment, such as filters, electrostatic precipitators, scrubbers etc., INTEXT QUESTIONS 27.1 1. Define pollution. ............................................................................................................................ 2. Name four types of pollution. ............................................................................................................................ 3. Name one effect on plants and one on human caused by excess SO in the air. 2 ............................................................................................................................ 27.2.2 Water pollution Addition of undesirable substances in water is called water pollution. Water pollution could be due to natural or human activities. Natural sources of water pollution are soil erosion, leaking of minerals from rocks, and decaying of organic matter, while human-made sources include domestic, agricultural and industrial activities. Many water sources have become a dumping ground for wastes. Water pollution is one of the main causes of human diseases in India. Any physical, biological or chemical change in water quality that adversely affects living organisms or makes water unsuitable for desired use is called water pollution. 27.2.2a Sources of water pollution There are two sources of water pollution on the basis of origin of pollutants: (i) point sources. and (ii) non-point sources. 218 BIOLOGYPollution MODULE - 4 Environment and Health (i) Point sources. Those sources which discharge water pollutants directly into the water are known as point sources of water pollution. Oil wells situated near water bodies, factories. power plants, underground coal mines, etc. are point sources of water pollution. (ii) Non-point sources. Those sources which do not have any specific location for discharging pollutants, in the water body are known as non-point sources of water pollution. Run-offs from agricultural fields, lawns, gardens, construction Notes sites, roads and streets are some non-point sources of water pollution. Water pollutants River, lake and sea water may be polluted in many ways. z Domestic sewage discharged into rivers from areas located on its banks z Industrial wastes effluents from urban areas containing high concentration of oil, heavy metals and detergents z Minerals, organic wastes and crop dusting from agricultural fields with phosphate and nitrogen fertilizers that reach lakes, rivers and sea (water becomes deoxygenated and poisonous, thus, cannot support aquatic life) z Chemical fertilizers, pesticides, insecticides, herbicides and plant remains z Industrial waste water containing several chemical pollutants, such as calcium, magnesium, chlorides, sulphide, carbonates, nitrates, nitrites, heavy metals and radioactive waste from nuclear reactor. z Excretory wastes of humans and animals in water bodies z Disposal of urban and industrial waste matter into water bodies Sdeiments Acid water Crop dusting from mine Industrial wastes Barn yard wastes Fertilizer runoff Nuclear reactor Sewage treatment plant Oil pollution Fig. 27.2 Water pollution due to human activities. 219 BIOLOGYMODULE - 4 Pollution Environment and Health 27.2.2b Effects of water pollution z Water pollution adversely affects the fish and other aquatic life. z The presence of acids/alkalis in water destroys micro-organisms, thereby disturbing the self purification process in rivers. z The toxic materials in water cause serious health hazards in human beings and Notes other animals. z Polluted water causes spread of epidemics, such as cholera, tuberculosis, jaundice, dysentery, typhoid and diarrhoea in human beings. z The use of polluted water from lakes, ponds and rivers for irrigation of agricultural fields, damages crops severely and decreases agricultural production. z The use of water contaminated with salts increases alkalinity of the soil. z Heavily polluted water affects the soil, decreases its fertility and kills soil micro-organisms and even certain useful bacteria. z Contamination of sea water due to oil slicks caused by the leakage of crude oil from oil tankers causes ecological disasters which results in the death of sea organisms including fishes. The sources and effects of certain water pollutants have been given in the following table 27.2 Table 27.2: Some major disturbances in the ecosystem due to water pollution Pollutant Sources Cause Effect Nitrates, Agricultural Plant nutrients Eutrophication phosphates, fertilizers, sewage, ammonium salts manure Animal manure Sewage, paper mills, Oxygen Death of aquatic and plant residues food processing deficiency animals wastes Heat Power plants and Thermal Death of fish industrial cooling discharge Oil slick Leakage from oil Petroleum Death of marine life ships due to non availability of oxygen dissolved in water Fertilizers and pesticides are widely used in agriculture. Their excessive use for increasing agricultural yield has led to the phenomenon of eutrophication and biomagnification. 