title: Is there evidence for synergy among air pollutants in causing health effects?
abstract: BACKGROUND
  Environmental air pollutants are inhaled as complex mixtures, but the long dominant focus of monitoring and research on individual pollutants has provided modest insight into pollutant interactions that may be important to health. Trends toward managing multiple pollutants to maximize aggregate health gains place increasing value on knowing whether the effects of combinations of pollutants are greater than the sum of the effects of individual pollutants (synergy).
  
  
  OBJECTIVE
  We reviewed selected published literature to determine whether synergistic effects of combinations of pollutants on health outcomes have actually been demonstrated.
  
  
  RESULTS
  We reviewed 36 laboratory studies of combinations of ozone with other pollutants that were reported in the recent U.S. Environmental Protection Agency Ozone Criteria Document. We examined original reports to determine whether the experimental design tested for synergy and whether synergy was demonstrated. Fourteen studies demonstrated synergism, although synergistic, additive, and antagonistic effects were sometimes observed among different outcomes or at different times after exposure.
  
  
  CONCLUSIONS
  Synergisms involving O3 have been demonstrated by laboratory studies of humans and animals. We conclude that the plausibility of synergisms among environmental pollutants has been established, although comparisons are limited, and most involved exposure concentrations much higher than typical of environmental pollutants. Epidemiologic research has limited ability to address the issue explicitly.
authors.affiliation: National Environmental Respiratory Center, Lovelace Respiratory Research Institute, Albuquerque, New Mexico 87108, USA. jmauderly@LRRI.org
authors.forename: Joe L
authors.initials: JL
authors.lastname: Mauderly
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Samet
mesh_terms: D000393:Air Pollutants / Q000633:toxicity*; D000818:Animals; D006801:Humans; D014481:United States; D014484:United States Environmental Protection Agency
chemical_list: D000393:Air Pollutants