Evaluation of physical health effects due to volcanic hazards: Crystalline silica in Mount St. Helens volcanic ash

This investigation has shown that crystalline silica has been identified as being present in the Mount St. Helens volcanic ash at levels of 3 to 7 per cent by weight. This identification has been established using X-ray powder diffraction, infrared spectrophotometry, visible spectrophotometry, electron microscopy, and Laser Raman spectrophotometry. Quantitative analysis by IR, XRD, and visible spectrophotometry requires a preliminary phosphoric acid digestion of the ash sample to remove the plagioclase silicate material which interferes with the determination by these methods. Electron microscopic analysis as well as Laser Raman spectrophotometric analysis of the untreated ash confirms the presence of silica and at levels found by the XRD analysis of the treated samples. An interlaboratory study of volcanic ash samples by 15 laboratories confirms the presence and levels of crystalline silica. Although several problems with applying the digestion procedure were observed in this hastily organized study, all laboratories employing the digestion procedure reported the presence of crystalline silica. These results unequivocally put to rest the question of the presence of silica in the volcanic ash from eruptions of Mount St. Helens in 1980. Shortly after Mount St. Helens erupted in 1980, a number of laboratories began to investigate the effects of volcanic ash in a variety of experimental systems in attempts to predict effects that might occur in the lungs of humans exposed to volcanic ash. The published results are remarkably consistent, despite the use of non-uniform ash samples and variability in the experimental approaches used. The data indicate that volcanic ash, even in high concentrations, causes little toxicity to lung cells in vitro and in vivo, as compared with effects of free crystalline silica, which is known to be highly fibrogenic. Volcanic ash does not appear to be entirely inert, however, possibly because of low concentrations of free crystalline silica in the ash. The published experimental studies suggest that inhaled volcanic ash is not likely to be harmful to the lungs of healthy humans, but the potential effects of volcanic ash in patients with pre-existing lung diseases are more difficult to ascertain from these studies.