622 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



gut transfer factors reported in these studies ranged from 1 X 10~^ to 3 x 10~^, 

 depending on a number of factors (chemical form, species of test animal, age of test 

 animal, etc.) (Hodge, Stannard, and Hursh, 1973). To our knowledge no studies have 

 been published which determine the fractional gut transfer factor for plutonium 

 incorporated in actual food materials. On the basis of the variability in data reported 

 above, one cannot rule out the possibility that this factor may be significantly greater 

 than the values used by the NCRP. In addition, plutonium releases in low-level effluent 

 streams from fuel-cycle processes or from burial grounds may be in a more available 

 chelated form, which is either due to release in a chelated form or to long-term 

 environmental transformation to the chelated form. These potential routes need to be 

 quantified, and the dominant mobile forms need to be idenfified. 



Even greater uncertainty arises when trying to predict probable plutonium con- 

 centrations in an aquatic food source for purposes of dosimetric calculations. This 

 predicted concentration is the product of three values, plutonium concentration in water, 

 Kd for plutonium in sediment, and the TTF for a given single transfer food chain (Critical 

 Exposure Pathway). Since the Kj is known to be very high (=^10^), if the TTF value is 

 greater than 10~ ^ , the potenfial dose from food intake could be higher than the value for 

 which the standards (based on water intake) were designed, notwithstanding the 

 uncertainties cited above. Since TTF values of 5 x 10"^ to 5 x 10~^ appear reasonable, 

 based on data presented in this chapter [laboratory results (Eyman and Trabalka, 1977; 

 Trabalka and Eyman, 1976; Trabalka and Frank, 1978; Beasley and Fowler, 1976a; 

 1976b) and apparent CR values in benthic biota of 500 to 5000], our hypothetical 

 individual consuming such aquatic food organisms exclusively (obtained from a water 

 source contaminated at MPC levels) could receive radiation doses significantly higher than 

 intended by the standards. Although the radiation doses projected above obviously 

 represent a purely hypothetical case, the conditions sufficient to produce such doses 

 cannot be excluded because of the present uncertainty associated with parameters used to 

 derive the dose estimates. Further, it should be recognized that certain cases involving the 

 assessment of the plutcnium contribution to human diet require that the TTF be 

 separated into its components (i.e., for animals that are not to be consumed whole). It is 

 not our purpose to "single out" plutonium or any other actinide as an unusual hazard. 

 Many isotopes released to the environment from various nuclear-fuel-cycle processes have 

 been subjected to similar scrutiny in attempting to assess transport to man. Several 

 (radionuclides of cesium, strontium, and cobalt) will undoubtedly contribute significantly 

 higher doses to man than expected for plutonium (Blaylock and Witherspoon, 1978). To 

 demonstrate that tlie conservative assumptions stated above are unwarranted, we must 

 develop a data base on the environmental behavior of actinides reasonably comparable to 

 existing information on cesium, strontium, and cobalt. 



Future research on the transport of plutonium to man from aquatic ecosystems 

 should concentrate on those food chains which have the lowest number of trophic 

 transfers between abiotic sources in the system and man. Data generated from such 

 research will provide critical information necessary for the evaluation of present standards 

 by determining plutonium concentrations in critical aquatic organisms that serve as food 

 sources to man. Additional research on the relationship between the chemical 

 characteristics of plutonium in abiotic components of the system and observed 

 concentrations in edible aquatic foods will strengthen our ability to predict potential 

 transfer of plutonium to man from aquatic ecosystems. 



