IOLOGIA MARINA EN DE ENIWETOK e las investigaciones sobre biologia en la zona de ensayo de Eniwetok. ‘leares efectuados desde esa fecha productos de fisidn y otros radioCo, Zn y 185W). El autor indica .uestras de plancton tomadas entre uminacidn, asi como la distribucién 1a. Los peces herbivoros contenian ‘nivoros contenian principalmente -NVESTIGATIONS < TEST SITE "MAN , UNIVERSITY OF WASHINGTON AMERICA s in the sea is of primary interest 2zard in his food materials derived the principal source of artificial eapons tests. In the future, howopment and the great volume of ’ surpass the present burden of onsigned to the sea in the future / In varying degrees from those in varison of the fates in the marine e two sources might appear to be e cycling of radioisotopes through isotopesin representative samples ars at the Eniwetok Test Site in ; of nuclear devices fired under a on of given radioelements from ths whether the fallout is mixed alline islands and reefs, or sodium ntially free of either of those nonioelements with similar chemical n marine organisms. The uptake 'y fallout is controlled primarily letermine the distribution of the he chemical factors which control the accumulation of the radioelements by the organisms in the sea. The chemical factors include the interaction of the radioelements with sea water and its contained salts, and the biochemical factors. Physical factors The distribution and availability of radioactive contamination with time in the sea is controlled primarily by the times at which the individual radioelements are condensed from a gas to a liquid within the fireball of the nuclear device, and by the physical half-lives of the constituent radioisotopes. ADAMS, FarLow and ScHELL (1), in a study of fallout particles at the Eniwetok Test Site, found that different ratios of radioisotopes were associated with different types of fallout particles. Unmelted calcium oxide particles collected their radioactivity in cooler parts of the fireball and at later times than did spherical particles formed of melted calcium oxide. Thelatter particles lost the porous structure characteristic of the unmelted particles, so that hydration in the particles of melted origin proceeded at a much slower rate. The particles also differed in their chemical constitution. Since iron and fission-product vapours from the nuclear device and associated structure were concentrated near the centre of the fireball, they tended to become incorporated more in the particles of melted origin than in the unmelted particles. Because the radioactive material condensed on to the unmelted particles in cooler parts of the fireball and at later times than on to the originally melted particles, a fractionating effect occurred in which the unmelted particles contained more of the volatile radioactive elements and, in the case of short- lived elements, their daughter products, The unmelted particles thus contained more radioactive barium (daughter of xenon) and strontium (daughter of krvpton). The effect of the physical half-life of the radioisotopes upon the distribution and availability of the contamination to the biomass in the sea is self-evident. Radioisotopes of short half-life will be available to the organisms for a limited time, after which the isotopes of longer half-lives will be of major importance. The distribution of radioactive contamination in space within the sea is largely determined by oceanographic effects and gravity. Distribution is altered to a much lower extent by the movement of organisms in and out of the contaminated area. The geographical distribution of the major masses ofradioactive contamination in the sea is probably determined primarily by ocean currents, although in the long run meteorological effects upon global fallout may be more important in world-wide distribution of marine contamination. Horizontal dispersion is dependent upon surface winds, currents, vertical and horizontal density gradients, and the size of the contaminated area. The rate of horizontal dispersion of radioactive material in sea-water was reported by REVELLE and SCHAEFER (2) to be about one million times the rate of molecular diffusion. Within the thermocline most of the motion of soluble and colloidal material occurs along surfaces of equal density, and thus dispersion in the lateral direction would be much greater than in the vertical. In observations made at the Pacific Proving Ground, DonaLpson ef al. (3), SEY- MouR ef al. (4), and PatumsBo and Lowman (unpublished) found the radioactivity mostly in the mixed layer and in some instances below the thermocline, but again the horizontal dispersion was much greater than the ‘ 107 ol Ak HEE