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Chapter 14 Environmental Chemistry:
|Section Name||Topic Name|
|14.6||Strategies to control Environmental Pollution|
- Environment means surroundings or conditions in which a person, animal or plant lives. It consists of air, water, soil, land i.e. everything around us.
- Due to certain undesired activities our environment is getting spoiled and the time is not so far when earth will not be able to sustain life
- Lets discuss few important threats and the preventive measures for them
- environment of atmosphere which further has many layer
- There are different layers of atmosphere which are as follows:
- We will consider all the layers of atmosphere in more detail as well as we will discuss about the different types of pollution and pollutants.
Atmosphere is actually an envelope of gases that surround us. Atmosphere serves very important functions like:
- Atmosphere Contain gases which are essential for the life like oxygen, carbon dioxideetc.
- It has water vapor that is important for all life.
- Ozone is present that protect us from ultra violet rays
- It maintains heat balance and by this it controls weather or climatic conditions etc.
“It is a branch of chemistry that deals with the study of chemical phenomenon occupying in the atmosphere.”
It can be defined as the “undesirable change in our surroundings that causes lot of harmful effects.”
The substances that are undesirable and cause lot of harm are called pollutants.
- There are different layers of atmosphere and the lower layer or region in which we live is known as troposphere.
- Troposphere contains air, watervapor, clouds; dustetc. in this layer the cloud formation takesplace.
- Atmospherepollution is mainly caused in troposphere and atmosphere.
- The protective layer that is ozone which is found in stratosphere is adversely affected by pollutants and this layer is very important to us as it prevent the entry of ultra violet rays which otherwise can cause lot of diseases.
The major causes of pollution are:
- Fast population growth
- Rapid urbanization
- Use of pesticides etc.
- Note :There is a difference between a contaminant and a pollutant which as follows:-
Contaminant is not present in nature but is introduced into the environment by human activity
Pollutant is a substance that are produced either by natural source or by human activity and due to increase its concentration the harm is caused to living forms
Threshold limit valueis the permissible limit of a pollutant in atmosphere to which if a healthy worker is exposed for 8hours or 40 hours a week there is no effect on him.
Types of pollutants
The classification of pollutant on the basis of their origin
- Primary pollutant
- Secondary pollutant
- These are those which after their formation enter the environment and remain as such.Example: nitrogen and oxygen gas become a pollutant if in excess amount and lead to harmful effect like cause of acid rain etc.
- These are harmful materials that are formed by chemical reactions between primary pollutants in atmosphere or hydrosphere
Example: hydrocarbons and oxides of nitrogen react in presence of sunlight to form compounds like PAN .so PAN is secondary pollutant as it is formed by reaction between primary pollutants.
Another classification of pollutants: on the basis of their degradation
Biodegradable: are materials that are decomposed by microorganisms either by themselves or by microorganisms.
Example: domestic sewage, cow dung etc.
Theseare materials that are not decomposed by either by itself or by microorganisms and their presence in environment leads to pollution. They may be a raw material for producing other toxic substances.
Example: plastics etc.
Types of pollution
Types of pollutiondepending on the substance or the resource that is contaminated
- Air pollution
- Water pollution
- Soil pollution
Types of pollution depending upon the nature of pollutant:
- Radioactive substances
- Acid rain
- Greenhouse effect
- Thermal pollution
- Smog and many more
“The contamination of air with harmful and undesirable substances “
Sources of pollutants:
- Natural sources
- Artificial sources
Natural –like volcanic eruption, pollen grains, forest fires, etc.
- Burning of fossil fuels
- Combustion of flukes in automobiles
- Increasing population
- Agricultural activities
The atmospheric pollution is basically contamination of troposphere and stratosphere.
Troposphere is mainly polluted by:
- Gaseous pollutants like carbon, Sulphuretc.
- Particulatepollutant’s like dust,mist,smoke etc.
There are five major pollutants of troposphere are like Carbon dioxide, Carbon monoxide etc.
Carbon monoxide: It is colourless and odourless gas and it is released in air by human activities like:
- incomplete combustion of fuels,
- forest fires
- dissociation of carbon dioxide at high temperature etc or
- natural sources like conversion of methane to carbon monoxide
- from decay of chlorophyll etc.
