Pollution is defined as a deviation from the natural composition of a part of the environment, resulting in adverse effects on life. Pollution is usually brought about by the addition to the environment of waste products of human activity. When the waste products are not efficiently assimilated, decomposed or otherwise removed by the natural, biological and physical processes of the biosphere, adverse effects may result as the pollutants accumulate or are converted to more toxic substances.
Primary pollutants are defined as those substances emitted directly from an identifiable source.
Secondary pollutants are substances derived from primary pollutants by chemical reactions. Pollutants need not be material substances. Noise can be a pollutant and even electromagnetic waves can be pollutants. Most of today’s problems are due to man as a pollution source. There is no way for nature to decompose many man made materials and return their elements to the cycle of nature. Such substances will just remain and will cause whatever harmful effects they can until they are somehow dispersed or diluted so that their action is no longer noticeable.
With the increase in population of man, arose the problem of balanced and clean environment. In large industrialized countries with large cities the problem of disposal of sewage and industrial wastes has become severe and polluted the air, water and soil.
Physical environment can be divided into 3 parts.
1. Lithosphere: In this environment are included rocks, sand etc. Plants take essential mineral elements from lithosphere.
2. Hydrosphere : In this environment water is present on lithosphere. It includes rivers, streams, lakes and sea. Water is essential for all living organisms.
3. Atmosphere : The lithosphere and hydrosphere are surrounded upto 200 miles by atmosphere. There are many gases e.g., Oxygen, Carbon dioxide and Nitrogen in a definite ratio and proportion in the atmosphere. The zone of atmosphere in which living organisms survive is upto 12 miles (20 km) above the lithosphere and hydrosphere.
Different Kinds of Pollutants :
Pollutants are residues of substances made by us, used by us and thrown away by us as wastes which pollute the environment in one or the other manner. Pollutants can be divided into following categories.
1. Biodegradable pollutants : If so much of the organic waste drain out of residential buildings which are easily degraded completely by microorganisms it becomes useful for the ecosystem. However if these pollutants enter the environment in such large quantities that complete degradation of all cannot take place then these pollute the biosphere.
2. Non-biodegradable pollutants : Many of such pollutants are usually not present in the environment e.g., Aluminium, Iron, Mercury salts, some phenolic compounds and DOT which are either not at all degraded or degradation is partial, pollute the environment. These substances are harmful even in low concentration and the harm increases with their concentration.
Different types of Pollution:
1. Air Pollution :
Due to the activity of living organisms different gases in the atmosphere are found in a definite ratio and proportion. There is cycling of the gases between the living organisms and atmosphere. It is due to organisms that oxygen and carbon dioxide are found in a balanced state in the atmosphere. Carbon-dioxide is constantly released into the atmosphere by respiration of living organisms and O2 is constantly taken up from atmosphere by the living organisms for respiration.
Green plants absorb CO2 for photosynthesis and release O2 as a byproduct of photosynthesis due to which balance of CO2 and O2 is maintained in the atmosphere. But man disturbs this balance in different ‘ways, by removal of plants and by development of various industrial establishments CO 2, nitrogen-oxides, chlorides and sulphur dioxide, silicon tetrafluoride and carbon particles enter the atmosphere. SO2 released from chimneys is an important pollutant.
Due to SO2 margin of leaf and portion of lamina in between vascular bundle dries up. In higher concentration, SO2 may cause death of cells. In addition SO2 absorbs water vapour from atmosphere thus forming sulphuric acid which is harmful to tissues. SO2 is harmful to eyes, throat and in high concentration enters our lungs. It is also harmful for stones, steel and paper etc,, and help in disintegration of the same.
CO2 is rising into the atmosphere slowly as a result of large scale burning of fossil fuels. CO2 allows solar radiations to pass through and strike earth’s surface but when it reradiates in the form of infra-red radiations, CO2 absorbs them and leads to warming up. Thus CO2 addition in atmosphere results into rise of temperature. This increasing temperature is likely to cause more melting of snow on poles and mountain tops that would flood most of the coastal and other land surfaces.
Another gaseous discharge due to the burning of coal in factories is fluorine (in the form of HF). This causes reduction in chlorophyll, and size of leaves and through plants animals are effected (swollen knee bones, tooth decay and general bad health).
Aerosols (particles in air less than 1 u) and dust (solid particles in air more than 1 u) or mist (liquids), cement dust, reduces photosynthesis and also leaf size thus reducing overall primary productivity. Many biological materials in the air, bacteria, fungal spores, pollen grains quite often cause allergy and bronchitis in man.
Jets, aeroplanes, motor buses, trucks, scooters, tractors and other vehicles where petrol, mobile oil, diesel and kerosene oil are used as source of energy, release smoke causing pollution. Ozone present in the atmosphere is harmful for clothes and rubber goods. Different gases released from manholes decrease the growth and productivity of plants and also cause abscission of leaves and fruits.
2. Water Pollution :
Water is essential for all living organisms. All plants absorb essential elements in dissolved form and water is the solvent. Translocation of food also takes place in solution form where water again is the solvent. In water are dissolved many mineral elements, organic substances and gases. If the concentration of already present substances increases or some other harmful substances usually not found in water gets dissolved in water it gets polluted.
If pathogenic bacteria, viruses and effluents from different industries (sodium cyanide, barium salts from heat treatment furnaces, cadmium, chromium, copper, manganese, nickel, zinc salts from electroplating units, mobile oil from vehicle repair shops), weedicides, pesticides and chemical fertilizers enter the water it become polluted.
Due to nitrogenous fertilizers nitrates go to drinking water and become toxic when their concentration exceeds 90 ppm, cause diarrhoea and cyanosis (blue jaundice) in infants. The digestive system converts these nitrates and nitrites into nitrisoamines and nitrosocompounds which are suspected as agents of stomach cancer in man. Recently the levels of fluorides in the drinking water has considerably increased in different parts of India, causing fluorosis — an incurable bone disease (mottling of teeth enamel, stiffness and pain in joints, bones and spinal deformities).
Cereal crops like jowar, maize and pearl millet grown on alkaline soil absorb higher amounts of fluoride and thereby contribute to spread of the disease. On the other hand traces of fluorides in the diet are essential to reduce incidence of dental decay specially among children below eight years. A high concentration (100-200 ppm) on the other hand retards growth and reproduction.