UPTAKE BY AQUATIC ORGANISMS 621 



sorption, gut labeling, and absorption from the gut. Again we stress that external 

 contamination with sedimentary particulate matter and gut loading are not considered to 

 represent true uptake and should be considered separately. The TTF, then, serves as a 

 realistic measure of plutonium discrimination in food chains. It should be noted that the 

 CR values for the Hanford waste pond fall into line with other data sets when considered 

 on this basis (Table 1). 



Some of the variation in TTF values observed can be explained by the relative trophic 

 position of the organisms analyzed. The number of intervening food-chain transfers 

 between the organism analyzed and the abiotic source of plutonium should be inversely 

 related to the observed TTF value. 



Conclusions and Recommendations 



To assess the potential transfer of plutonium to man from aquatic ecosystems, we 

 must concentrate on those food sources most closely linked to sediment as a measure of 

 maximum plutonium in human food. One could postulate, as an extreme, although 

 improbable, case, the direct consumption of sediment by man. Owing to the high Kd of 

 plutonium in sediments, direct ingestion could expose humans to plutonium con- 

 centrations up to several hundred thousand times tliose found in water. A more probable 

 projection, however, would be exposure to plutonium via a food chain involving a single 

 trophic transfer from sediment to an organism that is consumed by man. Such short, 

 single trophic transfer food chains should result in the highest plutoniumi concentrations 

 in human food derived from aquatic ecosystems (Critical Exposure Pathway). Some 

 examples would include bottom-feeding fishes, shellfish, and rooted macrophytes, such as 

 rice. Although we could find no data on the accumulation of plutonium in rice, this 

 information seems critical since it is representative of a single trophic transfer from 

 sediment to man and is a major dietary component of a large segment of the world 

 population. Further, both marine (Pillai and Mathew, 1976) and freshwater (Wahlgren 

 and Marshall, 1974) organisms associated with the sediment— water interface (i.e., 

 benthos) contain plutonium burdens that are one hundred times as high as those of 

 free-swimming forms. 



Present National Committee on Radiation Protection and Measurement (NCRP) 

 guidelines (Title 10, Part 20) for plutonium in food are derived by inference from 

 standards based on drinking water consumption at a fixed rate (International Commission 

 on Radiological Protection, 1959; National Bureau of Standards, 1959). The total 

 radioactivity ingested as food and/ or water cannot exceed the product of the Maximum 

 Permissible Concentration (MPC) times the consumption rate for water. Therefore, if an 

 individual is ingesting water contaminated at the MPC level, he or she cannot be exposed 

 to plutonium from any other dietary source. Weights of water and food ingested are 

 approximately equal for the Standard Man. It is apparent, therefore, that knowledge of 

 the expected dietary plutonium contribution from food is as important as that of the 

 contribution from water. 



The MPC for plutonium in drinking water was derived by using a fractional gut 

 transfer factor of 3 X 10~^ for ingested plutonium (International Commission on 

 Radiological Protection, 1959). The value of the human gut transfer factor is based on 

 studies whereby laboratory mammals were fed plutonium in a variety of chemical forms. 

 The value of 3 X 10~^ is based on plutonium administered in the nitrate form. Actual 



