Recombinant factor C (rFC) assay and gas chromatography/mass spectrometry (GC/MS) analysis of endotoxin variability in four agricultural dusts

Endotoxin exposure is a significant concern in agricultural environments due to relatively high exposure levels. The goals of this study were to determine patterns of 3-hydroxy fatty acid (3-OHFA) distribution in dusts from four types of agricultural environments (dairy, cattle feedlot, grain elevator, and corn farm) and to evaluate correlations between the results of gas chromatography/mass spectrometry (GC/MS) analysis (total endotoxin) and biological recombinant factor C (rFC) assay (free bioactive endotoxin). An existing GC/MS-MS method (for house dust) was modified to reduce sample handling and optimized for small amount (<1 mg) of agricultural dusts using GC/EI-MS. A total of 134 breathing zone samples using Institute of Occupational Medicine (IOM) inhalable samplers were collected from agricultural workers in Colorado and Nebraska. Livestock dusts contained approximately two times higher concentrations of 3-OHFAs than grain dusts. Patterns of 3-OHFA distribution and proportion of each individual 3-OHFA varied by dust type. The rank order of Pearson correlations between the biological rFC assay and the modified GC/EI-MS results was feedlot (0.72) > dairy (0.53) > corn farm (0.33) > grain elevator (0.11). In livestock environments, both odd- and even-numbered carbon chain length 3-OHFAs correlated with rFC assay response. The GC/EI-MS method should be especially useful for identification of specific 3-OHFAs for endotoxins from various agricultural environments and may provide useful information for evaluating the relationship between bacterial exposure and respiratory disease among agricultural workers.