The project has determined that radionuclides are removed from waters in an estuarine environment by several physical, chemical, and biological means. For example, radionuclides are absorbed in river-bed sediments at a rate varying directly with sediment particle size. Mollusks, such as clams, marsh mussels, oysters, and scallops, not only assimilate radionuclides selectively, but do so in sufficient quantity and with sufficient reliability to be useful as indicators of the quantity of the isotopes present. Clams and mussels are indicators for cerium-144 and ruthenium-106, scallops for manganese-54, and oysters for zinc-65 (most of which winds up in the oyster’s edible portions). It was learned that scallops assimilate more radioactivity than any other mollusk. Of the total radioactivity, manganese-54 accounts for 60%: The scallop’s kidney contains 100 times as much manganese-54 as any of the other tissues and 300 times as much as the muscle, the only part of the scallop usually eaten in this country.
On the left are mussels collected near the Columbia River in an environment containing abnormal amounts of zinc-65.
Mussels suspended in seawater in research to determine how fast they lose their zinc-65 radioactivity. (Photograph taken at low tide.)
In a surprising unintended result, it was determined that one acre of oyster beds, comprising 300,000 individual oysters, may filter out the radionuclides from approximately 10,000 cubic meters (18 cubic miles) of water per week!
The Radiological Laboratory scientists also have found that plankton are high concentrators of both chromium-51 and zinc-65, and that zinc apparently is an essential nutrient for all marine organisms. Some plants and animals appear to reach a peak of radionuclide accumulation quickly, which then tapers off even though the radiation concentration in the water is unchanged.
While the AEC’s oceanographic research budgets have not been large, they have contributed materially to knowledge of the oceanic environment. AEC-sponsored research at Scripps Institution of Oceanography has determined by a process known as neutron activation analysis[11] that the concentration of rare earth elements in Pacific Ocean waters appears to be only about one hundredth of the level previously reported. By analysis of naturally occurring radioisotopes, they have also discovered that it takes from one million to 100 million years for lithium, potassium, barium, strontium, and similar elements introduced into the ocean from rivers to be deposited in the bottom sediments. Aluminum, iron, and titanium are deposited in from 100 to 1000 years. They have also found that sedimentation occurs in the South Pacific at a rate of from 0.3 to 0.6 millimeter per thousand years, in the North Pacific at a rate several times that figure, and in the basins on either side of the Mid-Atlantic Ridge at a rate of several millimeters per thousand years.
The University of Miami has successfully developed two methods for determining the ages of successive layers of deep ocean sediments based on the relative abundances of natural radioelements, and thereby has established a chronology of climatic changes during the last 200,000 years during which the sediments were laid down.
The U. S. is not alone in its use of nuclear energy as a tool of science. The United Kingdom has carried out radiological studies of the marine environment for many years, particularly concentrating on the effects of radionuclides from nuclear power plants on the sea immediately contiguous to the British Isles. Both the European Atomic Energy Community and the International Atomic Energy Agency also encouraged marine radiological studies. Many laboratories and government agencies in Europe, North and South America, Africa, and the Middle East and Far East have well-established and productive programs under way.