220 BIOLOGYPollution MODULE - 4 Environment and Health Eutrophication With the use of high yielding varieties of crops, the use of fertilizers and pesticides has increased a lot. Excess fertilizers may mix with surface water and may get drained into water bodies (surface runoff). The enrichment of water with nutrients such as nitrates and phosphates that triggers the growth of green algae is called eutrophication. (Fig. 27.3) This fast growth of algae followed by decomposition depletes the water body of its dissolved oxygen. As a result Notes aquatic animals die of oxygen shortage. Sewage and/or fertilizer run off from fields ↓ Enriched nutrient content in lakes (Eutrophication) ↓ Algae multiply to produce an ‘algal bloom’ ↓ Algae use up oxygen and begin to die ↓ Decomposers (bacteria) multiply and use more oxygen ↓ Organisms (such as fish) die due to lack of oxygen 2. Allow microscopic plants to reproduce and grow rapidly 1. Excess nitrate and phosphate Oxygen Oxygen 4. So the microscopic plant die and are broken down by bacteria, which 3. But there are not enough use up oxygen. microscopic animals to eat the surplus plant Fig 27.3 Sequence of events that may occur as a result of eutrophication Biomagnification Non-biodegradable pesticides, such as DDT are widely used for crop protection. Once they enter the food chain, their concentration keeps on increasing with each trophic level (steps of a food chain). As a result, accumulation of these compounds takes place in the body of top consumers over a period of time. Entry of harmful non-biodegradable chemicals in small concentrations and their accumulation in greater concentrations in the various levels of food chain is called biomagnification. 221 BIOLOGYMODULE - 4 Pollution Environment and Health Consider the following food chain. Is there any difference in the concentration of DDT in water and that in the body of the Pelican bird? Water → Algae → Fish → Pelican bird (top consumer) 0.2 ppm 77 ppm 500-600 ppm 1700 ppm (ppm = parts per million) DDT used in small quantities to kill mosquitoes can enter the food chain and Notes may get concentrated in large concentration due to its non-biodegradable nature in the body of birds (top) consumer. This causes adverse effects, such as weak egg shells, resulting in decreased population. (Fig. 27.4). The insecticide makes only Each microscopic Each Small fish Each large The grebe eats a weak solution in the animal eats many eats many micro- fish eats several large fish water, but the microscopic microscopic plants scopic animals several small plants take up the DDT fish Fig. 27.4 How pesticides affect food chain Table 27.3 and 27.4 show respectively the industrial sources of water pollution and sources and effects of some water pollutants. Table 27.3 Sources of industrial pollution Type of Industry Inorganic pollutants Organic pollutant Mining Chlorides, various metals, ferrous sulphate, sulphuric acid, hydrogen sulphide, ferric hydroxide surface wash offs, suspended solid, chlorides and heavy metals Iron and Steel Suspended solids, iron cyanides, Oil, phenol and thiocyanate, sulphides, oxides naphtha. of copper, chromium., cadmium and mercury. Chemical Plants Various acids and alkalies, chlorides, Aromatic sulphates, nitrates of metals, compounds phosphorus, fluorine, silica and suspended particles Pharmaceuticals Protein, carbohydrates, organic solvents intermediate products, drugs and antibiotics. 222 BIOLOGYPollution MODULE - 4 Environment and Health Soap and Detergents Tertiary ammonium compound alkalies. Fats and fatty acids, glycerol, phosphates, polysulphonated hydrocarbons. Food processing Highly putrescible (easily rots) organic matter and pathogens. Notes Paper and Pulp Sulphides and bleaching liquors Cellulose fibre, bark, wood sugars organic acids, Table 27.4 Some water pollutants, their sources and effect on human health Pollutant Source Diseases in humans Lead Industrial waste Nervous disorders, Kidney failure. blood poisoning Tin Industrial dust Affects central nervous system (CNS) Affects, vision Mercury Industrial discharge Affects central nervous system and peripheral nervous system, kidney failure, Numbness of lips, muscles and limbs, Blurred vision Arsenic Industrial discharge Respiratory and skin cancer. Nervous disorder Nickel Aerosols, industrial dust Pulmonary disorders, dermatitis Cadmium Industrial discharge Kidney disorders, Pulmonary and skeletal diseases Uranium, thorium Radioactive waste Leucoderma, skin cancer cesium 27.2.2c Prevention and control of water pollution Water pollution can be controlled by z Treating industrial effluents before discharging into rivers, separate channels for river and sewage water z Avoid contamination of rivers, lakes and ponds by washing clothes, bathing. etc. z Not throwing waste, food materials, paper, biodegradable vegetables and plastic into open drains. z Setting up sewage water treatment plants z Use of septic tanks in houses to avoid direct outlet of faecal matter and other wastes z Effluents from distilleries and solid waste containing organic matter diverted to biogas plants to generate energy 223 BIOLOGYMODULE - 4 Pollution Environment and Health z Maintenance or safety standards for the effluents discharged into the water