Physico‐chemical fate of chromium compounds in the sheep lung model

Abstract

Transmission electron microscopy (TEM) equipped with energy‐dispersive x‐ray analysis (EDX), electron spectroscopy for chemical analysis (ESCA), secondary ion mass spectrometry (SIMS), and laser microprobe for mass analysis (LAMMA) were used to follow the fate of chromium compounds deposited in the sheep tracheal lobe. Four chromium compounds were used: two chromium(VI) compounds (lead chromate and chromium trioxide) and two chromium(III) compounds (chromic oxide and chromium sulfate). Chromium trioxide is very soluble and the other three are slightly soluble. The compositions, concentrations, and sizes of particles were determined in the bronchoalveolar lavages (BAD at d 2, 3, 5, and 30 after instillation and on the lung samples collected at d 31. The concentrations of particles in the BAL samples separated the chromium compounds in two groups where Cr₂O₃ and PbCrO₄ (as Pb) were higher than Cr₂(SO₄)₃, PbCrO₄ (as Cr), and CrO₃. The half‐life for alveolar clearance of Cr₂O₃ and Cr₂(SO₄)₃ has been calculated respectively at 11 and 80 d. Prismatic PbCrO₄ particles break up in the lung and sustain a high concentration of isometric particles of lead chromate and another lead‐containing compound in the BAL. The CrO₃ instilled particles react with endogenous compounds or are transformed to insoluble hydroxyl complexes instead of diffusing very rapidly through the alveolar‐capillary barrier. The alveolar clearance as measured in the BAL is not different from the control.