Submitted to: Journal of Occupational and Environmental Hygiene
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2010
Publication Date: 2/23/2011
Citation: Dungan, R.S. 2011. Airborne Endotoxin from Indoor and Outdoor Environments:Effect of Sample Dilution on the Kinetic Limulus Amebocyte Lysate (LAL) Assay. Journal of Occupational and Environmental Hygiene. 8:147-153.
Interpretive Summary: Endotoxins are derived from the cell wall of bacteria and can cause inflammatory reactions when inhaled. In this study airborne endotoxins were collected from a variety of agricultural environments, including dairy and swine housing units and downwind from crop production sites and a wastewater treatment plant. Endotoxin samples are typically analyzed using an enzymatic assay, known as the kinetic Limulus amebocyte (LAL) assay. When endotoxin samples are extracted for analysis, substances within the extracts can interfere with the reaction and produced skewed results. We found that diluting the samples 50- to 100-fold will decrease the interference from these substances. Airborne endotoxin samples should be checked for dilution dependent effects to assure that concentrations are as accurate as possible.
Technical Abstract: Airborne endotoxin in occupational environments are a potential respiratory hazard to individuals. In this study, total and inhalable airborne endotoxin samples were collected via filtration from inside animal housing units and downwind from agricultural production sites and a wastewater treatment plant. Filter extracts were then diluted to examine the effect of interfering substances on the kinetic Limulus amebocyte lysate (LAL) assay. In most cases, the overall endotoxin concentration was shown to decrease with increasing dilution up to 1,000-fold, suggesting the presence of enhancing substances in the filter extracts. This dilution dependent effect was most prominent in the inhalable endotoxin samples, while total endotoxin samples displayed little effect. Using a joinpoint regression model, it was determined that a dilution factor of 50 to 100 was generally sufficient to eliminate the presence of enhancing substances. After screening the data for dilution dependent effects, the airborne endotoxin concentrations were determined. The highest endotoxin concentrations, ranging from 2,841 to 49,066 endotoxin units (EU) m-3 of air, were found inside swine farrowing and finishing barns. Airborne endotoxin concentrations were 10- to 1,000-fold lower inside a dairy barn and downwind of other agricultural production sites and a wastewater treatment plant. Examination of dilution dependent effects should be considered essential when utilizing the LAL assay, especially if values are to be used for regulatory purposes.