On the Free and Combined Silica in Silicotic Lungs

Abstract

While more analytical results for total silica in lungs are needed, there is a much greater need for values for the concentration of free silica, since it is so definitely known to cause silicosis. In the literature on the subject only several publications in the analytical line have to do with free silica in lungs and these reports are limited either to semi-quantitative results 1 , 2 , 3 , 4 or to calculations of silica by difference. 5 , 6

By modifying and extending the method of determining free silica in dusts, to lung residues, we have been able to determine minimum free silica. Since the chemical method involves digestion of the finely-divided lung ash residue in hydrofluosilicic acid (H₂SiF_e) in order to dissolve away silicates, and since finely-divided free silica is appreciably soluble in the above acid, we can, however, report only minimum free silica values.

The solubility of free silica in hydrofluosilicic acid varies with particle size, among other factors. Particles of silica as long as 10 microns may gain entrance to lungs, although the great majority found are less than 5 microns, averaging around 1 to 3 microns according to several investigators. Although we have attempted to establish a solubility correction by experiments on fine quartz, so far we have not been successful.

Total silica was determined by the usual gravimetric hydrofluoric acid method. Essentially the free silica method consisted in digesting the ash residues at room temperature with hydrofluosilicic acid and then determining the undissolved free silica by the hydrofluoric acid method.

Table I indicates data and results on 14 silicotic lungs obtained from autopsies in Buffalo and vicinity. More cases would have been desirable but were not available.