title: Traffic-related air toxics and preterm birth: a population-based case-control study in Los Angeles County, California.
abstract: BACKGROUND
  Numerous studies have associated air pollutant exposures with adverse birth outcomes, but there is still relatively little information to attribute effects to specific emission sources or air toxics. We used three exposure data sources to examine risks of preterm birth in Los Angeles women when exposed to high levels of traffic-related air pollutants--including specific toxics--during pregnancy.
  
  
  METHODS
  We identified births during 6/1/04-3/31/06 to women residing within five miles of a Southern California Air Quality Management District (SCAQMD) Multiple Air Toxics Exposure Study (MATES III) monitoring station. We identified preterm cases and, using a risk set approach, matched cases to controls based on gestational age at birth. Pregnancy period exposure averages were estimated for a number of air toxics including polycyclic aromatic hydrocarbons (PAHs), source-specific PM2.5 (fine particulates with aerodynamic diameter less than 2.5 μm) based on a Chemical Mass Balance model, criteria air pollutants based on government monitoring data, and land use regression (LUR) estimates of nitric oxide (NO), nitrogen dioxide (NO2) and nitrogen oxides (NOx). Associations between these metrics and odds of preterm birth were estimated using conditional logistic regression.
  
  
  RESULTS
  Odds of preterm birth increased 6-21% per inter-quartile range increase in entire pregnancy exposures to organic carbon (OC), elemental carbon (EC), benzene, and diesel, biomass burning and ammonium nitrate PM2.5, and 30% per inter-quartile increase in PAHs; these pollutants were positively correlated and clustered together in a factor analysis. Associations with LUR exposure metrics were weaker (3-4% per inter-quartile range increase).
  
  
  CONCLUSIONS
  These latest analyses provide additional evidence of traffic-related air pollution's impact on preterm birth for women living in Southern California and indicate PAHs as a pollutant of concern that should be a focus of future studies. Other PAH sources besides traffic were also associated with higher odds of preterm birth, as was ammonium nitrate PM2.5, the latter suggesting potential importance of secondary pollutants. Future studies should focus on accurate modeling of both local and regional spatial and temporal distributions, and incorporation of source information.
authors: Department of Epidemiology, School of Public Health, University of California, Los Angeles, CA, USA. mwilhelm@ucla.edu
authors: Michelle
authors: M
authors: Wilhelm
authors: Jo Kay
authors: JK
authors: Ghosh
authors: Jason
authors: J
authors: Su
authors: Myles
authors: M
authors: Cockburn
authors: Michael
authors: M
authors: Jerrett
authors: Beate
authors: B
authors: Ritz
mesh_terms: D000328:Adult; D000393:Air Pollutants / Q000032:analysis / Q000633:toxicity*; D001724:Birth Weight / Q000187:drug effects; D002244:Carbon / Q000032:analysis / Q000633:toxicity; D016022:Case-Control Studies; D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D016015:Logistic Models; D015141:Los Angeles; D008297:Male; D008875:Middle Aged; D009566:Nitrates / Q000032:analysis / Q000633:toxicity; D009589:Nitrogen Oxides / Q000032:analysis / Q000633:toxicity; D052638:Particulate Matter / Q000032:analysis / Q000633:toxicity; D011084:Polycyclic Aromatic Hydrocarbons / Q000032:analysis / Q000633:toxicity; D011247:Pregnancy; D011256:Pregnancy Outcome / Q000453:epidemiology*; D047928:Premature Birth / Q000139:chemically induced*; D012044:Regression Analysis; D018570:Risk Assessment; D001335:Vehicle Emissions / Q000032:analysis / Q000633:toxicity*; D055815:Young Adult
chemical_list: D000393:Air Pollutants; D009566:Nitrates; D009589:Nitrogen Oxides; D052638:Particulate Matter; D011084:Polycyclic Aromatic Hydrocarbons; D001335:Vehicle Emissions; D002244:Carbon; C006568:ammonium nitrate