708 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



likely be disadvantageous and selected out of populations (National Academy of 

 Sciences-National Research Council, 1972;Muller, 1950). 



Application of Existing Data 



Existing data can be used to predict the magnitude of human or ecological hazard from a 

 given level of transuranic contamination. As mentioned, however, computational models 

 that reasonably simulate actual environmental and physiological processes require many 

 parameter values which in themselves vary with circumstances and site. Existing 

 knowledge of appropriate parameter values for plutonium behavior in extensively studied 

 areas, such as the Nevada Test Site, the White Oak Creek drainage at Oak Ridge, and 

 Rocky Flats, appears sufficient to develop models with reasonable credibility. Data that 

 could be applied to most other terrestrial environments, however, are essentially lacking. 

 This is especially true for transuranics other than plutonium. 



Complexities involved in computational models have been discussed in considerable 

 detail by Healy (1974), Anspaugh et al. (1975), and Martin and Bloom (1976). Healy 

 (1974) undertook the difficult task of calculating the levels of plutonium in soil which 

 might be considered standard or guideline levels for humans residing on and deriving 

 sustenance from such soils. The standard levels calculated could conceivably result in the 

 attainment of maximum permissible doses for members of the public. The computations 

 were general in application and used available experimental data and conservative 

 assumptions. The conceptual model considered surface soil to be the major reservoir and 

 source of plutonium and considered processes by which the material might reach the 

 critical organs of man. These processes included resuspension, atmospheric dispersion, 

 cloud depletion, deposition, inhalation, ingestion of soil and contaminated foods, skin 

 absorption, and metabolic behavior following intake. The calculations suggested that 

 4 X 10'"* iJiCi ^•'^Pu/g or 25 /iCi ^^^Pu/m^ in the top 3 cm of soil was probably a 

 conservative standard. 



Using a similar approach but with site-specific data from the Nevada Test Site, Martin 

 and Bloom (1976) calculated that 3 nCi ^^^Pu/g (soil) ( 1 70 idCi/nr ) could result m the 

 nonoccupational maximum permissible dose to the lung (1.5 rem/yr) of a standard man 

 living over and obtaining food from the soil in question. This model was presented in a 

 lucid and practical way, and the relative degree of confidence that can be placed on each 

 parameter used in the model was made clear. The basic approach relates intake rates for 

 ingestion and inhalation to surface soil concentrations; human metabolic and dose 

 calculations are based on International Commission on Radiological Protection (ICRP) 

 models and recommended parameter values. 



In the ecological context, it seems important to consider the concept of the "critical 

 organism." Although our primary concern, is focused on man, the general welfare of the 

 human population cannot be separated from environmental quality. Legal, moral, and 

 scientific justification exists for ensuring the protection of species other than man from 

 environmental contaminants. Indigenous species of plants and animals, by virtue of 

 proximity and life habitats, will receive substantially higher radiation dose rates than man 

 at many sites likely to receive transuranic contamination. On the other hand, many wild 

 species, because of shorter normal life-spans, may not live long enough to develop serious 

 pathology from chronic low-level exposures. In addition, tbr wildlife, society is generally 

 concerned about performance of the population, whereas for humans, we are concerned 

 about the more limiting case of individuals ( Auerbach, 1971 ). 



