The role of marine plankton in the vertical oceanic transport of alpha-emitting nuclides. Part of a coordinated programme on transuranic cycling behaviour in marine environment

The octopus is a littoral species common in temperate and tropical seas; even though the branchial hearts constitute a small fraction of the animal their concentrating powers are such that a mere gram or two, in dehydrated form, obtained from 4 or 5 largish animals, is sufficient to allow the detection of 241Am with an error of about 25% per sample. The potential of these organs as biological indicators of transuranics and certain natural radioactive elements is to be emphasized; the present results also suggest that they reflect element concentrations in the surrounding water. It has further been shown recently that the branchial hearts concentrate certain other elements effectively, e.g. vanadium and cobalt, with concentration factors of 3x103 and 2x104 respectively. Interestingly, vanadium and cobalt seem to behave similarly to americium, plutonium and thorium in that they are less concentrated in the hepatopancreas than in the branchial hearts. The branchial hearts are organs with circulatory and excretory functions. They are rich in iron and this metal is localized in intracellular granules composed of purple-brown pigments or adenochromes; 241Am appears to be associated with these intracellular granules. A detoxification system as described for other molluscs may be involved; many elements accumulated from sea water may be associated with the intracellular granules of the branchial hearts and thus rendered less susceptible to intoxicate the vital organs of the cephalopod