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The Medical Implications of Nuclear War, Institute of Medicine. @) 1986 by the National Academy of Sciences. National Academy Press, Washington, D.C. Possible Toxic Environments Following a Nuclear War JOHN W. BIRKS, PH.D., and SHERRY L. STEPHENS University of Colorado, Boulder, Colorado The direct effects of a nuclear war, the killing and maiming effects of the blast, the thermal pulse, prompt nuclear radiation, and fire storms, are too horrifying for the human mind to comprehend. Following a major nuclear war, approximately 1 billion people would be left dead, and millions more, probably hundreds of millions more, would be injured (Ambio, 1982, vol. 11, No. 2-3; Ehrlich et al., 1983; Harwell and Grover, 1985~. Still, 3 to 4 billion people around the world would find themselves alive, once the thousands of megatons of nuclear energy had been released. It is this realization that makes it so important to consider what the long- term environmental effects of a nuclear war would be not for the purpose of planning better bomb shelters and survival techniques, but in the hope that a clearer picture of life after a nuclear war may help provide the incentive necessary to bring about the "aroused understanding and insis- tence of the peoples of the world" (Einstein*), to bring nuclear weaponry under control. Besides the destruction of shelter, food, means of transportation and commun~cabon, arid radioactive contamination, nuclear war survivors would find their physical environment, particularly the atmosphere, radically *The full text of Einstein's statement of January 22, 1947, reads: "Through the release of atomic energy, our generation has brought into the world the most revolutionary force since prehistoric man's discovery of fire. The basic power of the universe cannot be fitted into the outmoded concept of narrow nationalism. For there is no secret and there is no defense; there is no possibility of control of atomic energy except through the aroused understanding and insistence of the peoples of the world." 155
156 PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES changed. Dust lofted by the clouds generated by atomic bombs and es- pecially smoke from fires in cities, forests, industries, and oil refineries would darken the sky. A simple calculation, in which one takes the total amount of smoke (about 200 million metric tons) that might be introduced into the atmosphere by the nuclear war fires and distributes it uniformly over the middle half of the Northern Hemisphere, indicates that more than 99 percent of the sunlight would be absorbed by the smoke cloud (Crutzen and Birks, 1982; Turco et al., 1983; National Research Council [NRC], 1985~. Although smoke highly absorbs the visible region of the solar spectrum, it is relatively transparent to the infrared region. As a result, land surfaces would cool, particularly near the interiors of continents where the buffering action of the oceans would be less effective. This nuclear winter effect is the exact opposite of the greenhouse effect which maintains most of the Earth's surface at above-freezing temperatures during the warmer seasons. Nuclear winter would have its greatest impact if the nuclear war occurred during the summer, because the incremental change in the amount of sunlight that would reach and warm the Earth's surface would be greatest then. Furthermore, during summer plants are not in their dormant states and would be most vulnerable to subfreezing temperatures. Of course, it is not possible to predict the season in which a nuclear war might break out. Some of the most sophisticated computer model calculations of the climatic effects of a nuclear war are presented in an accompanying article (Malone, this volume). Temperature perturbations are calculated to be in the tens of degrees Celsius, and in a fully interactive model the atmospheric lifetime of the particulate matter is enhanced so that the duration of nuclear winter would be at least a few months. These qualitative conclusions are also important in helping assess other environmental stresses associated with the atmosphere. These include (1) the distribution and transformation of toxic chemicals released from chemical plants and produced in the nuclear fires; (2) the partial destruction of the protective ozone layer, with a consequent increase in the level of biologically damaging ultraviolet radiation that would impinge on the biosphere once the smoke cloud has subsided; and (3) the possibility of a global photochemical smog. These additional environmental effects propagated by the atmosphere are the focus of this paper. TOXIC CHEMICALS A multitude of toxic pollutants would be produced by the pyrolysis and partial combustion of chemicals, petroleum products, and synthetic ma- terials stored in strategic, industrial, and urban areas. Military installations,
