Biological Effects of Radiation Exposure - Essay Example

Biological effects of radiation exposure The world's worst nuclear reactor disaster occurred at the Chernobyl Power Station in the USSR (now the Ukraine) on April 26, 1986. It is known as the worst nuclear disaster in history. The Chernobyl accident was a unique event, on a scale by itself. It was the first time in the history of commercial nuclear electricity generation that radiation-related fatalities occurred, and was for a long time the only such incident (since then an accident at the Japanese Tokaimura nuclear fuel reprocessing plant on September 30, 1999, resulted in the radiation related death of one worker on December 22 of that same year and another on April 27, 2000). The Chernobyl incident has also been compared to the Bhopal disaster. On December 3, 1984, a Union Carbide plant in Bhopal, India leaked 40 tons of toxic methyl isocyanate gas, which killed at least 15,000 people, and injured anywhere from 150,000 to 600,000 others (Hart, 2005, p. 15). 31 people died at the time of the disaster, and 28,200 sq. km. (10,900 sq. miles) of land and 1.7 million people were exposed to radiation. Figures from the Ukraine Radiological Institute suggest that over 2,500 deaths were caused by the Chernobyl accident. Because of the absence of systematic records, it is not clearly known how many of the 200,000 people involved in the clean-up operation died in the several years following the disaster. Though 60% of the radioactive fallout landed in Belarus, a portion of it drifted over parts of the western Soviet Union, Eastern Europe, Scandinavia, UK, and the eastern United States (p. 107, Hart, 2005). It is difficult to accurately assess the damage figures, as most of the expected long-term fatalities, especially those from cancer, have not yet actually occurred, and will be difficult to attribute specifically to the accident. The workers involved in the recovery and cleanup after the accident received high doses of radiation. In most cases, these workers were not equipped with individual dosimeters to measure the amount of radiation received, so experts can only estimate their doses. Even where dosimeters were used, dosimetric procedures varied. Some workers are thought to have been given more accurate estimated doses than others. According to Soviet estimates, between 300,000 and 600,000 people were involved in the cleanup of the 30 km evacuation zone around the reactor, but many of them entered the zone two years after the accident. In the first year after the accident, the number of cleanup workers in the zone was estimated to be 211,000, and these workers received an estimated average dose of 165 millisieverts (16.5 rem) (Hart, 2005, p. 34). The plume of radioactive debris has been said to be equal to the contamination of 400 Hiroshima bombs. This is correct, but misleading. The main effect of the bomb was the direct radiation from the gamma blast. Compared to that, the contamination was only a minor addition. Some children in the contaminated areas were exposed to high radiation doses of up to 50 grays (Gy) because of an intake of radioactive iodine-131, a relatively short-lived isotope with a half-life of 8 days, from contaminated milk produced locally (Hart, 2005, p. 35). Several studies have found that the incidence of thyroid cancer among children in Belarus, Ukraine and Russia has risen sharply. The IAEA notes "1800 documented cases of thyroid cancer in children who were between 0 and 14 years of age when the accident occurred, which is far higher than normal" (http://www.who.int), but fails to note the expected rate. The childhood thyroid cancers that have appeared are of a large and aggressive type but, if detected early, can be treated. Treatment entails surgery followed by iodine-131 therapy for any metastases. To date, such treatment appears to have been successful in the vast majority of cases. Right after the accident, the main health concern involved radioactive iodine, with a half-life of eight days. Today, there is concern about contamination of the soil with strontium-90 and caesium-137, which have half-lives of about 30 years. The highest levels of caesium-137 are found in the surface layers of the soil where they are absorbed by plants, insects and mushrooms, entering the local food supply. Recent tests (1997) have shown that caesium-137 levels in trees of the area are continuing to rise. There is some evidence that contamination is migrating into underground aquifers and closed bodies of water such as lakes and ponds (Hart 2005, p. 17). The main source of elimination is predicted to be natural decay of caesium-137 to stable barium-137, since runoff by rain and groundwater has been demonstrated to be negligible. The issue of long-term effects of Chernobyl disaster on civilians is very controversial. The number of people whose lives were affected by the accident is enormous. Over 300,000 people were resettled because of the accident; millions lived and continue to live in the contaminated area. On the other hand, most of those affected received relatively low doses of radiation; there is little evidence of increased mortality, cancers or birth defects among them; and when such evidence is present, existence