Inhalation dose assessment: Risk assessment of airborne particulates to workers in the Florida phosphate industry

Health risks to workers in the Florida phosphate industry due to inhalation of particulates containing radioactive materials were investigated. Site-specific particle database were established, and were integrated into a full dosimetry assessment. Particle mass concentration varies widely by plants and locations over 1 to 3 orders of magnitude. A majority of samplings indicate that particle mass is concentrated at large particle sizes. A unity shape factor was assigned for dose assessment after particle shape analysis. Mass density of the particles ranges from 1.6 to 1.7 g cm-3. Radioactivity concentrations of 238U, 226Ra, and 210Pb in products or particles range 1088--4151, 30--141, and 248--3204 Bq kg -1, respectively.; An application method of cascade impactor sampling data to dose assessment was presented. Effective dose scaling factors generated in this study reduce computational efforts for dose assessment.; Inhalation dose was calculated using site-specific particle size distribution data. Under the least conservative assumption of radionuclide-specific lung solubility, effective doses at granulator, storage, and shipping areas are 0.31 +/- 0.12, 0.27 +/- 0.07, and 0.22 +/- 0.02 mSv year -1, respectively. In contrast, under the most conservative assumption the effective doses are 2.24 +/- 2.53, 1.26 +/- 1.19, and 0.56 +/- 0.36 mSv year-1 at the same areas.; Solubility of uranium, thorium, and lead in particles were determined by an in-vitro solubility test. More than 94% of phosphate is dissolved in 1 day. However, 238U, 232Th, and 208Pb are not dissolved rapidly with the surrounding matrix. Retention of uranium and lead is similar to type M materials, and retention of thorium to type S materials as defined in the default clearance parameters of the ICRP 66 HRTM.; All measured data and dose calculation methods were integrated into a full internal dosimetry assessment. Site-specific effective doses range 0.24--0.68 mSv year-1 at granulator area, 0.21--0.49 mSv year-1 at storage area, and 0.21--0.27 mSv year-1 at shipping area. All results are smaller than dose limit of the general public. Compared with occupational dose limit, effective dose to workers in the Florida phosphate industry is extremely unlikely to approach or exceed the limit.