Endotoxin Exposure and Inflammation Markers Among Agricultural Workers in Colorado and Nebraska

Abstract

The adverse respiratory effects of agricultural dust inhalation are mediated in part by endotoxin, a constituent of gram-negative bacterial cell walls. This study quantified personal work-shift exposures to inhalable dust, endotoxin, and its reactive 3-hydroxy fatty acid (3-OHFA) constituents among workers in grain elevators, cattle feedlots, dairies, and on corn farms. Exposures were compared with post-work-shift nasal lavage fluid inflammation markers and respiratory symptoms. Breathing-zone personal air monitoring was performed over one work shift to quantify inhalable dust (Institute of Medicine samplers), endotoxin (recombinant factor C [rFC] assay), and 3-OHFA (gas chromatography/mass spectrometry). Post-shift nasal lavage fluids were assayed for polymorphonuclear neutrophils (PMN), myeloperoxidase (MPO), interleukin 8 (IL-8), albumin, and eosinophilic cation protein (ECP) concentrations. The geometric mean (GSD) of endotoxin exposure (rFC assay) among the 125 male participants was 888 ± (6.5) EU/m³, and 93% exceeded the proposed exposure limit (50 EU/m³). Mean PMN, MPO, albumin, and ECP levels were two- to threefold higher among workers in the upper quartile of 3‐OHFA exposure compared to the lowest exposure quartile. Even numbered 3-OHFA were most strongly associated with nasal inflammation. Symptom prevalence was not elevated among exposed workers, possibly due to endotoxin tolerance or a healthy worker effect in this population. This is the first study to evaluate the relationship between endotoxin's 3-OHFA constituents in agricultural dust and nasal airway inflammation. More research is needed to characterize the extent to which these agents contribute to respiratory disease among agricultural workers.

Acknowledgments

This work was funded by grants from the U.S. Centers for Disease Control (CDC) National Institute for Occupational Safety and Health (NIOSH): CDC NIOSH R01 OH007841 (New Methods for Evaluation of Organic Dust Aerosols) and CDC NIOSH 5U50 OH008085 (High Plains Intermountain Center for Agricultural Health and Safety). Dr. Burch was supported by a Career Development Award from the U.S. Department of Veterans Affairs, VISN-7, Charleston, SC, and by the William Jennings Bryan Dorn Department of Veterans Affairs Medical Center, Columbia, SC. The authors thank the Colorado Corn Growers Association, Pinnacol Assurance, the Colorado Livestock Association, and the Colorado Grain and Feed Handlers Association for assistance with the identification of eligible workers. The authors thank Jason Nakatsu for assistance with sample collection, Dr. Donald Milton for consultation on the GC/MS method, and Debjani Chanda and Mike Wirth for assistance with data analyses. Cambrex provided support for the rFC assay kits. The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health.