Environmental Chemistry

The study of physical, chemical, social, biological interaction with the surrounding is known as Environment Chemistry. 

What is Environment?

Environment refers to the surrounding of an object or organism. It includes every living and nonliving thing around us. Environment consists of living and nonliving components. The living component includes animals, plants and micro organics i.e all the living organisms. The non-living components include air, water, temperature, soil and all the other things that affect us in one or other way. Environmental studies deal with the sum of all social, economical, biological, physical and chemical interrelations with our surroundings.

• Atmosphere: This comprises a blanket of gaseous layer around earth. Atmosphere surrounding us can be divided into four regions ?troposphere ,stratosphere, mesosphere and thermosphere

• Hydrosphere: This comprises about 96% of earth’s surface & includes all sources of water like oceans rivers lakes, glaciers, ground water etc.

• Lithosphere: It refers to earth’s solid crust containing the outer mineral cover. It comprises soil, minerals, organic matter etc.

• Biosphere: It refers to the domain of living organism in covalent with atmosphere hydrosphere as well as lithosphere.

What is Environmental Chemistry?

One can define environmental chemistry as the branch of chemistry which deals with the study of the origin, transport, reactions, effects and fates of chemical species in the environment. It also includes the application of chemistry for understanding and solving the environmental changes, phenomenon and their effect on organisms. It also includes the application of chemistry to solve the problems related to environment such as environmental pollution.

Large number of substances (both toxic and non-toxic)  are being added to the environment by both natural events and human activities daily. These substances which are going continuously into environment due to undesirable consequences of modern civilization, industrialization and excessive use of natural resources bring about undesirable changes in our environment and adversely affect the life process of both animals and plants. 

We will  discuss some important aspects of environmental chemistry under the following topics:

• Pollution and Pollutants

• Air Pollution     

• Effects of Air Pollution

• Stratospheric Pollution

• Water Pollution

• Soil Pollution

• Environmental Pollution

What is Pollution?

The addition of any undesirable material to environment i.e. air, water or soil by any natural source or human activity which affects its quality is called natural pollution. The undesirable material which is added to the environment is called pollutant. Pollution is caused by fast population growth, excessive industrialization, rapid urbanisation and use of pesticides in agriculture. In short environmental pollution is the process of contamination of the environment with harmful wastes arising mainly from human activities.
 

Environment Pollution

The undesirable changes in the surroundings are known as environment pollution. Any substance that causes pollution is known as pollutant. Pollutant can be solid, liquid or gas. Pollutant can be released into the environment via natural process or man-made activities.

Atmosphere has different layers or regions in which it is divided -

• Troposphere is the lowest region where living organisms including human beings inhabit.

• Stratosphere is the layer above troposphere where ozone is present. Ozone prevents the ultraviolet rays from reaching the earth.

• Mesosphere is where the temperature is low. The air is thin to breathe.

• Thermosphere is the layer where rays from the atmosphere are first absorbed such as X-rays, UV-rays etc.
   

Tropospheric Pollution

It occurs when some solid or gaseous particles are suspended in air.

Pollutants are divided into gaseous air pollutants and particulate pollutants.
 

Gaseous Air Pollutants

• Oxides of Sulphur are formed when fossil fuels are burnt. The most common end product of burning of fossil fuel is Sulphur dioxide. The reactions are follows:

2SO₂ (g) +O₂ (g) → 2SO₃(g)

SO₂ (g) +O₃ (g) → SO₃(g) + O₂ (g)

SO₂(g) + H₂O₂(l) → H₂SO₄(aq)

• Oxides of nitrogen are formed when lightning strikes the oxygen at higher altitude. Burning of fossil fuels at high temperature, oxygen and nitrogen combines to form nitrogen dioxide and nitric oxide.

N₂ + O₂ → 2NO

Nitric oxide than reacts further with oxygen to form nitrogen dioxide.

2NO + O₂ → 2NO₂

High concentration of nitrogen dioxide causes damage to plant leaves. It also causes respiratory problems.

Hydrocarbons are composed to hydrogen and carbon. They are carcinogenic, that is, they are agents that causes cancer.

• Oxides of Carbon includes carbon monoxide and carbon-dioxide. Carbon monoxide is one of the toxic pollutant. It reduces the amount of oxygen that bind the hemoglobin. Incomplete combustion of carbon, automobile exhaust contains carbon-dioxide. As number of vehicles are increasing with increasing population, the concentration of carbon monoxide is increasing in the atmosphere.

