. even roughly in view of the variations of conditions under which nuclear explosion tests were conducted and in view of the long period of natural weathering since that time. Some laboratory measurements exist for leaching of cesium from wedron sand, which of course is not the same as coral. For thermal treatmont at 1200°C, which is certainly encountered in fireballs and clouds from nuclear tests, the time for leaching to halve the cesium is initially about four years; for treatment at 20°C it is about two years (Lane, 1970). After the 15 years at weathering at Eniwetok Atoll, certainly the easily leached radionuclides have been removed, and so the time for halving by leaching is probably much higher than the few years observed in these laboratory experiare ments, Thus, leaching and weathering / not very likely to significantly ‘ hasten the decay of radioactivity beyond the nuclear decay times. However, weathering processes are known to be complex and to depend upon many variables (Crocker, 1965). Distribution of Fallout in Water The distribution of radioactive contamination in the sea after having been deposited by fallout is largely determined in horizontal distances by oceanographic effects and in depth by gravity. Distri- bution is altered to a much lower extent by the movement of organisms The horizontal, or geographical, spreading is probably determined primarily by ocean currents, although other factors in the horizontal dispersion are surface winds, currents, and horizontal density gradients. ue MRR ORI OEOL ’ 12 SE A RMTUES OE PTI EIU a we 18 te A WR. yon in and out of the contaminated area (Lowman, 1960), tans Sete eeetem ee