POSSIBLE TOXIC ENVIRONMENTS FOLLOWING A NUCLEI Wow 157 chemical plants, gas and oil refineries, and urban centers contain vast stores of chemical and petroleum products, as well as the waste products of defense, industry, and everyday life. The tragedy of Bhopal, India, where a ruptured storage tank released methyl isocyanate, killing 5,000 people (Chemical and Engineering News, 1985), is a small indication of what might happen following a nuclear war as the result of explosions near chemical plants. Clearly, in heavily industrialized regions, the kill area for nuclear explosions could be greatly increased by the release of poisonous chemicals into the atmosphere. The first question that one might logically ask is whether chemical releases would make the atmosphere lethally toxic on a global or semi- global basis. The answer is no. Even if an entire year's production of organic chemicals were released and uniformly mixed over half of the Northern Hemisphere, the total concentration of all chemical compounds would still be a factor of 5,000 times less than the 50 percent lethal dose (LDso) of hydrogen cyanide gas. Of course, most compounds are not nearly so toxic, and probably only 5-10 percent of a year's chemical production is in storage at any one time. Similarly, it is also true that toxic compounds such as carbon monoxide, acrolein, hydrogen chloride, hydrogen cyanide, sulfur dioxide, phosgene, and the oxides of nitrogen produced in urban fires could be significant causes of death only on a local basis. Thus, for the long-term survivors of a nuclear war, the concern with chemical releases would be similar to concern with delayed radio- active fallout, namely, mutations leading to cancers and birth defects. In this sense, we might, by analogy, refer to these effects as arising from the chemical fallout. Many of the most important mutagens would be nonvolatile compounds and would be associated with particulate matter. Once deposited in the soil and water, many of these compounds would be very stable against chemical and biological degradation and would be subject to bioaccu- mulation in a manner similar to that of radioactive isotopes. For example, a community of people becomes very concerned when a transformer fire, such as that which occurred in Binghamton, New York, in 1981, contam- inates an office building with soot rich in polychlorinated biphenyls (PCBs) (Schecter, 1983~. However, as the result of a nuclear war, of the order of 1,000 cities of the Earth would become the equivalent of toxic waste dumps. Also, the lofting of toxic smoke to high altitudes by the fire storms and by the buoyancy of solar heating (Malone, this volume) would ensure that these pyrotoxins would be distributed on a global basis as well. Any realistic estimates of the levels of chemical contamination is vir- tually impossible, as thousands of different toxic chemicals would be produced, and the amounts of each would be highly dependent on the types and mixtures of fuels burned (e.g., wood, petroleum, asphalt, rub
158 PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES her, plastics) and the fire conditions, especially temperature and oxygen concentration. Estimates of biological effects are further complicated by the wide range of toxicities exhibited by the various isomers of a given parent compound. Dioxin, for example, is expected to be an important carcinogen introduced into the environment by the pyrolysis of PCBs and possibly other chlorine-containing compounds (Turco et al., 1983; NRC, 1985; Birks et al., 19851. However, the highly toxic compound 2,3,7,8- tetrachlorodibenzodioxin (TCDD) is only one of 75 dioxin isomers. As seen in Table 1, the relative toxicities of these various isomers span more than six orders of magnitude. While cognizant of the enormity of the uncertainty, it is still useful to make some calculations, however crude, of the increased cancer incidence that might be expected on a semiglobal basis for a few carcinogens, so that the seriousness of chemical contamination can be compared with that of radioactive contamination. To do this for PCBs and TCDD, we have used the average emission factors found in the Binghamton fire (Schecter, 1983~. Assume that approximately 30 percent of the current world supply of PCBs (0.3 teragram; 1 Tg = 1 million metric tons) are affected by nuclear fires, that the soot emission factor is 10 percent (by weight), and that 15 percent of the soot is composed of unburned PCBs. If the soot is unifo~ly deposited over one-half of the Northern Hemisphere and mixed to a depth of 10 cm of soil, the level of contamination is calculated to be 0.1 parts per billion. If the soot fell on one-fourth of the world's freshwater lakes and if it were evenly mixed throughout the water, it would result in a calculated concentration of 0.09 parts per trillion (Birks et al., 19851. In Binghamton, the TCDD isomer of dioxin averaged only about 3.5 parts per million of the soot, so that the calculated TCDD concentrations in soil and water would still be lower by more than four orders of magnitude. Using the same assumptions, the average concentrations of TCDD over half of the Northern Hemisphere are calculated to be 0.008 parts per billion in soil and 0.01 parts per quadrillion in freshwater. Using present recommendations for estimating cancer risk for those persons drinking water and eating fish from freshwater lakes (U.S. En- vironmental Protection Agency, 1984), the added risk of contracting can- cer is calculated to be 10-8 (one chance in 108) for PCBs and 10-5 (one chance in 105) for the dioxin isomer TCDD. Considering that the present risk of contracting cancer in one's lifetime is about 1 in 5, these numbers are not all that frightening. Of course, many other chemical carcinogens, about which we know even less, would be produced in the nuclear war fires. Nevertheless, these calculations strongly suggest that on a global or semiglobal basis, chemical carcino- genesis may not be a serious impact of nuclear war. We must realize, however, that the deposition of chemical toxins would be highly irregular.