• Carbon Dioxide is added to the atmosphere by respiration, burning of fossil fuels, and decomposition of limestone. Released carbon-dioxide is taken in by plants during photosynthesis to balance the carbon-dioxide released in the atmosphere. But as deforestation is increasing, the rate of carbon-dioxide taken in by plants decreases. 

Fig. 1. Causes and effects of Air Pollution

Acid Rain

Precipitation containing acidic components such as sulfuric or nitric acid in dry or wet form. Precipitation can be in the form of rain, snow, fog, dust, or hail etc. Normally rain water has pH of 5.6. When pH falls below 5.6, it is known as Acid Rain. The main cause of acid rain is human activities such as burning of coal, oil in power stations, furnaces, burning of petrol and diesel etc. 

2SO₂ (g) + O₂ (g) + 2H₂O (l) → 2H₂SO₄ (aq)

4NO₂ (g) + O₂ (g)+ 2H₂O (l) → 4HNO₃ (aq)

Acid Rain is harmful for agriculture, trees and plants. Acid Rain washes away the nutrients that are required for the growth of the plants. It causes respiratory problems in human beings and animals.
 

Particulate Pollutants

It includes minute solid particles or liquid droplets suspended in air. The source of particulate pollutants can be smoke particles from fires, vehicle emissions, ash, dust particles etc. Bacteria, viruses, moulds, algae also act as particulate pollutant.

• Smoke particulates formed during combustion of organic matter. For example, garbage, burning of fossil fuels, smoke from burning of oil.

• Dust are particles that are formed due to various sources such as crushing or grinding of solid particles. Sand, saw dust, fly ash, etc. are also important source of particulate matter.

• Mists are small water droplets that decreases the visibility in the atmosphere. For example, Mist from herbicide and insecticides.

• Fumes are another non-viable particulate pollutants that are formed due to condensation of vapors during distillation, boiling etc.

Smog

Combination of smoke and fog forms smog. There are two types of smog -

• Classical smog is a mixture of smoke, Sulphur dioxide and fog. It occurs in cool and humid environment.
• Photochemical smog is a combination of formaldehyde, acrolein, nitric oxide, ozone, and PAN. It occurs in warm and sunny environment.

Effects of Photochemical Smog

• Causes eye irritation

• Headache, chest pain, cough, difficulty in breathing

• Damage to the plant life

• Corrosion of stones and metals

• It also leads to cracking in rubber

Stratospheric Pollution

Stratosphere contains Ozone Layer that protects the earth from harmful ultraviolet rays. These ultraviolet radiations cause skin cancer in humans. Oxygen when absorbs ultraviolet rays, it breaks into oxygen atoms. Oxygen atoms when combine with oxygen, they form ozone.

The main pollutant behind the ozone depletion is Chlorofluorocarbon (CFCs) known as Freon. CFCs are used in refrigerators. These CFCs in atmosphere absorbs ultraviolet rays and forms chlorine free radical.

CF₂Cl₂ (g) → Chlorine^o (g) + C^o F₂Cl (g)

Cl^o (g) + O₃ (g) → ClO^o (g) + O₂(g)

ClO^o(g) + O^o (g) → Cl^o (g) + O₂ (g)

Note: For detailed study kindly refer to Environment Pollution
 

Definition of Water Pollution 

The contamination of water bodies such as oceans, rivers, lakes, aquifers etc., is known as water pollution.

Sources of Water Pollution

There are two sources of water pollution:

• Point Sources are those sources which arises from single, identifiable source. For Example, pipe or ditch.

Fig. 2. Sources of Water Pollution

• Non-point sources are those sources that arises from diffuse contaminants from more than one point or source. For Example, nutrient run-off from the agriculture land. 

Causes of Water Pollution

Fig. 3. Causes of Water Pollution

The causes of water pollution are divided into:

• Pathogens that causes water pollution such as Giardia lamblia, Salmonella

• Organic, inorganic, and macroscopic contaminants Detergents Insecticides and herbicides, Sulphur dioxide, Nitrates and phosphates, Acid drainage.

• Thermal solution

Effects of Water Pollution

• Death of aquatic animals due to depletion of oxygen.

• Imbalance of ecosystem.

• Contaminated water causes various diseases. Polluted water causes some of the deadly diseases like cholera, dysentery, diarrhea, tuberculosis, jaundice, etc. Approximately 80 per cent of diseases associated with stomach in India are caused by polluted water.

