Nevada Applied Ecology Group Model 



for Estimating Plutonium Transport 



and Dose to Man / ^ " ^ * 



DOCUMENl 



COLLECTION 



W. E. MARTIN and S. G. BLOOM 



A Standard Man is assumed to live in and obtain most of his food from a 

 plutonium-contaminatcd area at the Nevada Test Site (NTS). A plutonium-transport 

 model, based on the results of other Nevada Applied Ecology Group plutonium studies, is 

 used to estimate potential chronic rates of ^ ^ '^Pu inhalation and ingestion as functions of 

 the average concentration of ^^^Pu (C^, picocuries per gram) in the surface soil (0- to 

 5-cm depth) of the reference area. A dose-estimation model, based on parameter values 

 recommended in publications of the International Commission on Radiological Protec- 

 tion (ICRP), is used to estimate organ burdens, accumulated doses, and dose 

 commitments as functions of exposure time. Tliese estimates are combined with ICRP 

 recommendations for allowable public exposure to radiation to arrive at acceptable soil 

 concentrations at NTS. 



The plutoniimi-transport model is based on a relatively simple ecosystem that was 

 used as a preliminary model to guide data-acquisition studies at NTS. Tlie preliminary 

 model provides a framework for developing more detailed dynamic models of the 

 ecosystem, but at present there are insufficient data to implement these dynamic models; 

 so the estimates of inhalation and ingestion rates are based on simpler steady-state 

 models. If we assume the transport system to be in steady state, the estimated inhalation 

 and ingestion rates (picocuries per day) are 0.002 Cs and 0.2 Q, respectively. 



A number of dose-estimation models were examined, and calculations were made for 

 comparison. Tlie results of these calculations indicated that the dose estimates to the 

 most sensitive organs were comparable. The model recommended by the Task Group on 

 Lung Dynamics of ICRP was used for dose estimates at NTS because it is the model most 

 widely accepted. Estimated doses (rem) due to chronic inlialation and ingestion of^^'^Pu 

 for 50 vr at the rates indicated above are: thoracic lymph nodes, 0.610 C^: lungs, 0.025 

 Cs; bone, 0.014 C^; liver, 0.009 Cs; kidney, 0.003 Cs; total body, 0.0007 Cs; and 

 gastrointestinal tract (lower large intestine), 0.0002 Cs- Inhalation accounts for 100% of 

 the estimated dose to the lungs and thoracic lymph nodes and for about 95% of the 

 estimated dose to bone, liver, kidney, and total body. Ingestion accounts for >99%o of the 

 dose to the gastrointestinal tract. 



According to the ICRP (International Commission on Radiological Protection, 1966) 

 recommendations for individual members of the public, the dose rate to the lungs after 

 50 yr exposure should not exceed 1.5 rem/yr. Tlie plutonium-transport and dose- 

 estimation models described in this chapter indicate that the average concentration of 

 ^^^Pu in the surface (0 to 5 cm) soils of contaminated areas at NTS which could residt in 

 a maximum dose rate of 1.5 rem/yr to the lungs is approximately 2.8 nCi/g, or about 140 

 IdG/m'^ for soils weighing 1 g/cm^. 



459 



