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)?

Description:

The National Human Exposure Assessment Survey (NHEXAS) was developed by the Office of Research and Development (ORD) of the U.S. Environmental Protection Agency (EPA) early in the 1990s to provide critical information about multipathway, multimedia population exposure distribution to chemical classes. It was a population-based pilot study of the exposure of over 500 people in three areas of the U.S. to metals, pesticides, volatile organic compounds, and other toxic chemicals. Measurements were made of the air people breathed, the foods and beverages they consumed, and the soil and dust in/near their home. Chemicals in their blood and urine were measured. The participants also completed questionnaires to help identify possible sources of exposures and to characterize activities that might contribute to exposure. EPA's Science Advisory Board recommended that EPA develop a strategy to analyze the data to ensure the optimal use of the data (EPA-SAB-IHEC-ADV-99-004). To develop this strategy EPA/ORD began with a workshop at which about 70 scientific and policy experts from ORD, EPA program offices, EPA regions, other federal agencies, state health agencies, academia, and private institutions. Based on the projects identified, EPA/ORD developed a strategy for the analyses of the NHEXAS pilot study data. The Strategic Plan describes projects in six topic areas: descriptive statistics; predictors of exposure and dose; spatial and temporal variability; aggregate exposure, pathway analysis, and cumulative risk; evaluation/refinement of current exposure models and assessments; and designing exposure studies. Criteria were established for ranking projects within each of these topic areas based on both the near- and long-term value to EPA. This prioritization will be used as a guide for ORD to implement the analyses. The Strategy was reviewed by SAB/IHEC in July, 2000 (EPA-SAB-IHEC-00-018). The revised strategy (EPA/600/R-00/049) was made available on the EPA/NERL web-site at http://www.epa.gov/nerl/research/nhexas/strategy.pdf . This Task describes analysis projects being done by EPA/NERL scientists and the status of other projects that were initiated in FY01 and FY02.

Record Details:

Record Type:PROJECT

Start Date:10/01/2000

Completion Date:09/01/2003

Record ID: 29215

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Project Information:

Progress :During 1998, the Science Advisory Board's (SAB's) Integrated Human Exposure Committee (IHEC) conducted a review of the NHEXAS pilot studies. The SAB report "An SAB Advisory: The National Human Exposure Assessment Survey (NHEXAS) Pilot Studies (EPA-SAB-IHEC-ADV-99-004, February 1999)" praised the NHEXAS pilot studies and recommended that EPA develop a strategic plan for completing the analysis of the NHEXAS pilot data. To develop background information for this strategic plan, ORD convened a workshop to identify the types of scientific analyses needed to interpret the NHEXAS data. Based on the projects identified, EPA/ORD developed a strategy for the analyses of the NHEXAS pilot study data. The projects were grouped into six topic areas: 1) Descriptive Statistics, 2) Predictors of Exposure, 3) Spatial and Temporal Variability, 4) Aggregate Exposure, Pathway Analysis, and Cumulative Risk, 5) Evaluation/ Refinement of Current Exposure Models and Assessments, and 6) Designing Exposure Studies. In their review of the Strategy, the SAB/IHEC (Integrated Human Exposure Committee) agreed that EPA had done a very good job developing the NHEXAS data analysis strategy and noted that EPA did a commendable job of setting priorities and that the draft Strategy was logical, well thought out, and consistent with the recommendations of the IHEC in its 1998 review of NHEXAS. The revised strategy (EPA/600/R-00/049) was made available on the EPA/NERL web-site at http://www.epa.gov/nerl/research/nhexas/strategy.pdf and a plan for implementation of the strategy (i.e., selection of projects and vehicles) was developed in cooperation with NCEA.

Work in FY2001 focused pimarily on reviewing the databases from each study and preparing to make these publicly available as part of the Human Exposure Database System (HEDS), at http://www.epa.gov/heds/default.htm Due to the limited availability of the databases during FY01, analysis projects were initially limited to
1) within-study analyses that can be conducted by the study investigators,
2) analyses conducted by EPA investigators and their contract support.
Based on this limitation, the highest priority projects from the Strategy were compared with optional papers that were included in the current NHEXAS contracts to identify projects which could be initiated first. Prior to initiating work on each project, investigators are to prepare a short (approx. 5 page) "analysis plan." These include a description of the objectives for each project, the characteristics of the available data (e.g., distributions, sample sizes), the treatment of the data prior to analyses (e.g., weighted analyses, missing values, and values below detection limits), the statistical methods to be used, and the anticipated results.

The top ranked projects that were initiated in FY01 are listed below by research area, together with an indication of which study investigators (Arizona, Maryland, or Region 5) or EPA Laboratory (NERL or NCEA) will complete the project:

- Descriptive Statistics --

D-01. An Analysis of Media Concentrations, Exposure, and Biomarkers by Demographics [FY01, Arizona study],

D-02. Univariate Statistics for Use in Exposure and Risk Assessment [FY01-03, NCEA], and

D-03. Impact of Censoring and Method Sensitivity and Precision on Multimedia Exposure Distributions and Associations [F01, Region 5 and Arizona studies].

- Predictors of Exposure and Dose --

P-01. Analysis and Comparison of NHEXAS Exposure Data to Residential Pollutant Sources, Concentrations, and Activity Patterns [FY01-03, NERL],

P-02. Compare Traditional Indirect Method of Estimating Dietary Exposures with Duplicate Diet Data and Compare Methodologies Utilized in NHEXAS [FY01, Region 5 study], and

P-03. Identifying Predictors of Exposure [FY01, Region 5 and Arizona studies].

- Spatial and Temporal Variability --

ST-01. Temporal Va

Relevance :

Exposure research in this project integrates measurements and modeling to investigate critical information gaps about population-scale distributions of exposures to contaminant mixtures that people encounter on a day-to-day basis. This task was created in FY01 to respond to SAB recommendations to the Administrator that EPA and ORD conduct additional analyses of the pilot study data from the National Human Exposure Assessment Survey (NHEXAS). These data provide background levels of aggregate exposure to environmental contaminants and associated exposure factors in three regions of the U.S. The SAB/IHEC found NHEXAS to be an excellent project that will provide vital information to the EPA for addressing the many multimedia pollutant issues that the Agency is confronted with on a daily basis. When fully analyzed, the results of the NHEXAS pilot study should provide a basis for the design and implementation of an effective surveillance program for multimedia pollutants. Therefore, the NHEXAS pilot study is highly relevant to the Government Performance and Results Act (GPRA) and SAB's "Integrated Environmental Decision-making Framework" which emphasize performance evaluation as a key to effective environmental health protection.



Clients :EPA Programs--especially OPP (David Miller) and OPPT (Pat Kennedy), Regional Offices; other Federal Agencies e.g., NICHD, National Children's Study (Carol Kimmel, NCEA) for questionnaire analyses

Project IDs:

ID Code :9568

Project type :OMIS