Relative toxicity of inhaled metal sulfate salts for pulmonary macrophages

The effects of metal sulfate aerosols on respiratory defense mechanisms in hamsters were studied. Pulmonary macrophage phagocytic rates were measured by determining the in vivo uptake of radioactive colloidal gold (198Au) 1, 24, or 48 h after a single 4-h exposure. The concentrations of sulfate aerosols causing a 50% inhibition in pulmonary macrophage endocytosis (EC50) were determined. When hamsters were exposed for 4 h to cupric sulfate (greater than or equal to 4.8 mg/m3), zinc sulfate (greater than or equal to 3.1 mg/m3), ferric sulfate (greater than or equal to 7.8 mg/m3), or zinc ammonium sulfate (greater than or equal to 10.0 mg/m3), macrophage endocytosis was significantly reduced 1 h after exposure compared with that in unexposed control animals. Although the response was variable, 24 h after exposures to the higher sulfate concentrations the percent of gold ingested by pulmonary macrophages remained depressed. By 48 h, the rate of macrophage endocytosis in hamsters had returned to normal control values except in hamsters exposed to 4.8 mg/m3 cupric sulfate or 9.8 mg/m3 ferric sulfate. These hamsters showed significant increases in phagocytosis. The EC50 values in milligrams of sulfate per cubic meter for cupric sulfate, zinc sulfate, ferric sulfate, and zinc ammonium sulfate were 2.7, 4.5, 7.5, and 17.9, respectively. These results are negatively correlated with the ranking of sulfates using the criteria of relative irritant potency, as measured by increases in pulmonary flow resistance. Thus, rankings of related chemical structures are not absolute. Their relative toxicities vary depending on the end point selected.