On the interpretation of epidemiological studies of ambient air pollution

Abstract

Studies of the effects of ambient air pollution on human health are complicated by the fact that individuals are exposed to a complex mixture of toxic and non-toxic substances that vary in their make-up in space and in time. It is impossible using standard epidemiological designs to uniquely identify any individual component of air pollution as a causal agent of a health effect because of simultaneous exposure to all or a subset of ambient pollutants. Nevertheless, associations observed for a particular pollutant can be interpreted as a marker of toxicity of the mixture, and regulatory action on judiciously selected pollutants can benefit health, as such actions can modify the complex mixture. This paper argues that we may be able to further our understanding of the effects of air pollution on human health by investigating whether particular mixtures are more toxic through (1) conducting and reporting results for all measured components; (2) possibly characterizing the complex mixture by developing synoptic categorizations of daily air pollution, through cluster or latent profile analysis; (3) a careful analysis of differences in the mixtures between locations; and (4) toxicological studies and controlled studies on humans that make use of factorial designs for various components of the air pollution mixture.

Panel discussion review: session two — interpretation of observed associations between multiple ambient air pollutants and health effects in epidemiologic analyses

“…As in the case of the traditional principal component analysis, there is the implicit assumption that a weighted average across pollutants is appropriate. A more detailed discussion of the air pollution mixture and the use of cluster or latent profile analysis to examine the health effects of the mixture are presented in another publication in this special issue (Goldberg, 2007).…”

Quantifying human exposure to air pollution—Moving from static monitoring to spatio-temporally resolved personal exposure assessment

“…It is impossible to identify any individual air pollutant as a sole causal agent of an adverse health effect (Branis, 2010;Goldberg, 2007).…”

“…This means personal exposure is a function of concentration and time (Nuckols et al, 2004). As a consequence, individuals can be exposed in any environment to a large variety of pollutants and pollutant mixes (Branis, 2010;Goldberg, 2007).…”

On the importance of synoptic classification methods with respect to environmental phenomena

“…These two approaches were revealed as efficient tools relating circulation to climatically related variables such as air pollutants (e.g. McKendry, 1994;Moulin et al, 1998;Brook and Johnson, 2000;Schwarzhoff and Reid, 2000;Yarnal et al, 2001), heat wave mortality (Rainham et al, 2005) and epidemiology (Goldberg, 2007). Spatial synoptic classification clustered into weather types was recently used as an effective tool to evaluate air quality predictions (Hu et al, 2010).…”