Daily variability of ambient endotoxin concentrations in a livestock-dense region

Abstract

Background: Endotoxins are an important livestock-related respiratory health hazard. Health effects associated with ambient endotoxins are concentration-dependent, with both adverse and protective effects reported, yet little is known about their temporal variability, sources, or influencing factors. Objectives: We aimed to capture short-term fluctuations in ambient endotoxin concentrations, analyze temporal trends, and identify determinants. Methods: Daily PM10 samples were collected over two years using Automatic Sampling Devices at three sites in the Netherlands. The sites were located in a low-, medium-, and high-livestock density area. Endotoxin levels were analyzed using the Limulus Amebocyte Lysate assay. Associations with meteorological variables and pollen counts were examined using uni- and multivariable regression models. Results: Site average endotoxin concentrations ranged from 0.18 to 0.39 EU/m3 depending on livestock density. High day-to-day variability occurred with moderate inter-site temporal correlations of daily average concentrations (r = 0.6-0.7). Concentrations peaked in summer and autumn and were lowest in spring and winter. Positive associations with daily endotoxin concentrations were found for wind speed, precipitation, sunshine duration, and thunderstorms; negative associations were found for atmospheric pressure, relative humidity, and manure spreading periods. Models explained 20%-36% of the observed temporal variance (R2). Poaceae (grass) pollen was negatively associated with endotoxin levels, while Betula (birch) showed a positive association. Conclusions: Ambient endotoxin concentrations peak during warmer months, likely driven by unstable weather conditions and local livestock sources. These findings highlight that endotoxin is an important component influencing air quality related to livestock farming, with potential implications for both monitoring strategies and health risk evaluations.