PLUTONIUM TRANSPORT TO MAN INTRODUCTION Preliminary Model 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). As 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. 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 represent net transport via the pathways indicated. Arrows which cross the arbitrary boundary represent net transport out of the system. In this report, we utilize information provided by other NAEG studies to develop a plutonium transport model which attempts to characterize the general behavior of plutonium in a typical NTS ecosystem and provides a basis for estimating potential rates of plutonium ingestion and inhalation by the hypothetical Standard Man. The distribution of Pu in the contaminated areas of principal interest at the NTS has been described by Gilbert et al. (1975). Present levels of soil contamination in the areas of interest range from about 1.0 vCi/m? to >6,000 uCi/m?. Because these levels of soil contamination resulted from nuclear safety tests carried out from 1954 through 1963, and because current fallout rates are insignificant compared with existing levels of contamination, Figure 1 shows no current Pu input to the system. dose These estimates of inhalation and ingestion rates provide the input for a estimation model which is used to calculate potential organ burdens, cumulative of ingestion gugan doses, and dose commitments due to chronic inhalation and 233py, Though several are considered, the preferred dose estimation model is based entirely on the recommendations and publications of the International Commission on Radiological Protection (ICRP). Finally, a procedure is described whereby the combined results of the transport model and the dose estimation model may 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 insure consideration of laboratory and field studies which would provide the data and parameter estimates required for implementation of a more detailed transport and dose estimation model to be developed later in the program. Some of the parameters sought at the outset have proved to be elusive or model impossible to measure accurately and, consequently, the proposed dynamic to has not been fully implemented. This report represents our best effort the best judge and interpret the information currently available and to select The design available methods for estimating potential intake rates and doses. parameter and of the transport and dose estimation models plus the assumptions to bea values selected for their implementation comprise what we believe method for reasonable and conservative working hypothesis which provides a minated evaluating the potential health hazards associated with plutonium-conta As a working hypothesis, it is subject to continuing reapareas at the NTS. subject to unavoidpraisal, and the results or conclusions derived from it are these uncertainties able uncertainties. To a considerable extent, however, to result in overestiare compensated for by conservative assumptions which tend than underestimates of potential intake rates, organ burdens, and doses rather mates. ' Under these conditions, the Pu concentration in soil is the principal factor forcing the transport system. Air is contaminated by resuspension of Pu-bearing soil particles. Vegetation its contaminated internally by root uptake from soil and externally by deposition of resuspended particles. Pu input to herbivores is due to ingestion of soil and vegetation and to inhalation. Pu could reach man by inhalation of contaminated air, by accidental ingestion of contaminated soil, and by ingestion of milk or meat (skeletal muscle or internal organs) from animals raised in the contaminated area. Drinking water for herbivores and man is assumed to come from deep wells or from sources outside the contaminated area and to contribute nothing to Pu intakes by herbivores or by man. If it could be assumed that (1) the major ecosystem compartments and important transport pathways are as indicated in Figure 1, (2) the plutonium in each compartment the other contents of the compartment, ay, n n i#j iff ge 7 br agts ~ Yh aba Og 4 =1,2,3...0 where 622 is well mixed with and (3) the net rate of transfer from one compartment to another can be expressed as the product of a transfer coefficient and the quantity of plutonium in the transmitting compartment, then the intercompartmental flux of plutonium could be represented by a system of linear, first order, ordinary differential equations, the general formula for which is j is the compartment of reference and all other compartments are designated 1, 623 @)