ergo ee Concentration Guide for individuals in the general public, or 0.6 to 1.2%, for a suitable sample of the public. we Bee fh ae Thus, the levels of plutonium in the top layer of soil at Rocky Flats and at Palomares have not led to any situations of concern with respect to a possible airborne pathway to man. As discussed in the following section, the situation is expected to be even more favorable with respect to possible airborne plutonium at Bikini. Particle Size in Soil. Determination of the size of individual particles of plutonium oxide or plutonium oxide agglomerated with soil is almost impossible after the particle has reached the earth's surface and become mixed with other particles. It is the opinion of Dr. John Harley, HASL, and Dr. Wright Langham, LASL, that particle size studies of plutoniumbearing soil at Bikini or elsewhere would be unprofitable. Most particle size determinations for studies on plutonium are made on fallout samples collected by cascade impactor or selective filters. A number of particle size determinations were made on samples collected following Project 57 (during Operation PLUMBOB, NTS during 1957) and Operation ROLLER COASTER (Tonopah Test Range, 1963). A report of particle size determinations on air samples collected by cascade impactors following the Double Tracks event of ROLLER COASTER, indicated particle sizes ranging from 2.5 microns diameter to more than 35 microns diameter. To gain entry into lungs, the plutonium oxide must be in very fine "respirable" particles (i.e., less than 10 mic