-2- aeroso size, and total radioactivity per unit mass. Although necessary, these parameters are insufficient to describe the fraction of suspended radioactivity within the respirable size range and how either the concentration of radioactivity or the respirable fraction vary with surface conditions and local resuspending (dust-lifting) mechanisms. T ( Our investigations recently conducted on Bikini and Enewetak Atolls in the Marshall Islands-provided new data which have implications not only for the local dose assessment concerning rehabitation of those sites, but which are important ‘\ forunderstanding low-level inhalation exposure totoxic radionuclides in general. ---- . ““ “ ‘. BACKGROUND ‘This study conducted on Bikini Island in May 1978 provided a more complete . set of data, following our preliminary studies on Engebi Island of Enewetak Atoll in February 1977. The Bikini Island study utilized extensive soil sampling and in situ gamma spectroscopy to determine isotope concentrations in soil and vegeGtm Also various air sampling devices were used to determine particle size distribution and mass loading, and micrometeorol ogical techniques were used to determine aerosol fluxes. Subsequent wet chemistry analysis provided radionuclide and elemental concentrations in collected aerosols. Four simultaneous experiments were conducted: (1) a characterization of the normal (background) suspended aerosols and the contributions from sea spray off the windward beach leeward across the island, (2) a study of resuspension of radionuclides from a field purposely laid bare by bulldozers as a worst-case condition, (3) a study of resuspension of radioactive particles by vehicular and foot traffic, and (4) a study of personal inhalation exposure using small dosimeters carried by volunteers during their c“‘::: daily routines. Less complete studies similar to (1) and (2) had been performed previously on Engebi Island at Enewetak Atoll and background studies similar to (1) were performed later on Eneu Island’at Bikini Atoll. METHODS Soil and vegetation samples were collected for analysis of radionuclide 2S8PU, zsg+z40Pu, and 241Am concentrations were determined by concentrations. isotope dilution and alpha spectrometry and ‘oSr concentrations by yttrium-90 These analyses were performed by LFE Cor oration. separation and beta counting. ! Gamma spectroscopy using Ge(Li) diode detector was used to determine 13 Cs Also, because the ratios (241Am)/(23g+2q0Pu) and (238Pu)/ concentrations. (23g+240Pu~ are constant on Bikini, it was possible to estimate plutonium soil concentrations by measurinq 241Am soil concentrations usinq a qamma spectroscopy system consistin~ of a pla;ar, high-purity germanium diode-whi~h was cryogenically cooled to achieve a minimum detectability for 241Am less than 1.0 pCi g-l (l). The detector was mounted facing downward on a tripod so that the volume of soil integrated was contained in a circle of probable detection of nominally 3 m radius and 5 cm depth. Because the nuclear events causing the original contamination of Bikini Island were far removed, the fallout was relatively evenly dispersed across the Island. ,4 Impingers were used to collect water trap similar to the method of 0.36 m3 h-l (6 1 rein-l) through the added each day to replace evaporated / soluble sea spray aerosols in a 250 ml distilled and Whelan (2)., Air flow rates were water trap and measured amounts of water were water (nominally 40 cm3 day-]). Impingers HSU $ .● ✎ ✚ ... .,. L