SYNTHESIS OF THE RESEARCH LITERATURE 35 



purposes, but the levels have generally been orders of magnitude below those presumably 

 required to cause detectable ecological changes. Aquatic and terrestrial organisms exposed 

 to locally high levels of transuranic elements have been studied, but no evidence of 

 transuranic-related effects deleterious to a population has been reported (Bradley, Moor, 

 andNaegle. 1977). 



Numerous investigators have directly assayed plutonium and a few other transuranic 

 elements in tissues of a variety of environmentally exposed aquatic and terrestrial 

 organisms, including humans. In these experiments the tissue burdens and resulting 

 radiation dose rates have generally been less than dose rates experienced during 

 evolutionary time from natural sources of radiation. This is due to the low levels of 

 transuranic elements in the environment and also to their low solubihty and biological 

 mobility. At such low levels of radiation exposure, ecological changes would be 

 undetectable. Laboratory studies of a variety of aquatic and terrestrial species have shown 

 that radiation dose rates several orders of magnitude higher than those resulting from 

 natural background sources are necessary to produce gross changes in mortality or 

 natality. This is true even for tlte more radiosensitive stages of comparatively sensitive 

 organisms. 



Altliough gross ecological effects from transuranic elements are not Ukely to be 

 demonstrated at tlie levels hitlierto experienced in the environment, there is reason to 

 expect a statistically determined incidence of biological effects, such as tumors and 

 genetic alterations. In the absence of sufficient data to the contrary, a linear dose— effect 

 relationship is generally assumed for cancer induction and genetic mutations at low doses. 

 If this assumption is correct, then any dose, however low, imposes some risk. Since 

 concern for most plants and animals is generally for populations rather than for 

 individuals, modest increases in genetic or somatic effects are not expected to have 

 measurable consequences. A different attitude prevails for humans, however, where there 

 is concern for individual organisms. 



Dose rates can be calculated and compared with natural background or with literature 

 on dose— effect relationships. Table 16 lists dose rates calculated from measured tissue 

 concentration of plutonium in a variety of organisms exposed to elevated environmental 

 levels and in humans exposed to fallout. The data from Windscale, Rocky Flats, and the 

 Nevada Test Site apparently represent some of the organisms exposed to the higliest doses 

 of transuranic elements studied. Even in those higlily localized cases, calculated dose rates 

 are about tlie same as or less than those for natural background, and measurable 

 population-level changes are not expected (National Academy of Sciences-National 

 Research Council, 1972). Doses to humans exposed to fallout plutonium have been so 

 low that specific biological effects cannot be demonstrated (Thompson and Wacliholz, 

 this volume). 



Levels and distributions of transuranium nuclides in water, sediments, and selected 

 biota, particularly in locally contaminated freshwater and marine sites, have been 

 examined extensively. However, there are few data pertaining to biologic effects. In fact, 

 there have been no good opportunities to observe effects of transuranic elements in 

 natural aquatic ecosystems. Reported water concentrations of plutonium and other 

 transuranic elements in natural environments have been 1 pCi/liter or less, and dose rates 

 appear to be three to eight orders of magnitude less than dose rates required to produce 

 detectable effects (Templeton. this volume; Till. Kaye, and Trabalka, 1976). Present data 

 suggest that aquatic systems can receive several orders of magnitude more transuranic 

 activity than experienced in the past before ecological changes will be detectable. 



