Comparison of Synthetic Zeolite Catalysts and Alumina Binders Administered Intratracheally to Rats

Abstract

An intratracheal (IT) screening assay was performed in rats on a series of aluminosilicate catalysts (synthetic zeolites) and alumina binders to compare their relative ability to cause pulmonary fibrosis and related changes. Before initiation of IT screens, both the uniformity of deposition and residence time of a prototype catalyst in the lung were determined. Subsequently, the test materials were instilled and animals were evaluated 6 mo later for lung volumes, pulmonary pressure-volume curves, pulmonary hydroxyproline (OHPro) content, lung weights, and histopathology. Negative controls were saline and glass beads; the positive control was quartz. The test materials were organic-free ZSM-5 crystals, organic form of ZSM-5 crystals, alumina-bound ZSM-5, nickel/ZSM-5/ Al2O3 binder, used nickel/ZSM-5/Al2O3 binder, nickel-tungsten/ZSM-5/Al2O3 binder, and Bayer pseudoboehmite. For each, groups of 12 male rats were dosed once with either 25 or 50 mg of ground particles (> or =95% less than 2.4 microm). Second to quartz, the sample of alumina caused the most pronounced pulmonary reactions at 6 mo after dosing. Therefore, the effects of four aluminas were subsequently compared (Bayer pseudoboehmite, Bayer gammaAl2O3, Ziegler pseudoboehmite, and Ziegler gammaAl2O3). The results support the idea of a lack of long-term effects from exposure to normal concentrations of these materials in the workplace. Also, the IT assay proved to be a very useful tool for ranking the relative effects of this series of zeolites and aluminas.