A method for determining glass in rat lung after exposure to a glass fiber aerosol

Inhalation toxicology studies of glass fibers require a knowledge of the dose deposited in the lungs of exposed animals. A method is described which uses the quantity of acid-insoluble sodium present in rat lungs to determine the lung burdens of glass by mass after exposure to glass fiber aerosol. The glass fibers used contained 7.3% sodium. This sodium was measured in lung homogenates after acid washing and fusion in Li2CO3. The lower limit of detection was estimated as 40 microgram of this glass in rat lung. Results of an in vitro dissolution study indicated that a portion of the sodium present in the glass fibers was dissolved at a faster rate than the glass itself. This preferential dissolution may result in a small (5-25%) underestimation of glass in lung. This method was used to determine lung burdens of glass in rats after 1, 2, 4 or 5 exposures to a glass fiber aerosol (count median diameter: 0.11 micrometer, count median length: 8.3 micrometer). Five 6-hour exposures at an average concentration of 47 mg/m3 resulted in a lung burden of 176 microgram of glass. It was estimated that 41-48% of the lung burden was cleared between daily exposures.