Atoms, Nature, and Man: Man-made Radioactivity in the Environment — Key Ideas to Explore

uced a miscellany of radioactive products presenting unexplored possibilities of hazard. The word “fallout” was coined to describe the deposition on the earth of radioactive debris from nuclear explosions.

The first peacetime nuclear tests, conducted at Bikini in 1946 in a military-scientific exercise designated Operation Crossroads, were designed to assess the effects of nuclear weapons on naval vessels. The test organization, Joint Task Force One, an adaptation of the wartime joint task force combat concept, was a massive waterborne force including 42,000 members of the armed services, civilian scientists, consultants, and observers.

Bikini Atoll was selected for the tests because, among other things, it was remote from heavily populated areas, it offered a protected anchorage, and it had the relatively stable and predictable meteorological and oceanographic conditions considered essential to operations in which the unknowns loomed so large. Three test detonations originally were projected; two ultimately were carried out. The first, Test Able, was an airdrop of an atomic bomb on July 1, 1946, over a test fleet of 70 ships anchored in Bikini Lagoon. The second, Test Baker, was the detonation on July 25 of an atomic device suspended in the lagoon 90 feet below a small target vessel.

Although Crossroads was a military program, the mobilization of scientific interests was in many ways of historic proportions. For months before the explosions, oceanographers studied the waters and the structure of the mid-Pacific basin and meteorologists the winds and upper airs. Geologists, zoologists, botanists, and other specialists examined the atoll in detail. Bikini became, as it remains to this day, one of the most thoroughly familiar ocean structures in the world.

There was awareness, even then, of the significance of radioactivity as an element of nuclear effect. The task force made elaborate preparations to assure the safety of personnel and sent to the atoll thousands of radiation-detection instruments. Plans were made to observe the effects of radioactivity on test animals placed on ships of the target fleet.

The Underwater Detonation

The first of the Bikini events, Test Able, the explosion of a bomb dropped from an aircraft over the target fleet, sank a number of major vessels, left others sinking or crippled, contaminated many with radiation, and laid a plume of fallout northward over the rim of the atoll into the waters of the ocean. It was Test Baker, however, the underwater explosion, that would make Bikini the subject of radiobiological investigations for many years.

The Baker test was the first occasion in which nuclear debris was mixed with water and ocean sludge and returned to the area of detonation. The explosive device was of what later would be called nominal size, its force equivalent to 20,000 tons of TNT. The test still is regarded as a classic demonstration of the phenomena of shallow-water atomic explosion.

At the moment of release, the surface water of the lagoon was first lifted and then penetrated by a lighted bubble that vanished in seconds in a hollow column of water of gigantic dimensions—a column 2000 feet in diameter (its walls 300 feet thick) rising to a height of 6000 feet and containing 1,000,000 tons of water. At the base of the column, foam was churned upward for several hundred feet, and, moving out from the base, as the column sank back into the lagoon, surged a monstrous wave initially more than 80 feet high.

Radioactivity in the water was intense. The immediate total was described as equal to “many hundred tons of radium”. Decay and dilution of radioactive materials quickly reduced the total radioactivity. After 3 days, by which time water contamination had spread over an area of 50 square miles, the dose rate from the water was well within safe limits for persons remaining for brief periods. Yet it was several more days before inspection and scientific parties could spend useful time among the surviving target vessels.

At the bottom of the lagoon, below the point of detonation, Navy divers months later found that the explosion had scooped out thousands of tons of mud and coral sediment, creating a shallow basin half a mile wide. This basin, in the slow settling of returning sludge, became an area from which long-lived radioactivity entered Bikini’s biological system.

In 3 weeks of final work after Test Baker, the Bikini scientific teams took from the islands and the lagoon many hundreds of samples of plants, corals, crabs, fish, plankton, and water. They noted that radioactivity was present in all samples taken from every part of the atoll, which indicated an early uptake of radionuclides by the biota[9] and suggested that there was a continuing circulation of radioactive debris in the water. They took samples of fish in the open ocean outside the atoll and made comparative collections at other atolls. The instruments and techniques for analyzing radioactivity were far from refined, but all available evidence pointed to the need for more particular efforts to examine radiobiological results.

The Bikini Resurvey of 1947

A resurvey of Bikini, the first of many, was conducted with heavy radioenvironmental emphasis in July 1947, a year after the Crossroads tests. The scientific expedition was supported by 2 vessels and included 70 scientists and several hundred Navy personnel.

