| Abstract
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Endotoxins, or lipopolysaccharides (LPS), found in organic dust are a component of the cell membrane of Gram-negative bacteria that play an important role in respiratory disease. However, accurate endotoxin measurements are difficult in agricultural environments since agricultural dusts contain a complex mixture of biological and chemical agents. This dissertation research was designed to improve the understanding of the variability in endotoxin measurements in agricultural environments. The first study determined patterns of 3-OHFA distribution in dusts from dairy farms, cattle feedlots, grain elevators, and farms, and evaluated correlations between the GC/EI-MS and the rFC bioassay results. Patterns of 3-OHFA distribution varied by dust type; livestock dusts contained approximately two times higher concentrations of 3-OHFAs than grain dusts. Pearson correlations and multiple regressions showed higher correlations between GC/EI-MS and rFC results for livestock dusts than for grain dusts. Odd-chain length 3-OHFAs were found to correlate with rFC responses, as well as with even-chain length 3-OHFAs. The second study evaluated traditional LAL and novel rFC assay responses to endotoxins in chicken, dairy, horse, swine, and turkey dusts, and investigated potential interference with assays using GC/EI-MS. Strong positive correlations existed between LAL and rFC results, but responses to assays varied by dust type. LAL overestimated/rFC underestimated endotoxin exposures in chicken and horse dusts, and LAL underestimated/rFC overestimated endotoxin concentrations in dairy, swine, and turkey dusts. The variability in assay responses might be explained by differences in bacterial composition and other dust components; the rFC assay may react positively with Actinobacteria. The third study characterized agricultural tasks and evaluated determinants of personal dust and endotoxin exposures in dairy farms, cattle feedlots, grain elevators, and farms. Dust and endotoxin exposures differed by agricultural environment and by task and combinations of tasks varied by environment. Regression analysis indicated that hours at running legs in grain elevators was the major determinant of dust. Hours at running legs in grain elevator and hours at feeding livestock in cattle feedlots were two major determinants in endotoxin measurements. This dissertation addressed the need for understanding differences in agricultural environments for endotoxin exposure assessment.
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