460 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



An important goal of the Nevada Applied Ecology Group (NAEG) plutonium program is 

 to evaluate the potential radiological hazard to man due to the presence of plutonium in 

 various nuclear safety test areas at the Nevada Test Site (NTS). Since the contaminated 

 areas of interest are uninhabited, we have based our analysis on the assumption that a 

 Standard Man resides in and obtains most of his food from a plutonium-contaminated 

 area at NTS. 



In this chapter we use information provided by other NAEG studies to develop a 

 plutonium-transport model that attempts to characterize the general behavior of 

 plutonium in a typical NTS ecosystem and to provide a basis for estimating potential 

 rates of plutonium ingestion and inhalation by the hypothetical Standard Man. We discuss 

 the mechanisms involved in the transport processes and, in most cases, include 

 appropriate mathematical expressions for these mechanisms. However, the final form of 

 the transport model is determined by the available data, which often limits us to using 

 only the simplest mathematical expressions. 



The estimates of inhalation and ingestion rates provide the input for a dose-estimation 

 model that is used to calculate potential organ burdens, cumulative organ doses, and dose 

 commitments due to chronic inhalation and ingestion of ^^^Pu. Although several models 

 are considered, the preferred dose-estimation model is based entirely on the recommenda- 

 tions and publications of the International Commission on Radiological Protection (1959; 

 1964; 1966; 1972). 



Finally, a procedure is described whereby the combined results of the transport 

 model and the dose-estimation model can be applied to the practical problem of deciding 

 whether and to what extent environmental decontamination might be required to limit or 

 reduce potential health hazards due to plutonium. 



A preliminary model of potential plutonium transport from the environment to man 

 was introduced during the planning stage of the NAEG plutonium program to ensure 

 consideration of laboratory and field studies that would provide the data and parameter 

 estimates required for implementation of more detailed transport and dose-estimation 

 models to be developed later in the program. This model forms the basis for discussing 

 the various transport mechanisms in this chapter. Some of the parameters sought at the 

 outset have proved to be elusive or impossible to measure accurately, and consequently 

 the proposed dynamic model has not been fully implemented. This chapter represents our 

 best effort to ^udge and interpret the information currently available and to select the 

 best available methods for estimating potential intake rates and doses. Tlie design of the 

 transport and dose-estimation models plus the assumptions and parameter values selected 

 for their implementation comprise what we believe to be a reasonable and conservative 

 working hypothesis that provides a method for evaluating the potential health hazards 

 associated with plutonium-contaminated areas at the NTS. As a working hypothesis, it is 

 subject to continuing reappraisal, and the results or conclusions derived from it are 

 subject to unavoidable uncertainties. To a considerable extent, however, these uncer- 

 tainties are compensated for by conservative assumptions, which tend to result in 

 overestimates of potential intake rates, organ burdens, and doses rather than underesti- 

 mates. 



Plutonium-Transport Model (Preliminary Model) 



Figure 1 is a diagram of the potential transport pathways considered in the preliminary 

 planning model. The large square represents an arbitrary boundary of a contaminated 

 area. Boxes represent the principal ecosystem compartments of interest, and arrows 



