Part 6

Radiobiological developments on land result from combinations of environmental influences. Studies in the Rocky Mountains show that ecological conditions above the timberline, particularly in areas where snowbanks accumulate, are efficient in concentrating fallout radionuclides. Concentrations thus take place in the snow-packed heights that are the sources of mountain streams flowing to the plains far below.

Atmosphere

The environment of the earth is a product of “weather”—of the transport of moisture, of the actions between winds and oceans, of the cycling of energy through biotic systems. Understanding of biological potentials of atmospheric factors involves understanding of atmospheric motions affecting transport and mixing of contaminants and the processes of deposition of radionuclides from atmosphere to earth.

At some thousands of feet above the earth’s surface—at 30,000 to 40,000 feet in the middle and polar latitudes and at 50,000 to 60,000 feet in the tropics—there is a level, the tropopause, at which air temperature, rather than decreasing, becomes constant or increases with height. Below this level is the troposphere, the turbulent zone of clouds, rain, and fog. Above it is the stratosphere, where there is no turbulence and only a slow mixing of dry and cloudless air. The stratosphere continues to a height of about 100,000 feet. Investigators have noted the importance of rain or snow in washing fallout particles from the air in the troposphere. There is disagreement on the precise modes of distribution of radioactive materials projected into the stratosphere.

In the detonation of low-yield nuclear devices, fission products are not projected beyond the troposphere, and fallout is washed down in periods of days or weeks. Because winds move principally in east-west directions, tropospheric fallout appears on the earth in bands centered approximately at the latitude of detonation. But when high-yield explosions propel contaminants into the stratosphere, the pattern of subsequent developments is less clear. It once was believed that fallout from the stratosphere was distributed more or less evenly—though over long periods of time—over the surface of the earth. The present view is that fallout debris placed in the stratosphere remains in that hemisphere in which the explosion occurs. This concept is based on an atmospheric circulation theory that air enters the stratosphere at the equator and descends again in temperate and polar latitudes each spring. The theory presumes a much shorter “residence time” of stratospheric air and thus a quicker return of fallout particles to the turbulent troposphere.

The presence of radionuclides in the atmosphere has provided clues to cyclical movements of biological importance. During the period of nuclear tests in the Pacific, observers noted spring “pulses”, or increases, of strontium-90 deposition in the northern hemisphere, a phenomenon difficult to verify or explain satisfactorily while testing was proceeding. Later, when testing had been suspended, the spring peaks reappeared. The observation seemed to support the theory that nuclear debris injected into the stratosphere was descending years later through a gap in the tropopause.

Samplings of nuclear debris by balloon have been under way for several years at altitudes of 100,000 to 150,000 feet, and rocket-borne air samplers and other systems have been developed for taking atmospheric samples up to 200,000 feet.

Programs for studying airborne contamination from industrial activities—operated at the more accessible but equally difficult levels of the atmosphere—have been sponsored by the Atomic Energy Commission near the Hanford Plant, Washington, and at the Oak Ridge, Argonne, and Brookhaven National Laboratories in Tennessee, Illinois, and New York. The Hanford studies were started before plutonium production was begun in 1943, and findings on industrial stack-discharge rates established patterns for meteorological programs at other sites.

PROBLEMS AND PROJECTS

The range and variety of environmental studies now in progress make it almost impossible to provide any all-encompassing statement of results. Almost all places associated with nuclear programs have become focal points of research in environmental biology. Fallout, deposited in patterns determined by the mechanisms of the atmosphere, has created at certain points on the earth’s surface—the Arctic, for example—ecological conditions that require investigation. New information of bioenvironmental significance has come in bits and fragments. We can, however, attempt to summarize what has been learned and to show, in broad terms, how radiobiological experience has extended appreciation of the earth as a single ecosystem—a system comprised of an infinity of interactions of water, land, and atmosphere, and of all living things.

