ea pores fend to be deposited here by pravitaticngl gttine, ¢ aud if thes are The prob- “insoluble they may reside in the alveoli for a considerable time. le is that, under a number of conditions (Anderson, B.V., etal., 1987; Fraser, D.C., 1987; Kirchner, R,A., 196; Mann, J.R., et al., 1967; Stewart, K., 1993; “Wilson, R.H. et al., 1967) olutonium tends to form aerosols of a size that are preferentially deposited in deep .ung tissue. x‘ Plutonium dioxide, which is a principal offender, is insoluble and may be immobilized in the lung for hundreds of days before being cleared to the . throat or to Yr) the lymph nodes aroun nd the lunge (Mealth Physics, 1966). An aerosol is comprisedof particles of many different sizes, and their radioactivity may differ by factors of thousands or even more. T will simolify’ the argurnent and ssay that there is a class of these particles, the largest ones deposited in the deep lung tissue, that can be expected to have a different potential of cancer induction than the particles of the smaller class. This is because they are sufficiently radioactive to disrupt ech populations in the volume. of cell tissue which th ey expose (G D.P., 1968a). aman, An example might be a particle that emits 5000 helium “ nme & nuclei per day. ° It would subject between 1 and 20 alveoli to intense radi- ation, sufficient to inflict substantial cell death and tissue disruption. kor reference, the alveoli ure the basic str uctural units of the deep lung. They are shaped and bunche dl roughly like hollow grapes 0.9 millimeter In dinineter. Theie walls are thin, a few thocsasdihs of a riillimeter, eed they are a highly ctructined tissue with mony cell types. Totense ex- Poeldre Of focal tissues by a raedionetive purtici is referred tous tho hot a 3Nie meg : "SU. - § caeDnoF oe: Ke ‘os . a =