Environmental population may be regarded as the addition of extraneous (foreign) materials to air,
Water or land which adversely affects the quality of life. Pollution may be caused by physical, chemical or biological process.

The term Pollutant refers to a substance which increases in quantity due to human activity and adversely affects the environment (e.g. carbon monoxide, sulfur dioxide, lead). A substance which is not present in nature but released during human activity is the contaminant (e.g. methyl isocyanate, DDT, parathion). A contaminant however is regarded as a pollution may be considered in different ways- industrial pollution; agricultural pollution; pollution due to gaseous wastes, liquid wastes and solid wastes.

The major components of air include nitrogen (78.1%), oxygen (20.93% and carbon dioxide (0.03%), along with water vapor and suspended particles. The rapid growth of industries coupled with changing lifestyles of man (urbanization, smoking, use of motor vehicles etc.) largely contribute to air pollution. The major chemical constituents of air pollution are sulfur dioxide, oxides of carbon, (CO2 and co), oxides of nitrogen, hydrocarbons and particulates. The biochemical effects of air pollution are described.

Sulfur dioxide (SO2) is the most dangerous pollutant gas to man, industrial activities such as burning of coal and oil emit large quantities of SO2.

Sulfur dioxide pollution primarily affects respiratory system in man. Irritation of the respiratory tract and increasing always resistance are observed. Lung tissue may get damaged due to acidic PH. Further, dispalmityl lecithin, the phospholipid acting as the lung surfactant, gets affected. Continuous exposure to SO2 (>1 ppm) for several days causes bronchitis and in some individuals lung cancer, atmospheric SO2 when dissolved in rain water becomes very acidic (acid rain) damaging soil, plants and vegetables. Exposure of plants to so2 destroys leaves.

Carbon monoxide (CO) is mostly produced by incomplete combustion of fuel or carbon containing compounds. Automobiles, aircrafts, rail engines and burning of coal in factories contribute to CO pollution.

Carbon monoxide combines with hemoglobin to form carboxyhaemoglobin . This causes a drastic reduction in the supply of O2 to tissue. At a CO concentration around 1 ppm, impairment in mental performance and visual perception take place. With a further increase in CO level, headache, dizziness and loss of consciousness occur. Death may be inevitable in persons exposed to above 750 ppm of CO.

Carbon dioxide (CO2), constituting only a fraction a (0.03%) of the atmospheric gases, plays a significant role in controlling the climate. This is done by trapping the heat radiation from the earth's surface. Without the presence of CO2, the earth would be as cold as moon.
Carbondioxide is often referred to as greenhouse gas. The term greenhouse effect refers to an elevation in CO2 near earth's surface that traps sunlight and increases atmospheric temperature. Deforestation, burning of coal, oils etc., elevate atmospheric CO2 resulting in greenhouse effect. Hence the global propaganda for increased plantation of trees
Fortunately, marginal variations in atmospheric CO2 are tolerated by the cells. The body gets adapted to prolonged exposure to higher concentrations of CO2 (even upto 1% ) with minor alterations In electrolyte balance.

Nitrogen dioxide (NO2) like carbon monoxide (CO), Comines with hemoglobin and reduces the supply of O2 to the tissues. NO2 is more harmful to human health than CO. It is fortunate that the human health atmospheric concentration of NO2 is relatively lower.

Nitrogen dioxide (in the form of HNO3) along with O2 ( as H2SO4) contribute to acid rain.

Many hydrocarbons polluting the environment affect human life. The aromatic hydrocarbons cause irritation to injuries.

The solid dust particles suspended in the atmosphere constitute postulates. The sources if particulates are grinding, spraying, erosion, smoking etc.

The articulates have ill-effects on humans. These include interference in respiratory function (coughing, sneezing) and toxicity caused by the absorption particulate chemicals. Further, the dust particles carry microorganisms and other infective agents to spread diseases.

Ozone is formed from atmospheric oxygen during high energy radiations of electrical discharges. This ozone forms a layer above the earth's surface (15-35 km). It absorbs harmful ultraviolet radiations of sum each would otherwise cause skin diseases and mutations, besides increasing the temperature of earth.

In recent years, a decrease in the ozone layer is observed due to chemical pollution in the air nitrogen oxides ( related from engines of aero planes) ad chlorofluoro carbons ( used in refrigerators and air conditioners) deplete the ozone layer.

Water is the most predominant constituent of living matter. The very existence of life is unimaginable without water.

As such, pure water does not exist in nature. The available water contains dissolved gases, minerals and some suspended particles. Pollution of water occurs due to waste disposal from industries, agriculture and municipalities, the pollutants may be organic, inorganic, sediments radioactive, thermal etc.., in nature.