system 27.2.2d Treatment of sewage The sewage can be treated by a modern technique involving three steps— primary treatment, secondary treatment and tertiary treatment. In primary treatment sewage is passed through a grinding mechanism. This is then Notes passed through several settling chambers and lime is added to neutralise it. The neutralised sewage still contains a large number of pathogenic and non-pathogenic organisms and sufficient amount of organic matter. In the secondary treatment, these neutralised effluents are passed through a reactor called UASB (Upflow anaerobic sludge blanket). In this reactor, the anaerobic bacteria degrades the biodegradable material into neutralised effluents. In this process, the foul odour and methane are released and the sewage is converted into clean water. This water is sent to aeration tanks where air and bacteria are added to it. This process is called biological or secondary treatment. (b) Secondary (a) Primary Primary Grit chamber sedimentation tank Acration tank Sludge setting tank Grate Air pump Sludge return Sludge line Sludge is incinerated composted, or used as soil munendment Sludge drying bed Chlorination tank Trickling bed evaporation Lagoon or (c) Tertiary marsh Fig. 27.5 Treatment of sewage The water obtained as a result of secondary treatment is still unfit for drinking and needs further purification. This is done by tertiary treatment. In this treatment, which is a disinfecting process, final traces of disinfecting bacteria and any dissolved 224 BIOLOGYPollution MODULE - 4 Environment and Health organic solids arc removed. Then, the chlorination, evaporation and exchange absorption methods arc employed to obtain clean water. INTEXT QUESTIONS 27.2 1. Give two examples of natural sources of water pollution. Notes (i) .................................................................................................................. (ii) .................................................................................................................. 2. What is biomagnification? ............................................................................................................................ 3. Give the technical term for enrichment of water bodies with nutrients coming from fields. ............................................................................................................................ 4. Give one source of and one disease caused by from the following pollutants (i) lead ............................................................................................................ (ii) Tin ............................................................................................................. (iii) Nickel ........................................................................................................ 27.2.3 Soil Pollution Addition of substances that change the quality of soil by making it less fertile and unable to support life is called soil pollution. 27.2.3a Sources of soil pollution Soil pollution is caused due to : z Domestic sources : plastic bags, kitchen waste, glass bottles, and paper z Industrial sources : chemical residue, fly ash, metallic waste, and z Agricultural residues : fertilizers and pesticides. Harmful effects of soil pollution z Decrease in irrigated land thereby reduction in agricultural production. z Decrease in soil productivity. z Carry over of pollutants into the food chain. z Damage to landscape 27.2.3b Control of Soil Pollution z Judicious use of chemical fertilizers and pesticides. z Proper and appropriate irrigation practices z Conversion of farm wastes into compost and much use of bio fertilizers and manure in farming. 225 BIOLOGYMODULE - 4 Pollution Environment and Health z Ensure use of pollution free or treated waste water only for irrigation. z Recycling of waste material for example plastic, metal and glass are recyclable and incineration of non recyclable, wastes. 27.2.3c Soil Erosion The process of detaching and removal of loosened soil particles by water (running water, ground water, rain, sea waves) and wind is known as soil Notes erosion. Soil may be eroded by water and wind, each contributing towards a significant amount of soil loss every year in our country. Types of soil erosion Wind erosion Erosion of large quantity of fine soil particles and sand from deserts by wind is known as wind erosion. It is spread over the cultivated land and thus, destroys fertility of that land. Sheet erosion When water moves over the land surface as a sheet, it takes away the topmost thin layer of soil. This phenomenon occurs uniformly on the slopes of hilly areas, riverbeds and areas affected by floods. This type of erosion is known as sheet erosion. Gully erosion When water moves down the slope as a channel, it scoops out the soil and forms gullies which gradually multiply and spread over a large area. This type of soil erosion is known as gully erosion. Effects of soil erosion Soil erosion may have several adverse effects such as, z The top layer of productive land may be washed away. z Roads, fences, bridges, trees and houses may get damaged. z Fine soil may be transported far away. z Crops and pasture lands may be destroyed either by being washed out or by getting covered with mud. z Flooded fields may take a long time to recover and fertilizers may also be washed out leading to reduction in agricultural yield. z Organic matter of the soil, residues or any applied manure, is relatively light- weight and can be readily washed off the field. Crop emergence, growth and yield are directly affected by the loss of natural nutrients and fertilizers in the soil. Seeds and plants can get disturbed or completely removed from the eroded soil. z Soil erosion changes the composition of soil leaving infertile rock behind. Soil quality, structure. stability and texture may also be affected. 