618 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



mammals. The highest observed retention (whole body) at 63 days was 3.8% of ingested 

 dose for ^^^Pu citrate, whereas retention of the fulvate was 0.6%. Reduced uptake of the 

 fulvate complex is thought to be due to either its high molecular weight (> 10,000) or its 

 stability in metabolic systems. Increased uptake of ^'^^Pu citrate is attributable to both 

 high gut permeability and instability of the complex in metaboHc systems. Chelation can 

 either enhance or reduce the uptake of ingested plutonium relative to plutonium 

 hydroxide (monomer) in channel catfish. Approximately two-thirds of the initial body 

 burden of plutonium (administered as citrate) was lost within 63 days after gut clearance. 

 These results suggest that the observed retention pattem of plutonium in channel catfish 

 was due to plutonium labehng of the gut followed by subsequent turnover by cell-renewal 

 processes. This suggestion is based on the observed slow gut-cell renewal times in fish (20 

 to 30 days) (Hyodo-Taguchi, 1968) compared with those in mammals (48 hr in mouse) 

 (Lesher-, Wahlburg, and Sacher, 1964). 



Tissue-distribution studies in channel catfish revealed that relatively little (<10%) of 

 the intracardially injected plutonium citrate was excreted. Blood clearance rates were 

 similar to those found in small mammals, the plutonium being associated primarily with 

 the plasma protein transferrin. The fractional body burdens in bone, Uver, and kidney 17 

 days after injection were 31, 24, and 9% of the injected dose, respectively. High kidney 

 burdens relative to mammals are expected since the kidney functions as the major site of 

 hemopoiesis in teleosts. The absence of significant excretion of plutonium reinforces tlie 

 previous suggestion that a short half-life component of elimination following gut 

 clearance in gavage studies is due to plutonium uptake by, and subsequent turnover of, 

 cells in the gut wall. 



A distribution coefficient of 9 x 10^ was observed for sediment in a year-old aquatic 

 microcosm spiked with ^^^Pu nitrate. A materials balance at 90 days postspike provided 

 the following estimates of plutonium distribution: 0.001% in water, 0.04% in biota, and 

 over 99.9% in sediments. Concentrations of ^^ ^Pu in whole animals, including fish, were 

 surprisingly uniform (within a factor of 10, 1.2 to 9.9% of mean sediment concentrafion). 

 This was related to gut loading of sediments and/or surface contamination. The uptake by 

 emergent macrophytes not exposed to surface contamination was quite small: <0.03 to 

 0.1% of the sediment concentration. 



On the basis of this set of laboratory experiments, sorption to plant surfaces, on gut 

 walls, and on exoskeletons appears to provide the dominant sites for plutonium 

 deposition in or on submerged components of aquatic systems. Interestingly, the 

 sediment distribution coefficient observed in the laboratory microcosm study was well 

 within the range of values reported from a wide variety of laboratory and field studies 

 (Table 6). 



In a study of crayfish from the Great Miami River, Wayman, Bartelt, and Groves 

 (1976) reported that most of the plutonium was concentrated in soft tissues rather than 

 in the sclerotized shell. Similar results were reported earlier by Nelson and Noshkin 

 (1973) for the Tridacna clam and lobster in marine studies at Enewetak Atoll. Noshkin 

 (1972) reported higher concentrations of 2 3 9,240p^ j^ ^g gj^^jj ^^ -^^ ^^^ body of 



scallops, whelks, and moonshells collected off Cape Cod. Ward (1976) also observed that 

 the calcified shell appeared to accumulate 2 3 9,2 4 Op^ ^^ ^ rapid rate. A very high 

 proportion (89.5%) of the total plutonium was in the skeleton, which accounted for 

 about 43% of the total weight of the lobster. Concentration factors for shells were on the 

 order of 200, and gills were about 100. The flesh, which comprised about 28.7% of the 

 total body weight, contained only 1.2% of the plutonium present in the entire body. The 



