Inorganic Agricultural Dust Exposure Causes Pneumoconiosis among Farmworkers

Abstract

Early studies of agricultural respiratory diseases focused on allergic disorders due to organic dust exposure. However, agricultural workers in dry climate regions are exposed to substantial concentrations of inorganic dusts from agricultural soils. Exposures to inorganic dusts are dependent on the specific crop and task, but are commonly several milligrams of respirable dust per cubic millimeter. In vitro toxicity studies show the dust's cytotoxicity to be intermediate between controls and crystalline silica. However, in some assays of reactive oxygen species generation, such as H(2)O(2), hydroxyl radical, and nuclear factor kappaB generation, the agricultural dusts are more potent than silica. A recent study of human lung samples among deceased Latino males characterized the deposition of agricultural dusts in the lung and the pulmonary response to these dusts. Careful histologic analyses in this study demonstrated that farmwork was significantly associated with mineral dust small airways disease and pneumoconiosis (macules and/or nodules). These associations persisted in multivariate analysis. Cigarette smoking was independently associated with these outcomes, but the interaction of mineral dust and smoking was not significant. Limited studies of farmworkers exposed to inorganic dusts show respiratory symptoms and restrictive pulmonary function with exposure. Overall, the evidence supports a causal association of mineral dust exposure and pneumoconiosis. Inorganic mineral dusts should no longer be considered merely a nuisance, but rather a cause of mixed-dust pneumoconiosis. The prevalence and natural history of this disorder are unknown.