Advances in space-time technology for assessing human exposure to environmental contaminants

In recent decades, digitally georeferenced data and Geographic Information Systems (GIS) have played a growing role in human exposure assessment for environmental epidemiologic studies. Despite the increased use of GIS in exposure assessment research, spatio-temporally varying datasets, such as daily activity spaces, residential histories, and time-varying maps of environmental contaminants are poorly characterized in the GIS environment. While GIS-based methods allow for integrating datasets that contain spatial variability, until recently datasets exhibiting spatio-temporal variability have been largely unmanageable, and researchers have been forced to simplify the complicated nature of their datasets by reducing or eliminating the spatial or temporal dimension. However, recent advances in space-time technology enable exposure scientists to more fully incorporate spatial and temporal variability into human exposure assessment. Whereas traditional GIS are based on spatial data structures--the "what, where" diad that inadequately displays changes through time, space-time technology is based on space-time data structures that enable characterization of the "what, where, when" triad needed for effective representation of data used to analyze health outcomes. Space-time technology allows the user to observe and quantify how geographies change with time, thereby enabling powerful exposure reconstruction procedures that are not possible through "space only" GIS. The continual expansion of space-time databases, coupled with the recognized need to incorporate human mobility in general and residential history in particular in environmental epidemiology, has highlighted the deficiencies of GIS-based software to visualize and process space-time information. This need is most pressing in retrospective studies where collection of individual biomarkers is unattainable or prohibitively expensive, and where models and software tools are required for exposure reconstruction. Advances in new space-time technology will profoundly improve our ability to reconstruct time-resolved individual exposures to environmental contaminants.