TRANS URANIC RADIONUCLIDES IN MARINE ENVIRONMENT 535 



TABLE 2 23 8p^/23 9 + 240p^3nji24,^j^/23 9 + 240p^^^jj^jjy 



Ratios in Mediterranean Surface Waters 



^'Iirrors are given in standard deviations. 



phanes norvegica were combined with soluble plutonium excretion experiments to arrive 

 at the flux rates of plutonium through the organism. Essentially 99% of the plutonium 

 taken up by M. norvegica is excreted by fecal pellets. A crude estimate of the removal 

 time of plutonium from the mixed layer by fecal-pellet production alone is 3.6 yr. 

 Although the uncertainties of such an estimate were willingly admitted by the authors, it 

 is interesting to note the approximate order-of-magnitude agreement between this 

 estimate and that of Hodge, Folsom, and Young (1973) and Folsom (1975), which 

 ranged from half removal times of 3.5 yr to complete removal times of 1 yr from the 

 surface layers of the ocean. 



Although evidence is accumulating on vertical transport mechanisms for the 

 transuranics as a result of planktonic biological processes (at a painfully slow rate!), we 

 are unaware of any published data on the redistribution of these elements either 

 horizontally or vertically by other marine organisms except reports that attribute the 

 redistribution of plutonium and americium from surface to deeper sediments to 

 bioturbation (Livingston and Bowen, 1976a; Livingston, Bowen, and Burke, 1976). 



Conclusions 



The amount of information now in hand Concerning the biokinetic behavior of 

 transuranic radionuchdes in marine organisms is astonishingly small and, as discussed 

 earlier, is plagued with difficulties inherent with experiments of this type. Even so there is 

 now evidence that certain marine organisms exhibit relatively high assimilation 

 efficiencies for the transuranics which are quite unlike those seen for terrestrial 

 vertebrates. There is increasing evidence to suggest that, despite similar aqueous 

 chemistries, fractionations among transuranics in the ocean can occur and are mediated 

 by the nature of the particulate matter to which they are adsorbed. Removal rates to 

 deep water and sediments would thus be quite different through thd world oceans. A 

 single attempt at numerically estimating the importance of zooplankton metabolic 

 products as a transport mechanism of plutonium to depth has shown that such 

 particulates are Ukely a key mode of removal. Yet this evidence comes from investigations 