226 BIOLOGYPollution MODULE - 4 Environment and Health z The breakdown of aggregates and the removal of smaller particles or entire layers of soil or organic matter can weaken the structure and even change the texture. Textural changes can in turn affect the water-holding capacity of the soil making it more susceptible to extreme conditions, such as drought. z Sediment which reaches streams or water-courses due to soil erosion clog drainage and stream channels, deposit silt in reservoirs and reduce quality downstream water. Notes Causes of Soil Erosion (i) Natural Sources Water Erosion: During rainfall, drops of rain can break down soil aggregates and disperse them. The loosened soil particles are transported with the runoff water. If vegetation is depleted by drought, raindrops are free to hit the soil, causing erosion during rainfall. Wind Erosion: Wind can move large amounts of soil. Wind erosion is a serious means of soil erosion. Blowing soil not only leaves a degraded area behind but can also bury and kill vegetation where it settles. Winds blow away the fine particles of soil during drought. (ii) Anthropogenic (Produced by humans) z Extensive cutting down of forests and trees exposes the ground surface to the direct impact of rain and wind. For example, in the absence of proper vegetation cover there is no interception of rainfall and the falling rain strikes the soil surface directly resulting in the throwing up of loose soil particles in the air which are washed away by rainwater. z Construction work, mining, digging canals and ditches change the structure of soil. This accelerates soil erosion due to high-speed winds as well as rainwater. z While making roads. soil is cut and massive digging of earth takes place. This leads to soil erosion by water or wind. z Excessive use of plough, machines, fertilizers and irrigation may damage the land. z In many areas, trees and grasses are depleted because of overgrazing by animals. This makes the soil susceptible to erosion. Prevention of soil erosion Some methods to control soil erosion are discussed below. z The roots of the trees hold soil material together. Therefore, we should protect our forests and trees from being cut down. Afforestation means planting trees in place of cut-down forest trees. Planting of trees along river-side, waste lands and mountaineous slopes reduces excessive erosion of soil that takes place in these regions. It is also effective in controlling wind erosion. 227 BIOLOGYMODULE - 4 Pollution Environment and Health z Grazing by domesticated animals in a planned way reduces soil erosion by protecting vegetation cover specially on the hill slopes which are more prone to soil erosion. z Protected channels for water movement must be provided to stop soil erosion. 1f the waterways are properly maintained the speed of water gets reduced and soil erosion decreases. Dam should be constructed on rivers to control flooding and consequently soil erosion. This can also be done by diverting water to dry Notes areas through canals, in a planned way. z Obstructions known as bunds should be constructed in lands affected by gully erosion. z Terracing is a method of farming to conserve the thin soil layer on the mountain slopes. This helps in controlling soil erosion and using water resources of these areas more economically and effectively for growing crops on these terraces. z Ploughing and tilling of land along the contour levels in order to cause furrows to run across the land slopes is known as the contour ploughing. This method is most suited to areas that have a rolling landscape. z Windbreaks which means planting trees to protect bare soil from the full force of wind also help in preventing soil erosion by wind. Windbreaks reduce the velocity of wind thereby decreasing the amount of soil that it can carry away. INTEXT QUESTIONS 27.3 1. What is soil erosion? ............................................................................................................................ 2. Name the various types of soil erosion. ............................................................................................................................ 3. Name any two natural factors responsible for soil erosion. ............................................................................................................................ 