Is There Evidence for Synergy Among Air Pollutants in Causing Health Effects?

Abstract

BackgroundEnvironmental 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).ObjectiveWe reviewed selected published literature to determine whether synergistic effects of combinations of pollutants on health outcomes have actually been demonstrated.Methods and resultsWe 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.ConclusionsSynergisms 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.

An overview of the MILAGRO 2006 Campaign: Mexico City emissions and their transport and transformation

“…Ozone and PM represent a common persistent problem in several cities, with important effects on public health (Craig et al, 2008). Although recent attention has been brought towards understanding the role of multipollutants interactions in air pollution related health effects (Mauderly and Samet, 2009), current methodological approaches have focused on ozone (Samoli et al, 2009) and, more importantly, in PM as the criteria pollutant with stronger associations with most of the described health effects.…”

Identifying Vulnerable Populations through an Examination of the Association Between Multipollutant Profiles and Poverty

“…For example, evidence for synergy among pollutants in causing health effects has been recently reviewed by Mauderly and Samet. 16 Several studies have confirmed that synergisms exist between O 3 and other pollutants in laboratory studies involving humans and animals. 17 Thus, the highly correlated nature of air pollution exposures and the potential for synergies raise questions about the adequacy of marginal, single-pollutant models.…”

Short-term Associations between Ambient Air Pollutants and Pediatric Asthma Emergency Department Visits

“…To help advance understanding of the relationships between ambient air pollutant concentrations and asthma exacerbations in children, further characterization of the dose-response and pollutant lag effects are needed, as are investigations of pollutant species beyond the commonly measured urban air pollutants (3,7). Further investigation of pollutant mixtures and effect modification may also provide insights (8,9); for example, there have been reports of stronger pollution effects during the warm season (10-15) even though pediatric asthma rates peak during the cold season (16). To lessen concerns about uncontrolled confounding, aggressive control for variables, such as meteorology and seasonal asthma trends, is required.…”