Emanation coefficients for Rn in sized coal fly ash.

Emanation coefficients for 222Rn in sized samples of dry coal fly ash were evaluated as a function of source and particle size using a modification of the "sealed-can, gamma-only" technique. The emanation coefficient is defined as the fraction of Rn atoms that escape the solid particles of a source. Diffusible Rn was separated from nondiffusible Rn by adsorption on charcoal, and each was measured independently by gamma-ray spectrometry of the Rn daughter, 214Bi. Samples of ash from eastern bituminous coal, western bituminous coal and mid-western bituminous coal with aerodynamic equivalent diameters of less than 15 micron were examined, and the measured emanation coefficients ranged from 0.098 down to 0.007. These values were dependent on both the size and source of the fly ash. The emanation coefficients and the specific activities generally decreased monotonically with increasing aerodynamic equivalent diameter. For unfractionated standard fly ash, SRM 1633a, from the U.S. National Bureau of Standards, the emanation coefficient for 222Rn was found to be 0.018. The results suggest that only a small fraction of the Rn in lung-deposited fly ash will be removed by exhalation.

Lung-clearance classification of radionuclides in coal fly ash.

Lung-clearance classifications for 238U, 232Th, 230Th, 228Th, 226Ra, 210Pb and 210Po in respirable coal fly ash were estimated for use with the lung clearance model proposed by the ICRP Task Group on Lung Dynamics. Estimates were based on measurements of the dissolution rates for these radionuclides from sized fly-ash samples into simulated lung fluid at 37 degrees C. The estimates were expressed in the classification terms of the model, i.e. D, W and Y, indicating lung clearance half-times of 0-10 days, 11-100 days, and more than 100 days, respectively. Ash from eastern bituminous coal, western bituminous coal and mid-western bituminous coal was examined. Both Class-D and Class-Y components of 238U were found in all samples, whereas all the other radionuclides dissolved very slowly and were classified 100% Class Y. The fraction of 238U in Class D increased with decreasing particle size and increased linearly from 0.02 to 0.17 as the concentration of U in the volatile-metal portion of the samples increased. This relationship suggests that a major fraction of the U in coal fly ash may be shielded from exposure to simulated lung fluid by more-abundant metals deposited on the outer surface of fly ash during coal combustion.

Levels of 234U, 238U and 230Th in excreta of uranium mill crushermen.

Pacific Northwest Laboratory conducted a research program to measure uranium and thorium levels in excreta of uranium mill crushermen who are routinely exposed to airborne uranium ore dust. The purpose of this work was to determine whether 230Th was preferentially retained in the body over either 234U or 238U. Urine and fecal samples were obtained from 14 active crushermen with long histories of exposure to uranium ore dust, plus four retired crushermen and three control individuals for comparison. Radiochemical procedures were used to separate out the uranium and thorium fractions which were then electroplated on stainless steel discs and assayed by alpha spectrometry. Significantly greater activity levels of 234U and 238U were measured in both urine and fecal samples obtained from uranium mill crushermen, indicating that uranium in the inhaled ore dust was cleared from the body with a shorter biological half-time than the daughter product 230Th. The measurements also indicated that uranium and thorium separate in vivo and have distinctly different metabolic pathways and transfer rates in the body.

Mount st. Helens ash from the 18 may 1980 eruption: chemical, physical, mineralogical, and biological properties.

Samples of ash from the 18 May 1980 eruption of Mount St. Helens were collected from several locations in eastern Washington and Montana. The ash was subjected to a variety of analyses to determine its chemical, physical, mineralogical, and biological characteristics. Chemically, the ash samples were of dacitic composition. Particle size data showed bimodal distributions and differed considerably with location. However, all samples contained comparable amounts of particles less than 3.5 micrometers in diameter (respirable fraction). Mineralogically, the samples ranged from almost totally glassy to almost totally crystalline. Crystalline samples were dominated by plagioclase feldspar (andesine) and orthopyroxene (hypersthene), with smaller amounts of titanomagnetite and hornblende. All but one of the samples contained from less than 1 percent to 3 percent free crystalline silica (quartz, trydimite, or cristobalite) in both the bulk samples and 1 to 2 percent in the fractions smaller than 3.5 micrometers. The long-lived natural radionuclide content of the ash was comparable to that of crustal material; however, relatively large concentrations of short-lived radon daughters were present and polonium-210 content was inversely correlated with particle size. In vitro biological tests showed the ash to be nontoxic to alveolar macrophages, which are an important part of the lungs' natural clearance mechanism. On the basis of a substantial body of data that has shown a correlation between macrophage cytotoxicity and fibrogenicity of minerals, the ash is not predicted to be highly fibrogenic.