Environmental Chemistry

Environmental Chemistry

Environmental chemistry is very important branch of scince where we deals about nature and our environment.

Environment means surroundings or conditions in which a person, animal and 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 the earth will not be able to sustain life

Let us discuss a few important  problems and the preventive measures for the environment of the atmosphere which further has many layers.

There are different layers of atmosphere which are as follows:

• Atmosphere

• Hydrosphere
• Lithosphere
• Biosphere
  We will consider all the layers of the atmosphere in more detail as well as we will discuss the different types of pollution and pollutants.

Atmosphere: The atmosphere is gaseous mixtures of air that surround us. Its different layer is:

• Troposphere:  It is the lowest region of the atmosphere extending from earth’s surface to the lower boundary of the stratosphere. It contains water vapors and affect by air pollution.
• Stratosphere: The layer of the earth’s atmosphere above the troposphere and below the mesosphere, is  stratosphere. The ozone layer is present in this region.
• Mesosphere:  It is the region of the earth’s atmosphere above the stratosphere and below the thermosphere. It is the coldest region (temperature – 2 to 92°C) of the atmosphere.
• Thermosphere: The upper region of the atmosphere above the mesosphere is thermosphere.It is the hottest region (temperature up to 1200°C).
• Exosphere: It is the uppermost region of the atmosphere. It contains atomic and ionic O₂, H₂ and He₂. 

• Hydrosphere: It is the aqueous envelope of the earth e.g., oceans. lakes etc.
• Lithosphere: The solid rocky portion of the earth make up the lithosphere.
• Biosphere:  The biological envelope which supports life is the biosphere. e.g., animal, human beings.

Environmental Chemistry:

“It is a branch of chemistry that deals with the study of chemical phenomenon occupying in the environment”

Environmental pollution: It can be defined as the “undesirable change in our surroundings that causes a lot of harmful effects.”

The substances that are undesirable and cause a lot of harm are called pollutants.

Environmental Pollution:

It may be described as contamination of the environment with harmful wastes mainly arising from certain human activities. These activities release materials which pollute the atmosphere, water, and soil.

The major causes of pollution are:

• Fast population growth
• Rapid urbanization
• Industrialization
• Use of pesticides etc.

Difference between a Contaminant and a Pollutant:

Contaminant	Pollutant
It is not present in nature	A substance that is produced either by natural source or by human activity
They introduced into the environment by human activity	Increasing its concentration is harmful to living forms.

Threshold limit value is the permissible limit of a pollutant in the atmosphere to which if a healthy worker is exposed for 8 hours 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

Primary pollutant:

• These are directly emitted from the source in the environment and remain. Example:
• Nitrogen and Oxygen gas become a pollutant if in excess amount and lead to a harmful effect like a cause of acid rain etc.

Secondary pollutant:

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 the presence of sunlight to form compounds like PAN. So PAN is secondary pollutant as it is formed by a reaction between primary pollutants.

Another classification of pollutants: on the basis of their degradation:

• Biodegradable
• Non-biodegradable

Types of pollution:

Types of pollution depending on the substance or the resource that is contaminated:

• Air pollution
• Water pollution
• Soil pollution

Types of pollution depending upon the nature of pollutant:

• Plastic
• Radioactive substances
• Chemicals
• Acid rain
• Greenhouse effect
• Thermal pollution
• Smog and many more

Air Pollution:

“The contamination of air with harmful and undesirable substances”

Sources of pollutants:

• Natural sources
• Artificial sources
• Natural –like a volcanic eruption, pollen grains, forest fires, etc.
• Man-made like:

Burning of fossil fuels
Combustion of flukes in automobiles
Increasing population
Industries
Agricultural activities
Wars

The atmospheric pollution is basically contamination of troposphere and stratosphere.

The troposphere is mainly polluted by:

• Gaseous pollutants like carbon, Sulphuretc.
• Particulatepollutant’s like dust,mist,smoke etc.

