PRECONCENTRATION OF PLUTONIUM RADIONUCLIDES FROM NATURAL WATERS K. M. Wong, V. E. Noshkin, and T. A. Jokela Lawrence Livermore Laboratory Livermore, California ABSTRACT A large-volume water sampler using manganese dioxide impregnated car- tridges for the in sttu separation of plutonium in seawater and ground- water was studied. Plutonium concentrations obtained by this technique are compared with a radiochemical coprecipitation method. Consistent results were obtained between the two methods for water samples from the Pacific Ocean and Enewetak lagoon. Different results were noted from samples collected in the Enewetak reef and groundwater stations. We were able to demonstrate, using this preconcentration technique and the coprecipitation method, that the physical-chemical characteristics of Pu in Enewetak reef and groundwater are different from the lagoon and open ocean. INTRODUCTION Accurate measurements of plutonium in the marine environment require very large samples due to the extremely low concentration of Pu which originates mainly from worldwide fallout. For example, measurement of a surface seawater sample with a 239>240py concentration of 2 x 10716 Ci/liter, a typical surface seawater concentration in the 30-40 N latitude (Noshkin et al., 1978), would require 100 liters of sample and 1 week of counting time to obtain a one sigma counting error of 10% (assuming 80% chemical recovery and 30% counting efficiency). Even larger samples would be needed to determine 238py concentration. The Battelle Large Volume Water Sampler (Silker et al., 1971), BLVWS, has been used for concentrating im sttu plutonium from natural water (Emery et al., 1974; Schell and Watters, 1975), but the interpretation of the quantitites collected by the BLVWS is not without problems 583 (Noshkin