528 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



molluscs, which derive their plutonium from reprocessing wastes, tissue concentrations 

 often exceed those found in the shell, and concentration factors for benthic fishes appear 

 higher as well (Hetherington, Jefferies, and Lovett, 1975; Hetherington et al., 1976; Pillai 

 and Mathew, 1976; Guary and Fraizier, 1977; Guary, Masson, and Fraizier, 1976). This 

 discrepancy may result from differences in (1) bioavailability of physicochemical form, 

 (2) absolute levels in the environment, (3) duration of exposure, and (4) environmental 

 processes in various ecosystems. 



Data on the biokinetic behavior of plutonium in marine fishes are scarce. Pentreath 

 (personal communication, 1977) has studied the direct uptake of ^^''Pu(+6) from 

 seawater by the plaice (Pleuronectes platessaj, as well as assimilation from Nereis sp. 

 injected with the isotope. Sixty-three days following direct uptake from water, the 

 whole-body concentration factors were <1. Complete dissections of the fish showed that 

 ^^''Pu had concentrated in all fish in the stomach (concentration factor, 1 to 2), upper 

 gut (1 1 to 26), and lower gut (2 to 10). Concentration factors for skin and gill were 1 and 

 2 to 3, respectively. Plutonium was detectable in the livers of six of the seven fish used in 

 the experiment (0.8 to 1.7), and only traces were measurable in blood cells, plasma, and 

 bone of two fish. 



The retention of ^^'''Pu by plaice fed injected Nereis sp. [both Pu(+4) and Pu(+6)] 

 and subsequently fed unlabeled A^ere/s sp. as maintenance rations ranged between 0.4 and 

 3.0% 5 days after exposure. The measured Tb^ values of ^^"^Pu for 10 fish in the 

 experiment ranged from 9 to 49 days. By contrast, the retention of parenterally 

 administered ^^^Pu(+4) in five fish that had been injected in the right dorsal muscle was 

 relatively high; T^i^ values ranged between 642 and 877 days. Similar results were 

 obtained from fish that had been injected directly in the body cavity (Tbvi, ^^~ ^° WOO 

 days). Redistribution of the isotope within the fish 158 days postinjection was marked; 

 the highest accumulations occurred in the liver, kidney, and spleen. Similar distributions 

 were observed for both injection sites. 



Unlike the plaice the thornback ray (Raja clavata) appears to assimilate more ^^"^Pu 

 from Nereis sp. when the isotope is injected into the worm. Measurable amounts of the 

 isotope are detected in the liver at dissection (Pentreath, personal communication, 1977). 

 Crab digestive gland, which was incubated with ^^"^Pu and subsequently fed to both 

 plaice and rays, produced results similar to those from experiments in which A^ems sp. 

 was used. Clearly, the digestive physiologies of the two fish are sufficiently different that 

 enhanced plutonium uptake occurs in the ray. 



The most recent evidence suggesting efficient assimilation of plutonium from labeled 

 food by invertebrates is the work of Fowler and Guary (1977a) in which crabs {Cancer 

 maenas and Cancer pagurus) were fed ^^''Pu-labeled TV. diversicolor. Remarkably high 

 assimilation efficiencies ranging from 20 to 60% were observed. Of the ^^''Pu absorbed 

 across the gut wall, 43 to 85% was found in the hepatopancreas, 8 to 43% in the shell, 

 and 5 to 10% in the gill. It appears to make no difference whether the initial plutonium 

 labeling solution contains Pu(+6) or Pu(+4). Initial results from experiments in which 

 mussel (M. galloprovincialisj tissue labeled by ^^''Pu uptake from water and phyto- 

 plankton was fed to starfish indicate similarly high assimilation efficiencies (Fowler and 

 Guary, 1977b). These latter experiments would tend to support the earlier contention of 

 Noshkin et al. (1971) that food-chain magnification in the simple food chain mussel- 

 starfish can occur. That crabs efficiently take up plutonium from labeled environments 

 has equally been demonstrated by the work of Guary, Masson, and Fraizier (1976) and 

 Guary and Fraizier (1977). 



