Overall Human Exposure Based on Spatial Range and Persistence. D. H. Bennett, W. E. Kastenberg, and T. E. McKone, UC Berkeley, Berkeley, CA 94720
The environmental decision making community is now confronting the potential adverse health effects of persistent chemicals such as metals and organic pollutants. Persistence allows adequate time for environmental interactions and long range transport to populations far from the source. These chemicals can cross local regulatory boundaries and in some cases international boundaries, thus becoming a global risk issue. We have developed methods to quantify the spatial range and persistence for semi-volatile organic pollutants in a multimedia environment. Short or long term health and environmental effects are determined by the persistence; while the spatial range determines whether a chemical will have a local, regional, or global scale effect. To evaluate the extent of the potential impacts of a chemical release, we quantify the overall human exposure based on the spatial range and persistence. The measure of total human exposure can be used by decision makers in several environmental analyses, including risk assessments, life cycle analyses, and regulatory impact studies. In this research, both persistence and spatial range are determined for a four-compartment steady-state system with air, plants, and two soil layers. The steady-state mass distribution is found to sufficiently represent the actual environment for characterizing persistence and spatial scales, while retaining sufficient simplicity to complete calculations in a tractable form. Persistence depends on the distribution among the different environmental media because decay rates often differ between environmental media. The spatial range is derived analytically from a moving Lagrangian air cell and non-moving compartments. The concentration is reduced with distance based on degradation in air, transfer to and subsequent degradation in vegetation and soil. These methodologies are appropriate for continual, area-source (non-point) emissions, including urban areas with releases from traffic, combustion and industrial activities or regional pesticide use. Using the spatial range, persistence, and mass distribution, the measure of overall human exposure is calculated based on multiple exposure pathways. This knowledge can be used to improve human health by determining more effective ways to regulate these chemicals.
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