Associated with the use of 238Pu in thermoelectric power sources for space probes is the potential for human exposure, primarily by inhalation and most likely as 238PuO2. Several models have been developed for assessing the level of intake and predicting the resulting radiation dose following human exposure to 239Pu. However, there are indications that existing models do not adequately describe the disposition and dosimetry of 238Pu following human exposure. In this study, a canine model that accounts for these differences has been adapted for use with human excretion data. The model is based on existing knowledge about organ retention of plutonium. An analysis of the sensitivity of the model to changes in aerosol-associated properties indicated that predictions of urinary excretion are most sensitive to changes in particle solubility and diameter and in the ratio of fragment:particle surface area. Application of the model to urinary excretion data from seven workers exposed to a 238Pu ceramic aerosol gave estimated intakes of 390-8,200 Bq and associated initial pulmonary burdens of 80-1,700 Bq. The resulting 50-y dose commitments to critical organs per Bq of 238Pu intake were estimated to be 0.5 mSv for the thoracic region, 0.2 mSv for the liver, and 1 mSv for the bone surfaces.

This paper reviews the data generated in studies of land radioactivity and indoor airborne radon progeny associated with mined and reclaimed phosphate lands in Florida. Highest indoor radon progeny levels are associated with the slab-on-grade type of construction. Concentrations exceeding 0.03 WL are associated with overburden soils, deposits and fill, while concentrations up to about 0.03 WL are associated with tailings. The lower limit for distinguishing increases above non-enhanced natural concentrations is on the order of 0.01-0.02 WL. Results of this study show that about 25% of the land produced by present methods of mining and reclamation practices would require restrictions on the type of construction or would require special construction methods. It is projected that with modification of mining and tailings disposal practices, virtually all of the land produced by mining and reclamation would be satisfactory for unrestricted construction use.

Measurement of 137Cs body burdens in nearly 300 persons with the University of Florida whole-body counter from 1965 to date shows that Florida residents had levels of 137Cs two to three times as high as those reported elsewhere in the conterminous United States during the same time period. Analysis of the data by year shows that the levels did not drop with time as rapidly as levels reported in other areas of the United States.Cesium-137 levelsin Florida residents averaged 0.395,0.353, and0.318 nCi/kglean body mass in 1965, 1966 and 1967, respectively. For the entire 1965-1967 period these levels averaged 0.350 and had a range of 0.044-1.667nCi/kg lean body mass. In contrast, non-Florida residents measured at the same facility had an average of 0.151 nCi/kg lean body mass. Reproducibility of the measurements was within 10%.These levels correlate with the reported levels of 137Cs in Florida-produced foods, which in general are much higher than the average for the United States.