Lack of spatial variation of endotoxin in ambient particulate matter across a German metropolitan area

Abstract

In this study, we describe the spatial variation of endotoxin across an urban setting using Geographic Information Systems (GIS) methods. We also identify potential sources of endotoxin that account for between-site variability and compare endotoxin levels in particulate matter with a 50% aerodynamic cut-off diameter of 2.5 mm (PM2.5) and of 10 mm (PM10). In 1999–2000, we collected PM2.5 and PM10 in Munich urban air and measured soluble endotoxin concentrations in both particle fractions. Using Teflon filters and Harvard impactors, PM2.5 was collected at 40 outdoor monitoring sites across Munich and PM10 at a subset of these sites (n ¼ 12). Approximately four samples were collected at each site for a total of 158 PM2.5 samples and 48 PM10 samples. We visited and characterized the surrounding 100 m of each site for potential endotoxin sources. The geometric mean endotoxin concentration for all sites was 1.46 EU mg1 PM2.5 (95% confidence intervals (CI): 1.21–1.77) and at the subset of the sites was 1.30 EU mg1 PM2.5 (95% CI: 1.01–1.67 EU mg1 PM2.5). Endotoxin levels in PM10 were higher, 3.91 EU mg1 PM10 (95% CI: 3.03–5.03 EU mg1 PM10), than in PM2.5 and were moderately correlated, r ¼ 0:51. All endotoxin concentrations measured in this study were o5.5 EU m3 and thus lower than the accepted thresholds for acute adverse health effects for occupational exposures. Sites with more potential sources (nX3) had slightly higher mean endotoxin levels (MR: 1.30 for EU mg1 PM2.5 and 1.13 for EU m3 PM2.5) than sites with no identified sources. Based on the ranges of endotoxin levels at the different sites, we found very little spatial variation in ambient endotoxin concentrations across the metropolitan area of Munich using inverse distance weighting method (IDW) methods (R2 ¼ 0:013 for EU mg1 PM2.5 and R2 ¼ 0:020 for EU m3 PM2.5). Potential sources of endotoxin surrounding the sites only partly explained the variation seen