near (but not necessarily adjacent to) the area of the larger or more numeroustests. Isolated small regionswith relatively high concen- trations of 2°9*44°Pyare evidentin some of the less contaminated areas of the lagoon. The distribution of other long-lived, persistent radionuclides (including cesium- 137, strontium-90, europium-155, cobalt-60, bismuth-207, and technique haseffected a 100- to 800-fold reduction in sample size and has eliminated the high cost and inconvenience of transporting large-volume water samples to our homelaboratory. Figure 2 shows water, collected in barrels, being processed for plutonium onboard a research vessel funded by the Department of Energy. Table 1 summarizes the arithmetic mean of 229+2* Pu con- centrationsin filtered water sam- ples collected during different periods from the regions of Enewetak and Bikini. Concentrations in surface water collected 1 to 2 miles west and south of the Bikini and Enewetak atolls and levels in the surface North Equatorial Pacific americium-241) are equally com- plex and unique. It is generally believed that, following their introduction to the open ocean from any source, plutonium radionuclides become associated with particles and settle rapidly to the sea floor where they remain immobile after deposition. The concentrations of 299*?py and other long-lived radionuclides in the lagoon water column during any year subsequent to 1958 should, therefore, equal the tem- poral fallout concentration levelsin the North Equatorial Pacific surface water. Accurate assessment of the con- ceniration of plutonium in waterre- quires analysis of large-volume water samples. Such analyses were facilitated by a specially developed! technique for the rapid separation of plutonium from 50 to 400litres of water in the field. This new FIG. Large-volume water samples are collected in large containers and processed onboard research ships to separate plutonium and other radionuclides. This process eliminates the high cost and inconvenience of transporting large volumes of water samples to our home laboratory. 10