POSSIBLE TOXIC ENVIRONMENTS FOLLOWING A NUCLEAR WAR TABLE 1 Acute Lethality of Dioxin Isomers Isomers Cl Positions LDso (~g/kg) in Guinea Pigs 2,8 2,3,7 2,3,7,8 1,2,3,7,8 1,2,4,7,8 1,2,3,4,7,8 1,2,3,6,7,8 1,2,3,7,8,9 1,2,3,4,6,7,8 1,2,3,4,6,7,8,9 300,000 29,000 1 3 1,125 73 100 100 7,200 4 x 1 o a In mice. 159 It is possible that a large fraction of the smoke aerosol would be removed within the first few hours by precipitation. For example, an estimated 5 to 10 cm of rain fell in Hiroshima 1 to 3 hours after the blast. Dust, rubble, and large amounts of radioactive matter were concentrated in the black rain that spread over a wide area, creating many secondary victims (The Committee for the Compilation of Materials on Damage Caused by the Atomic Bombs in Hiroshima and Nagasaki, 19811. It has been sug- gested (Knox, 1983) that under certain meteorological conditions, con- vective clouds would form over burning cities and effectively scrub out much of the smoke. This remains one of the hotly debated criticisms of the nuclear winter theory. For the lack of any better evidence, it has been common to assume that about half of the smoke produced by nuclear fires would be promptly removed (e.g., NRC, 1985~. The 1985 NRC study assumed that a total urban area of 250,000 km2 would bum. Assuming that half of the toxic smoke was promptly deposited in an area of 1 million km2, then the average concentrations of chemical toxins in soil and water within these urban areas would be higher than the concentrations calculated above by a factor of about 60. Of course, these areas would contain a large fraction of the surviving population. Cancer risks from chemical carcinogens would likewise be increased. The average cancer risk because of TODD, for example, would be increased to 7 x 1O-4 for those persons remaining in the urban areas. This is approximately 10 percent of the cancer risk resulting from exposure to 50 reds of ionizing radiation, which has been estimated as the average ra- diation dose to nuclear war survivors (Turco et al., 19831. Considering that this calculation is based on one specific isomer of one class of com- pounds and that many other carcinogens would be produced by the nuclear fires, it is not unreasonable to suspect that long-term human and biological
160 PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES effects of the chemical fallout would be as important, if not more im- portant, than that of radioactive fallout. Estimates of the increased cancer incidence because of inhalation of asbestos fibers released to the atmos- phere by a nuclear war, for example, is also of the order of 10 percent of that due to radiation exposure (Birks et al., 19851. It is important to note that it is possible that synergisms between chemical exposure and radiation exposure could also increase the cancer incidence following a nuclear war, but insufficient data exist to evaluate such effects. An important difference between chemical toxins and radionuclides is that radioactive contamination is readily detected by relatively inexpensive Geiger counters, while the TCDD isomer of dioxin, like many other toxic compounds, can only be determined by use of a gas chromatograph cou- pled to a mass spectrometer; the cost of the latter instruments are in the range of $100,000 to $500,000. Thus, an important characteristic of chem- ical fallout is that living environments, food, and water could not be readily surveyed in order to determine their safety. ULTRAVIOLET SPRING It was first recognized in 1972 that oxides of nitrogen produced in nuclear fireballs and lofted to the stratosphere could result in severe ozone depletion (Foley and Ruderman, 1973; Johnston et al., 19731. Ozone in the stratosphere serves as a protective shield against ultraviolet radiation. Particularly significant to the biosphere is radiation in the ultraviolet-B (UV-B) region (280-320 nary). This finding that nuclear explosions could affect stratospheric ozone came as a result of the earlier recognition by Crutzen (1971) and Johnston (1971) that oxides of nitrogen serve as ca- talysts for ozone destruction according to the now well-known cycle of reactions: NO + O3 ~ NO2 + O2 NO2 + O > NO + O2 O3 + he ~ O2 + O Net: 203 > 3O2 Note that nitric oxide (NO) initiates the ozone destruction process, but is regenerated, so that no net consumption of nitrogen oxides occurs. In fact, each NO molecule introduced into the stratosphere can destroy about 10~2 to 10~3 ozone molecules during its residence time in the stratosphere (Brasseur and Solomon, 19841. In 1975 the National Academy of Sciences evaluated the effect of a 10,000-megaton (Mt) nuclear war on the stratospheric ozone shield (NRC, 19751. That study estimated a 30 to 70 percent reduction in the ozone
