Radiobiological Studies at the Eniwetok Test Site and Adjacent Areas of the Western Pacific

Page 1

RADI OBI OLOGICAL STUDIES AT THE ENIWETOK TEST SITE AND ADJACENT AREAS OF THE WESTERN PACIFIC Laboratory of Radiation Biology University of Washington

Page 2

RADIOBIOLOGICAL STUDIES AT THE ENIWETOK TEST SITE AND ADJACENT AREAS OF THEWESTERN PACIFIC Laboratory of Radiation Biology University of Washington The nuclear experiments conducted at Bikini and Eniwetok Atolls in the Marshall Islands are more than experiments to measure physical forces; they are unparalleled scientific experiments involving a great number of scientific disciplines. Among the disciplines represented, biology is taking a leading role. Biologists have been a part of this scientific team activity since the inception of the atomic tests at Bikini in 1946. Studies with the radioactive materials resulting from the weapons tests and deposited in the sea and on the islands have made it possible to follow the biological cycling of these materials even where they have become diluted to infini - tesimal quantities, by standards of ordinary chemical analysis. Hines (105 1) has described the general problem of evaluation of this research. Much attention has been given to the more immediate effects of the weapons tested upon the fauna and flora of the atolls but such studies,

Page 3

important as they are, have not occupied the total planning, thinking and execution of the program of biological studies. Extensive investigations using the facilities, personnel, and equipment available at the test organizations and test sites have answered many questions relating to the economy of the sea, have opened up new knowledge of the life zones of coral atolls, and have reshaped cepts of biological science. By ala available and the methods of in important ways some of the basic conmicrochemist and physicist, biology has advanced to a more exact science. Since the pre-test preparations for Operation Crossroads in 1946, representatives of marine biology, oceanography, and geology have made intensive studies at some of the atolls in the northern Marshall Islands, with the result that few oceanic areas have been studied as intensively by such a variety of specialists as have Bikini and Eniwetok Atolls. Notable contributions have been made to the knowledge of the geology of atolls by Tracey et al. (1948) and Ladd (1952).—— reported on the water circulation in Bikini lagoon, waves on Bikini reefs has been described by Munk Von Arx (1954) has and the action of ocean Robinson (1954) made studies of the sea temperature in the Marshall Islands. Barnes et al. (1948) reported on the ocean circulation in the—— Marshall Islands area, and Mao and Yoshida (1954) described the physical oceanography of the same region. Schultz et al. (1953) have described the—— fishes of the Marshall and Mariana Islands. The plants of Bikini, etc. were

Page 4

studied and reported on by Taylor (1950), Fosberg (1953), St. John (1949), and E3iddulph (1952). Dawson (1957) has reported on the algae of Eniwetok Studies on the distribution of radioactive materials produced by the atomic tests conducted in the Marshall Islands have been published by the Laboratory of Radiation Biology, * University of Washington, as research and development reports for the U. S. Atomic Energy Commission. An atoll may be described as a roughly oval, coralline reef rising 15, 000 feet above the ocean floor. Within the surrounding reef there is enclosed a shallow lagoon generally with a maximum depth of about 180 feet. The lagoon is open to the ocean by one or more passes cutting through the reef, most of which is awash except at low tides. Emergent land consists of low sandy islands with an elevation seven to ten feet above sea level; elevations as high as twenty feet are rare. The islands occupy only a small fraction of the total area of an atoll. Bikini lagoon covers 229 square miles (Handbook on the Trust Territory of the Pacific Islands) and has a dry-land area of two and a third square miles divided among some thirty-six islands and islets; Eniwetok lagoon covers 388 square miles, has a dry-land area of two and one-fourth square miles, and forty islands. These atolls lie in a zone of the northeast trade winds. Because of the constancy of direction of the winds, there are distinct differences in reef form between the windward and leeward sides of the atoll. The windward side is generally considered the region of most rapid growth and is *Formerly the Applied Fisheries Laboratory