There are five major pollutants of the troposphere are like Carbon dioxide, Carbon monoxide, etc.

Carbon monoxide: It is colourless and odourless gas and it is released in the 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 the decay of chlorophyll etc.

Though the CO is produce still its level does not rise in the atmosphere because of conversion of CO to carbon dioxide 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 because of less soil.

Effects of carbon monoxide:

The carbon monoxide is a poisonous gas if inhaled can combine with hemoglobin (Hb) to form a defective complex that can lead to suffocation and also death, therefore, it is a fatal gas.

Carbon dioxide: It release in the atmosphere because of burning; respiration etc. Excess of it is removed by plants as they use it for photosynthesis. However, increased in its concentration leads to global warming.

Global Warming in Environmental Chemistry

Global warming “is the increase in the concentration of certain gases like carbon dioxide, methane, etc. in the air because of which infra-red rays get trapped in it and it leads to an increase in the overall temperature of the earth.”

Green House Effect in Environmental Chemistry

The rays that come from the Sun comprise visible light, infra-red rays, and ultraviolet rays. Out of these, only infra-red rays and visible light reaches the 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 passing through the earth’s atmosphere, get trapped inside the gas molecules.

As we know, it leads to heating effect. Therefore, the overall temperature of the earth’s surface rises. One reason for global warming is the greenhouse effect.

• In winter, we advise it to keep plants in greenhouses only. The roof allows infra-red rays to enter but after reflection; it does not allow them to go back.
• As a result, they get trapped inside the greenhouse and it stimulates the growth of plants because it achieves the optimum temperature inside the greenhouse.

Oxides of Sulphur

They are produced by burning of Sulphur containing fossil fuels.

Sulphur dioxide can cause respiratory problems like asthma, emphysema, irritation to eyes, redness in eyes, etc.

2SO₂ +  O₂ (air) →  2SO₃

Oxides of nitrogen:

The nitrogen oxides are formed due to lightning strikes at higher altitudes and also due to the burning of fossil fuels.

2NO(g) +  O₂(g) → 2NO₂(g)

NO(g) +  O₂(g) →NO₂(g) + O₂(g)

It causes irritant red haze, damage leaves of a plant, retard the rate of photosynthesis also respiratory disorders.

• Both Sulphur dioxide and nitrogen dioxide are the cause of acid rain.

Acid Rain in Environmental Chemistry:

• It is one of the major causes of causing cancer.
•  formed when rainwater mixes with pollutants present in the 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:
• As a result, rainwater no longer remains only pure water it becomes acidic

Harmful effects:

• It causes cancer.
• Combines with marble and deteriorates the marble.
• Affects ph. of soil and makes it unfit for growing plants.
• Also affects aquatic life too.

Hydrocarbons:

It produces them because of combustion of fuels are carcinogenic that causes cancer. They also harm plants as they cause aging in plants, shedding of leaves, etc.

Chlorofluorocarbons:

It releases them into the atmosphere from industries and are actually manmade industrial chemicals used in air conditioners, refrigerators, etc. and their vapours do not remain in lower layers of atmosphere they move up and cause thinning of ozone.

CF₂Cl₂(g) +  hv → Cl^•(g)  +  ^•CClF₂(g)

^•Cl(g)  +  O₂(g) → Cl^•O(g)  +  O₂

ClO^•(g)  + O₂ → Cl^•  +  Cl^•         Cl^•(free radical)

Ozone:

• It is a molecule comprising three oxygen atoms, i.e. O₃. It is present in the stratosphere.
• It forms ozone when u-v rays in the upper atmosphere split oxygen atoms that are: –
• When an oxygen molecule splits into atoms, each atom combines with the undissociated molecule of oxygen to form ozone.
• Ozone protects us from ultraviolet radiations as it doesn’t allow ultraviolet rays to enter earth’s atmosphere that if they enter earth may harm us such as

• They may raise the temperature of the earth.
• It can cause global warming.
• Cause skin disorders, eye disorders and many more.
• The thinning of the ozone layer by air pollutants is ozone depletion.

