Association of Plutonium with soil organic matter

A significant association of environmental plutonium with the organic components of U.K. soils has recently been demonstrated by sequential leaching experiments on samples influenced by discharges from both the Dounreay and Sellafield nuclear fuel reprocessing plants. This relationship has been further studied by alkali extraction, fractional precipitation, and dialysis to isolate both the humic and fulvic acid fractions of a Cumbrian soil. The /sup 239,240/Pu activities of these extracts were 31 and 7.7 Bq g/sup -1/, respectively, greater than the activity of the bulk soil (5.9 Bq g/sup -1/). Gel filtration on Sephadex gels G-50 and G-150 further showed that the humic acid extract is composed of relatively large molecules, with approximately 65% of the plutonium in the largest of these; fulvic acid is of lower molecular weight, and its plutonium content is distributed more evenly throughout the molecular weight spectrum. In both humic and fulvic acids, iron is concentrated in the largest molecular weight (>150,000) fractions.