4. How does terracing prevent soil erosion? ............................................................................................................................ Biodegradable and non-biodegradable waste material The waste generated from various sources can be categorized into two types: (i) Biodegradable waste includes substances that can be degraded by microbes into harmless and non-toxic substances. Sewage, kitchen waste, agricultural and animal wastes like leaves, twigs. hay, dung, etc. are biodegradable waste. (ii) Non-biodegradable waste cannot he easily degraded. Aluminium cans, plastics, glass, DDT, etc, are examples of non-biodegradable wastes. Radioactive wastes produced during nuclear reactions take a long time to decay and are harmful to human beings. 228 BIOLOGYPollution MODULE - 4 Environment and Health If a waste material is processed by some means and converted to a product, we call the process recycling. Recycling helps in efficient management of wastes and also reduces the load on natural resources. Use of cow dung for the production of biogas is a good example of recycling of waste for the production of energy. 27.2.4 Noise pollution Notes Noise can be simply defined as “unwanted sound’’. It is generally higher in urban and industrial areas than in rural areas. Workers using heavy machinery are exposed to high noise levels for long period of work hours every day. Intensity of sound is measured in a unit called decibel or dB. The lowest intensity of sound that human ear can hear is 20 dB. 27.2.4a Sources of noise pollution The major sources of noise pollution are : z Use of loud speakers, loud music system and television at public places z Means of transport i.e. automobiles, railways, aircrafts, etc. z Heavy machines in industries fireworks Plane Rocket thunder Home Machine Street talk Car Whisper Quit office Decibels loudness Zero Fig. 27.6 Sources of noise pollution 229 BIOLOGYMODULE - 4 Pollution Environment and Health 27.2.4b Effects of noise pollution z Inability to sleep, slow recovery from sickness. z Irritability and interference in communication. z Temporary loss of hearing, earache, sometimes even leading to permanent deafness. z Inability to concentrate, headache. z Ringing of ears (a feeling, sound coming from within the ear in a very quiet Notes environment). z Increased blood pressure, irregular heart beat. 27.2.4c Prevention and control of noise pollution Following steps can be taken to control or minimize noise pollution : z Control the noise emanating from your radio and television. z Use automobile horn only in case of emergency. z Do not burn fire crackers as they are noisy and also cause air pollution. z Get all machinery and engines properly tuned and serviced at regular intervals and by the use of silencers. z Use of sound proof cabins and sound-absorbing materials in the walls. z A green belt of vegetation is an efficient absorber of noise. z Not playing loudspeakers during odd hours. It is legally banned and should be reported to the police immediately. 27.3 GREENHOUSE EFFECT AND GLOBAL WARMING In the earlier classes, you have studied about greenhouse effect and global warming. Greenhouse is an enclosure usually made of glass in which temperature inside is higher than outside. An increase in the percentage of greenhouse gases which prevent the escape of heat from earth, would increase the average temperature on earth worldwide known as greenhouse effect. Solar radiation reflected by earth Absorbed radiation Green house re-emitted by gases green house gases Trapped solar radiation Glocal warming Fig. 27.7 (a) Green house effect 230 BIOLOGYWarm surface radiates energy back A proportion of the long waves is absorbed by the atmosphere Pollution MODULE - 4 Environment and Health Greenhouse gases in the atmosphere behave much like the glass panes in a greenhouse. They allow sunlight to enter the atmosphere of earth. When the sunlight enters the surface of the earth, sun’s energy is absorbed by land, water and biosphere. Some of this energy is reflected back to the atmosphere by earth. Some of this energy passes back into the space. However, most of the energy remains trapped in the atmosphere by the greenhouse gases causing global warming on earth. Notes 27.3.1a Causes of global warming Carbon dioxide (CO ), Chlorofluorocarbons (CFCs), Methane (CH ) and Nitrous 2 4 oxides (N O) are the main greenhouse gases that cause global warming. An increase 2 in the concentration of these greenhouse gases leads to an increased trapping of long wave radiations resulting in an increase in earth’s temperature causing global warming. Sun Earth's surface absorbs energy ... and warms up Fig. 27.7 (b) Global warming There are various sources which add these greenhouse gases to the atmosphere. z Human activities such as burning of fossil fuels in homes, industries and automobiles, biomass burning in agricultural practices etc. add large amount of carbon dioxide to the atmosphere. z Marshes, paddy field, cattle sheds and biogas plants add methane to the atmosphere. 231 BIOLOGY Radiant energy for the Sun Short wave lengths penetrate the atomsphere