For this, some synthetic chemicals are responsible like ChloroFloro Carbons present in refrigerators, air conditioners, etc.

Ozone hole:

• Because of continuous use of certain harmful chemicals like CFC’s etc. they have caused thinning of the ozone layer to an extent that we see a hole in the ozone layer near Antarctica.
• This hole is not a hole actually we can say it is the extreme thinning in some parts because of extreme reactions taking place with certain harmful chemicals that are not stable in the upper atmosphere and react with ozone causing its depletion.

ClO^•(g)  + NO₂ →^•ClONO₂(g)

Cl^•(g)    +  CH₄ →^•CH₃  +  HCl(g)

Montreal protocol in Environmental Chemistry:

It is an 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.

Particulate pollutants in Environmental Chemistry:

They are minute solid or liquid particles present in the air and are release 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 the nature and size of particles. They are as follows:-

Smoke

It comprises of solid and liquid particles formed during the combustion of fuels etc.

Dust

They compose it of fine solid particles produced during the crushing, grinding of solid particles, like sawdust 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 a 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 the lungs.

Smog and Photochemical smog in Environmental Chemistry

• Smog is a combination of smoke and fog.
• A thick fog-like layer in the atmosphere, especially during winters it is smog as they make it up of smoke and fog.
• Smoke may contain oxides of nitrogen that combine with other air pollutants and fog to form smog. The smog causes breathing difficulties such as asthma, cough and wheezing in children.

Photochemical Smog

• They cause it because of hydrocarbons and nitric oxide. When their concentration rises beyond a limit, a chain reaction occurs from their interaction with sunlight in which it converts NO into nitrogen dioxide.
• This nitrogen dioxide 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 unburnt hydrocarbons in the 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 pines etc can metabolize nitrogen dioxide and Catalytic convertors which prevent the release of nitrogen oxide and hydrocarbons should be used in vehicles.

Water Pollution

We define water pollution 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 include bacteria etc. that enter the into water bodies etc.

Human excreta usually contain E.coli bacteria and streptococcus bacteria that cause a lot of gastrointestinal problems.

Organic wastes

• It includes leaves, grass, and leads to excessive growth of plants in water bodies.
• The bacteria act on these waste as they are biodegradable.and consume oxygen dissolved in water and is a concentration of oxygen is very important for aquatic life.
• Both the bacteria aerobic and anaerobic have harmful effect as anaerobic bacteria break 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 a sample of water is biochemical oxygen demand (BOD) of water.

Chemical Pollutants

Disposing of a lot of metals, chemicals, etc. 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:  results from 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 because of  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: We use these as fluids in transformers etc. They are resistant to oxidation and when released in atmosphere they cause skin disorders.

International standards of drinking water in Environmental Chemistry

There are certain substances in the water which are essential but only up to certain limits. They are as below:

• Fluoride:

We should test water for fluoride ion concentration. Its deficiency in water causes harmful diseases like tooth decay, etc.

The fluoride ion in water help in the enamel of teeth much harder by converting hydroxyl-apatite into much harder flour-apatite

• Lead:

The presence of an increased concentration of lead can harm the kidney, liver and reproductive system.

Ca—EDTA + Pb⁺²  →  Pb—EDTA + Ca⁺²

• Sulphate:

Excessive sulfate can cause laxative effect.

• Nitrate:

The maximum limit of nitrate is 50 ppm. Excess nitrate cause methemoglobinemia.

Soil Pollution

The contamination of soil with an undesirable and harmful substance”

Composition of soil

It contains mineral matter, organic matter, living forms like algae, etc., water and air.

