title: Temporal and spatial patterns of ambient endotoxin concentrations in Fresno, California.
abstract: BACKGROUND
  Endotoxins 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.
  
  
  OBJECTIVE
  We 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)].
  
  
  METHODS
  Between 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.
  
  
  RESULTS
  Daily 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.
  
  
  CONCLUSIONS
  Our 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.
authors.affiliation: Division of Epidemiology, School of Public Health, University of California, Berkeley, California 94720, USA. ibt@berkeley.edu
authors.forename: Ira B
authors.initials: IB
authors.lastname: Tager
authors.forename: Frederick W
authors.initials: FW
authors.lastname: Lurmann
authors.forename: Thaddeus
authors.initials: T
authors.lastname: Haight
authors.forename: Siana
authors.initials: S
authors.lastname: Alcorn
authors.forename: Bryan
authors.initials: B
authors.lastname: Penfold
authors.forename: S Katharine
authors.initials: SK
authors.lastname: Hammond
mesh_terms: D000393:Air Pollutants / Q000032:analysis* / Q000633:toxicity; D001249:Asthma / Q000503:physiopathology; D002140:California; D002648:Child; D015331:Cohort Studies; D004731:Endotoxins / Q000032:analysis* / Q000633:toxicity; D006801:Humans
chemical_list: D000393:Air Pollutants; D004731:Endotoxins