Examining Environments
Seeds produced by plants grown in soil of a radioactive waste disposal area pass (in aluminum cups) on moving belt through a radioactivity detector as part of a study of movement of radioisotopes in food chains.
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
An ecologist inspects cages placed around bagworm infestations of a red cedar tree that had been injected with radioactive cesium-134 to determine uptake of radioactivity in the larvae.
Checking pine seedlings exposed to ionizing radiation from a radioactive source (on tripod) in a controlled ecosystem. Seedlings on left were fully exposed, those in the middle were exposed on their tops only, and those on the right were exposed on their stems only.
Biologist studying the root distribution of plants by injecting radionuclides into the soil and measuring plant uptake.
A thriving Messerschmidia plant growing on Rongelap Atoll is studied for growth-rate and root-systems data after the island was accidentally subjected to radioactive fallout.
Aerial view of a “Gamma Forest”, where growing trees are exposed to chronic irradiation from a source at the center of the picture. This environmental biology study shows varying sensitivity of various trees. Trees in the center were killed by extremely high doses of radiation for 20 hours a day over a 6-month period.
Apparatus containing a strong radiation source being installed by biologists in a semitropical rain forest for 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.