Similarity of ²⁴¹Am and ⁵⁹Fe specification in selected freshwaters and of their adsorption on crayfish exoskeleton

The particulate fraction (measured by filtration through 0·45 μm filters) and the organically complexed fraction (measured by gel filtration chromatography) of freshly added ²⁴¹Am and ⁵⁹Fe were determined in 21 prefiltered surface waters. The adsorptive behaviour of both radionuclides on a biological surface (isolated carapace segments of crayfish) was tested simultaneously. A striking similarity was observed in the chemical and adsorptive behaviours of both radionuclides. The stoichiometry of particulate formation revealed a 3/4, Am to Fe ratio. This same stoichiometric relationship was observed in organic complexation, while adsorptive behaviour was characterised by a 1/1, Am to Fe ratio. It is concluded that Am predictably follows the chemistry of freshly added Fe at least over a 15 day period. This observation may find interesting application in risk assessment where use can be made of the well-known geochemical cycling of iron to predict the behaviour of man-made Am.