Page 5

characterized by a narrow, slightly elevated ridge near the reef edge, the Lithothamnion ridge, which is lacking on the leeward side. The latter drops off vertically to depths of 100 to 200 feet on the seaward side, while the seaward slope of the windward reef falls away at an angle of about On the reef and in the lagoon, there is an abundance of colorful plant and animal life in which the keen competition between different species for space and food is very evident. On every hand there is evidence of rapid growth and simultaneous destruction. Masses of reef-building coral are competing with each other and with the coralline marine algae for space, one often overgrowing the other. Schools of green parrot - fish gnaw wide scratches on the coral. Fleshy patches of algae are pressed tightly against the surface of the coral to hold against the surges of the water pushed across the reef by the crashing breakers. Sea urchins and clams grind niches into the stantly feeding on the cover of bacterial stantly being replaced. The clams, the hard coral, some of and algal film which corals, some small other forms are ceaselessly removing from suspension in the water the small, often microscopic, plants, animals, and bits of debris which make up the plankton. In regions of quieter water, where sand has been deposited, sea cucumbers and spider snails, among the larger forms, turn the sand again and again in their gleaning for food.

Page 6

Large schools of goatfish, mullet, surgeon-fish, and other plant and plankton feeders are a common sight. Preying on unwary or disabled of these schools are the carnivorous fish -- the groupers, tuna, sharks. Ultimately the waste products and carcasses of these carnivores are returned to the lagoon and reef to complete the Little or no time is lost between steps in the biological cycling of materials for there is not only an abundance of organisms but also a wide variety of species -- some 700 among the fishes alone (Schultz et al.—— 1953) -- so that whatever is not utilized by one is quickly taken by another. There is here a perfect economy of use of substances essential Available substances are rapidly taken up by the biota, never remaining long in the water to be diluted and washed away. This is dramatically demonstrated following an atomic test in which radioactive materials are deposited in the water. Within hours, the great bulk of these materials is to be found in the living organisms. Plankton and some of the algae, which are the key organisms in the food chain, may concentrate within themselves more than a thousand times the amount of radioactive substances found in the sea water. The herbivorous fish and invertebrates have lower concentrations of radionuclides at any given time than do the plants on which they feed, and progressing along

Page 7

the food chain to the carnivores the concentrations become lower and lower. Within each organism tissue to tissue, the digestive the other tissues, where a more topes has taken place. More specifically, plankton, there is a differential concentration from organs having a higher concentration than selective deposition as to specific iso - the oceanic plants and animals that drift about passively with little or no resistance to may influence greatly the distribution of radioactive materials in the sea. These forms include many groups of organisms from the simple one-celled plants to the larval forms of vertebrates. Plankton acquire radioisotopes by absorption, adsorption, or both. Plankton, especially phytoplankton, present a greater absorptive surface to the environment than any other group of marine organisms. Thus, the major initial concentration of radioactive isotopes probably occurs in the phytoplankton -- the same organisms which comprise the foundation of the food chain in the sea. The isotopes especially concentrated by these forms are, for the most part, representatives of those elements which tend to form strong complexes with organic material. They include nearly all of the anionic radioisotopes, with the exception of iodine, and the cationic radioisotopes produced by neutron induction, including radioactive zinc, cobalt, iron and manganese. AU of the cationic radioisotopes concentrated in the plankton are biologically important elements comprising the essential parts of enzyme

Page 8

s ys terns and, on one case at least, an essential vitamin. The levels of radioisotopes present in the plankton vary with time after release of the radioactive materials, mainly because of the variation in availability due to physical decay of the individual radioisotopes (Bonham,1958 ). In general, however, plankton contain the three radioactive isotopes of cobalt, C057, C058 and C060, at a level of 11 to 50 percent of the total radioactivity. Zn65 is present at a level of 12 to 47 percent; Fe55 ’59 at a level of 1 to 40 percent; Mn54 in trace amounts, and the fission products Zr g5-Nbg5 at levels of 3 to 44 percent; Ru106and Cs 137 in trace amounts, if present at all (Lowman 1958 ). SrgOYg 0 has not been found in plankton. Once the radioactive materials have been absorbed or adsorbed by the plankton, their distribution is likely to be greater both vertically and horizontally than if distribution were solely dependent upon the surface currents. One reason for a greater distribution would be that absorption by plankton makes the radionuclides available to larger organisms which can move beyond the current’s boundaries. Similarly these materials also become available to the local resident populations and, as they are recycled through the food chain, the effect is a delay in their distribution away from the original area of contamination. Another factor influencing the distribution of radioactive materials by plankton is their diurnal vertical migration. If this migration were great enough to take the plankton below the current stream, it would extend the vertical