Though the CO is produced still its level do not rise in atmosphere because of conversion of CO to carbondioxide by the bacteria present in soil so we can say microorganisms act as a sink for carbon monoxide but this sink is not available in urban areas due to less soil.
Effects of carbon monoxide:
The carbon monoxide is a poisonous gas if inhaled can combine with haemoglobin (Hb) to form defective type of complex that can lead to suffocation and also deathTherefore it is a fatal gas.
Carbon dioxide: it is released in atmosphere due to burning; respirationetc.Excess of it is removed by plants as they utilize it for photosynthesis.However, increased in its concentration leads to global warming.
Green House Effect
Global warming “is the increase in the concentration of certain gases like carbon dioxide, methane, etc. in air due to which infra-red rays get trapped in it and it leads to increase in overall temperature of earth.”
- The rays that come from the Sun consist of visible light, infra-red rays and ultra violet rays. Out of these, only infra-red rays and visible light reaches earth’s surface. On reaching earth, the infra-red rays are reflected back and a portion of it is absorbed by earth’s surface. The reflected ones when pass through earth’s atmosphere, get trapped inside the gas molecules. As we know, itleads to heating effect. Therefore, the overall temperature of earth’s surface rises. One of the reasons for global warming is greenhouse effect.
- In winters, it is advised to keep plants in green houses only. The roof allows infra-red rays to enter but after reflection, they are not allowed to go back. As a result, they get trapped inside the green house and growth of plants is stimulated because optimum temperature is achieved inside the green house.
Oxides of Sulphur:They are produced by burning of Sulphurcontaining fossil fuels. This Sulphur dioxide can cause respiratory problems like asthma, emphysema, irritation to eyes, redness in eyes etc.
Oxides of nitrogen: The nitrogen oxides are formed due to lightning strikes at higher altitudes and also due to burning of fossil fuels.It causes irritant red haze, damage leaves of plant, retard rate of photosynthesis also respiratory disorders.
Both Sulphur dioxide and nitrogen dioxide are cause of acid rain
Acid rain ( Environmental Chemistry )
- It is the one of the major causes of causing cancer. It is formed when rain water mixes with pollutants present in air. These pollutants are mainly Nitrogen dioxide and Sulphur dioxide gas emitted in exhaust of vehicles.
When rain falls, these gases combine and the following reaction takes place:
SO2 + H2O H2SO4
NO2+ H2O HNO3
As a result, rain water no longer remains only pure water it becomes acidic
- It causes cancer.
- It combines with marble and deteriorates the marble.
- It affects ph. of soil and makes it unfit for growing plants.
- It affects aquatic life too
Hydrocarbons:They are produced due to combustion of fuels are actually carcinogenic that causes cancer. They also harm plants as they cause ageing in plants, shedding of leaves etc.
Chlorofluorocarbons:They are released into the atmosphere from industries. They are actually manmade industrial chemicals used in air conditioners, refrigeratorsetc. and their vapours do not remain in lower layers of atmosphere they move up and cause thinning of ozone.
Ozone ( Environmental Chemistry )
Ozone: It is a molecule consisting of three oxygen atoms i.e. O₃. It is present in stratosphere.
Ozone is formed when u-v rays in upper atmosphere split oxygen atoms that are: –
When oxygen molecule splits into atoms then each atom combine with undissociated molecule of oxygen to form ozone.
Ozone protect us from ultra violet radiations as it doesn’t allow ultra violet rays to enter earth’s atmosphere that if enter into earth may harm us in many ways such as:
- They may raise the temperature of earth
- It can cause global warming
- It may cause skin disorders, eye disorders and many more.
- The thinning of ozone layer by air pollutants is called ozone depletion.
For this some synthetic chemicals are responsible like ChloroFloro Carbons that are used in refrigerators, air conditioners, etc.
- Due to continuous use of certain harmful chemicals like CFC’s etc. they have caused thinning of ozone layer to an extent that a hole is observed in ozone layer in the region of Antarctica.
- This hole is not a hole actually we can say it is the extreme thinning in some parts due to extreme reactions taking place with certain harmful chemicals that are not stable in upper atmosphere and react with ozone causing its depletion
- It is agreement made by industrialized nations to freeze the production of CFC’s and make use of some alternative source.
- It was done in 1987 UNEP (United Nations Environment Program)
Now, instead of using CFC’s; HFC’S and PFC’s are used that is somehow helping in saving the ozone layer.