Fig. 4. Diseases caused due to Water Pollution

Methods to Control Water Pollution

• Sewage treatment is one of the method to control water pollution. Construction of toilets and pits will promote sewage treatment.

• Wastes should be treated before discharge.

Fig. 5. Methods to detect Water Pollution

• Water hyacinth (Eichhornia crassipes) are used to treat wastewaters. It easily absorbs, heavy metals such as lead, cadmium, mercury, and nickel. 

• Ion exchange is also one of the method to control water pollution.

• Reverse osmosis is also another method for controlling water pollution. It is a method of purification of water via semipermeable membrane.

• Precipitation is also used to control water pollution.

• Recycling is another method to control water pollution.

Note: For detailed study kindly refer to Water Pollution
 

Definition of Soil Pollution 

Alteration in the natural soil due to human activities is known as Soil Pollution or Soil Contamination.

Causes of Soil Pollution/Sources of Soil Pollution

There are different causes of soil pollution which are as follows:

Fig. 6. Main sources of Soil Pollution

• Industrial Activities are one of the main cause of soil pollution. Extraction of minerals from the earth is responsible for affecting soil fertility.

• Agriculture Activities such as use of insecticides and pesticides for a long period causes soil pollution. The repeated use of pesticides and insecticides causes insects and pests to become resistant to it. Use of DDT, Aldrin and Dieldrin makes insects resistant against them. DDT has been banned because of its toxic effects.

Fig. 7. Structure of Aldrin and Dieldrin

These pesticides are also water soluble and non-biodegradable. These toxic materials are then passed from lower trophic level to higher trophic level and gets accumulated. This is known as Biomagnification.

• Waste disposal is a serious issue that causes soil pollution.

• Accidental oil spills also promote soil pollution. Oil leaks from fuel stations deteriorates the quality of soil.

• Acid rain dissolve away the important nutrients of the soil, thus makes it unsuitable for agriculture.

• Nuclear waste also promotes soil degradation.

• Heavy metals such as lead, if mixes with soil degrades its nutrients quality.

Effects of Soil Pollution

• It affects the health of the humans. Crops or plants grown on such contaminated soil absorbs toxic material from the soil. When animals or human beings consume these crops, or plants the toxic material is passed into their body. Organophosphate pesticides inhibit nerve impulse transmission as it acts as inhibitor of acetylcholine.

• It affects the growth and the yield of the plants.

• Soil fertility decreases as soil nutrients are either drain away due to acid rain.

• It alters the ecosystem balance by affecting the growth of the living organisms.

• Harmful materials are passed from one trophic level to another trophic level. This increases mortality rate and extinction rate.

Prevention of Soil Pollution

• Contaminated soil site should be properly aerated.

• Use plants to extract heavy metals.

• Minimize the use of toxic pesticides and insecticides.

• Land farming

• Bioaugmentation can be beneficial for treating the contaminants.

• Bioremediation is another method to prevent soil pollution.

Note: For detailed study kindly refer to Soil Pollution

Definition of  Industrial Waste

Waste produced by industries are known as Industrial Waste. Industrial waste can be biodegradable or non-biodegradable.

Classification of Industrial Waste

Hazardous Industrial Waste

It can be solid, liquid or gas. It harms health as well as the environment. There are various sources of hazardous waste such as heavy metals such as lead, cadmium, mercury, hydrocarbons, pesticides, organic chemicals etc.

Non-Hazardous Waste

This waste is non-toxic so does not need special care. It includes domestic waste, wood, cardboard, textiles etc.
 

Some common terms used in Environmental Chemistry

1. Pollutant:  Any substance or species produced either by a natural source or by human activity, which produces adverse effect on the environment.

2. Contaminant: A substance which does not occurs in nature but is introduced by human activity into the atmosphere affecting its composition. Contaminant is called pollutant when it has harmful effects

3. Source: The site from which the pollution or contaminants originate. Every pollutant has some source.

4. Sink: The material or medium which consumes or interacts with a long lived pollutant is called sink. For example, Marble acts as the sink for the sulphuric acid present in acid rain. 

CaCO₃ + H₂SO₄ → CaSO₄ + H₂O +CO₂

1. Receptor : Anything that is affected by the pollutants. For example , Human beings are the receptor for smog.

2. Threshold limit value (TLV) : This indicates the permissible limit of a pollutant in atmosphere to which a healthy worker is exposed during hours a day or 40 hours a week for life time without any adverse effects. TLV are determined by experimentation on animals, by use of medical knowledge, epidemiology surveys & environmental studies.

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