title: Seasonal variability of endotoxin in ambient fine particulate matter.
abstract: Endotoxin is a toxic, pro-inflammatory compound that has been detected in indoor air and dust in homes and occupational settings, and also in outdoor air. Data on the outdoor sampling of endotoxin are limited. Currently, little is known about the seasonal variation and influence of temperature on outdoor endotoxin levels. In the present study, we report endotoxin levels in fine fraction particulate matter with a 50% aerodynamic cutoff diameter of 2.5 microm (PM2.5) and describe the seasonal variation of endotoxin in Munich, Germany. In 1999-2000, PM2.5 was collected at forty outdoor monitoring sites across Munich. Approximately four samples were collected at each site for a total of 158 samples. Endotoxin concentrations in the PM2.5 samples were determined using the kinetic chromogenic Limulus Amebocyte Lysate (LAL) assay. The geometric mean endotoxin concentration was 1.07 EU mg PM2.5(-1) (95% C.I.: 0.915-1.251) or 0.015 EU m(-3) of sampled air (95% C.I.: 0.013-0.018). Munich endotoxin levels were significantly related to ambient temperature (p < 0.0001) and percent relative humidity (p < 0.0001). Sampling periods with higher average temperatures yielded higher levels of endotoxin in PM2.5 (r = 0.641), whereas decreases in percent relative humidity were associated with increased endotoxin levels in PM2.5 (r = -0.388). Endotoxin levels were significantly higher during the warmer seasons of spring [means ratio (MR): 2.5-2.7] and summer (MR: 2.1-3.0) than during winter. Although temperature and relative humidity do not explain all of the variability in endotoxin levels, their effects were significant in our data set. Temperature effects and seasonal variation of endotoxin should be considered in future studies of outdoor endotoxin.
authors.affiliation: GSF-National Research Center for Environment and Health, Institute of Epidemiology, Ingolstaedter Landstrasse 1, D-85758 Neuherberg, Germany.
authors.forename: Cara L
authors.initials: CL
authors.lastname: Carty
authors.forename: Ulrike
authors.initials: U
authors.lastname: Gehring
authors.forename: Josef
authors.initials: J
authors.lastname: Cyrys
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Bischof
authors.forename: Joachim
authors.initials: J
authors.lastname: Heinrich
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D002947:Cities; D004731:Endotoxins / Q000032:analysis*; D004784:Environmental Monitoring; D005858:Germany; D006813:Humidity; D012016:Reference Values; D012621:Seasons; D013696:Temperature
chemical_list: D000393:Air Pollutants; D004731:Endotoxins