- They are minute solid or liquid particles present in air.These are released by vehicle exhaust, dust and ashes of hydrocarbons.
- They may be viable like bacteria etc. and non-viable like ash etc.
Non-viable particulates are classified according to nature and size of particles. They are as follows:-
Smoke: Itconsists of solid and liquid particles formed during combustion of fuels etc.
Dust: It is composed of fine solid particles produced during crushing, grinding of solid particles, like saw dust from wood, fly ash from factories etc.
Mist:They are produced by particles of spray liquids and condensation of vapors in air, like insecticides etc.
Fumes:They are obtained by condensation of vapors during sublimation, distillation, boilingetc., like metallic and non-metallic oxides
- The particulate matter harm but degree of harm depends upon the size of particles particulate pollutants bigger than 5 microns can block nasal passage whereas particle of size micron can even enter lungs.
Smog and Photochemical smog
- Smog is formed by combination of smoke and fog.
- A thick fog-like layer in the atmosphere, especially during winters it is known as smog as it is made up of smoke and fog.
- Smoke may contain oxides of nitrogen which combine with other air pollutants and fog to form smog. The smog causes breathing difficulties such as asthma, cough and wheezing in children
- It is caused due to hydrocarbons and nitric oxide.When their concentration rises beyond limit a chain reaction occur from their interaction with sunlight in which NO is converted into nitrogen dioxide.
- This nitrogen dioxide in turn absorbs energy and breaks into nitric oxide and free oxygen atoms.
- These oxygen atoms combine with oxygen gas molecules to produce ozone .This ozone is a toxic gas it combines with un-burnt hydrocarbons in air to produce chemicals like formaldehyde, acrolein and PAN.
Harmful effects of photochemical smog
- It causes serious earth problems
- Ozone and PAN are eye irritant
- Ozone and nitric oxide irritate nose, throat, causes dryness in throat, cough and difficulty in breathing.The smog leads to cracking of rubber and extensive damage to plant life.
Photochemical smog can be controlled as:-
- Plantation of certain plants like pinesetc can metabolise nitrogen dioxide and Catalytic convertors which prevent the release of nitrogen oxide and hydrocarbons should be used in vehicles
Water pollution is defined as: “It is the contamination of water with undesirable and harmful substances.”
Polluted water has certain characteristics:
- Bad taste
- Offensive odour
- Unpleasant color
- Unchecked growth of weeds
- Oil or grease floating on surface
Sources of water pollution
- Sewage and domestic waste spread Pathogens:-
- They form the major part of pollutant. They includebacteria etc. that enter the into water bodies etc. Human excreta usually contain E.coli bacteria and streptococcus bacteria that cause lot of gastrointestinal problems.
- Organic wastes:
- It includes leaves, grass etc. it leads to excessive growth of plants in water bodies.
- The bacteria act on these waste as they are biodegradable.They consume oxygen dissolved in water and tis concentration of oxygen is very important for aquatic life.
- Both the bacteria aerobic and anaerobic have harmful effect as anaerobic bacteria breaks down the organic matter and result in the formation of chemicals that give foul smell and are harmful to human health whereas aerobic bacteria degrade the organic matter and lower the concentration of oxygen .
- Oxygen consumed by microorganism in decomposing the waste present in certain volume of sample of water is called biochemical oxygen demand (BOD) of water.
- Chemical pollutants:
- The lot of metals, chemicalsetc. are disposed in the water bodies and cause lot of harm like metals are very dangerous as we can’t excrete them therefore they can damage kidneys, CNS,liver etc. petroleum and its products also pollute water .
- The excessive disposal of chemicals in water bodies leads to eutrophication.
Eutrophication is a result of excessive disposal of chemicals that leads to excess growth of algae in water bodies that is water bloom and this water bloom results in oxygen depletion and aquatic life suffers a lot due to this effect.
Radioactive discharge: They enter the water bodies from different sources like nuclear reactions, nuclear tests etc. they emit very harmful radiations.
Polychlorinated biphenyl’s: These are used as fluids in transformers etc. They are resistant to oxidation and when released in atmosphere they cause skin disorders.
International standards of drinking water
There arecertain substances in water which are essential but only up to certain limits.They are as below:
- Water should be tested for fluoride ion concentration.Its deficiency in water cause harmful diseases like tooth decay etc.The fluoride ion in water help in enamel of teeth much harder by converting hydroxyl-apatite into much harder flour-apatite.
