-12- the uptake and metabolism of other elements by plants or animals and that an over-abundance of one element may, after a time, reduce or increase the uptake of itself and related elements according to the organism. d. It is desirable to determine the intermediate steps involved in the retention of radioactive contami- nation within a food chain by using single isotopes. However, the end results for a given type of detonation near or under water can be obtained in a much shorter time by using mixed isotopes as laboratory checks against data collected in the field. 4. What are the advantages of working at Eniwetok rather than in continental sites? a. Bikini and Eniwetok represent the only under or near water detonations. All the continental sites used to date have been in desert areas b. far removed from water. Very complete biological surveys have been made at Eniwetok and at other locations in the Marshall Islands Sy. Ss. Atomic Energy Commission report, MDDC-496.