TRANS URANIC RADIONUCLIDES IN MARINE ENVIRONMENT 525 



data in hand simply indicate that uptake by organisms either by assimilation or by surface 

 adsorption is greater for certain species than for others. 



Biokinetics of Transuranics in Marine Organisms 



The pubhshed information deaUng with the uptake, assimilation, and loss of the elements 

 plutonium, americium, curium, and neptunium in marine organisms is limited. Apart 

 from the general lack of concern regarding transuranics as potential marine pollutants 

 until the late 1960s, there are other reasons why progress in this field has been retarded. 

 First, the number of laboratories having access to fresh flowing seawater and the culture 

 facilities necessary to undertake such research are limited. Second, the extensive radiation 

 protection measures required to conduct even modest tank experiments with these 

 alpha-emitting radionuclides coupled with the analytical task of making large numbers of 

 low-level alpha measurements have discouraged most investigators. Finally, thos5 

 laboratories which have been involved in marine transuranic measurements are reluctant 

 to house even small amounts of these radioelements so as to preclude the possibiHty of 

 sample contamination, which would compromise their low-level determinations. 



It is surprising that as early as 1966 Todd (1968) and Todd and Logan (1966) had 

 demonstrated the feasibiUty of using ^^'^Pu (T^ = 45,6 days), which decays by electron 

 capture, as a tracer for metaboHc studies. However, it was not until 1974 that Bair et al. 

 (1974) used this isotope in a dual-labeling experiment with 239,240p^ j^^ ^ comparative 

 study of the distribution and excretion of the element in beagle dogs, and only recently 

 Fowler, Heyraud, and Beasley (1975) used the isotope to perform metabolic studies with 

 marine organisms. Because of its high specific activity (curies per gram), it is possible to 

 approach lov/ atom concentrations in labeling solutions more comparable to those found 

 in environments contaminated by the lower specific-activity isotopes ^^^■^'^^Pu and 

 ^^^Pu. In addition, the 100-keV X ray emitted in the deexcitation of ^^''Np permits easy 

 detection by Nal(Tl) scintillation techniques and therefore permits whole-body counting 

 techniques to be used with small marine organisms. Therefore, for plutonium many of the 

 obstacles for laboratory tank experiments can be minimized, even though current 

 production costs of ^.^^Pu are high ($500 per microcurie) and small amounts of ^^^Pu 

 and ^^^Pu are present in the purified ^^''Pu. 



Although laboratory experiments can be performed with care using ^^^ Am as a tracer 

 and counting its 60-keV X ray by scintillation techniques, relatively high activity levels 

 must be used and small experimental animals must be used to preclude serious geometry 

 problems associated with the absorption of the weak X ray in the organisms. For curium 

 and neptunium, there are no isotopes of long enough half-Hfe and decay characteristics to 

 permit in vivo measurements; thus one must use the more demanding techniques of total 

 alpha counting by thick source measurements (Cherry, 1964; Guary and Fowler, 1977) or 

 chemical isolation of the isotopes and alpha spectrometry. It is not an exaggeration, 

 therefore, to say that much time and effort will be expended before sufficient data are in 

 hand to present a reasonable picture of the biokinetic behavior of transuranics in aquatic 

 organisms. 



Plutonium 



Perhaps the first open-literature publication dealing with the uptake and tissue 

 distribution of plutonium in a marine organism was the work of Ward (1966). Using the 

 lobster Homarus vulgaris, she demonstrated that direct uptake of ^^^'^'^'^Pu from labeled 



