[Illustration: _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.