_ ig at first, slower later, but always decreasing. Although it would be impractical to calculate MPC values on a basis other than a constant exposure level, the fact that the exposure level usually is changing needs to be considered in evaluating hazard from MPC values. The specific radioactivity of the ocean waters decreases with distance from the Bikini-Eniwetok test site because of decay of the isotopes and dilution within the ocean, but because plankton and fish concentrate certain elements from the sea, radioactivity was detected in some fish caught by Japanese fishermen in waters to the westward of Bikini-Eniwetok Atolls. Japanese research ship, of the test site, During the 1954 survey by the “Shunkotsu Maru," in the vicinity radiological analyses were made of both fish and water samples. Also during the summer of 1954 radiological analyses were made of tuna and other fishes caught by Japanese fishermen during regular fishing operations in the central and western Pacific Ocean. A radiological survey of fish at the ports of landing in Japan begain in March and continued until November. When the Japanese fishing vessel, "Fortunate Dragon," which had been caught in the fallout of March 1, at Bikini Atoll, 1954 from a test returned to Japan and it was found that