Exposures and health effects from inorganic agricultural dusts

Most studies of respiratory disease from dust exposure in the agricultural workplace have focused on allergic diseases caused by inorganic dusts, spec ifically occupational asthma and hypersensitivity pneumonitis. Exposures to inorganic (mineral) dusts among farmers and farm workers may be substantia l. Such exposures are most frequent in dry-climate farming regions. in such locations farming activities that perturb the soil (e.g., plowing, tilling ) commonly result in exposures to farm operators of 1-5 mg/m(3) respirable dust and greater than or equal to 20 mg/m(3) total dust. The composition of inorganic dust in agriculture generally reflects the soil composition. Cry stalline silica may represent up to 20% of particles, and silicates represe nt up to 80%. These very high concentrations of inorganic dust are likely t o explain some of the increase in chronic bronchitis reported in many studi es of farmers. Pulmonary fibrosis (mixed dust pneumoconiosis) has been repo rted in agricultural workers, and dust samples from the lungs in these case s reflect the composition of agricultural soils, strongly suggesting an eti ologic role for inorganic agricultural dusts. However, the prevalence and c linical severity of these cases are unknown, and many exposures are to mixe d organic and inorganic dusts. Epidemiologic studies of farmers in diverse geographic settings also have observed an increase in chronic obstructive p ulmonary disease morbidity and mortality. It is plausible that agricultural exposure to inorganic dusts is causally associated with chronic bronchitis , interstitial fibrosis, and chronic obstructive pulmonary disease, but the independent contribution of mineral dusts beyond the effects of organic du sts remains to be determined.