Special Content

volume-10, 8 - 14 June 2019

Understanding Basics of Environment-II

Shreya Bhattacharya

A balanced environment is essential for sustainable development, growth and reproduction for all living organisms. All the components required by the organisms are present in the environment. When the balance of the environment gets disturbed for one reason or the other, survival of living organisms becomes difficult. This balance of the environment may be disturbed by the entrance of some harmful and unwanted components in the environment. In this second article of the special series on environment, we will discuss about various types of Environmental pollution and their adverse impact. Environmental pollution is one of the most pressing issues facing humanity and other life forms on the Earth today.


Pollution is the introduction of contaminants into the environment that damages it or affects it adversely and cause harm to human beings, animals, plants and other living organisms. Environmental pollution can also be defined as "the contamination of the physical and biological components of the earth/ atmosphere system to such an extent that normal environmental processes are adversely affected. It takes place when the environment cannot process and neutralise harmful by-products of human activities  like solid industrial wastes or green house gas emissions, in due course without any structural or functional damage to its system. This unfavourable alteration of our surroundings is wholly or largely a by product of man's actions. It adversely affects the usefulness of the resources. Pollution can come in the form of chemical substances as solid, liquid or gaseous substance, or energy such as heat, light or noise.


Substances that cause pollution are known as pollutants. They can be naturally occurring substances or energies, but are considered contaminants when in excess of natural levels. Pollutants can be chemicals like nitrogen oxides or sulphur oxides, geochemical substances like dust or sediment, biological organisms or products, or physical substances like heat, radiation or sound wave that is released by man into the environment with actual or potential adverse, harmful or inconvenient effects. The nature and concentration of pollutant determine the severity of effect of pollution. Ecologically, pollutants can be divided into two types:

  1. Degradable or non - persistent pollutants: The pollutants that can be rapidly decomposed by natural processes is called degradable or non-persistent pollutants. E.g.- sewage, paper products, vegetables, juice, seeds and leaves. They are only harmful when present in large quantities within the environment. These pollutants can be broken down into simpler, harmless, substances in nature in due course of time by the action of micro-organisms like certain bacteria.
  2. Non - degradable pollutants. Some pollutants can not be decomposed by natural processes are called non-degradable pollutants. They cannot be broken down into simpler, harmless substances in nature. E.g. - plastics, polythene, bags, DDT, insecticides, pesticides, mercury, lead, arsenic, etc.

Classification of pollution

The Environmental pollution can be is divided into following types:

  1. Air pollution
  2. Water pollution
  3. Noise Pollution
  4. Marine pollution
  5. Soil Pollution
  6. Thermal pollution
  7. Nuclear hazards.

In this article we will discuss two major types of Environmental pollution, namely, air pollution and water pollution.

  1. Air Pollution

92 percent of people worldwide do not breathe clean air.

Air pollution costs the global economy $5 trillion every year in welfare costs.

Ground-level ozone pollution is expected to reduce staple crop yields by 26 percent by 2030.

Air pollution is defined as the contamination of the atmosphere by substances present at concentrations above their natural levels and capable of producing adverse effects to humans, other living organisms, and the ecosystem in general. These substances or air pollutants include gases, liquid droplets, and solid particles. They are classified according to the source of emission into two main groups: primary and secondary pollutants.


Primary Pollutants: Pollutants that are emitted directly from either natural events or from human activities are called primary pollutants. The natural events are dust storms; volcano etc and human activities can be emission from vehicles, industrial wastes. About 90% of global air pollution is constituted by five primary pollutants. These are

  1. Carbon mono-oxides (CO): Carbon monoxide (CO) is a colourless, odourless and toxic air pollutant, formed when the carbon doesn't completely burn in fuels such as gasoline, natural gas, oil, coal, and wood. It is usually produced by motor vehicles and industry. Carbon monoxide levels are typically highest during cold weather, because cold temperatures make combustion less complete and traps pollutants close to the ground. Carbon monoxide causes harmful health effects. The air pollutant when inhaled, combines with blood haemoglobin to form carboxy haemoglobin at a rate 210 times faster than the oxygen forms oxyhaemoglobin, impairing respiration. It reduces the amount of oxygen reaching the brain, heart and other body's organs and tissues. The high levels of carbon monoxide can even cause death.
  2. Hydrocarbons: A hydro-carbon is an organic compound consisting of only hydrogen and carbon atoms. Almost all hydrocarbons occur naturally in crude oils, like petroleum and natural gas, that are considered the driving force for modern civilisation. Some common hydrocarbons are Methane (CH4), Ethane (C2H6), Propane (C3H8), Butane (C4H10), Pentane (C5H12) and Hexane (C6H14). Hydrocarbons pose no risk on their own; however, they undergo a chemical reaction when exposed to sunlight or nitrogen oxides, contributing to the greenhouse effect and depletion of the ozone layer. They reduce the photosynthetic ability of plants, increase the risk of respiratory illness in human and animals and also increase cancer rates.

III.       Nitrogen oxides: Nitrogen oxides are produced naturally by lightning, and also by microbial processes in soils. However, they are majorly produced in fossil fuel combustion (gasoline and diesel engines) in urban areas, while agricultural practices such as the use of synthetic fertilizers are its main sources in rural areas. Nitrogen oxides have a variety of ill effects on the respiratory system.