Page 9

distribution and also slow down the horizontal distribution, because the plankton would be moving horizontally more slowly than the water. Plankton may carry radioactive materials from the deeper waters of the lagoons to the surface or even up onto the reefs and eventually to the islands by vertical migration. At Bikini it has been observed, for example, that these materials were picked up by the plankton in the deeper waters of the lagoon during the daytime. The concentrated radionuclides in the plankton were then transported to the surface by the diurnal vertical migration of these minute forms. At the surface, their presence at night caused the surface radiation content to increase measurably over the daylight readings. The fouling organisms on the bottoms of the ships and the plankton feeders on the reef became increasingly radioactive at night as the transport of the radioactive proI t can be said then that plankton may cause the distribution of radionuclides in the sea to be different from that which would be ex - petted from the distribution by currents alone in the following respects: (1) a delay in the movement from the area of original contamination, (2) a slower down-current movement, (3) a limited dispersion up-current or beyond the currents’ boundaries, (4) a greater vertical distribution, and (5) an over-all greater dispersion of relatively lower concentrations. Aquatic plants or algae may be free-floating (as are the phytoplankton), attached to the reefs, or growing in the shallow water. Just as do land

Page 10

plants, the algae contribute to the food supply of animal populations. Minerals as well as organic materials, concentrated and incorporated into the algae, are passed on in the food chain to the animals that feed upon them. Thus the radioactive materials pass through the algae to the animals in the normal course of food gathering. The affinity of algae for some of the radioisotopes For example, Asparagopsis, a marine alga found on is well known. the reefs at Bikini and Eniwetok, has a great affinity for iodine (Palunibo, 1955 ). In the presence of 1131 and along the food The land plants of Asparagopsis becomes radioactive. This alga sought by fishes; thus the 1131 passes to the the tropical islands of the Pacific atolls become contaminated with radioactive materials in two ways: (1) by fallout of material from the air or from the rain water with direct absorption through the leaves, and (2) by absorption from the soil. The soils of the atolls are generally deficient in potassium. This deficiency speeds the uptake of Cs 137 by the plants. Although Ce 144 is present in the soils it is so firmly bound there that little is available to The radioisotopes remain concentrated in the top two inches or less of soil. The rooting habits of the plants, therefore, are associated with uptake of the radioisotopes. The plants with feeder roots close to the surface thus take up more of the radionuclides than do While all of the tissues of the plants may contain those with deeper

Page 11

major concentrations are to be found in the leaves, bark, seeds, corms or nuts. Since these are the most used portions of the plant for animal foods, the plants pass the radioactive materials on to the animals where they are incorporated into the animal tissue, only to be released in the normal biological cycle and passed back to the land The invertebrates, or animals without backbones, make up the great bulk of the animal life of an atoll. The role of these animals in the cycling of radioactive materials in an atoll is as varied as the invertebrate forms. Sea cucumbers have been compared with earth worms in their ceaseless turning of the gravel and sand as they obtain their nutriment from bacteria and algae. Corals and clams remove microorganisms and particulate matter from the water and also are host to the unicellular algae, Zooxanthellae, which are found in their tissues. The Zooxanthellae may be thought of as a vast reservoir of trapped plankton. Their relationship to their host is not completely understood but it is probable that they play an important part in the removal of phosphate wastes. Corals and clams are eroded by algae and sponges, which bore holes in the skeleton buting to a return of carbonates to the water. or shell, thus contri - worms and others also attack the skeleton of the corals. land crabs contribute to the deposition of radioisotopes sea onto the islands by dragging fish and algae ashore Some of the

Page 12

In short, within the invertebrates and their symbionts alone complete biological cycles occur from land to sea and back again, from inorganic substances to organic and back again. The fishes of the waters in and about the Marshall Islands have received a major share of the attention in the study of the of radioactive materials (Applied Fisheries Laboratory, and South, 1957 ; Welandeq 1958 ). Despite detailed study, the …