High Concentrations of Transuranics and Natural Radioactive Elements In the Branchial Hearts of the Cephalopod Octopus vulgaris

Abstract

Data are reported which show elevated levels of plutonium and americium in the branchial hearts of the common cephalopod Octopus vulgaris. These levels were verified in both a laboratory experiment and in environmental samples. At the same time data for certain naturally-occurring radioactive isotopes of thorium, polonium and lead are given for comparison. Attention is d~rec ted to the potential of these small organs as monitors of transuranics and, probably, certain other elements in the marine environment. The behaviour of transuranic elements in marine organisms is currently the subject of detailed study. Development of the nuclear industry will require that monitoring of plutonium, in particular, be continued in marine samples, and the identification of organisms, or organs thereof, which consistently accumulate transu r a n i c ~ to elevated levels is a matter of importance. Investigations are usually of two types: either a laboratory investigation is carried out, in which animals are exposed to sea water and/or food labelled with an appropriate radioactive isotope (Vilquin et al., 1975; Guary and Fowler, 1977; Fowler and Guary, 1977), or measurements are made of the transuranic elements at the very low levels at which they are found in environmental samples (Pillai et al., 1964; Noshkin, 1972; Higgo et al., 1977). The former are less tedious, but their interpretation is frequently ambiguous because it is very difficult to reproduce exactly in the laboratory such factors as the physico-chemical form of the element and the partitioning of its mode of uptake into the animal via the alternative routes of food and water. We report here the results of an investigation in which both approaches were used. Unambiguous confirmation was obtained of elevated levels of plutonium and americium in the branchial hearts of the common octopus; also reported are levels of certain naturally' On leave from the Phys~cs Department, University of Cape Town occurring radioactive isotopes of thorium, polonium and lead in the same organs. We suggest that these small organs have considerable potential as monitors of transuranics and, probably, other elements in the environment. Four individuals of the molluscan cephalopod Octopus vulgaris, ranging in wet weight from 80 to 140 g, were caught off Monaco. They were placed in filtered and aerated sea water maintained at 13 + l C; the sea water was spiked with 237P~ adjusted to the + 4 state (Fowler et al., 1975) at 0.7 kBq (20 nCi) 1-' for two of the cephalopods, and with 2 4 1 ~ m (assumed to be in the + state) at 1 kBq (30 nCi) 1-' for the other two. Throughout a 15-d period the activity of the test animals was monitored regularly by gamma-spectrometry using a 3 NaI (Tl) crystal; at the end of this period the cephalopods were dissected and the concentrations of the nuclides in the various organs were measured. Details of the uptake phase, the many organs involved, etc., will be given elsewhere; for our present purposes, the data given in Table 1 are of primary importance. They highlight the situation in the branchial hearts vis-a-vis the hepatopancreas; it is well-known that the latter organ accumulates many elements effectively. The high percentages of both nuclides in the branchial hearts, which constitute a mere 0.3 % by weight of the whole animal, are immediately apparent, as are the high concentration factors with respect to the labelled sea water. We next performed an elimination experiment. Four further Octopus vulgaris (300 to 400 g wet weight each) were placed in 2 7 P ~ and 2 4 1 ~ r n labelled sea water for 10 d, under the same conditions as previously. Each individual was then transferred to flowing (unlabelled) sea water, and was fed daily with crabs and gamma-counted regularly. For both nuclides the loss curve showed a three component loss. The first component (representing desorption) was very rapid and contained about 24 % of the Pu and Am; the