- The presence of increased concentration of lead can harm kidney, liver and reproductive system.
- Excessive sulphate can cause laxative effect.
- The maximum limit of nitrate is 50ppm. Excess nitrate cause methemoglobinemia.
Soil pollution is defined as:
“The contamination of soil with undesirable and harmful substance “
Composition of soil:
It contains mineral matter, organic matter, living forms like algae etc., water and air.
The causes for soil pollution are:
- Agricultural pollutants:
- They are toxic chemicals.
- The continuous use of similar pesticides gives rise to pest that are resistant to same type of pesticides making their effect ineffective.
- These high persistent toxins are transferred from lower level to higher tropic levels occur due to which bio magnifications takes place.Therefore, metabolic and physiological disorders. a new series of more biodegradable products called organophosphates and carbamates are introduced in market.But these chemicals cause severe nerve toxins and hence more harmful.These days herbicides such as sodium chlorate, sodium arsenate and many other are toxic to mammals.These chemicals take few months to decompose.Some herbicides cause birth defects.
- Industrial waste:
- Industrial solid waste is also divided out biodegradable and non-biodegradable.
- Biodegradable waste is generated by cotton miles etc., are also generated in thermal plants which produce fly ash, integrated iron and steel plants which produce blast furnace slag and steel melting slag.Industries manufacturing aluminium, zinc and copper produce mud. Fertilizer industries produce gypsum. hazardous waste like inflammables, composite explosives or highly reactive substances are produced by industries dealing in metals,drugs,chemicals, pharmaceutical dyes, pesticides, rubber etc. a new innovation have led to different uses of waste materials.Now a day’s fly-ash and slag from steel industry are utilized by the cement industry.A large quantity of toxic waste is destroyed by control incineration where small quantities are burn along with factory garbage in open bins.
- Urban waste:
- It consists of soil refuse containing garbage and rubbish material like paper; glass etc. These wastes emit poisonous gases, toxic hydrocarbons and microbes that cause diseases.
- Radioactive pollutants:
- Dumping of nuclear waste in soil has greater result in soil pollution.
- Industrial solid waste is also divided out biodegradable and non-biodegradable.
The improper disposal of waste is one of the major causes of environmentaldegradation.
The two main sources of waste:
- Household waste
- Industrial waste
There should be proper way of collecting and disposal of waste which is referred as waste management
- Domestic waste is collected in small bins which are then transferred to community bins by private or municipal workers
- From these bins these are collected and are carried out to disposal site.At the site garbage is sorted out and separated in to bio or non-biodegradablesubstances.
- The non-biodegradable such as plastics, glass etc are sent for recycling.The biodegradable waste are deposit in landfills and are converted into compost .
- All domestic waste should be properly collected and disposed.The poor management causes health problems leading to epidemics due to contamination of ground water.
Management of industrial waste
They should also be sorted as bio or non-biodegradable.We can make them harmless before disposing.
Some methods that are employed are to manage industrial waste:
3r’s: Reduce, Recycle and Reuse.
It means use lesser natural resources.
- Switch off the electrical appliances when not needed
- Save fuels by walking, etc.
- Save food by not wasting food
- It means processing of waste to form new products.
- Practicing recycle saves resources, saves cost, also reduces the piling of waste materials.
- It means using article again and again.
- We can again use the used envelopes
- The containers of jams and pickles are reused by storing other things.
- Use cloth bags instead of using plastics.
Green chemistry means producing the chemicals of our daily needs using such reactions or chemicals which are don’t use toxic chemicals or emit chemicals in atmosphere.
It stresses on use of friendly reagents like sunlight,microwaves, sound waves and enzymes.
- It is the way of thinking in how to utilize the existing knowledge and principles of chemistry and other science to reduce the adverse impact on environment. Green chemistry is a production process that would break about minimal pollution or deterioration to the environment.
- The bi products generated during the process if not used add to the environmental pollution such process isnot only environmentalunfriendly but also cost ineffective. The waste generation and its disposal both are economical unsound.
- Utilization of existing knowledge base for reducing the chemical hazards along with the developmental Activities that are eco-friendlyis green chemistry.
In total it is a cost-effective approach which involves reduction in materials, energy consumption and waste
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