Temporal and Spatial Patterns of Ambient Endotoxin Concentrations in Fresno, California

Abstract

BackgroundEndotoxins are found in indoor dust generated by human activity and pets, in soil, and adsorbed onto the surfaces of ambient combustion particles. Endotoxin concentrations have been associated with respiratory symptoms and the risk of atopy and asthma in children.ObjectiveWe characterized the temporal and spatial variability of ambient endotoxin in Fresno/Clovis, California, located in California’s Central Valley, to identify correlates and potential predictors of ambient endotoxin concentrations in a cohort of children with asthma [Fresno Asthmatic Children’s Environment Study (FACES)].MethodsBetween May 2001 and October 2004, daily ambient endotoxin and air pollutants were collected at the central ambient monitoring site of the California Air Resources Board in Fresno and, for shorter time periods, at 10 schools and indoors and outdoors at 84 residences in the community. Analyses were restricted to May–October, the dry months during which endotoxin concentrations are highest.ResultsDaily endotoxin concentration patterns were determined mainly by meteorologic factors, particularly the degree of air stagnation. Overall concentrations were lowest in areas distant from agricultural activities. Highest concentrations were found in areas immediately downwind from agricultural/pasture land. Among three other measured air pollutants [fine particulate matter, elemental carbon (a marker of traffic in Fresno), and coarse particulate matter (PMc)], PMc was the only pollutant correlated with endotoxin. Endotoxin, however, was the most spatially variable.ConclusionsOur data support the need to evaluate the spatial/temporal variability of endotoxin concentrations, rather than relying on a few measurements made at one location, in studies of exposure and and respiratory health effects, particularly in children with asthma and other chronic respiratory diseases.

Spatiotemporal Distributions and Land-Use Regression Models of Ambient Bacteria and Endotoxins in the Greater Taipei Area

“…In the present study, the endotoxin concentrations ranged < LOD to 20.62 EU/m 3 , with an overall mean and median of 2.75 and 1.27 EU/m 3 , respectively. This concentration range is comparable with those reported in other studies that have investigated ambient endotoxin concentrations in various countries (i.e., USA, Germany, Sweden, and Hong Kong) (Mueller-Anneling et al, 2004;Morgenstern et al, 2005;Tager et al, 2010;Nilsson et al, 2011;Cheng et al, 2012). However, the concentration range observed in the present study was lower than those reported in previous studies conducted in occupational settings, wherein the measurements were generally performed at the sources of endotoxins (Su et al, 2002;Madsen and Nielsen, 2010;Rimac et al, 2010).…”

“…Regarding endotoxins, studies conducted in California, USA, reported spatial variability of endotoxins throughout the study area. Endotoxin concentrations have been associated with agricultural and pastureland areas, particularly in the downwind direction (Mueller-Anneling et al, 2004;Tager et al, 2010). However, a low spatial variability was also reported in a study by Morgenstern et al,(2005), which investigated the spatial distribution of endotoxins in Munich, Germany; this may be due to the similar characteristics of the sampling sites, which were all located in an urban area.…”

“…In a study designed to investigate the risk factors of childhood asthma, air samples were collected from several locations throughout Fresno, a city in central California, USA; the study revealed that the endotoxin concentrations varied among various geographical regions. Higher concentrations were closely associated with cropland, pastureland, and animal feeding areas such as dairy farms (Tager et al, 2010). However, the types of land use did not prove as significant predictors of endotoxin concentrations in a study conducted in Munich, Germany, by using an inverse distance weighting method (IDW) to fit the regression model (Morgenstern et al, 2005).…”

“…However, outdoor exposure is also crucial. Studies have indicated that bacterial and endotoxin concentrations vary among different types of outdoor environment, with considerable seasonal variations as well (Mueller-Anneling et al, 2004;Morgenstern et al, 2005;Bowers et al, 2010;Tager et al, 2010;Jeon et al, 2011;Bowers et al, 2012;Haas et al, 2013;Woo et al, 2013).…”

“…Although bacterial communities and endotoxin concentrations have been reported in several studies (Gorny and Dutkiewicz 2002;Park et al, 2002;Herr et al, 2003;Oppliger et al, 2005;Rusca et al, 2008;Tendal and Madsen, 2011), only a few studies have evaluated their relationships with the types of land use (Mueller-Anneling et al, 2004;Madsen, 2006;Bowers et al, 2010;Tager et al, 2010;Woo et al, 2013). In a study designed to investigate the risk factors of childhood asthma, air samples were collected from several locations throughout Fresno, a city in central California, USA; the study revealed that the endotoxin concentrations varied among various geographical regions.…”