Introduction
Radiation is best described as energy which is passing through space or a medium (Khan 2010). There are two categories of radiation; non-ionizing and ionizing radiation. Non-ionizing radiation is important in the life systems and can be exemplified by heat, visible light, or radio waves; however, overexposure may be toxic. Ionizing radiation is the one commonly implied whenever the term radiation is used. Ionizing radiation has enough energy to change atoms which may result in changes in cell molecules leading to alterations within the cells and thus cell damage. Radiation is measured by the unit, rem, which is ‘roentgen equivalent in man’ (Khan, 2010).
Both types of radiation possess the potential to harm living organisms, though ionizing radiation has the potential to cause more damage per unit than non-ionizing. This is because ionizing radiation even at low doses can cause genetic damage. However, non-ionizing radiation is dangerous in proportion to the levels of thermal energy it possesses, and is harmless when there is no significant change in temperature (MIT, 2011).
The effects of radiation (ionizing) result in alterations of the genetic composition of cells which is harmful. Ionizing radiations include electromagnetic radiation (gamma, and x-rays), and particulate radiation (beta, alpha, neurons). Ionizing radiation can also be transmitted by the nuclei of heavy ions like nitrogen, argon, carbon. Radiation can be applied usefully in various occupational settings but must be controlled to avoid causing harm to workers. Examples of its applications are: smoke detectors; thickness control in the paper industry; sterilizing; radioactive dating; radioactive tracing; metal welding; and cancer treatment (OEF, 2011). This paper will explore in detail the effects of radiation on biological and genetic systems.
Effects of Radiation on Genetic Material (DNA)
DNA (deoxyribose nucleic acid) is one of the most crucial molecules in a living organism. DNA contains a double strand of chromosomes and it is on these strands that genetic information s encoded. For a particular molecule to be built, only a small section of the DNA is read. Each cell in an organism is engaged in reading sections of its DNA to form new molecules (RER, 2011). Ionizations which occur as a result of radiation can act either act directly on the cells or indirectly on the molecules of water, resulting in water radicals (RERF, 2011). These radicals usually react with water to break chemical bonds or the oxidation of molecules (oxygen addition). A DNA molecules contain double strands and when damage occurs to one strand, the other strand contributes to it repair. When the damage occurs on the double strands, it is much more complicated to repair it. These can result in cell death, chromosomal aberrations, and mutations (RERF, 2011). This is because when cells are exposed to radiation, cell death or mutagenesis may occur. Different types of abrasions occur on the DNA strands. The strands may be ruptured, bases may be changed, sugars may be destroyed, or dimer formation and crosslinks may be formed.
The main type of DNA damage occurs after exposure to irradiation is deletion which is caused by: misrepair; and cleaning. Misrepair occurs when two individual splits in DNA molecule where a fragment maybe lost between the splits or the two external ends may be attached. Cleaning is the enzymatic digestion of the constituent molecules of DNA called nucleotides where there are split ends before they are rejoined to mend the break in the double strand (OEF, 2011).
Radiation and Genetic Mutations
Radiation causes changes in the DNA of an organism. Nonheritable or somatic effects on cells take place after a mutation has occurred, causing damage, and death to the cells. The most noteworthy somatic effect that occurs in the long term is cancer (American Cancer Society, 2011). Any mutations which arise in germ cells (sperms and ova) are passed on to future generations and are termed heritable or genetic effects. When a genetic mutation as a result of radiation takes place, it increases the occurrence of similar mutations which occur spontaneously and continuously in their natural existence (Khan, 2010). It is difficult to distinguish the mutations which occur as a result of radiation and those which occur due to other causes.
The risk associated with mutations is referred to as the doubling dose. As explained by (Khan, 2010), this is the quantity of radiation that would result in additional mutations equivalent to those that are occurring naturally from other causes; thus doubling the rate of natural rate of mutation. Mutation rates are generally dependent on the dosage and there is no existing threshold beneath which mutations do not increase.
Biological Effects of Radiation
In the United States, approximately half of radiation exposure on citizens arises from natural sources (University of Toronto, 2011). Medical procedures used for diagnostic purposes account for the other half. On average, (University of Toronto, 2011) posits that radiation from natural origins accounts for approximately 310 millirem of exposure. These natural sources are radon and thoron gases, terrestrial, internal, and cosmic sources. Natural radiation is not known to cause harmful health effects. In addition, man-made radiation sources of radiation from commercial, medical, or industrial sources account for an extra 310 mrem of the US annual exposure to radiation (University of Toronto, 2011). CT scans (computed tornography) is the largest source, 150mrem, while other medical procedures contribute another 150 mrem. Industrial sources like fertilizers, smoke detectors, tobacco and others contribute only 10 mrem of radiation exposure.
Figure 1: Sources of Radiation in the US
There are very little or negligible biological effects of radiation under conditions of low exposure on humans. This is because the human body possesses repair mechanisms which correct any damage caused by radiation and/ or chemical carcinogens. Living cells which are exposed to radiation may result in three different outcomes: the damaged cells may restore themselves, thus no long-term damage; the cells may die and are replaced by the organism’s regular processes; or the cells may repair themselves erroneously, causing changes in the biophysical constitution of the cell (RERF, 2011).
When a population is exposed to elevated levels of ionizing radiation, the incidences of cancer development are heightened. Notable examples are the survivors of the Hiroshima atomic bomb attack and patients receiving certain diagnostic or therapeutic medical measures (OEF, 2011). High exposure levels (above 50, 000 mrem) can result in certain cancers like breast, bladder, colon, leukemia, stomach, ovarian, and other cancers. The length of time between which radiation exposure takes place and the cancer detection is called the latent period and may extend for many years. It is impossible to tell a cancer whose development has been stimulated by radiation exposure and that which is caused by other carcinogens. This is because lifestyle, chemical, and physical hazards also contribute considerably to these cancers.
It is difficult to indicate a dosage of radiation which is harmful because radiation exposure affects each individual differently. However, it is estimated that half a population would pass away within a period of thirty days after exposure to a dose of 350,000-500,000 mrem; this exposure should have occurred in a period of a few minutes to hours (MIT, 2011). In case such exposure occurs to only a particular body part, a localized reaction like a skin burn may take place. In contrast, minimal doses (less than 10,000 mrem) extended over stretched durations (years) do not result in immediate problems to organs in the body. Changes would only be observed at cellular levels ad changes may be observed only approximately 5-20 years after exposure to the radiation.
The main effects of radiation exposure are cancer development and genetic effects. After exposure to radiation, the probability of developing cancer are five times higher than a genetic defect like congenital abnormalities, still births, infant and child mortality, occurring. Genetic defects occur as a result of mutations in reproductive cells which affect the offspring immediately or after several generations depending on whether the modified genes are recessive or dominant (EPA, 2011). Cells display different sensitivities to radiation. Cells which are re
There are two types of health effects; stochastic and non-stochastic health effects (EPA, 2011). Stochastic effects are experienced after chronic (low level, long term) exposure. Cancer development is the primary stochastic effect where cells proliferate uncontrollably. Cell growth is controlled in an organism and cellular changes as a result of radiation destroy the cells’ processes, causing uncontrolled growth of these cells. Non-stochastic effects are related to acute, high level exposure to radiation. The effects are also noncancerous, and dissipate quite quickly. These effects include radiation sickness and burns; radiation sickness causes death or premature death (MIT, 2011).
Nagasaki and Hiroshima, Japan 1945
Most people who died after the attack at Hiroshima and Nagasaki died from radiation exposure, not from the bombing. One week to ten days after the explosion of the atomic bomb, many people passed on. They died from the burns they had sustained after turning into a mulberry color resembling worms (OEF, 2011).
Those who survived the attacks suffered from leukemia, malformed offspring, cataracts, premature aging, other cancers, and social discrimination. A few months after the attacks, there was an abnormal increase in cases of leukemia were reported. With time, the incidences of leukemia reduced but those of thyroid cancers, breast cancers, lung cancers, and other cancers were reported (OEF, 2011).
Chernobyl, 1986
At Chernobyl, in the previous Soviet Union, a nuclear accident occurred as a result of an electrical fault. The Chernobyl nuclear plant was composed of four power reactors which were one thousand megawatts (OEF, 2011). A chemical explosion occurred which caused the evaporation of fifty tons of nuclear fuel and an ejection of an additional seventy tons from the core’s periphery (OEF, 2011). This resulted in a massive release of radiation, comparable to approximately ten Hiroshimas. There were many deaths that resulted as a result and to date, more people continue to die.
Applications of Radioactivity
Radiation is used in smoke detectors which contain a source of Americium-241, (half-life 460 years). Alpha particles are released which ionize the atmosphere, making it conduct electricity and allowing a small flow of current (Khan, 2010). When smoke enters the alarm, the alpha particles are absorbed reducing the current and setting off the alarm. Radioactivity is also used in paper mills to determine the paper thickness by measuring the amount of beta radiation going through the paper onto a Geiger counter (Khan, 2010). In the measurement of plastics or paper, beta radiation is employed because alpha radiation does not pass through paper.
Gamma rays are used in the sterilization process; in the food industry they are used to destroy mould, bacteria, or insects. This extends the food’s shelf-life though it may change its taste. Gamma rays are employed in the sterilization of hospital equipment like plastic syringes which are damaged by heat (Khan, 2010). Radiation is also used in radioactive dating. Living organisms (plants and animals) have a set ratio of carbon-14 within their tissues. After these organisms die, the levels of carbon-14 begin to depreciate at a rate which is known because it has a half-life of 5700 years. Radioactive dating is usually used by architects to estimate the age of organic materials from the ancient eras by determining the quantity of carbon-14 left in the material.
Radioactive tracers can be used in industry and medicine to determine problems within systems. A popular tracer is known as Technetium-99, which only emits gamma radiation and is safe because it does not cause much radiation. This tracer can be used in industries to detect leakages in pipes; small quantities are injected into the pipes and leakages are detected using a Geiger counters laced above the ground. In medicine, a blocked kidney can be detected by using iodine-123 which is injected into the patient and Geiger counters are positioned above the kidneys (Gate and Baranov, 2011).
Gamma rays are used in cancer treatment to destroy cancerous cells to eliminate the need for surgery; this is termed as radiotherapy (American Cancer Society, 2011). When cancerous cells are destroyed by radiotherapy, they are unable to restore themselves in the same way as healthy cells. Radiotherapy is easier to apply in certain cancers because of the ease of accessing the cancer cells. It is easier to focus gamma rays on a breast tumor, but more difficult to do so with a lung cancer without destroying healthy cells (American Cancer Society, 2011)
Conclusion
Radiation causes changes in cell structures by destroying chemical bonds especially in the DNA. The effects of radiation can result in both long-term and short term results. Acute exposure can lead to death and burns while chronic exposure can cause cancer. Exposure to radiation can cause genetic mutations which can take place over a long period of time. Tragic events in history have clearly demonstrated the toxicity of radiation, for example the disaster at Chernobyl in 1986, whose effects are still being experienced to date. However, radiation does have some very useful applications in industries and medicine. It is noteworthy to appreciate the use of radiotherapy in cancer treatment. Gamma radiation is focused on the cancerous cells and destroys them, eliminating the need for surgery.
Conclusion
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