POSSIBLE TOXIC E - IRONME=S FOLLOWING A NUCLEI Wow 161 column over the Northern Hemisphere and a 20 to 40 percent depletion for the Southern Hemisphere. Since that time, there has been a modern- ization of the nuclear arsenals; large multimegaton warheads have been replaced by more numerous warheads (due to MIRVing Multiple, In- dependently Targetable, Reentry Vehicles), typically having individual yields of 100 to 500 kilotons (kt). The degree of ozone depletion is highly dependent on the height of injection of oxides of nitrogen, and these smaller warheads produce bomb clouds that stabilize at much lower al- titudes. The altitude distributions of the nitric oxide injections for the two scenarios evaluated in the recent 1985 study of the National Academy of Sciences (NRC, 1985) are superimposed on the ozone concentration profile in Figure 1. The NRC baseline scenario utilizes exactly half of the strategic warheads of every type in both the U.S. and Soviet arsenals, except for any weapons with yields greater than 1.5 Mt. For this scenario oxides of nitrogen would only be carried to altitudes as high as 18 km, and the maximal ozone depletion in the Northern Hemisphere, as shown in Figure 2, would be 17 percent. An excursion scenario considers that an additional 100 bombs with yields of 20 Mt each would be detonated. (There are 60 50 40 10 o Regions of NOX Injection Baseline lo OO ° oo Excursion ~ + . ~ _:~: .: - . :0: . :~^ ~ ~ ^ ~.% or -~-.\ .. ~-v A-.-.-.-.-.-. ~ -, 1 \ 1 1 1o1 1 O3 DENSITY (cm~3) 1 o1 2 low FIGURE 1 Altitudes of injection of oxides of nitrogen for the NRC baseline and excursion nuclear war scenarios. The normal ozone concentration profile is also shown by the solid line. (National Research Council, 1985.)
162 -10 PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES I -20 by ~_30 C: of N - 0 o - - - - , _ ~Computed Hemispheric Average Ozone L ~Column Change as a Function of Time 1 ~ B = Baseline Scenario (6500 Mt) \ ~E = Excursion Scenario _\ E ~(Baseline plus 100 x 20 Mt) -50 1 1 1 1 1 1 1 1 1 J 0 2 4 6 8 10 TIME (yr) FIGURE 2 ~ Ozone depletion as a function of time following a nuclear war for the NRC baseline and excursion scenarios. (National Research Council, 1985.) thought to be 300 such warheads in the Soviet arsenal.) For this scenario, oxides of nitrogen would reach an altitude of 37 km, and the maximal ozone depletion would be 43 percent. Note that the maximum in ozone depletion would occur after a period of 8 to 12 months, and it would take on the order of 10 years for ozone concentrations to return to normal. Thus, once most of the smoke and dust was removed from the atmosphere and sunlight began to break through, the biosphere would not receive normal sunlight but, rather, sunlight highly enriched in ultraviolet radia- tion. No estimates of ozone depletion have yet taken into account the large perturbations in atmospheric physics and chemistry resulting from the dust and smoke emissions. The recent finding by Malone (this volume) that the solar-heated smoke clouds would rise into the stratosphere is extremely important in this regard. The introduction of smoke aerosol to the strat- osphere would be expected to add to ozone destruction in at least three ways: (1) The absorption of short-wavelength radiation by the smoke would reduce the rate of oxygen photolysis, thereby decreasing the rate at which ozone would be produced in the stratosphere. (2) The absorption of solar radiation by the smoke particles would heat the stratosphere and increase the rates of reactions that catalyze ozone destruction (e.g., the NO + O3 reaction given in the cycle above). (3) Reaction of ozone at
POSSIBLE TOXIC EWIRONME=S FOLLOWING A NUCLEI Wow 163 the particle surfaces would directly destroy ozone. The particle surface could catalyze the conversion of ozone to oxygen (2O3 ~ 302) or be oxidized by ozone to form products such as carbon monoxide t03 + C (solid) ~ O2 + CO (gas)~. The latter reaction would act to consume the particles and thereby shorten the duration of the nuclear winter. Although ozone would be destroyed in either case, UV-B radiation would also be strongly absorbed by soot particles, so that the effects on the biosphere would not be felt until most of the soot was either destroyed by ozone or removed from the stratosphere. This is a very important problem that should be treated by model calculations in the near future. We are currently obtaining laboratory data on the reactions of ozone with carbonaceous particles (S. Stephens, M. Rossi, and D. Golden, manuscript in prepa- ration) for input into such models. An increase in UV-B radiation would affect the