of a causal link to radioactive contamination is uncertain. An increased incidence of thyroid cancer among children in areas of Belarus, Ukraine and Russia affected by the Chernobyl accident has been firmly established as a result of screening programs (Hart 2005, p. 102) and, in the case of Belarus, an established cancer registry. The findings of most epidemiological studies must be considered interim, say experts, as analysis of the health effects of the accident is an ongoing process. Though the disaster of Three Miles Island US nuclear power plant on March 28, 1979, seems to be less grave, the accident still produced serious economic and public relations consequences and the cleanup process was slow and costly. The accident unfolded over the course of five tense days, as a number of agencies at the federal, state, and local level attempted to diagnose the problem (the full details of the accident were not discovered until much later), and decide whether or not the on-going accident required a full evacuation of the population. In the end, the reactor was brought under control. No nuclear plant has been built in the United States since 1978 (Walker 2004, p. 231). These civilian nuclear disasters have led to an overall decline in the popularity of nuclear power plants. To understand the problem better we have to know what radiation is and how dangerous it can be. Radiation consists of subatomic particles such as neutrons, electrons and alpha particles. These particle travel at a speed of 100,000 miles per second and can cause serious damage to living cells and tissues. If the affected cell is a normal one, it may lead to cancer. Apart from this feared disease, the other significant impact of low-level radiation is the genetic disorders (in case if the affected cells are the reproductive ones) which can range from color blindness to mongolism (Bertell 2000, p. 150). Other effects of radiation include developmental abnormalities among children exposed to radiation in uterus. This is a well-known fact and there is also extensive human evidence from medical exposures and from studies of the Japanese A-bomb survivors. It may lead to physical deformities and mental retardation. Experts also say that it may pose a large risk for childhood cancer. This is how Novick describes it: "When one of these particles or rays goes crashing through some material, it collides violently with atoms or molecules along the way. . . . In the delicately balanced economy of the cell, this sudden disruption can be disastrous. The individual cell may die; it may recover. But if it does recover, after the passage of weeks, months or years, it may begin to proliferate wildly in the uncontrolled growth we call cancer." (Novick 1969, p. 125) However, only a large number of such particles can cause any serious damage. The probability for one of these particles to cause cancer is very low, about 1 chance in 30,000,000,000,000,000. Still, every single one of them has the same potential. We often use mrem (millirem) to quantify the radiation exposure. One millirem of the radioactive exposure corresponds to being struck by approximately 7 billion particles of radiation (Novick 1969, p. 90). During the Three Mile Island accident, average exposures in the surrounding area (President Commission Report, 1979) were 1.2 mrem. For each millirem of radiation we receive, our risk of dying from cancer is increased by about 1 chance in 4 million. This is the result arrived at independently by the U.S. National Academy of Sciences Committee on Biological Effects of Ionizing Radiation (NASC Report, 1990, p. 55) and the United Nations Scientific Committee on Effects of Atomic Radiation(UNSC Report, 1988, p. 21). There are other units to represent radiation exposure. Some of them are listed below: (Novick 1969, p. 221) Biological effects of radiation begin with atom ionization. The energy absorbed by the human tissues is sufficient to excite and remove electrons from the atoms that make up molecules of the tissue. This often leads to the breaking of the bonds and hence the molecules. It may also affect the chromosomes, which are the most critical part of the cell. Also there are very effective repair mechanisms at work constantly which repair cellular damage - including chromosome damage. If the damage is not critical, cell will eventually recover and start functioning normally. If the damage is critical, cell may try to repair itself and then function normally (NASC Report, 1990, p. 67). Even the chromosomes' damages are generally repaired. If a damaged cell is either unable to perform the repair functions or performs its function incorrectly or incompletely after the repair, they may reproduce at an uncontrolled rate. Such cells are the underlying causes of cancers. Different cells react differently to the radiation exposure. In general, cells which divide rapidly are prone to radiation exposure damage. The following table (NCRP Report No. 138, 1988, p. 26) demonstrates how radiation affects on various levels of biological organization: Level of Biological Organization Important Radiation Effects Molecular Damage to enzymes, DNA etc. and interference to biological pathways. Subcellular Damage to cell membranes, nucleus, chromosomes