The organic pollution include agents carrying water borne disease, oxygen demanding wastes and organic chemicals.

Several pathogenic organisms find their entry into water and cause diseases. The water borne disease includes typhoid, paratyphoid, cholera, ameoebiasis, giardiasis and infectious hepatitis. This disease can be prevented by disinfection techniques employed for the treatment of water.

Sewage and wastes from industries and agriculture provide good nutrients for algae. As the algae grow utilizing the wastes, oxygen depletion occurs. This phenomenon of water deoxygenation is technically referred to as eutrophication. As a consequence of eutrophication, fish and other aquatic animals die(due to lack of 02) , causing foul smell.

The organic chemical pollutants of water include pesticides and several synthetic compounds (detergents, plaints, plastics, pharmaceuticals, food additives etc.)

Pesticides is a broad term used for insecticides, herbicides, fungicides and rodenticides. Based on their structure, pesticides are classified.
(a) Chlorinated hydrocarbons: e.g. aldrin, dieldrin, endrin, dichlorodiphenyltrichloroethane (DDT).
(b) Organophosphates: e.g. Malathion, diazionon.
(c) Ccarbamates e.g. baygon, carbaryl (sevin)
(d) Ccholorophenoxy e.g. 2,4-dichlorophenoxy acetic acid.

The use of pesticides has helped in controlling certain diseases (malaria, typhus), besides booting food production. However, pesticides pollute water and cause several health complications to humans, besides damaging aquatic life.

DICHLORO-DIPHENYL TRICHLOROETHANE (DDT) is a widely used pesticide to control cotton and peanut pests, besides malaria. However, continuous use of DDT leads to its accumulation in food causing ill effect (hence banned in some countries like USA).
DDT, being fat soluble, accumulates in the adipose tissue and is not excreted. Thus , its concentration in the body goes on increasing. DDT causes nervous irritability, muscle twitching and convulsions.

Aldrin and dialdrin are also fat soluble and their effects on humans are comparable with that of DDT.

Organophosphates and carbonates are powerful neurotoxic agents. They prevent the transmission of nerve impulse by inhibiting the enzyme choline esterase.

Heavy metals (lead, mercury, cadmium, aluminum, arsenic etc.) are the most dangerous among the inorganic pollutants.

Lead is the most common inorganic pollutant found in water, air, food and soils. The sources of lead pollution include petrol, gasoline, paints, cigarettes, news papers, lead pipes and Xerox copies. The plasma concentration of >25 mg/dl in adults and > 10 mg/dl in children results in toxic manifestations.

The principal target of lead toxicity is central nervous system. In the growing children, Pb causes learning disabilities, behavioral changes (hyper recitability) and mental retardation. In adults, confusion, irritability, abdominal colic and severe anemia are associates with lead toxicity.
Lead inhibits several enzymes, particularly, δ-aminolevulinate (ALA) syntheses, ALA dehydrates and ferrochelatase of heme synthesis. This results in severe anemia. There has been an increasing awareness world over on the toxic manifestations of lead. This has lead to the supply of unleaded petrol in many countries.

Mercury is a common industrial (plastic, paints, electrical apparatus, (fungicides) pollutant. Acute mercuric poisoning cause's gastritis, vomiting and pulmonary edema. Chronic manifestations of Hg include emotional changes, loss of memory and other neuropsychiatric disturbances. In additions, deposition of mercuric salts may cause renal failure.

Organic mercuric poising is commonly referred to as minimata disease( as it first occurred in minamata, Japan in 1953-60 by consuming fish containing methyl mercury, as industrial pollutant).

The outbreak of cadmium toxicity was reported in Japan in the form of itai itai or ouch disease.
Cadmium poisoning causes fragile bones, anemia bone marrow disorders and kidney damage. Biochemically, cadmium replaces zinc and adversely influences several metabolic reactions.

The sources of aluminum include cooking vessels, building material, food additives and cosmetics. Aluminum toxicity is associated with Alzheimer's disease, anemia and osteomalacia.

Arsenic, commonly found in many insecticides and fungicides is toxic to the body. Arsenic binds with-SH groups of several enzymes and inhibits biochemical reactions example pyruvate dehydrogenase. Further arsenic causes coagulation of proteins and blockage of ATM generation.

The unwanted sounds in noise which is a major urban environmental pollutant. Man can tolerate noise up to 100 decibels( speaking-60 decibels; telephone bell 70 decibels; motor cycle 110 decibels; rocket 170 decibels) .A noise above 150 decibels is uncomfortable.

The affects of noise pollution include headache, increased blood pressure, irritability, neuromuscular tension, confusion, disturbed vision and digestion, depression and loss of hearing.

About Author / Additional Info: