It is by the combination of several fairly unique circumstances that this radionuclide has been the major radionuclide of concern from the viewpoint of food contamination for both nuclear weapons tests and for reactor accidents. Substantial amounts of I activity are created by nuclear explosions; this radionuclide is also volatile and does not condense on particles until late, at which time it becomes associated with the surfaces of fallout particles.
The smaller particles are also preferentially retained by vegetation, 24 from which they are lost with a half-retention time of about 10 days.
A milk cow, if it is receiving its full quota of food from fresh pasture, will consume per day the amount of I that is contained on about 50 square meters, 25 and it will secrete up to 1 percent of that daily intake into a liter of milk. The thyroid is a very small gland, weighing about 20 grams in adults and only about 2 grams in infants.
Thus, iodine is preferentially retained on vegetation, which the cow efficiently samples and rapidly secretes into milk; an infant then concentrates a large fraction of that iodine in milk into an extremely small gland, thus producing a relatively large dose. Goats are also of more concern; they graze less territory, but they secrete about 10 times more of their daily intake of iodine into 1 liter of milk. For nuclear explosions outside the United States, the consumption of milk from other animals, such as sheep, horses, and camels, should be considered. The milk-transfer factors for these animals are not well known.
Scientists at the National Cancer Institute are conducting a research program to determine such factors, but the results are not yet published. For a hypothetical device with approximately 50 percent fission fraction, i. These results are scaled from published calculations made for NTS shots. Other radionuclides of concern in terms of contaminated foods are 89 Sr, 90 Sr, and Cs.
These share the characteristics of high fission yield the fraction of fissions that produce the radionuclide or its precursors , volatility of the radionuclide or its precursors , and efficient secretion into milk. Other organs of concern are the digestive tract, red bone marrow, and bone surfaces. So far, it has been assumed for this discussion that the persons and the milk animals are collocated. This is frequently not the case. Reconstruction of thyroid dose from past events has included elaborate attempts to reconstruct sources of milk or movement of milk from one region to another.
It is important to note that this pathway, consumption of contaminated food, can be relatively more important for fallout from nuclear explosion accidents in nonurban areas in the sense that milk animals are more likely to be located in rural areas. The problem of contaminated milk supplies following a. Such elimination of this pathway would require that local inhabitants were adequately warned; that sufficient monitoring devices, iodine supplies, and distribution systems were available; and that alternate food supplies were available. Contamination of other types of food crops would also occur.
After milk, the food of most concern is fresh, leafy vegetables. Such vegetables are efficient in capturing fallout and are typically consumed fresh on a daily basis during the growing season. This practice provides an opportunity for a direct and rapid pathway to humans following deposition of fallout but, again, this pathway can be eliminated by an informed population with an adequate infrastructure.
Other types of food crops typically have less ability to capture fallout or have more indirect and longer pathways to humans. The longer pathways allow for both radioactive decay and the loss of retained material from the crops. Pathways of possible concern include the consumption of meat from grazing animals, poultry, and eggs.
Grain crops are not usually of concern unless they are harvested immediately after deposition of fallout. The consumption of contaminated food is unlikely to result in any acute health effects, but it could in some circumstances increase significantly the number of latent cancers that would be expected in the affected population. An accurate estimate of the number of latent cancer fatalities from this exposure pathway would require estimating the amount of contamination in milk and various other foods, the consumption of these foods by the population, the internal dose from each radionuclide to each organ, and the use of organ-specific risk coefficients.
The computer codes used for this study do not consider deposition at very great distances.
Public Health And War
If clouds are lofted to substantial heights and later encounter precipitation systems, there can be areas of enhanced deposition very far away. This deposition was eventually detected only after contaminated straw used in the packing of x-ray film was noted to have exposed the film. Of more recent interest were the areas of enhanced deposition that resulted from the Chernobyl accident.
Contamination was sufficiently high in areas of several countries far from the accident e. Such fallout returns to Earth slowly, and with a half-time of about 1 year, most of the short-lived radionuclides would have decayed before the fallout returned to Earth. It takes a large explosion to produce such injections, on the order of hundreds of kilotons. Much of the experience with global fallout resulted from the large tests conducted by the United States and the Soviet Union from to , although earlier large tests in , , , and also produced global fallout.
Concern was largely focused on 90 Sr and Cs, each of which has a half-life of about 30 years.
Under unusual circumstances, such as the large-scale subsidence of air masses or the penetration of large thunderstorms into the stratosphere, the deposition of I was also noted. The health effects resulting from attacks with conventional weapons on nuclear-weapon storage facilities depend on the detailed design of the nuclear weapons being attacked. Because the design details of enemy nuclear weapons are unknown and could not be discussed in this document in any case , the committee cannot provide quantitative estimates. The greatest such risks would arise from weapons containing plutonium.
Even in this case, however, the dispersal of plutonium from tens of weapons would be unlikely to cause deaths or acute illnesses in civilian populations. Dispersal of plutonium could, however, result in thousands of latent cancer deaths if kilogram quantities of plutonium aerosol were dispersed in densely populated areas. In this case, the effects on nearby civilian population would be similar to those estimated in Figure 6. It seems probable that even an early-stage nuclear country or group would desire some degree of safety in order to preserve both the weapon and the nuclear material for the use for which it was intended.
Consequently, other techniques will likely be employed to create safe operating conditions for the weapons. For example, the weapon components can be kept in separate locations, ready to be assembled quickly for possible use as was done with a number of U. There may also be mechanical safety devices in place that lead to a low probability of unintentional detonation even if not as quantitative as the one-point safety criterion.
As a result, the probability of significant nuclear yield from a conventional attack is quite low—but cannot be completely ruled out. In that case an upper limit for the effects is similar to the limits estimated in Figure 6. However, the most likely outcome of such an attack is dispersal of the nuclear material, the equivalent of the dirty bomb scenario discussed below. The dispersal of radioactive materials from a non-nuclear explosion would be possible, for example, if sympathetic detonation of high explosives led to dispersal of the radioactive material either in weapons or in a facility such as a reprocessing plant.
A radiological weapon could involve a device using any of hundreds of radionuclides, in quantities ranging from harmless to lethal, in physical and chemical forms that are easy or impossible to disperse efficiently. Accordingly, the committee expects that a conventional attack on a facility containing radiological weapons or radioactive materials would be unlikely to produce a substantial number of civilian deaths or acute illnesses, beyond those caused directly by the conventional attack itself. The number of latent cancer deaths that might result from a dispersal of radioactive material would depend sensitively on the type and amount of material dispersed as well as the density of nearby civilian populations and whether these populations were evacuated from the area after the.
Uncertainties in the source term make quantitative estimates impossible, but the estimates given above for plutonium dispersal indicate the consequences of the dispersal of a very large mass of highly radioactive material. Following the explosion of a nuclear weapon, the fallout area is intensely radioactive. However, as noted above, the rate of external exposure to gamma radiation decreases rapidly with time, and the denial of land use due to fallout is not of great concern relative to other effects of fallout. This is in marked distinction to the situation to be expected following a major reactor accident such as that at Chernobyl, 39 because of the much greater releases of long-lived l37 Cs.
Denial of the use of water would be expected to be of even less concern, except under very unusual circumstances, because of the very rapid dilution of fallout deposited on surface waters. It is unlikely that significant contamination of groundwater would occur, except in areas immediately adjacent to an explosion of an earth-penetrator weapon.
Although underground facilities could be built below the water table and kept dry by diversion and pumping, most facilities are expected to be above the water table. The groundwater in the immediate area of an underground burst would be contaminated, but the greatest release of radioactivity would be from activated materials that are spread onto the surface.
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A bunker facility is highly unlikely to be built in groundwater. Groundwater is likely to be in the fallout area. However, the greatest release of radioactivity would be from activated material that is spread onto the water surface.
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The transport of radionuclides due to the movement of groundwater will be difficult to evaluate with any useful certainty as it is a very site-specific phenomenon. Such effects of groundwater will be far less than the effects of blast, fire, and on-the-ground fallout. The radiation sensitivity of all other mammals is generally about the same as that for humans. Thus, in areas where humans are killed or injured by radiation, the same lethality for animals would be expected.
If large herds of farm animals were affected, poor sanitation could become a significant problem.
Plant species have a broad range of sensitivity to radiation. Thus, it is conceivable that forests could be killed, which in turn could result in forest fires. The demise of the pine forest near the Chernobyl plant was one notable example of this effect. It is not likely that effects in excess of that indicated for pine forests would occur. Recently, there has been a focus on evaluating the possible effects of radiation on other members of an ecological system. It is not expected that effects other than those mentioned above would be of significance.
Thank You, Deeply
In the past there has been concern that large numbers of nuclear explosions might lead to large-scale disruption of the environment, including depletion of stratospheric ozone due to nitrogen oxides produced by the fireball, and changes in climate due to the soot and other aerosols released from burning cities. These concerns are relevant only with the detonation of thousands of high-yield weapons.
No significant environmental disruptions would be expected to occur beyond the areas directly affected by the prompt effects from one or a few nuclear explosions and the fallout that, depending on the amount of soil entrained and the fission fraction of the weapon s , can persist at dangerous levels for at least a year. In this context, there are three important questions:.
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To what extent can conventional or nuclear weapons destroy such facilities or the chemical and biological agents that they contain? To what extent would a conventional or nuclear attack on such a facility result in the release of chemical and biological agents? If chemical or biological agents are released as a result of an attack, what would be the health consequences for the nearby civilian population?
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The answers to the first two questions depend critically on detailed information about the facility, including its location, construction, and layout; the type and number of agent containers and their placement within the facility; and the amount and type of agent and the form in which it is stored. This information would provide the basis for targeting, selecting weapons, and estimating how much agent might be destroyed or released.