The resurvey group, entering an oceanic environment that had been completely undisturbed for nearly a year, established at once that traces of residual radioactivity still were cycling in Bikini’s ecosystem. For 6 weeks the scientists probed every realm of the atoll environment, sampling biota, making inventories of plant and animal communities, and obtaining core samples from the lagoon floor. When the data had been assembled and reviewed and the reports filed, months later, there was consensus that Bikini had produced no evidence that radioactivity, as a separate and identifiable factor, was having any immediate effect on the health of the atoll, and probably no cumulative effect, either.

There were, of course, unknowns. So long as radioactivity remained in the biological cycles there were possibilities of future developments. In 1947 no other place on earth offered an opportunity to observe the natural processes by which radiation contamination is eliminated from an environment. It therefore seemed prudent to compile a longer record, consisting of other, purely radiobiological surveys at Bikini.

By 1947 the new U. S. Atomic Energy Commission had taken over from the wartime Manhattan Engineering District the management of the national effort in the field of atomic energy. A primary responsibility of the AEC in that period was to press ahead with nuclear weapons development, but the agency also had specific obligations and interests in the fields of biology and medicine. Meantime, the testing of nuclear weapons had been started at a new proving ground at Eniwetok Atoll, 190 nautical miles west of Bikini.

Studies at Nuclear Test Sites, 1948-1958

The first test series at Eniwetok, Operation Sandstone (1948), incorporated no formal radiobiological studies, but radiobiologists visiting Bikini also made surveys at Eniwetok in 1948 and 1949. Then, for a time, world events intervened. The detonation of an atomic device by the U.S.S.R. in 1949 was followed in 1950 by the outbreak of the Korean War, and these events produced a national mood oriented toward national defense. By 1951, because events in the Pacific had interrupted tests there, the Atomic Energy Commission had established a continental test site in Nevada. In that year, too, tests were made at Eniwetok preliminary to the detonation of the first thermonuclear device.

After 1951 each of the test programs had its radiobiological component. In the Pacific, radiobiological surveys were associated with Operation Ivy (1952), Operation Castle (1954), Operation Redwing (1956), and Operation Hardtack (1958). A small field station, the Eniwetok Marine Biology Laboratory, was established for use by scientists conducting biological studies. Bikini was incorporated into the Pacific Proving Ground in 1953, and new biological surveys were performed there in connection with the tests of 1954 and later.

In these years, 1951 to 1958, the U.S.S.R. was testing nuclear weapons, as was Great Britain after 1952. Fallout from these contributed to the total of man-made radioactivity potentially available to the environments of the world.

The years between the establishment of the Pacific Proving Ground and the signing of the 1958 nuclear test moratorium were years in which the quest for environmental information could not keep pace with the rapid growth of nuclear capability. But the growth in the field of weapons served to underline the need for information and produced certain landmark developments in environmental research.

The detonation of the first thermonuclear device projected the problem of environmental contamination to the stratosphere and, literally, to every part of the earth. This explosion, Test Mike, largest on earth to that time, was set off on Elujelab Island, on the north rim of Eniwetok Atoll, on November 1, 1952. In the reef where Elujelab had been, the blast left a crater almost a mile in diameter and 200 feet deep. The towering nuclear cloud rose in 15 minutes to a height of 130,000 feet.

Test Mike marked a point of change. Before, fallout from nuclear detonation had been principally local, touching the waters and reefs of an atoll or a desert landscape. After Test Mike, the implications of fallout obviously were global.

A mishap in connection with a 1954 thermonuclear test at Bikini contributed in two important ways to the enlargement of environmental investigations. Fallout from the test, swept off its predicted pattern by unexpected winds at high altitudes, deposited debris on Rongelap, an inhabited atoll east of Bikini, and on fishermen aboard a Japanese vessel operating in the Bikini-Rongelap area. The accident, unfortunate in its consequences at Rongelap and in Japan, had other results of even wider impact. From it came the first international approaches to the problems of ocean contamination and, later, long-term bioenvironmental studies at Rongelap itself.

Wide-ranging studies of ocean-borne radioactivity were initiated by the Japanese. The experience of the fishermen produced in Japan a fear of contamination of fisheries resources as a result of the United States tests. One result was the organization, in the summer of 1954, of a government-sponsored ocean survey expedition that cruised from Japan into and through the Bikini-Eniwetok area to determine what amounts of radioactivity were being carried, by water and by aquatic organisms, toward the shores of Japan.

The expedition made significant observations of the role of plankton[10] in the biological utilization of ocean fallout. A United States scientific team, following up the Japanese effort, made a similar but far more extensive cruise through the Western Pacific early in 1955 and went on to Japan to discuss its findings with the Japanese. During and after the test series in the Pacific in 1956 and 1958, United States surveys of the ocean were made routinely. Exchanges of information between scientists of Japan and the United States continued.

