Human Exposure Measurements: National Human Exposure Assessment Survey (NHEXAS)

Purpose

The National Human Exposure Assessment Survey program was designed to address some of the limitations of single-chemical, and single media exposure route studies. The purpose of NHEXAS is to evaluate comprehensive human exposure to multiple chemicals on a community and regional scale. Ultimately, the EPA anticipates that the information gained from NHEXAS will help individuals, communities, states, the EPA, and other organizations understand the greatest health risks from various chemicals and decide whether steps to reduce those risks are needed.

The current set of NHEXAS studies were developed as part of a three-phase process:

Design, field evaluation (feasibility/scoping), and demonstration projects (Phase 1),
Human exposure field studies (Phase 2), and
Special studies (e.g., follow-up on highly exposed populations; special topics, e.g., long-term exposures) (Phase 3).

Results from the initial "Phase 1" studies will be used to determine the feasibility and costs of alternative study designs and methods for the collection and analysis of environmental, exposure, and biological samples. In addition, the value or need to make direct personal measurements of multimedia, multipathway and multichemical exposures will be evaluated (or demonstrated) through the application of these data to exposure and risk assessments and through comparison with estimated exposure distributions obtained using existing data and models.

Research Objectives

Objectives for the first phase (feasibility/demonstration) of NHEXAS were:

to evaluate the utility of NHEXAS concepts and data for improved risk assessment and management decisions;
to test the hypothesis: that the distribution of exposure given by modeling and extant data does not differ from the measurement-based distribution of human exposure;
to define the distribution of total human exposures for a relatively large geographic area (e.g., characterize high-end exposures; provide baseline data; evaluate pathways; identify predictors; make comparisons with body burden);
to identify and test key elements for multimedia human exposure studies, including:
- the feasibility and success of protocols and study designs,
- estimation of the cost (survey, monitoring, and analytical) and variance components,
- determination of temporal variability in long-term exposures, and
- provide information to establish Data Quality Objectives (DQOs) for future multimedia human exposure studies; and
to stimulate scientific investigations of multipathway exposure assessment issues, and forging strong working relationships between government and nongovernment scientists.

Approach

The approach for NHEXAS is to describe the distribution of human exposure to multiple chemicals from multiple routes on a community and regional scale and its association with environmental concentrations and personal activities. NHEXAS focused on the exposure of people to environmental pollutants in their daily lives. To accomplish this, hundreds of subjects were randomly selected from several areas of the country and asked to participate. Researchers measured the levels of chemicals in the air participants breathe; in food, drinking water, and other beverages; and in the soil and dust around their homes. Measurements were also made of chemicals in biological samples (including blood and urine) provided by some participants. Finally, participants completed questionnaires to help identify possible sources of exposure to chemicals. NHEXAS in its fullest sense is a conceptual design which utilizes (a) representative sampling (probability-based sampling of a given population), (b) environmental sampling of air, water, soil/dust, (c) personal monitoring of air, food and beverages (duplicate diet) and dermal measurements, (d) biomarkers, and (e) questionnaires.

Major Findings Significance

The NHEXAS Phase 1 field sample collection and laboratory analyses were completed in 1998. A number of oral presentations have been made at conferences and a number of papers were submitted to peer-reviewed journals based on preliminary descriptive analyses. Additional statistical analyses of the data (comparisons between exposures, environmental concentrations, biomarkers, and questionnaire data) are being performed currently. The major finding of the NHEXAS Phase 1 studies is that it is technically feasible to conduct population-based, multimedia, multipathway exposure studies. The three projects have provided background levels of total exposure to environmental contaminants in three regions of the U.S. Note that very few incidences of contaminants exceeding health related action levels were encountered. As the data analyses continue and population-weighted distributions of contaminants are developed, the NHEXAS data can be used as baseline data in exposure and risk assessments in determining if specific populations are exposed to increased levels of environmental contaminants.

Research Collaboration and Publications

Currently, NHEXAS consists of three interrelated projects, all of which were funded as cooperative agreements and coordinated by the EPA's Office of Research and Development:

A study of several hundred Arizona residents by the University of Arizona, Battelle Memorial Institute, and the Illinois Institute of Technology.
A study of several hundred residents from the states of Illinois, Indiana, Michigan, Minnesota, Ohio, and Wisconsin by the Research Triangle Institute and the Environmental Occupational Health Sciences Institute.
A study of about 50 Maryland residents by Harvard University, Emory University, Johns Hopkins University, and Westat.

