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Sunday, February 5, 2012

Biological hazards due to ionizing and non-ionizing radiations

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High doses of radiations may produce serious consequences in the environment that lead to dangerously hazardous conditions. By radiation hazards in the present context we mean the biological effects of radiations, radionuclides and radioactive fallout. As we know that radiations have been classified into ionizing and Non-ionizing categories, the biological impacts of these radiations are being mentioned here separately.


A. Biological Hazards due to Ionizing Radiations


Various ionizing radiations are electrons, positrons, alpha particles, Gamma rays and X-rays. Some nuclides may affect externally and may cause superficial injury. On the other hand there are nuclides like Beta particles or X-rays that penetrate deeply and cause seriously hazardous effects on skin and tissues. One or more atomic nuclei, identifiable as being of the same element by having the same number of protons and same energy content, are called as nuclides. This term was coined during the mid-20th century. The Biological effects of ionising radiations are mentioned below.


(i). Accumulation in the Critical body organs: These radiations accumulate in the critical organs of our bodies like liver, thyroid gland, spleen, lungs and bone marrow. For example bone and adjacent bone marrow are body organs vulnerable to plutonium, radium, and strontium. Radio Iodine collects in the thyroid gland. 


(ii). Hazards due to Nuclear Fall out: The deposition of airborne radio active contaminants on earth due to nuclear testing, explosions, and war bombing is called as nuclear fall out. It allows the radio active isotopes to join food chains through different media and to accumulate in the vital parts of living bodies.Strontium-90 is the hazardous nuclide which accumulates in high concentration in the skeleton of higher animals for many years. These radiations cause serious injuries and cancers, Leukaemia and the like diseases.


(iii). Hazards due to Long Lived Radioisotopes: The long lived radioisotopes cause most serious hazards in human bodies due to the fact that they persist there for very long periods. Such types of radioisotopes like caesium-137, strontium-90, and plutonium-239, if contained in the radioactive fall out are sure to enter the bodies of humans, animals (both fresh water and marine) and plants through the natural food chains. The fall out of Iodin-131 can be easily detected out of the food chains. This radioisotope emits beta and gamma rays and it can cause thyroid cancer and various types of metabolic disturbances especially in children if absorbed in high doses.


(iv). Major Radiation Injuries in Human Beings: In Human Beings injuries caused due to radioisotopes can be divided into two broad categories – Somatic and Genetic. 


Somatic injuries pertain to the injuries in human bodies, whereas Genetic injuries are Genetic Effects that pertain to the injuries, alterations, translocations, dislocations and mutations of genetic materials like chromosomes, genes and DNAs. These may also include death of cells, alterations in the pattern of cell division, and damage to genes or the Genetic Mutation. 


Mutation is the sudden, permanent and heritable change in the body of an organism due to the exposure of some radiation or effects of some chemicals. Genetic mutation occurs when the form or structure of a gene is changed permanently to produce genetic defects. A disease known as the ‘sickle- cell’ anaemia is also caused by genetic mutation. The Genetic Mutation due to radiations is the nuclear event in which nucleotide sequence of Deoxyribose Nucleic Acid is altered and a new sequence is passed on to the off springs to produce different types of defects in the offspring. 


In fact, Mutation is the genetic event that causes sudden heritable changes in individuals. During 19th century Rutherford had proposed that one element can be transmutated into some other element. The word transmutation relates to a complete transformation of a substance or an element. In the present context radiological mutations can cause a complete transformation of an element thereby making it more harmful to life.


Somatic Effects of exposure to radiations usually occur for shorter periods like the inhibition of cell division. But there are some somatic effects of exposure to radiations that occur years or decades after the exposure of radiation. The radiation induced cancer comes under this category. Still, there are stochastic and non-stochastic types of somatic effects of radiations. The stochastic effects are those for which no threshold dose is known to exist where as the non-stochastic effects are those which occur only in response to the exposure to some considerable dose of radiation, like skin cancer.


Some major examples of the effects of radiations on body organs are- skin injuries, deaths of blood forming cells of the bone marrow, ulcerations of gastrointestinal tract, sterility in men and women, opacity or damage to eye lens, damage to brain and sensory organs, radiation sickness, alterations in growth and development of embryos, incidence of different types of cancers, and shortening of life pawn etc.


B. Biological Hazards due to Non- Ionizing Radiations


The effects of non-ionizing radiations are summarized below-


(i). Effects of visible and Ultra Violet light: The Ultra Violet light contained in the sun light is more intense and hazardous. These rays are highly toxic below the wavelength of 2200 angstroms. The UV rays of these wavelengths are highly absorbed by nucleic acids of cells that are the main constituents of the genetic material. These rays are mutagenic and due to this characteristic these may cause skin cancer on exposure. These rays are also emitted out from mercury vapour, xenon, and hydrogen arc lamps.


(ii). Photodynamic Actions: Light sensitivity causes a number of diseases in animals and also in human beings. Intense light may cause blisters on parts of body exposed to sunlight. This disease is called as hydroa. This disease is caused due to the presence of a light sensitive compound called as porphyrin which remains present in the skin. A number of chemical substances that are synthesized in the skin make cells light- sensitive. These chemicals are called as photodynamic substances and the adverse action of light due to these substances is called as Photodynamic actions. 


Some important photodynamic substances are Rose Bengal, hematoporphyrin, and phylloerythrin. These photodynamic pigments cause several diseases in many of our domestic animals when they ingest plants containing these toxic and fluorescent substances. A disease known as phagopyrism is produced in animals when they eat buck weeds. The disease Xeroderma pigmentosum, which is somewhat a heritable disease, is caused by lesions of nucleic acids produced due to the action of UVlight on exposed skin. The cells that lack nucleic acid essential for repairing nucleic acid lesions (a genetic defect), develop tumours that finally leads to death at an early age.


(iii). Effect on Development: Light has profound effects on growth and spatial orientation of plants. On the other hand the presence of illumination modifies cellular activities in plants. Here is an important example in support of this fact. Some species of blue green algae carry out photosynthesis in the presence of light but the process of cell division stops in that condition. The Chromatophores found in the skins of Chameleons, Frogs and Octopuses can change colour under the influence of light. 


(iv). Effects on Eyes: The wavelength of light which causes sun burn can cause inflammation of the cornea of human eye also. The Ultra violet radiations cause cataracts of the eye lens. This condition originates when the protein of which the eye lens is made up of, is denatured due to the exposure to UV rays. Visual pigments of eye are bleached by large doses of visual and infra red light. This accident is called as sun blindness and it is an irreversible process. Abnormal sensitivity to light causes Photophobia in human beings. It is a condition when reflex movement of the iris and the reflex dilation of the blood vessels of conjunctiva lead to eye-pain. Workers who are exposed to atomic flashes need to wear protective glasses in order to escape conditions like these.


The exposure to radiations may cause permanent damage to life and property. A nuclear reactor accident took place in 1896 in Chernobyl, Ukraine, which killed at least 31 people and forced more than 200, 000 people to vacate and relocate. A number of chemical and radiological accidents, and also a large number of marine accidents have been reported through history that has proved serious hazards from time to time. But, we are not concerned with the discussion about those hazardous accidents as they are covered under disasters.


Key Words :Hazard,ionizing, exposure, radiation, Chernobyl, accidents

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