Particle size and chemical phase distribution of plutonium in an estuarine sediment

Plutonium in Lake Michigan sediments has been shown to be associated predominantly with hydrous oxides and exhibits an activity maximum in particles less than 4 μm in diameter. However, since plutonium exhibits variable size and charge characteristics in waters of differing ionic strength and chemical composition, an investigation was undertaken to determine if the particle size and chemical fraction distribution of plutonium in other sediments might be different. A sample of marine sediment was collected from 60 ft of water in Buzzard's Bay, Massachusetts, with sealed Smith-MacIntyre grab having a surface area of approximately 1 ft2. The loose floc layer overlying the consolidated sediment was removed by suction and was lyophylized. Three subsamples of the dry material were taken for determination of the ash/dry weight ratios and total 239240Pu concentration; sequential extraction to determine the distribution of plutonium among various chemical fractions of the sediment; and separation into five size classes by wet sieving and elutriation in a carbonate-oxalate dispersant, followed by the determination of the 239240Pu concentration in each size class. The results of the sequential extraction clearly indicate that most of the 239240Pu is found in the citrate-dithionite extract as is the case for Lake Michigan sediments