The Rongelap case produced results of another kind. The Rongelap people were found to have suffered exposure requiring medical attention and continued observation. Evacuated from their atoll because it was not safe, members of the community were given care at other atolls until they could be repatriated in 1957, and received continued medical supervision thereafter.

The bioenvironmental condition of Rongelap was unique. The fallout had made the atoll the only place in the world contaminated on a single occasion by relatively heavy deposition of radioactive debris without also being disturbed by a nuclear explosion. In 1957-1958, after the Rongelapese had been returned to a new village constructed on their atoll, Rongelap was the site of a long and thorough study of the circulation of radionuclides in the terrestrial-aquatic environment.

Before the 1963 Test Ban Treaty

The first break in the pattern of nuclear testing came in 1958, when the nuclear powers agreed to a 1-year test moratorium. The world’s political and emotional climates were changing. For more than 5 years, the United States, which had announced its Atoms-for-Peace Program in December 1953, had been endeavoring to place emphasis on the use of atomic energy for constructive purposes. The Atomic Energy Act of 1954, liberalizing provisions of the 1946 law, contemplated for the first time private development of nuclear power resources and established authority for international activities. In 1957 the Atomic Energy Commission initiated its Plowshare Program for the development of peaceful uses of nuclear explosives.[11]

Amid such changes there was arising, too, a wider apprehension concerning the possible effects of fallout. The United Nations in 1955 appointed a committee of scientific representatives of 15 nations to study the effects of radiation on man. In the United States the National Academy of Sciences published in 1956 the first of its summary reports on the biological effects of atomic radiation.

Nuclear testing was not ended by the 1958 agreement, yet the moratorium—which was renewed annually until 1961, when the U.S.S.R. broke the agreement by initiating a new test series—was significant as an experiment in nuclear restraint. After the United States conducted a final test series near Christmas Island in 1962, new discussions of ways to halt successive rounds of nuclear test programs were held. Finally, in 1963, the Nuclear Test Ban Treaty was signed by most of the nations of the world. The treaty was, among other things, a declaration against worldwide fallout.

THE ATOM IN ENVIRONMENTAL STUDIES

Although his experience with radioactivity has been brief, man probably already knows more about the effects of radiation than he knows about the effects of many other contaminants that alter his environment. Even so, he knows far less than he needs to know to make certain that atomic energy is wisely managed in the future.

There has been neither time nor opportunity, for example, to gather radiation-effects data on more than a few hundred of the 1,500,000 kinds of living organisms inhabiting the earth. Nor is it possible to predict the extent to which life can adjust itself to environmental changes resulting from scarcely perceptible alterations of natural radiological balances. Also undetermined is the relation between environmental changes and the biological exchanges making up the often mentioned, but insufficiently understood, “balance of nature”.

The case of carbon-14 is an example of a permanent man-made modification of the environment. From the early ages of the earth, carbon-14 has been created in the upper atmosphere by the transmutation of nitrogen in cosmic-ray reactions. Carbon itself is an almost universal component of living matter, and the ratio between stable carbon and radioactive carbon is believed to have been unchanged for thousands of years. It is this circumstance that permits the use of carbon-14 as a tool for “dating”, or determining the ages of, fossil remains, prehistoric artifacts, and geologic formations. But carbon-14 also is produced in nuclear fusion, and the testing of thermonuclear devices after 1952 produced an estimated increase of 4% in the amount of carbon-14 on earth. This is enough to disturb the natural equilibrium. Since the half-life[12] of carbon-14 is some 5800 years, the addition will be a factor of environmental consideration for scores of human generations.

Nuclear tests, although not the only sources of man-made radioactivity, have been until now the most significant ones and the only sources touching large areas of the earth. The total product of nuclear testing is small in relation to the natural burden of radioactivity, raising the level of radiation to which all life is subject by a factor of one-tenth or less. But it is the unknown element, the degree to which fallout radioactivity may introduce new influences into the environment, that gives concern.[13]

When a nuclear device is detonated, the release of energy is due to the fission of uranium or plutonium atoms or to the fusion of hydrogen atoms. At the instant of fission, some 75 radionuclides, or fission products, are created.

From these primary fission products, about 100 other radionuclides may be formed, some existing only for microseconds and others for thousands of years. The radionuclides of significance to biologists are those that exist long enough—no matter how brief the time—to have an impact on a biological system.

