Distribution and Administration of Potassium Iodide in the Event of a Nuclear Incident (2004) / Chapter Skim
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4 Health Consequences of Radiation Exposure
4 Health Consequences of Radiation Exposure
Pages 44-67
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From page 44... ...
Among the nuclear power plant accidents discussed, particular attention is paid to the 1986 Chornobyl accident because of the high levels of fallout to which a large population was exposed. One of the most important conclusions is that evidence on both external and internal radiation shows that very young children are the most sensitive to the carcinogenic effects of radiation to the thyroid; the risk decreases with increasing age, and there is no appreciable risk to adults, particularly those over 40 years old.
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From page 45... ...
Radiation from any source including ingested or inhaled isotopes, medical or dental investigations with x rays, and direct radiation from an atomic bomb- can damage DNA and thus pose a risk of tumors and, in high doses, cell death. The main expected consequences of exposure of the thyroid to radiation are an increase in the incidence of thyroid tumors and an increase in the occurrence of loss of thyroid function (hypothyroidism, myxedema)
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From page 46... ...
Population exposure to radioisotopes in fallout began in 1945 with the atomic bombs in Japan, although these detonations were more relevant to direct external radiation from neutrons and gamma rays. Between 1951 and 1962, the aboveground testing of nuclear weapons in Nevada led to the release of large amounts of 3, the
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From page 47... ...
One particular US test carried out in the Pacific Ocean led to a significant exposure of the population of the Marshall Islands. Aboveground tests were also earned out by the USSR and in smaller numbers by the UK and France, mostly in the Southern Hemisphere, and other countries have tested a small number of nuclear weapons.
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From page 48... ...
The health effects in a populated area are dominated by the blast and thermal waves and the direct radiation. The external radiation from neutrons and gamma rays, unlike internal radiation from isotopes of iodine, does not irradiate the thyroid gland to a greater extent than the other tissues of the body, and KI will not prevent thyroid damage from external radiation.
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From page 49... ...
One test of a large nuclear device led to the release of large amounts of iodine isotopes, and an unpredicted weather change led to exposure of the population of some of the Marshall Islands to large amounts of radioisotopes of iodine. Marshall Islands On March I, 1954, on Bikini Atoll in the northern Marshall Islands, a ~ 5-megaton thermonuclear device was detonated on a tower in an atmospheric nuclear test code-named BRAVO.
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From page 50... ...
Recalculated doses from the internal radionuclide burden would be derived later from estimated thyroid content of five radioiodine isotopes and two tellurium radionuclides, all with shorter half-lives than ~ At. Most of the thyroid absorbed dose was from short-lived isotopes.
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From page 51... ...
The Marshall Islands Nationwide Thyroid Disease Study found a high prevalence of thyroid nodules in the entire population of the Marshall Islands that appears to correlate with increasing age
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From page 52... ...
and doubled the estimated prevalence of nodules. Nevada Tests Over 90 aboveground tests were carried out at the Nevada Test Site between 1951 and 1962; after this period, aboveground tests ceased, and the underground tests that followed released negligible amounts of radioactive iodine into the atmosphere.
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From page 53... ...
This ban was continued for over a month in the most affected areas. The avoidance of contaminated milk, the main route through which radioisotopes of iodine in fallout reach the human thyroid, greatly reduced the risk to the population.
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From page 54... ...
Unbeknownst to the operators, valves had been closed so that the emergency feed water pumps could not discharge water from the auxiliary pumping system. When the reactor core cooling system temperature and pressure began to increase the reactor scrammed (control rods were suddenly inserted into the reactor core)
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From page 55... ...
Most of our understanding of the consequences of exposure of a population to radioiodine in fallout comes from studies of the population in Belarus, northern Ukraine, and part of the Russian Federation exposed after the Chornoby! accident, in which large quantities of radioiodine were released and a large population was exposed.1 The incident, which occurred on April 26, 1986, resulted from a combination of an inappropriate experiment and human error No adequate distribution of stable iodide in the exposed areas was carried out.
