Water Pollutants and their Sources & Control Of The Water Pollution

CLASSIFICATION OF AIR-POLLUTANTS

The air pollutants may be classified in different ways as follows:-

a) According to origin:-

1) Primary pollutants which are directly emitted in to the atmosphere and are found as such, e.g., CO, NO² So4, and hydrocarbons.

2) Secondary pollutants whicir are derived from the primary pollutants due to chemical or photo-chemical reactions in the atmosphere, e.g., Ozone, Peroxy-acyl nitrate (PAN), Photo-chemical smog, etc.

Biochemical Effects Of Some Important Air Pollutants

1) Oxide of Sulphur (SOx)
SOx comprises of SO² and So³ They are Colourless, heavy water soluble with pungent and irritating odour. SOx pollution is due to volcanic activity, combustion of fuels, Coal fired stations, transportation, Refineries, metallurgical operations, chemical plants and other naturai and human activitiesAn atmosphere oxidation of SO² in to SO³ by photolytic and Catalytic processes in presence of 0³, NOx, or hydrocarbons) giving rise to the formation of photochemical smog. In humid conditions of the atmosphere SO³, reacts with water vapours to produce droplets of H,SO, aerosols, give rise to the so called "Acid Rain".

So² +0³---> so³ +  O²
So³ + H²O ----> H²So4

2) Oxides of Nitrogen (NOx)  Characteristics :-
NOx mostly comprises of NO, NO² N²O. NO is colourless gas and is slightly soluble in water. NO² is reddish brown gas, somewhat wafer-soluble oxidizing agent, can react with water to form HNO³ which is a powerful oxidizing agent and capable of reacting with almost all metals and many organic compounds. NO² can travel into the respiratory system. It is also involved jn the formation of ozone in the atmosphere.

Biochemical effects :-

Oxidises cellular lipids, Forms bonds with haemoglobin and reduces the efficiency of oxygen transport. Disrupts some cellular, enzyme systems. Higher levels and prolonged exposires may cause pulmonary tibrosis, inflammation of lung lissues and may eventually lead to death. Causes nitric acid mediated effects some of which are similar to that of H²SO4 described above. NO can form addition compound with haemoglobin, if it enters the blood stream.

3) Carbon monoxide (CO) :-  Characteristics: Colourless, odourless, toxic gas, slightly water soluble but still is extremely dangerous because it has a greater affinity for haemoglobin than that of O²

Biochemical effects :-

It competitively inhibirs combination of O² and haemoglobin. It attacks haemoglobin and displaces 0² to form carboxyhaemoglobin, and thus reducing the oxygen carrying capacity of blood.

Biochemical effects :-
Oxidize cellular constitues PAN and ozone toxicity is produced via generation of free radicals.The free radicals produced may damage DNA and thus alter cellular genetic integrity to the toxic effects of ozone are manifested after inhalation and absorption in the Jungs causing accumulation of fluids the lungs (pulmonary edema), damaging lung capillaries and mortality if continued or high level exposures occur.Both O³ and photochemical smog cause irritation of the eyes and respiratory tract.The free radicals produced by O³ and other photochemical oxidants attack the sulphydryl groups on the enzymes and also inactivate enzymes like isocitric dehydrogenase, malic dehydrogenase and glucose-6-phosphate dehydrogenase, which are so much involved and essential for citric acid cycle and generation ofcellular energy O³ may also inhibit the activity of some enzymes involved-in-synthesis-of cellulose and lipids in plants Among the sulphur containing amino-acids, cysteine is strongly attacked by PAN Hydrocarbons.

Effects of Air Pollutants on Man and his Environment the :-

I) Damage to materials :- The materials that may be affected by air pollutants include metals; building materials, rubbers, elastomers, paper, textiles, leather, dyes, glass, enamels and surface contings. The types of possible damage to these materials by air pollutants include corrosion, abrasion, deposition, direct chemical attack and indirect chemical attack The intensity of damage depends upon factors such as mojsture, trmperature, sunlight, air movement and of course the nature and concentration of the pollutants.

II) Damage to Vegetation :-

Air pollutants, such as sulphur dioxide, HF, particulate fuorides, smog. oxidants ozone ethylene (from automobiles), NOx, chlorine and herbicide and weedicide sprays exert toxic effects on vegetation. The damage usually manifests in the form of visual injury such as chlorotic marking, banding, silvering or bronzing of the underside of the leaf. Retardation planit growth may also ocur in some cases. The extent of damage to a plant depends upon the nature and concentration of the pollutant, time of exposure, soil and plant condition, stage of growth, relvative humidity and ectent of sunlight.

4) Darkening of sky and reduction in visibility :-

Sky darkening may be caused by heavy Smoke and fog or by dust storms.The reduction in visibility may be due to smoke , fog and industrial fumes which contain particulates in the size range of 0.4 to 0.9u m that scatter light . The intensity of these effects depends upon the particle size , the angle of the sun , aerosol density , thickness of the affected air mass and meteorological factors such as inversion height , wind speed and humidity.