AN OVERVIEW OF THE NATIONAL HUMAN EXPOSURE ASSESSMENT SURVEY (NHEXAS) PHASE I STUDIES
The National Human Exposure Assessment Survey (NHEXAS) Phase I studies were sponsored by EPA's Office of Research and Development (ORD) to address critical information needs for assessing human exposures to multiple chemicals from multiple pathways and media. These studies were implemented with extensive research collaboration, including scientists from leading academic research institutions, the EPA, CDC, and other federal agencies. Key goals for the first phase of NHEXAS included evaluating the feasibility to conduct a complex measurement study with representative populations, documenting population distributions of exposure, understanding factors that contribute to human exposures, and improving the accuracy of exposure models.
These studies measured distributions of human exposures to a variety of high-risk target chemicals, including metals, volatile organic compounds (VOCs), and pesticides. In these studies, approximately 500 volunteer participants were randomly selected from three areas of the country: the state of Arizona, the greater Baltimore, Maryland area, and the EPA Region 5 states (IL, IN, MI, MN, OH, and WI). Measurements were made of the air people breathed, the foods and beverages they consumed, and the dust and soil in/near their home. Measurements were also made of chemicals or their metabolites in biological samples, including blood and urine. The participants completed questionnaires to help identify possible sources of exposures and to characterize activities that might contribute to exposure. Individual investigators were able to use alternative and innovative approaches to conduct multimedia measurements, and were able to target some specific concerns or hypotheses to be investigated in each study. Two of the groups focused on representing exposures of larger populations at one time, while another group studied fewer people but repeated the measurements six times over the year to examine temporal variability for the exposures and activities of interest.
The NHEXAS studies have provided unique information on the range of actual exposures in the general population for three areas of the U.S. for use as "benchmarks" in site-specific investigations and for health risk assessments. The data have also been analyzed to characterize differences in exposure between demographic groups, to compare exposure measurements and the biomarkers, and to evaluate changes in exposures over time. Following a recommendation from EPA's Science Advisory Board (SAB), the EPA developed a strategy to identify and prioritize additional analyses. EPA held a workshop to obtain a wide range of expert opinion regarding scientific analyses necessary to interpret the NHEXAS data. In addition, the NHEXAS databases and protocols are being made publicly available, and "lessons learned" and recommendations for future studies are being documented. These include a broad range of activities required for large scale exposure studies: project leadership, design, survey operations, field sampling, analytical laboratories, database development, quality assurance, and communication of results. This information will be critical in effectively designing and implementing future large scale human exposure surveys.
This work has been funded wholly or in part by the United States Environmental Protection Agency. It has been subjected to Agency review and approved for publication.
These studies measured distributions of human exposures to a variety of high-risk target chemicals, including metals, volatile organic compounds (VOCs), and pesticides. In these studies, approximately 500 volunteer participants were randomly selected from three areas of the country: the state of Arizona, the greater Baltimore, Maryland area, and the EPA Region 5 states (IL, IN, MI, MN, OH, and WI). Measurements were made of the air people breathed, the foods and beverages they consumed, and the dust and soil in/near their home. Measurements were also made of chemicals or their metabolites in biological samples, including blood and urine. The participants completed questionnaires to help identify possible sources of exposures and to characterize activities that might contribute to exposure. Individual investigators were able to use alternative and innovative approaches to conduct multimedia measurements, and were able to target some specific concerns or hypotheses to be investigated in each study. Two of the groups focused on representing exposures of larger populations at one time, while another group studied fewer people but repeated the measurements six times over the year to examine temporal variability for the exposures and activities of interest.
The NHEXAS studies have provided unique information on the range of actual exposures in the general population for three areas of the U.S. for use as "benchmarks" in site-specific investigations and for health risk assessments. The data have also been analyzed to characterize differences in exposure between demographic groups, to compare exposure measurements and the biomarkers, and to evaluate changes in exposures over time. Following a recommendation from EPA's Science Advisory Board (SAB), the EPA developed a strategy to identify and prioritize additional analyses. EPA held a workshop to obtain a wide range of expert opinion regarding scientific analyses necessary to interpret the NHEXAS data. In addition, the NHEXAS databases and protocols are being made publicly available, and "lessons learned" and recommendations for future studies are being documented. These include a broad range of activities required for large scale exposure studies: project leadership, design, survey operations, field sampling, analytical laboratories, database development, quality assurance, and communication of results. This information will be critical in effectively designing and implementing future large scale human exposure surveys.
This work has been funded wholly or in part by the United States Environmental Protection Agency. It has been subjected to Agency review and approved for publication.
Impact/Purpose
The NHEXAS analysis projects being conducted by NERL address the following scientific issues/questions:
- Do exposure distributions vary by demographic group?
- What is the impact of censoring (BDL) on multimedia distributions and associations?
- Which questionnaire/diary items are most useful in explaining variability or identifying "high exposure" groups?
- How do exposure classifications and measurements compare in their ability to explain variability in exposures and biomarkers?
- Can changes in exposures over time be explained by dietary and questionnaire/activity information?
- How well do NHEXAS findings compare with existing models/assessments (e.g., NATA)?
- Do exposure distributions vary by demographic group?
- What is the impact of censoring (BDL) on multimedia distributions and associations?
- Which questionnaire/diary items are most useful in explaining variability or identifying "high exposure" groups?
- How do exposure classifications and measurements compare in their ability to explain variability in exposures and biomarkers?
- Can changes in exposures over time be explained by dietary and questionnaire/activity information?
- How well do NHEXAS findings compare with existing models/assessments (e.g., NATA)?
Citation
Quackenboss, J J., L S. Sheldon, K. Hammerstom, G L. Robertson, S C. Hern, AND K W. Leovic. AN OVERVIEW OF THE NATIONAL HUMAN EXPOSURE ASSESSMENT SURVEY (NHEXAS) PHASE I STUDIES. Presented at 11th Annual Meeting of the International Society of Exposure Analysis, Charleston, SC, November 4-8, 2001.