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From page 56... ...
That resulted in an explosion equivalent to that of 30-40 tons of TNT that destroyed the reactor building, which lacked secondary containment. Fires erupted, including fire in the graphite moderator in the reactor core.
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From page 57... ...
in adults. In Kiev, where the radioiodine contamination was lower, the estimated individual thyroid doses for five age groups were assessed; these range from 104 mGy (10.4 red)
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From page 58... ...
The stress of known or suspected radiation exposure, lack of information, concern for children, and the forced evacuation also had considerable health consequences. Apart from those related to stress, the first indication of health problems in the population exposed to fallout came 4 years after the accident with reports from hospitals in Minsk, the capital of Belarus, and Kiev, the capital of Ukraine, of an increase in the numbers of children with thyroid carcinomas.
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From page 59... ...
Those who were born more than 6 months after the accident show no increase in thyroid cancer; because of the short half-life of the iodine isotopes they would not have had appreciable exposure. Three factors contribute to the high sensitivity of very young children to the risk of thyroid cancer after exposure to iodine isotopes: a high intake of isotopes mainly through milk, the high uptake of radioiodine by the infant thyroid, and increased biologic sensitivity.
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From page 60... ...
Infants are also more sensitive to the risk of carcinogenesis, probably because of the way the thyroid develops growing rapidly during the early years of life but hardly at all during adult life. Although thyroid cancer has been the main thyroid consequence of exposure to fallout from Chornoby1, benign thyroid tumors also appear to be increasing in frequency; this is similar to the findings after exposure to x rays (Shore et al., 1993~.
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From page 61... ...
it should be noted that no similar effects were found in studies of those exposed to external radiation from the atomic bombs (Kodaira et al., 1995~. An accurate estimate of the overall effect of the Chornoby!
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From page 62... ...
One of the most important findings in the studies of the largest exposure to have occurred is the greatly increased sensitivity of the youngest children to thyroid carcinogenesis after exposure to radioactive iodine in fallout. Thyroid cancer has also been shown to occur after external radiation from x-rays used in treatment of nonthyroid diseases, and both here and in atomic-bomb follow-up studies it has also been shown that young children are more likely than older children to develop carcinoma (Ron et al., 1995~.
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From page 63... ...
Because iodine, including radioactive iodine, is concentrated in breast milk, lactating mothers must take every precaution to reduce exposure (see Chapter 2~. The great drop in sensitivity to thyroid carcinogenesis with increasing age suggests that iodine prophylaxis in adults is of little value.
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From page 64... ...
The evidence derived from studies of the effects of internal irradiation of the thyroid for medical reasons, of external radiation from the atomic bombs, and of internal radiation from iodine isotopes after Chornobyl shows that the group most susceptible to the development of thyroid cancer is young children and that the risk falls rapidly with increasing age at exposure. The studies also suggest that there was no appreciable risk of thyroid cancer in those who were adults at the time of exposure to radiation from radioiodine, although reliable information on the risk to those who were adults at the time of exposure to fallout from Chornobyl is not available, and future work in this area is needed.
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From page 65... ...
Experimental studies suggest that external radiation is I-3 times as effective as radiation from i3~l in inducing thyroid tumors (Lee et al., 1982~. We therefore use the data from external radiation to estimate the relationship between thyroid radiation dose from iodine isotopes and risk of thyroid cancer, knowing that the actual risk is likely to be lower than the predicted risk.
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From page 66... ...
The averted dose would in practice be reduced or abolished by evacuation or sheltering. We have assumed that neither sheltering nor evacuation take place and that no stable iodine is taken, again, to avoid underestimating the risk.
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From page 67... ...
. Exposure to external radiation or internal radiation from radioactive iodine is linked to a dose-dependent increase in thyroid-cancer incidence.
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