etc. Cellular Disruption to central nervous system, bone marrow, intestinal tract. Induction of cancer Tissue, Organ Disruption to central nervous system, bone marrow, intestinal tract. Induction of cancer Whole Animal Death; 'radiation life shortening' Populations Changes in the genetic characteristics of individual members Depending on the absorbed dose, radiation can produce different effects on certain organs and body parts, as the table below represents: The radiation exposure may also lead to somatic effect which may be immediate or delayed. In the famous paper 'No Immediate Danger' the author (Dr. Rosalli Bertell) studies nuclear radiation and its biological effects. He tabulates the health effects as shown below: Probable Health Effects resulting from Exposure to Ionizing Radiation Doses (in rems) Immediate Health effects Delayed Health Effects >1,000 Immediate death. Frying of the brain'. None 600-1,000 Weakness, nausea, vomiting and diarrhoea followed by apparent improvement. After several days: fever, diarrhoea, blood discharge from the bowels, haemorrhage of the larynx, trachea, bronchi or lungs, vomiting of blood and blood in the urine. Death in about 10 days. Autopsy shows destruction of hematopoietic tissues, including bone marrow, lymph nodes and spleen; swelling and degeneration of epithelial cells of the intestines, genital organs and endocrine glands. 250-600 Nausea, vomiting, diarrhoea, epilation (loss of hair), weakness, malaise, vomiting of blood, bloody discharge from the bowels or kidneys, nose bleeding, bleeding from gums and genitals, subcutaneous bleeding, fever, inflammation of the pharynx and stomach, and menstrual abnormalities. Marked destruction of bone marrow, lymph nodes and spleen causes decrease in blood cells especially granulocytes and thrombocytes. Radiation-induced atrophy of the endocrine glands including the pituitary, thyroid and adrenal glands. From the third to fifth week after exposure, death is closely correlated with degree of leukocytopenia. More than 50% die in this time period. Survivors experience keloids, ophthalmological disorders, blood dyscrasis, malignant tumours, and psychoneurological disturbances. 150-250 Nausea and vomiting on the first day. Diarrhoea and probable skin burns. Apparent improvement for about two weeks thereafter. Foetal or embryonic death if pregnant. Symptoms of malaise as indicated above. Persons in poor health prior to exposure, or those who develop a serious infection, may not survive. The healthy adult recovers to somewhat normal health in about three months. He or she may have permanent health damage, may develop cancer or benign tumors, and will probably have a shortened lifespan. Genetic and teratogenic effects. 50-150 Acute radiation sickness and burns are less severe than at the higher exposure dose. Spontaneous abortion or stillbirth. Tissue damage effects are less severe. Reduction in lymphocytes and neutrophils leaves the individual temporarily very vulnerable to infection. There may be genetic damage to offspring, benign or malignant tumours, premature ageing and shortened lifespan. Genetic and teratogenic effects. 10-50 Most persons experience little or no immediate reaction. Sensitive individuals may experience radiation sickness. Transient effects in lymphocytes and neutrophils. Premature ageing, genetic effects and some risk of tumours. 0-10 None Premature ageing, mild mutations in offspring, some risk of excess tumors. Genetic and teratogenic effects. (Bertell 2000, p. 25-29) Any level of radiation exposure, no matter how small, carries some risk with it. Because radiation affects different people in different ways, it is not possible to indicate what dose is needed to be fatal. However the risk involved in low level is comparable to or smaller than risks we encounter in other occupational risks. It is naturally present in our environment and has been since the birth of this planet. Controlled low level radiation exposure is often used for treatment of cancer. To properly assess the effect of acute and chronic radiation exposure on human health, more research is required. References: Bertell, Rosalie (2000). No Immediate Danger, Prognosis for a Radioactive Earth, The Book Publishing Company -- Summertown, Tennessee, p. 25-29, 150-151 Hart, G. (2005). Chernobyl: the true scale of the accident. New York, p. 15-16, 34-35, 102, 107 retrieved April 6, 2006. NASC Report, National Academy of Sciences Committee on Biological Effects of Ionizing Radiation, "Health Effects of Exposures to Low Levels of Ionizing Radiation" (BEIR-V), Washington, D.C. (1990). NCRP Report No. 138. College of William and Mary, Chemistry Department RMIT University, Department of Medical Radiations Science. Novick, S. (1969). The Careless Atom. Dell Publishing, New York, p. 90, 124-125, 221 "Report of the President's Commission on the Accident at Three Mile Island," Washington, D.C. (1979). UNSC Report, United Nations Scientific Committee on Effects of Atomic Radiation (UNSCEAR), "Sources, Effects, and Risks of Ionizing Radiation," United Nations, New York (1988). Walker, S.J. (2004) Three Mile Island: A Nuclear Crisis in Historical Perspective. Berkeley: University of California Press, p. 231. Read More