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NATIONAL HUMAN EXPOSURE ASSESSMENT SURVEY (NHEXAS): OPPORTUNITIES AND LESSONS LEARNED
Citation:
Graham, J A. NATIONAL HUMAN EXPOSURE ASSESSMENT SURVEY (NHEXAS): OPPORTUNITIES AND LESSONS LEARNED. Presented at NIEHS Human Exposure Assessment Workshop, Rockville, MD, September 22-24, 1999.
Description:
The National Human Exposure Assessment Survey (NHEXAS) in its fullest sense is a conceptual design, which upon implementation, will have long-term implications to exposure research and assessment. The ultimate goal is to document national distribution of human exposure to potentially high-risk chemicals for improving the accuracy of exposure (and risk) assessments, to identify potential mitigation approaches, and to evaluate whether and how exposures (and corresponding risks) are changing over time with the application of risk management steps. However, such an extensive program requires much preparation, including making improvements in the state of exposure science. The Phase I scooping or demonstration projects, which are currently being analyzed, are the beginning. Based on the scientific advances from this first phase of NHEXAS, two follow-up phases are envisioned. One encompasses special studies to test particular hypotheses related to issues. The other is the undertaking of a national exposure survey.
Phase I of NHEXAS (hereafter referred to as just NHEXAS) is perhaps the most ambitious study ever undertaken to evaluate aggregate and cumulative human exposure to multiple chemicals on a community and regional scale. It focuses on the exposure of people to environmental pollutants during their daily lives. To accomplish this, approximately 500 volunteer participants were randomly selected from AZ, IL, OH, IN, MI, MN, and WI to obtain a population-based probability sample. NHEXAS scientists measured the levels of a suite of chemicals to which participants were exposed in the air they breath (indoors, outdoors, and personal), in the foods and beverages they consume, in the water they drink, and in the soil and dust around their homes. Measurements were also made of chemicals or their metabolites in biological samples (including blood and urine) provided by the participants. Finally, participants completed questionnaires to help identify possible sources of chemical exposures, and to characterize major activity patterns and conditions of home environment. The suite of chemicals included metals, VOCs, pesticides, and PAH's. A correlated study in Baltimore investigated temporal relationships of exposure to several of the same chemicals. The data have been collected and are being analyzed; a database is in preparation and will be made publically available.
Because of the increasing need to understand human exposure, we are beginning to create the partnerships needed to build a full survey. For example, such a survey could identify whether people were being exposed to concentrations of chemicals that were likely to cause adverse health effects, identify what sources and pathways of exposure carried most risk (and hence are in need of intervention), and provide measures of the success of exposure interventions(e.g., regulatory reductions in emissions). Details of a national survey must await the analyses of key elements of the NHEXAS pilot study, but as recommended by EPA's Scientific Advisory Board, it is important to initiate planning. We are seeking partners from all sectors: governmental (both other Federal Agencies and the States), academic, non-governmental organizations, industry, and others. The study will be shaped by the stakeholders, but generally will involve a core program that operates over the long-term to provide national status and trends information. Modules, which will be short-term in nature, will be hypothesis-directed and gain economies from association with the core.