Sources of Soil Pollution

• Agricultural pollutants e.g., chemicals like pesticides, fertilizers, bactericides, fumigants. insecticides, herbicides, fungicides.
• Domestic refuge and industrial wastes.
• Radioactive wastes from research centers, and hospitals.
• Soil conditioners containing toxic metals like Hg, Pb, As. Cd etc.
• Farm wastes from poultries, dairies and piggery farms.

Control of Soil Pollution

• Use of manures: Prepared from animal dung is much better than the commonly used fertilizers.
• Use of biofertilizers: These are the organisms which are inoculated to bring about nutrient enrichment of the soil. e.g., nitrogen-fixing bacteria and blue-green algae.
• Proper sewerage system: A proper sewerage system must be employed and we must install sewage recycling plants.
• Salvage and recycling: Rag pickers remove a large number of waste articles such as paper, polythene, cardboard. rags. empty bottles and metallic articles. These are subjected to recycling and this helps in checking soil pollution.

Radioactive Pollution in Environmental Chemistry

Cosmic rays that reach the earth from outer space and terrestrial radiation from radioactive elements are natural radiations.

This natural or background radiation is not a health hazard due to its low concentration.

Man-made sources of radiations include mining; and refining of plutonium and thorium, atomic reactors and nuclear fuel.

It produces during during preparation of radio-isotopes. These are of two types: electromagnetic (radio waves UV, IR, α-rays) and particulate.

Other Sources of Radioactive Pollution

Atomic explosions: Atomic explosions produce radioactive particles which are thrown high into the air as huge clouds.
The process releases a large amount of energy as heat. Because of the atomic explosion nuclear fallout. These radioactive elements may reach human beings through the food chain.
Radioactive wastes: Wastes from atomic power plants come in the form of spent fuels of uranium and plutonium. People working in such power plants, nuclear reactors, fuel processors, etc., are vulnerable to their exposure.
Radioisotopes: Many radioactive isotopes like C¹⁴ I¹²⁵, P^32, and their compounds are used in scientific researches. The wastewater of the research centers contains the radioactive elements which may reach human beings through water and food chains.

Effects of Radiations

• Strontium-90 accumulates in the bones to cause bone cancer and tissue degeneration in a number of organs.
• 1-131 damages WBCs, bone marrow, lymph nodes and causes skin cancer, sterility, and defective eyesight.
• These may cause ionization of various body fluids, chromosomal aberrations, and gene mutations.
• Radioactive iodine may also cause cancer of thyroid glands.
• Cesium-137 brings about nervous, muscular and genetic change.
• Uranium causes skin cancers and tumors in the miners.
• Radon-222 causes leukemia, brain tumors, and kidney cancers.

Bhopal Gas Tragedy in Environmental Chemistry

On Dec. 2, 1984, a dense cloud of methyl isocyanate gas (MIC) leaked from a storage tank of the Union Carbide ltd plant in Bhopal. It caused a great loss of life to people and animals. Methyl Isocyanate was prepared by the reaction of methyl amine with phosgene and stored in abundance.

CH3NH2     +	COCl2  →	CH3—N=C=O + 2HCl
Methyl Amine	Phosgene	(MIC)

Strategies to control environmental pollution: Waste management

The improper disposal of waste is one of the major causes of environmental degradation.

The two main sources of waste

1. Household waste
2. Industrial waste

Waste management is a proper way of collecting and disposal of waste.

• We collect domestic waste in small bins which are then transferred to community bins by private or municipal workers
• From these bins, we carry these out to the disposal site. At the site, garbage is sorted out and separated into bio or non-biodegradable substances.
• The non-biodegradable such as plastics, glass etc are sent for recycling. The biodegradable waste is deposit in landfills and are converted into compost.
• All domestic waste should be properly collected and disposed of. The poor management causes health problems leading to epidemics because of contamination of groundwater.

Management of industrial waste in Environmental Chemistry

They should also be sorted as bio or non-biodegradable. We can make them harmless before disposing of. Some methods that are employed are to manage industrial waste

3r’s: Reduce, Recycle and Reuse.

