-16- about 10 percent of the 2710p, organ burdens of heavy smokers, the effects may be correspondingly greater because the total population is exposed, and the inhalation exposures begin at birth. If the health risks attributable to fallout plutonium exceed 10 percent of the risks of heavy smoking, then inhalation exposure at ~20 times " fallout (the surface soil concentration of plutonium which corresponds to the interim soil standard adopted by the Colorado Board of Health in 1973) would give rise to organ burdens more than twice that of heavy smokers. Exposing children to such levels would be tantamount to their smoking four packs of cigarettes per day, beginning at birth. This estimate assumes, as I believe to be the case, that the inhaled, insoluble radioactive smoke particles give rise to the serious health effects of smoking. For the estimation of organ burdens which may result from the inhalation ' of soil contaminants, it is common practice to attempt to determine the average surface soil concentrations, the applicable resuspension factors, inhalation exposure patterns, particle size distributions, lung retention, clearance and translocation patterns and rates, etc. The large cumulative errors and uncertainties in the prediction of the ultimate organ burdens from long-term exposure to contaminated surface soils and urban dusts by - > such a long sequence of complex processes serve to make this procedure an almost useless exercise. There is a move direct approach which sould give more reliabie estimates. Lewis et a>?) show that the adult lung burden of ‘mitric acid-insoluble particles increases almost linearly with age, with about 1.5 grams per kilogram of lung tissue at age 60. It seems reasonable to assume that andividuals chronically exnosed to soil dust and urban dusts will acquire just such burdens of the insoluble constituents in the respirable size fraction of dust particles (1.e., particles less than ~5 um diameter). It should be noted that Pu0, 2 particles are highly insoluble and friable.