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Water pollution may be defined as the addition of any substance (pollutant) to water resource which may change the physical and chemical characteristics in any way which may interfere with its use for legitimate purposes.
Causes for Water Pollution
The water pollution may be caused by the wastewater discharges either from point source or non-point sources. Point sources include effluent outfalls from industries, waste treatment plants etc., that discharge effluents of varying quality directly into the water resources. Non-point sources include contaminants that enter the water resources such as human waste washed off from open defecated area via pesticide runoff from farm fields as well as runoff of automotive fluids and other chemicals from roads, parking lots, and other surfaces.
Classification of Water Pollutants
The Pollutants can be broadly classified into organic, inorganic and radio active substance.
Organic pollutants are oxygen depleting wastes which include the following domestic and industrial bio-degradable organic wastes;
- Infectious disease may cause wastes containing pathogenic micro-organisms such as Bacteria & Virus.
- Synthetic organic pollutants, which are the man-made chemicals such as detergents, pesticide, food additives, pharmaceuticals, insecticides, paints, synthetic fibers, Synthetic organic pollutants, which are the man-made chemicals such as pesticide, detergents, food additives, pharmaceuticals, insecticides, synthetic fibres, solvents, plasticizers, plastics and other industrial chemicals.paints solvents, plasticizers and other industrial chemicals.
- Organic nutrients such as nitrate and phosphates carried by agricultural run-off from agricultural lands.
- Oil pollution in water may take place due to oil spills from cargo tankers on the seas, losses during off shore exploration and production of oil, accidental fires in ships and oil tankers, accidental or intentional oil slicks.
Inorganic pollutants comprise of mineral acids, inorganic salts, finely divided metals or metal compounds, trace elements, heavy metals, sulfates, nitrates, organo metallic compounds and complexes of metals with organics include toxic chromium, lead, mercury and chloride.
The radioactive water pollutants may originate from:
- Mining and processing of ores, e.g., Uranium tailings.
- Increasing use of radio-active isotopes in research, agricultural and medical applications.
- Nuclear power plants and nuclear reactors.
- Testing and use of nuclear weaponry.
Radio active pollutants are known as carcinogenic.
Effects of Water Pollution
Effects on human health
- The toxic substances render the water unfit for the downstream use, · Contamination of drinking water resulting in the transmission of water-borne diseases such as cholera, typhoid, diarrhea, dysentery, polio and infectious hepatitis in humans.
- Nitrates restrict the amount of oxygen reaching the brain causing blue-baby syndrome (mathemaglobanemia) in infants Nitrogen also linked to digestive tract cancer and affect lungs.
- Most of synthetic organic chemicals are potentially toxic to plants, animals and humans and known as carcinogen.
- Oil spills can cause skin irritations and rashes.
Effect on ecosystems
- Water pollution effects the depletion of dissolved oxygen (DO) in surface water bodies, thus affecting the fish and other aquatic life,
- Invasive species can compete native species and reduce biodiversity. Invasive plants can contribute debris and bio molecules (allelopathy) that can alter soil and chemical compositions of an environment, often reducing native species competitiveness
- Pollution disrupts the natural food chain. Toxic pollutants such as lead, chromium, mercury, cadmium etc., are consumed by tiny animals. Later, these animals are consumed by fish and the food chain continues to be disrupted at all higher levels. Eventually, humans are affected by this process as well.
- Organic nutrients such as nitrates and phosphates may stimulate the growth of algae and other aquatic weeds in the receiving water body. This unwildly plant-growth results in the degradation of the water quality, intended for drinking and other uses by causing odour, taste etc.
- The increased water temperature due to discharge of effluent from thermal power stations causes the heat stress or death of sensitive species; and enhanced microorganism respiration.
Water Pollution Control
The important parameters to measure the magnitude of water pollution are temperature, pH.Total suspended solids (TSS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), Toxic substances and Faecal coliforms.
Water pollution control means the control of effluents into water or soil. Without pollution controls the undesirable wastewater from domestic, industrial and agricultural activities, mining, and other sources will accumulate and degrade the aquatic ecosystem. In the hierarchy of controls, pollution prevention and waste minimization are more desirable than pollution control.
Water pollution is controlled by treatment of wastewater. The methods used for the treatment of wastewater depend upon the characteristics of the particular wastewater ( sewage treatment), contaminants present and final mode of disposal.