Lung cell toxicity experimentally induced by a mixed dust from Mexicali, Baja California, Mexico.

Lung disease caused by nonoccupational exposures to inorganic particles from the soil has been reported in several areas of the world. We tested the toxic potential of dust samples from a Mexican city (Mexicali) that is frequently affected by dust storms and is geographically related to the area of San Diego, CA, where constituents of the soil have been reported to be fibrogenic. We found that samples of Mexicali dust are a mixture of approximately 75% potassium aluminum silicates (illite) and approximately 20% silica. Respirable size particles were highly hemolytic and induced lactic dehydrogenase release from alveolar macrophages exposed in vitro. Animals instilled intratracheally with the dust developed a multifocal interstitial lung disease associated with deposits of the aluminum silicates, which were identified by X-ray microanalysis. Inhalation studies in rats demonstrated that the majority of particles were deposited preferentially at the first alveolar duct bifurcations. Twenty-four hours later, numerous particles had been ingested by alveolar macrophages that had migrated to those sites of deposition. It is proposed that alveolar macrophages are attracted to the deposited particles by complement fragments since Mexicali dust is capable of activating complement proteins from both serum and bronchoalveolar lavage. Activation resulted in alveolar macrophage chemotaxis. Mexicali dust induced biological activities and lung changes similar to those of asbestos and silica, suggesting that this material could be an etiologic agent of pulmonary fibrosis in exposed individuals.