Global Warming
✅Global warming occurs when carbon dioxide (CO2) and other air pollutants collect in the atmosphere and absorb sunlight and solar radiation that have bounced off the earth’s surface.
✅Normally this radiation would escape into space, but these pollutants, which can last for years to centuries in the atmosphere, trap the heat and cause the planet to get hotter.
✅These heat-trapping pollutants—specifically carbon dioxide, methane, nitrous oxide, water vapor, and synthetic fluorinated gases—are known as greenhouse gases, and their impact is called the greenhouse effect.
Water Pollution
✅Water pollution is the addition/presence of undesirable substances to/in water such as organic, inorganic, biological, radiological, heat, which degrades the quality of water so that it becomes unfit for use’.
✅Natural sources of pollution of water are soil erosion, leaching of minerals from rocks (due to natural solubility and solubility triggered by acid rain) and decaying of organic matter.
Point and non-point sources of pollution
✅When pollutants are discharged from a specific location such as a drain pipe carrying industrial effluents discharged directly into a water body it represents point source pollution.
✅In contrast, non-point sources include discharge of pollutants from diffused sources or from a larger area such as runoff from agricultural fields, grazing lands, construction sites, abandoned mines and pits, etc.
Causes of Water Pollution
Sewage Water
✅Sewage water includes discharges from houses and other establishments.
✅The sewage contains human and animal excreta, food residues, cleaning agents, detergents, etc.
✅Domestic and hospital sewage contain many undesirable pathogenic microorganisms.
Dissolved Oxygen (DO)
✅Presence of organic and inorganic wastes in water decreases the dissolved oxygen content of the water.
✅Water having DO content below 8.0 mg/L may be considered as contaminated.
✅Water having DO content below. 4.0 mg/L is considered to be highly polluted.
✅DO content of water is important for the survival of aquatic organisms.
✅A number of factors like surface turbulence, photosynthetic activity, O2 consumption by organisms and decomposition of organic matter are the factors which determine the amount of DO present in water.
✅The higher amounts of waste increase the rates of decomposition and O2 consumption thereby decreases the DO content of water.
Biological Oxygen Demand (BOD)
✅Water pollution by organic wastes is measured in terms of Biochemical Oxygen Demand (BOD).
✅BOD is the amount of dissolved oxygen needed by bacteria in decomposing the organic wastes present in water. It is expressed in milligrams of oxygen per litre of water.
✅The higher value of BOD indicates low DO content of water.
✅Since BOD is limited to biodegradable materials, it is not a reliable method of measuring water pollution.
Reasons of water pollution
Industrial Wastes
✅Discharge of wastewater from industries like petroleum, paper manufacturing, metal extraction and processing, chemical manufacturing, etc., that often contain toxic substances, notably, heavy metals (defined as elements with density > 5 g/cm3 such as mercury, cadmium, copper, lead, arsenic) and a variety of organic compounds.
Agricultural sources
✅Agricultural runoff contains dissolved salts such as nitrates, phosphates, ammonia and other nutrients, and toxic metal ions and organic compounds.
✅Fertilizers contain major plant nutrients such as nitrogen, phosphorus and potassium.
✅Excess fertilisers may reach the groundwater by leaching or may be mixed with surface water.
✅Pesticides include insecticides, fungicides, herbicides, etc. They contain a wide range of chemicals such as chlorinated hydrocarbons (CHCs. E.g. DDT, Endosulfan etc.), organophosphates, metallic salts, carbonates, etc.
✅Many of the pesticides are non-degradable, and their residues have a long life.
✅Wastes from poultry farms, piggeries and slaughterhouses etc. reach the water though runoff.
Thermal and Radiation Pollution
✅Power plants – thermal and nuclear, chemical and other industries use a lot of water for cooling purposes, and the used hot water is discharged into rivers, streams or oceans.
✅Discharge of hot water may increase the temperature of the receiving water by 10 to 15 °C above the ambient water temperature. This is thermal pollution.
✅Increase in water temperature decreases dissolved oxygen in the water.
✅Unlike terrestrial organisms, aquatic organisms are adapted to a uniform steady temperature of the environment. A sudden rise in temperature kills fishes and other aquatic animals.
✅One of the best methods of reducing thermal pollution is to store the hot water in cooling ponds, allow the water to cool before releasing into any receiving water body
✅Nuclear accidents near water bodies or during natural calamities like tsunami and earthquakes pose the risk of radiation leakage (radiation exposure) into water bodies. E.g. Fukushima Daiichi nuclear disaster.
✅Radiation exposure causes mutations in the DNA of marine organisms. If those mutations are not repaired, the cell may turn cancerous.
Smog
✅Smog is a harmful mixture of fog, dust and air pollutants such as nitrogen oxides, volatile organic compounds, etc. which combine with sunlight to form a dense layer of ground-level ozone.
✅Ozone present high in the atmosphere is good, but when nearer to the ground, it can cause irritating health effects.
Smog can be caused by:
✅Large amounts of coal-burning in an area
✅Slash-and-burning of crops (a major source in Delhi)
✅Smog-forming pollutants generate from automobile exhausts, power plants, fireworks, even paint, hairspray, charcoal starter fluid, and plastic popcorn packaging.