  1. Particulate matter: Particulate matter, also known as particle pollution or PM, is a term used for extremely small solid particles and liquid droplets suspended in air. They can be made up of a variety of components including nitrates, sulphates, organic chemicals, metals, soil or dust particles. This pollution arises mainly from motor vehicles, wood burning and industry.
  2. Sulphur dioxide: Sulphur dioxide is highly reactive gas with very strong odour. Its main source is anthropogenic and is formed by fossil fuel combustion at power plants and other industrial facilities. Natural processes like volcanic eruptions, decomposition and combustion of organic matter, release sulphur gases. It contributes to the formation of particulate matter pollution. Sulphur dioxide irritates the lining of the nose, throat and lungs and may worsen existing respiratory illness especially asthma. It has also been found to exacerbate cardiovascular diseases.

Secondary Pollutants: A secondary pollutant is an air pollutant formed in the atmosphere as a result of the chemical or the physical interactions between the primary pollutants themselves or between the primary pollutants and other atmospheric components. Examples are ground-level ozone, acid rain and nutrient enrichment compounds.

  1. Ground-level ozone: Hydrocarbons and nitrogen oxides combine in the presence of sunlight and stagnant air to form Ozone. It is a colourless, highly irritating gas with sweet smell. Its exposure may cause premature mortality and major health issues. Ozone also affects vegetation, crop productivity and damages synthetic materials and textiles such as cotton and polyester.
  2. Acid rain: Acid rain is a form of precipitation with acidic components, such as sulfuric or nitric acid that fall to the ground from the atmosphere in wet or dry forms. This can include rain, snow, fog, hail or even dust that is acidic. The wind carries the acidic compounds into the air, and they later fall to the ground in either dry or wet form. On the ground, acid rain damages plants and trees and increases the acidity levels of soils and bodies of water, causing damage to ecosystems. Acid rain also causes decay to buildings and can irritate the eyes and airways.
  3. Water Pollution: Water pollution is the contamination of water bodies such as lakes, rivers, oceans and so on, with toxic substances or pollutants that get dissolved in them, lying suspended in the water or depositing on the bed. This degrades the quality of water. Surface water and groundwater are the two types of water resources that pollution affects. There are also two different ways in which pollution can occur.
  4. Point-source pollution: When pollution comes from a single location, such as a discharge pipe attached to a factory, it is known as point-source pollution. Other examples of point source pollution include an oil spill from a tanker, a discharge from factory chimney, or someone pouring oil from their car down a drain. When point-source pollution enters the environment, the place most affected is usually the area immediately around the source.
  5. Diffuse or Non-point source pollution: When pollution occurs, not from one single source, but from many different scattered sources, this is called nonpoint-source pollution. Much of the marine pollution is non-point and therefore comes from multiple sources.

Main sources of water pollution

  • Sewage
  • Nutrients
  • Waste water
  • Industrial waste
  • Chemical waste
  • Radioactive waste
  • Oil pollution
  • Plastics

The most polluting of them are the sewage and industrial waste discharged into the rivers. The facilities to treat waste water are not adequate in our country, and the major quantity is discharged into our water bodies. Due to this, pollutants enter groundwater, rivers, and other water bodies. The highly contaminated and disease carrying water eventually ends up in our households. Agricultural run-off, or the water from the fields that drains into rivers, is another major water pollutant as it contains fertilizers and pesticides. While discussing water pollution, it is pertinent to talk about a few important concepts like Dissolved Oxygen, Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). The water system produces as well as consumes oxygen. Running water, because of its churning, dissolves more oxygen than still water. Respiration by aquatic animals, decomposition, and various chemical reactions consume oxygen. Waste water from sewage treatment plants often contains organic materials that are decomposed by micro organisms, which use oxygen in the process. Oxygen is measured in its dissolved form as dissolved oxygen (DO). If more oxygen is consumed than is produced, dissolved oxygen levels decline and some sensitive animals may move away, weaken, or die. DO is an important parameter in assessing water quality because of its influence on the organisms living within a body of water. A dissolved oxygen level that is too high or too low can harm aquatic life and affect water quality. Water having DO content below 8.0 mg L-1 is considered as contaminated, while DO content below 4.0 mg L-1 is considered to be highly polluted. Water pollution by organic wastes is measured in terms of Biochemical Oxygen Demand (BOD). BOD is the amount of dissolved oxygen used by microorganisms in the biological process of metabolizing organic matter in water. BOD is directly proportional to the quantity of the organic matter in water bodies. Greater BOD implies the lower amount of dissolved oxygen available for higher animals such as fishes. One of the main reasons for treating wastewater prior to its discharge into a water resource is to lower its BOD-i.e., reduce its need of oxygen and thereby lessen its demand from the streams, lakes, rivers, or estuaries into which it is released. As BOD is limited to biodegradable matter only, it is not considered as a reliable method of measuring water pollution. A better way to measure water pollution is Chemical oxygen demand (COD). It is the amount of oxygen necessary to oxidise all of the organic carbon completely to CO2 and H2O. The COD test uses a strong chemical oxidising agent  (potassium dichromate or potassium permanganate) to chemically oxidise the organic material in the sample of wastewater under conditions of heat and strong acid.

The author is a Mumbai based journalist. Email  shreyabh. journo@ gmail.com

Views expressed are personal.

(Image Courtesy : Google)