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♤ The effects of radioactive pollutants depend upon
i. half-life
ii. energy releasing capacity
iii. rate of diffusion and
iv. rate of deposition of the pollutant.
v. Various environmental factors such as wind, temperature, rainfall also influence their effects.
Period of Radioactivity
♤ Each radioactive nuclide has a constant decay rate. Half-life is the time needed for half of its atoms to decay. Half-life of a radio nuclide refers to its period of radioactivity. The half-life may vary from a fraction of a second to thousands of years. The radio nuclides with long half-time are the chief source of environmental radioactive pollution.
♤ Radiations are of two types with regard to the mode of their action on cells.
1. Non-ionising radiations:
♤ They include short-wave radiations such as ultraviolet rays, which forms a part of solar radiation.
♤ They have low penetrating power and affect the cells and molecules which absorb them.
♤ They damage eyes which may be caused by reflections from coastal sand, snow (snow blindness) directly looking towards sun during eclipse.
♤ They injure the cells of skin and blood capillaries producing blisters and reddening called sunburns.
2. Ionising radiations.
♤ They include X-rays, cosmic rays and atomic radiations (radiations emitted by radioactive elements).
♤ Ionising radiations have high penetration power and cause breakage of macro molecules.
♤ The molecular damage may produce short range (immediate) or long range (delayed) effects.
i. Short range effects include burns, impaired metabolism, dead tissues and death of the organisms.
ii. Long range effects are mutations increased incidence of tumors and cancer, shortening of life-span and developmental changes.
iii. The mutated gene can persist in living organisms and may affect their progeny.
♤ The actively dividing cells such as Embryo, foetus, cells of skin, intestinal lining, bone marrow and gamete forming cells are more sensitive to radiations.
♤ Some species of animals and plants preferentially accumulate specific radioactive materials. For example, oysters deposit 65Zn, fish accumulate 55Fe, marine animals selectively deposit 90Sr.