Two other federal agencies - the Food and Drug Administration and the Centers for Disease Control and Prevention - assisted the EPA with sample analysis. The National Institute for Standards and Technology provided quality assurance support.

The following results were published in the Journal of Exposure Analysis and Environmental Epidemiology (Volume 9, Number 1, January-March 1998):

Whitmore, R.W., Byron, M.Z., Clayton, C.A., Thomas, K.W., Zelon H.S., Pellizzari E.D., and Quackenboss, J.J.,"Sampling Design, Response Rates and Nonresponse Compensation for the National Human Exposure Assessment Survey (NHEXAS) in EPA Region 5."
Clayton, C.A., Pellizzari, E.D., Whitmore, R.W. Perritt, R.L., and Quackenboss, J.J., "National Human Exposure Assessment Survey (NHEXAS): Distributions and Associations of Lead, Arsenic and Volatile Organic Compounds in EPA Region 5."
Pellizzari, E.D., Fernando, R., Cramer, G.M., Meaburn, G.M., and Bangerter, K., "Analysis of Mercury in Hair of EPA Region 5 Population."
Thomas, K.W., Pellizzari, E.D., and Berry, M.R., "Population-based Dietary Intakes and Tap Water Concentrations for Selected Elements in the EPA Region 5 National Human Exposure Assessment Survey (NHEXAS)."
Freeman, N.C.G., Lioy, P.J., Pellizzari, E.D., Zelon, H., Thomas, K.W., Clayton, C.A., and Quackenboss, J.J., "Responses to the Region 5 NHEXAS Time/Activity Diary."
Reed, K.J., Jimenez, M., Freeman, N.C.G., and Lioy, P. J., "Quantification of Children's Hand and Mouthing Activities Through a Videotaping Methology."
Edwards, R.D., and Lioy, P.J., "The L Sampler: A Press Sampler for the Quantitative Estimation of Dermal Exposure to Pesticides in House Dust."
Scanlon, K.A., MacIntosh, D.L., Hammerstrom, K.A., and Ryan, P.B., "A Longitudinal Investigation of Dietary Exposure to Selected Elements."
MacIntosh, D.L., Needham, L.L., Hammerstrom, K.A., and Ryan, P.B., "A Longitudinal Investigation of Selected Pesticide Metabolites in Urine."
Echols, S.L., MacIntosh, D.L., Hammerstrom, K.A., and Ryan, P.B., "Long-Term Average Microenvironmental Time Budgets in Maryland."
O'Rourke, M.K., Fernandez, L.M., Bittel, C.N., Sherrill J.L., and Robbins, D.R., "Mass Data Massage: An Automated Data Processing System Used for NHEXAS Arizona."
O'Rourke, M.K., Rogan, S.P., Jin, S., and Robertson, G.L., "Spatial Distributions of Arsenic Exposure and Mining Communities from NHEXAS Arizona."
Gordon, S.M., Callahan, P.J., Nishioka, M.G., Brinkman, M.C., O'Rourke, M.K., and Lebowitz, M.D., "Residential Environmental Measurements in the National Human Exposure Assessment Survey (NHEXAS) Pilot Study in Arizona: Multimedia Results for Pesticides and VOCs."
Moschandreas, D.J., Berry, M.R., O'Rourke, M.K., and Lo, D.L., "Ranking Foods Contributing to the Dietary Exposure to Selected Chemical Residues Included in the NHEXAS-Arizona Exposure Study."
O'Rouke, M.K., Van de Water, P.K., Jin, S., Rogan, S.P., Weiss, A.D., Gordon, S.M., and Lebowitz, M.D., "Evaluations of Primary Metals from NHEXAS, Arizona: Methods Distributions and Preliminary Exposures."
Robertson, G.L., Lebowitz, M.D., O'Rourke, M.K., Gordon, S., and Moschandreas, D.J., "The National Human Exposure Assessment Survey (NHEXAS) Study in Arizona-Introduction and Preliminary Results."

More Information on NHEXAS

Future Research

The NHEXAS Phase 1 studies have provided a wealth of information that is being used in the design of future exposure studies. Much of this will be will be published in journal articles describing the results of the study. Scientists in the EPA's National Exposure Research Laboratory continue research on human exposure to characterize residential exposure to environmental contaminants. The goal is to develop cost effective screening techniques, both analytical and questionnaire, that will allow precise measurement techniques to be applied where they will be most effective in reducing uncertainties in human exposure measurements.

Human Exposure and Atmospheric Sciences

Research & Development | National Exposure Research Laboratory

Human Exposure Measurements: National Human Exposure Assessment Survey (NHEXAS)

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