Is There Evidence for Synergy Among Air Pollutants in Causing Health Effects? Joe L. Mauderly1 and Jonathan M. Samet2 1National Environmental Respiratory Center, Lovelace Respiratory Research Institute, Albuquerque, New Mexico, USA; 2Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA 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. Methods and 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. Key words: air pollution, combined exposures, mixtures, ozone, synergy. Environ Health Perspect 117:1–6 (2009) . doi:10.1289/ehp.11654 available via http://dx.doi.org/ [Online 22 August 2008] Address correspondence to J.L. Mauderly, National Environmental Respiratory Center, Lovelace Respiratory Research Institute, 2425 Ridgecrest Dr., SE, Albuquerque, NM 87108 USA. Telephone: (505) 348-9432. Fax: (505) 348-4983. E-mail: jmauderly@LRRI.org This review was supported by the National Environmental Respiratory Center, a multipollutant laboratory research program funded jointly by numerous government and industry sponsors (J.L.M.) , and by the U.S. Environmental Protection Agency (EPA ; RD-8324170-3) (J.M.S.) . Although the research described in this article was funded in part by the U.S. EPA through grant/cooperative agreement RD-8324170-4 to J.S., it has not been subjected to the agency’s required peer and policy review and therefore does not necessarily reflect the views of the agency and no official endorsement should be inferred. The authors declare they have no competing financial interests. Received 1 May 2008 ; accepted 22 August 2008. The full version of this article is available for free in HTML or PDF formats. |