Factors of biological transport and concentration of long-lived radionuclides make efforts to assess possible environmental effects particularly difficult. It has been asserted, for example, that probably every living cell formed since the early 1950s contains some of the radionuclides produced by nuclear testing. No one knows the significance of such a condition, if it indeed exists. It is certain only that some of the long-lived radionuclides already placed in the environment will be detectable there for hundreds of years and hence will continue to provide material for biological studies.

Examining Environments

When radioactivity is injected randomly into the atmosphere by a nuclear detonation, biological disposition begins in many ways, each related to the character of the explosion and the environment in which it occurs. Fallout studies thus involve the tracing of mixed fission products in the biosphere and the collection and analysis of thousands of samples of plant and animal tissue, and usually of water and soils, at many successive times. The radiobiologist then attempts to interpret the accumulated evidence of uptake of radionuclides. Some fallout studies may require sampling over large areas of the earth. Other investigations of fallout or of radioisotopes introduced deliberately into controlled field plots may require years of patient observation in small and circumscribed areas.

Studies of ocean fallout, for example, have ranged over hundreds of thousands of square miles of open water. The 1955 United States survey of the Western Pacific was conducted by a scientific team aboard a Coast Guard vessel, the _Roger B. Taney_, in a program called Operation Troll. In 7 weeks the team cruised 17,500 miles, making collections of water and marine organisms at 86 ocean stations on a route extending from the Marshall Islands through the Caroline Islands and the Mariana Islands to the Philippines and finally to Tokyo. The expedition took samples of plankton at depths down to 200 meters and water from the surface down to depths of 600, 800, 1000, and 1200 meters.

Environmental studies at nuclear test sites or in controlled ecosystems involve not only long-term, periodic sampling of plants and animals but also years of detailed examination of soils, meteorological conditions, and other factors.

TERRESTRIAL ECOLOGY RESEARCH

In programs of such scope and duration, the problems of interpretation are great. Broadly, environmental studies give consideration to:

1. The amounts and kinds of radioactivity released to the environment.

2. The rates of uptake by the biological system.

3. The amounts and kinds of radioactivity within the system.

4. The rates of metabolic transfer or elimination.

5. The amounts and kinds of radioactivity concentrated in tissue and acting internally.

6. The time required for biological processes to be completed and for any biological effects to develop.

Biological Inventories

Familiarity with the biological components of an ecosystem is essential to meaningful radiobiological assessment.

Inventories of natural components were not made in the early nuclear test programs because of inadequate realization of the biological potential. Later, they could be made only after radionuclides already had been introduced into the environments.

The survey of the mid-Pacific region before Operation Crossroads represented the earliest effort to examine an environment in detail before a nuclear detonation, but was designed so that it had only inferential value for other long-range biological research. The test surveys were useful, however, in expanding knowledge of specific environments. In addition, it was standard practice to make comparative collections of organisms in regions removed from the test sites to establish base lines, or “controls”, against which to measure radiobiological developments.

The most extensive inventory of an environment—an inventory designed specifically in relation to an anticipated nuclear detonation—was that made between 1959 and 1962, as a preliminary phase of Project Chariot, in the Cape Thompson area of Northwest Alaska. Chariot was a part of the AEC Plowshare Program in which it was proposed to excavate a harbor at the mouth of the Ogotoruk Creek, which empties into the Chukchi Sea. Although the excavation project actually never was undertaken, the “predetonation” environmental investigations involved 3 years of coordinated research into the climatic, marine, coastal, and terrestrial aspects of the region, and detailed studies of the history and the radiological and ecological situations of the human population.

The program was an effort to make a model environmental inventory. Its significance was both in its assessment of the base for determining the “biological cost” of the proposed operation and in the thoroughness of its documentation of the environmental features of a part of the world that previously had been virtually unexplored. It was a prototype for future studies.

Measurements and Interpretations

Determination of the amounts and kinds of radioactivity in a biological sample is a process wholly dependent on instruments, since radiation usually cannot be detected by the senses.

A biological sample is any material of measurable biological significance. A sample of tissue or similar organic material usually is dried or reduced to ash in a muffle furnace before it is examined with a radiation counting device.

Improved instruments now permit the counting of radioactivity at levels so low as to have been imperceptible a few years ago. The samples, placed in lead chambers for maximum shielding from background radiations, are examined by multichannel analyzers capable of recording radiation emissions continuously over long periods of time.

Data-processing techniques have been employed in the handling and interpretation of information from long-range biological sampling and analysis programs. Analog computers have been used experimentally for theoretical projections of results.