14 Lo: Question 2 / It seems that every American already carries a "body burden" of man-made radionuclides. What is the present average American body-burden? What fraction of it is from naturally occurring nuclides, and what ' fraction from man-made nuclides? How does the total 1968 body~burden compare, numerically, with 194? With 19512 With 1958? With 1963? Is this known data? From currently known data, could anyone provide or assemble charts which would show American body-burdens of radioactive nuclides: by year? by area/region? by age groups? by source (Natural vs. man-made)? by nuclide (e. g., potassium-40, tritium, carbon-Uy, radium-226)? Won't such data kept up to date, be necessary in order to see the big | picture and to assess future risks? . Is better understanding of low-dose radiation effects presently hampered by an insufficieney of historical data, or is sufficient data available to the scientific community? Answer The simplest approach to this question is to detail the body burdens for individual nuclides. These burdens can then be summarized on the basis of dose and compared with doses from natural radioactivity. Thus the re- ply to this question will show the amounts of individual nuclides in the body withan indication of how they vary by year, region and age. The data presented are the results of continuing programs of measure- ~ ments and it is expected that they will be kept up to date. The nuclides emphasized are those that are considered to present the greatest hazard