Reduce:

It means use lesser natural resources. Like:

• Switch off the electrical appliances when not needed
• Save fuels by walking, etc.
• Save food by not wasting food

Recycle:

• It means the processing of waste to form new products.
• Practicing recycle saves resources, saves cost, also reduces the piling of waste materials.

Reuse:

• It means using the article again and again.
• We can again use the used envelope.
• The containers of jams and pickles are reused by storing other things.
• Use cloth bags instead of using plastics.

Green chemistry

Green chemistry  involved in the design, development, and implementation of chemical products and processes to reduce or eliminate the use and generation of substances hazardous to human health and the environment.
Thus, the goal of green chemistry is ‘to promote the development of products and processes that reduce or eliminate the use or generation of toxic substances associated with the design, manufacture, and use of hazardous chemicals. Some important principles and method of green chemistry are:

• It is better to prevent waste than to treat or clean up waste after they form it.
• They should design synthetic methods to maximize the incorporation of all materials used in the process into the final product.
• We should design synthetic methodologies to use and generate substances that possess little or no toxicity to human health and the environment
•  we should design Chemical products to preserve the efficiency of function while reducing toxicity.
• Using an auxiliary substance (e.g., solvents, separation agents, etc.) should try to avoid as far as possible.
•  Energy requirements should be recognized for their environmental and economic impacts and should be minimized.
• We should conduct synthetic methods at ambient temperature and pressure.

Important Question & Answers in Environmental Chemistry:

1. The gas emitted by supersonic jet planes that slowly depletes the ozone layer is:

(a) CO                                         (b)  SO₂

(c)  NO                                         (d)  O₂

ANS:   Hence, the correct option is (b)  SO₂

2. The process of ‘eutrophication’ is due to:

(a) increase in the concentration of insecticide in water.

(b) increase in concentration of fluoride ion in water.

 (c) the reduction in concentration of the dissolved oxygen in the water due to phosphate pollution in water.

(d) attack of younger leaves of a plant by peroxyacetyl nitrate.

ANS:  Hence, the correct option is (c) the reduction in the concentration of the dissolved oxygen in the water due to phosphate pollution in water.

3. Excess nitrate in drinking water can cause:

(a) methemoglobinemia                              (b)  kidney damage

(c)  liver damage                                         (d) laxative effect

ANS:  Hence, the correct option is (a) methemoglobinemia.

4.Formation of London smog in:

(a) Summer during day time                      (b) Summer during morning time

(c) Winter during morning time                    (d)Summer during day time

ANS:  Hence, the correct option is (a) summer during day time 

5. In Antarctica, ozone depletion is due to the formation of the following compound:

(a) Acrolein                                                 (b) peroxy acetyl nitrate

(c) SO2 and SO3                                         (d)chlorine nitrate

ANS:  Hence, the correct option is (d)chlorine nitrate.

6. Which of the following is not a greenhouse gas?

(a) Methane                                                 (b) Ozone

(c) Carbon dioxide                                      (d) Nitrogen

ANS:  Hence, the correct option is (d) Nitrogen.

7. All are primary pollutants except:

(a) SO₂                                                (b) H₂S0₄

(c) NO₂                                                (d)Particulate matter

ANS: Hence, the correct option is (b) H₂S0₄

8. The aromatic compounds present as particulates are:

(a) Benzene                                         (b) Toluene

(c) Nitrobenzene                                 (d) Polycyclic hydrocarbons 

ANS:  Hence, the correct option is (d) Polycyclic hydrocarbons.

1..Differences between Biodegradable and Non-biodegradable substances:

Biodegradable	Non-biodegradable
Items decompose or break down naturally	Large volumes of non-biodegradable waste take up excess waste and are potentially damaging to the environment.
Biodegradable waste can be used to generate energy as compost and biogas.	Non-Biodegradable waste can be separated and recycled but the process is very cost