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.

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The chemical speciation, ionic plus particulate forms, of long-lived isotopes of Pu, Am, Cm, Cs, Sr, Ni, I, and Tc was determined in four contaminant plumes at the Chalk River Nuclear Laboratories. Comparative data were also determined for shorter-lived isotopes of Ce, Eu, Fe, Co, Ru, Zr and Sb. Anionic species were the predominant solution species, and hence the mobile form, for many of the elements. Complexation by organic ligands, both natural and synthetic, was postulated to be important in mobilizing Co, Ce, Cs, Eu, Sb, Zr, Fe, Ni, I, Pu and possibly Am. Thermodynamically-predicted aqueous speciation was consistent with our data for only four elements; Ru, Sr, I and Tc. The chemical speciation of Am was found to be particularly anomalous in the study sites. On the basis of our data we conclude that the predictions of Kd-based models for radionuclide mobility must be carefully evaluated with respect to the adequacy of the speciation assumptions of the Kd approach.

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