Airborne endotoxin in different background environments and seasons.

Endotoxin is a cell wall component from Gram-negative bacteria, and inhaled endotoxin contributes significantly to the induction of airway inflammation and dysfunction. Background levels of endotoxin have not yet been extensively described. In this study, airborne endotoxin was measured with a standardized protocol in 5 types of background environment (169 samples) in Denmark from October to May. Endotoxin levels in a greenhouse (median = 13.2 EU/m3) were significantly higher than in the other environments. The air from biofuel plants (median = 5.3 EU/m3), the air on congested streets (median = 4.4 EU/m3) and on an agricultural field (median = 2.9 EU/m3) had higher endotoxin contents than the air in industrial areas (median = 1.3 EU/m3) or in towns (median = 0.33 EU/m3). Levels in industrial areas were significantly higher than in towns. A literature study revealed background levels of endotoxin on different continents between 0.063-410 EU/m3, with median or mean values between 0.063-3.6 EU/m3. Endotoxin concentrations in towns and industrial areas were higher in April and May than in autumn and winter, and were higher in October than in winter. These data of exposure in background environments and of seasonal variation are helpful for public health practitioners, epidemiologists and industrial hygienists.