Pulmonary Reactive Components of Winter Wheat Grain Dust at Colorado Farms and Elevators

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Abstract
Surveys were conducted during the 1992 and 1993 harvests and the intervening winter shipping season to characterize the pulmonary reactive dust components and exposure concentrations at wheat farms and country elevators in Colorado. The following parameters were measured or identified: respirable dust (RD) and respirable silica (RS) by the 10-mm cyclone; total dust concentration (TDC) and particle mass median aerodynamic diameter (MMAD) by personal cascade impaction and gravimetric analysis; organophosphate pesticides (OPs) by gas chromatography; microbial colony-forming units (CFU) per cubic meter for mesophilic (F) and thermotolerant fungi (TF), total bacterial plate count (TPC), and gram-negative bacteria (GNB) by standard microbial culture techniques; and bacterial endotoxin units/m3 (EU/m3) by the Limulus amoebocyte lysate test. Airborne fungi, GNB, and arthropods present during harvest and storage were identified by morphological and/or chemical characteristics. Mean concentrations found at farms during the 1992 harvest were: TDC, 8.45 mg/m3; RD, 0.28 mg/m3; RS, 0.03 mg/m3; MMAD, 5.05 μm; OP, 3; F, 2.1 × 104 CFU/m3; TF, 3; TPC, 7.6 × 104 CFU/m3; GNB, 2.4 × 104 CFU/m3. Arthropod pests were found in low numbers during winter at two of four farms examined. The highest dust, silica, and fungal exposures occurred during bin cleaning or bin unloading. Concentrations at elevators at the 1992 harvest were: TDC, 27.33 mg/m3; RD, 0.97 mg/m3; RS, 0.04 mg/m3; MMAD, 5.84 μm; OP, 3; F, 2.2 × 105 CFU/m3; TF, 3; TPC, 11.6 × 105 CFU/m3; and GNB, 4.2 × 105. In 1993 total dust and microbial exposures were lower. All but two airborne total dust samples exceeded the recommended threshold limit value for total grain dust of 4.0 mg/m3. Endotoxins ranged from 20 to 237 EU/m3 in 1993 and were positively correlated to dust levels, but were lower than generally required for organic dust toxic syndrome. The most common culturable microbes during harvest were Alternaria and Cladosporium spp. (fungi), and Enterobacter agglomerans (bacteria).

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