The spectrum of environmental investigation—investigations using man-made radioactivity—incorporates research in which:

1. Fallout radioactivity is assessed as a potential specific hazard to human populations.

2. Conditions created by fallout are examined for their potential long-term ecological significance.

3. Radionuclides introduced into the environment by nuclear tests, reactor operations, or other means are used as trace materials in basic studies in biological systems.

4. Radioactive forms of minerals and nutrients are deliberately introduced into biosystems—in measured amounts and under conditions of control—for studies of metabolic cycles and rates of flow of energy and nutrition.

It will be useful to look in detail at some typical programs and results.

ANIMAL RESEARCH

Wasps and Radioactive Mud

At Oak Ridge National Laboratory, Tennessee, it was discovered in 1964 that two kinds of mud-dauber wasps were building their mud nests in equipment, cabinets, and electronic gear in the vicinity of a field station on the Oak Ridge reservation.

Some nests, investigation disclosed, were built of radioactive mud. It seemed obvious that the wasps were obtaining mud from radioactive waste pits or from the White Oak Lake bed, which is the site of a former 40-acre lake used for 12 years as a detention pool for radioactive wastes.

The mud daubers were carrying mud as far as 650 feet from the contaminated sources. Almost 90% of 112 nests built by the yellow-legged mud-dauber species were radioactive, and the mud was delivering to the wasp eggs each hour a dose of penetrating radiation equal to that received by a man from all natural sources over a period of many years. The development presented no human health problems, but further observation revealed a fascinating circumstance.

At the same time, another variety of wasp, the pipe-organ mud dauber, was building nests only of nonradioactive mud. Of 150 pipe-organ wasp nests examined, none was radioactive. The nests were found in similar locations, and it was apparent that the same sources of nest materials were available to both species.

WASP NEST RESEARCH

Mud-dauber wasps, building nests of radioactive mud in a waste disposal area near an Oak Ridge, Tennessee, atomic plant, are the object of intensive environmental radiation study. A shows radioactivity reading from a nest. B is an enlarged view of the nest with two tiny dosimeters in place to measure radiation. In C an ecologist inspects new nests built in a laboratory flight cage from radioactive mud provided in pans at the bottom. In D wasps are anesthetized, marked with tiny plastic disks for future identification, and released.

The question, then, was why wasps of one species were using radioactive mud while the other species seemingly discriminated against contaminated mud. The muds appeared to be entirely alike. X-ray-diffraction studies showed no material differences, nor were there detectable differences in “feel”, smell, or plasticity. Radioactive isotopes in the mud included cesium-137, cobalt-60, ruthenium-106, and zinc-65. Oak Ridge scientists began to try to find out whether the pipe-organ wasps actually were discriminating against muds containing all or some of these radioisotopes or against the ionizing radiation from them. If so, how could the wasps detect it? These investigations were continuing in 1965. There is no answer yet.

Survival of an Animal Population

The case of Bikini already has been discussed as an example of a predominantly aquatic environment apparently recovering from association with nuclear experiment. Eniwetok offers an instance of the toughness of an animal population exposed both to direct and long-range radiological impact.

Engebi Island, on Eniwetok’s northeast reef, is the home of a wholly self-contained colony of Pacific rats living in a network of burrows in the shallow coral sands. After 1948 Engebi was exposed repeatedly to atomic detonations, and in 1952 the whole island was swept clean of growth and overwashed by waves from the thermonuclear explosion of Operation Ivy. On each of these occasions, exposure of the rat colony to radiation was intense. In 1952, by later estimates, the animals aboveground received radiation doses of 2500 to 6000 roentgens per hour, and those in burrows doses of 112 to 1112 roentgens per hour. The island environment was so altered by atomic forces and by contaminated water that radiobiologists believed it impossible that any of the rats had survived. Because there was no natural route by which the island could be repopulated, scientists even considered introducing a new rat colony for study of a population growth in a mildly radioactive environment.