The reader is referred to their paper for details concerning the assumptions and parameter values used in the model. Turning to Figure 1, we see that the hypothetical 239pu concentrations in lung, bone, and kidney of Standard Man for 433 days residence in an area with soil concentrations of 0.07 nCi/g are less by factors of (roughly) 2, 22, and 6 than the mean 2739pu concentrations in these same tissues for the beef cattle The hypothetical values for human that grazed 433 days in the outer compound. of soil are factors of 5 nCi/g lung and bone for 180 residence days at 0.55 and 8 less than obtained for cow 2, which grazed 176 days in the inner compound (no data are available for the kidney of cow 2). Factors of 2 and 5 are perhaps not unexpected for lung since in the model the inhalation rate of plutonium (pCi/day) for beef cattle is taken to be (based on NTS studies) 5.5 times greater than that of man (see eq. 1 and the discussion on cattle inhalation rates in Martin and Bloom). tions in lung and bone at the MPC_ Hypothetical human concentra- level (3 nCi/g of dry soil) for 180 residence days are about equal to concentrations found in these two tissues of cow 2. According to the model, human tissue concentrations in lung, bone, and kidney increase by factors of 3, 6, and 6 in the time span from 180 to 720 residence days when soil is at the MPC_ level. The 239pu concentrations in these human organs increase by factors of roughly 2, 80, and 70, respectively (according to the model), between residence times 720 days and 55 years for soil at MPC... The greater increases for bone and kidney between 720 days and 55 years occur because the model assumes no losses of plutonium from these organs (see Figures 3 and 4, Martin and Bloom). Discussion We don't have now, nor are we likely to have in the near future, estimates of the accuracy (bias) of these hypothetical human tissue concentrations since no humans live in these contaminated areas. We also do not have any precise knowledge of the precision (variability) of these model estimates. We presume this variability is largely due to the high variability of most estimates of parameters used in the model. As new information becomes available from the continuing NAEG studies, and we learn how to design better field studies and extract more information from the data collected (see next section), the model will undoubtedly be modified and improved. As Martin and Bloom stress, the present model is not the last word on the subject. More data are clearly needed to obtain better estimates of plutonium burdens in tissues of small vertebrates and grazing cattle, particularly for GZ areas. Considerably more data will soon be available, at which time Figure 3 should be revised. Information is also available on concentrations of 238py, 238y , and *4lam that needs to be related to concentrations for soil, vegetation, and small vertebrates. 251