Using geographic information systems for exposure assessment in environmental epidemiology studies

Abstract

Geographic information systems (GIS) are being used with increasing frequency in environmental epidemiology studies. Reported applications include locating the study population by geocoding addresses (assigning mapping coordinates), using proximity analysis of contaminant source as a surrogate for exposure, and integrating environmental monitoring data into the analysis of the health outcomes. Although most of these studies have been ecologic in design, some have used GIS in estimating environmental levels of a contaminant at the individual level and to design exposure metrics for use in epidemiologic studies. In this article we discuss fundamentals of three scientific disciplines instrumental to using GIS in exposure assessment for epidemiologic studies: geospatial science, environmental science, and epidemiology. We also explore how a GIS can be used to accomplish several steps in the exposure assessment process. These steps include defining the study population, identifying source and potential routes of exposure, estimating environmental levels of target contaminants, and estimating personal exposures. We present and discuss examples for the first three steps. We discuss potential use of GIS and global positioning systems (GPS) in the last step. On the basis of our findings, we conclude that the use of GIS in exposure assessment for environmental epidemiology studies is not only feasible but can enhance the understanding of the association between contaminants in our environment and disease.

Figure 1. Structure and functionality of a GIS.

Figure 2. Exposure assessment process. Steps for which use of GIS is discussed in this article are highlighted in blue.

Figure 3. Distribution of landfill sites in the Great Britain, buffered to 2 km, with an inset showing details of the buffer zones in pink (SAHSU 2001). The high density of sites in many areas results in considerable overlap of the buffer zones used to define exposures, and thus means that many areas are classified as exposed from a number of different landfill sites (see inset).

Figure 4. Exposure zone in original RMA study (ATSDR 1996) and refined resolution of predicted exposure to TCE by census block as reported by Reif et al. (2003).

Figure 5. Modeled ambient air concentrations of NO₂ emissions from all sources (1980 data) using reconstructed emission data for this index pollutant together with dispersion modeling (Bellander et al. 2001).