Sediment from the Ravenglass estuary has been fractionated by procedures which might be expected to bring about no change in the chemical forms of the bound plutonium and americium. The action of molten N-methylmorpholine-N-oxide (NMMNO) on the sediment extracts 20% of the 239Pu and 241Am, possibly in forms associated with humic-like materials. On dialysis, these extracts appear to lose 40% of the 239Pu and 20% of the 241Am. However, on pretreatment with base there is no significant loss of radioactivity on subsequent dialysis and this may indicate the existence of cationic forms of these elements. High gradient magnetic separation (HMGS) has fractionated the clay constituents (<0.2 μm and 0.2-2.0 μm) into three subfractions. From an analysis of the 239Pu/241Am ratio it would appear that there is no conservation of isotopic ratios; this might indicate that the environmental forms of 239Pu and 241Am exhibit markedly different affinities for the organo-mineral phases of the sediment.