already stressed eco- systems of our planet in several ways (Ehrlich et al., 19831. UV-B wave- lengths of light are absorbed strongly by peptide bonds and by nucleic and amino acids (National Research Council, 1982), and these energetic photons can cause chemical changes which affect biological structure and function. Productivity of terrestrial plants and marine plankton is known to decrease with even small increases in UV-B levels (Caldwell, 1981; National Research Council, 19821. Immune system suppression (National Research Council, 1982), blindness (Pitts, 1983), and other physiological stress factors caused by UV-B increases would lead to increased incidence of disease in humans and other mammals. Even normal processes of DNA repair in bacteria are suppressed by increased UV-B exposure (National Research Council, 19821. PHOTOCHEMICAL SMOG FORMATION The chemistry of the troposphere (the region of the atmosphere between the ground and the stratosphere, 0-12 km) is very complicated and would become even more complicated by the addition of millions of tons of dust, smoke, and gaseous chemicals. A mild example of tropospheric pertur- bation is seen in a heavily polluted urban center. These population centers are sources of oxides of nitrogen, carbon monoxide, partially combusted hydrocarbons, and particulates; it is the interaction of these species with sunlight that results in the formation of strong oxidants such as ozone. The potential of a severe global photochemical smog following a nuclear war was suggested by Crutzen and Birks (1982~. However, a necessary ingredient to photochemical smog formation is sunlight, and it was their concern that the absorption of sunlight by smoke might reduce the levels of oxidant formation that led them to make the first estimates of the amount of smoke produced in nuclear war fires.
164 PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES The darkness of nuclear winter would certainly prevent a photochemical smog from forming during the early weeks following a nuclear war, and the parallel removal of gaseous pollutants and particulates would tend to ameliorate the rate of oxidant formation at later times (Penner, 19831. Reactions of oxidants with particle surfaces would also tend to prevent a photochemical smog from forming (Birks et al., 1985~. However, pho- tochemical smog with high concentrations of ozone could occur near the edges of pollutant clouds for the period of time that the particulate cloud cover is still patchy. Because of their damaging effects on plants and animals, atmospheric oxidants are generally viewed as undesirable. However, these oxidants, particularly the hydroxyl radical (OH) derived from the photolysis of ozone, provide the useful function of cleansing the atmosphere. For ex- ample, of the order of 100 million tons of reduced sulfur compounds such as hydrogen sulfide and dimethyl sulfide are emitted to the atmosphere each year by microoganisms in the soil and ocean. The oxidation of these compounds to sulfuric acid in the normal atmosphere is initiated by OH. The highly soluble sulfuric acid is then rapidly removed by rain. Under the dark clouds of nuclear winter, the OH radical and other oxidants would be greatly reduced in concentration, and as a result such biogenic emissions would accumulate to unusually high levels in the atmosphere. Although lethally toxic levels are not expected to be reached, at least for the sulfur compounds it is likely that the concentrations would build up to levels well above the threshold for human smell (Birks et al., 1985~. CONCLUSIONS Those who would survive the prompt effects of a nuclear war would face a radically altered physical environment. A period of weeks to months of darkened days and subfreezing temperatures would stress the ecosys- tems, on which mankind ultimately depends, in ways unprecedented in recorded history. Not only would the distribution of existing food stores be interrupted, but the growing of food would become impossible. As the sooty smoke is slowly removed from the atmosphere and the sunshine begins to break through, it is likely that this light would be highly enriched in damaging ultraviolet radiation adding a further insult to the already injured biosphere. There would always be great uncertainty about the safety of any food eaten, because it could be contaminated by chemical toxins, in addition to radioactivity. With the lack of sophisticated analytical instruments, chemical contamination would be impossible to detect. That the nuclear winter and other environmental effects of a nuclear war were overlooked for so long should make us wary; the worst effects
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