United States Environmental Protection Agency	Office of Research and Development

National Exposure Research Laboratory
FY02 Research Abstract

Government Performance Results Act (GPRA) Goal 8
APM31

Significant Research Findings:

National Human Exposure Assessment Survey (NHEXAS) Results

and Databases

To evaluate the health risks posed by chemical pollutants in the environment,
the U.S. Environmental Protection Agency (EPA) must be able to estimate the
number of people exposed to the pollutants as well as the magnitude and
duration of these exposures. In the absence of actual measurements, these
estimates are often based on "default assumptions," thereby introducing
uncertainties into aggregate exposure estimates. Aggregate exposure refers
to the total exposure of humans to single chemicals through all relevant
pathways and routes. The National Human Exposure Assessment Survey
(NHEXAS) studies provide real-world data on individual exposures and
activities to evaluate many multimedia and media-specific risk management
issues, and to improve exposure factors and models. The reports and
databases described here will be useful to all Regional and Program Offices
that are developing or applying exposure or risk assessment models. The
study designs and protocols will aid state and federal risk
assessors/managers and all researchers who plan to collect exposure
measurements or make comparisons with the NHEXAS data.

Research	The NHEXAS studies measured human exposures to potentially high-risk

Approach	chemicals, including pesticides. Over 500 volunteers were randomly

selected from three areas of the country: the state of Arizona, the greater
Baltimore, Maryland area, and the EPA Region 5 states (Illinois, Indiana,
Michigan, Minnesota, Ohio, and Wisconsin). In addition, pesticide
exposures for about 100 children between the ages of three and 13 were
studied in Minnesota. The studies measured people's direct exposures to
environmental pollutants and indirect biological indicators of exposure, or
"biomarkers," in their blood or urine. The principal goals for the data
analyses described in this abstract were to identify factors that explain or
predict which individuals or groups are more likely to be exposed and to
develop and evaluate aggregate exposure models and estimates.

Scientific
Problem and
Policy Issues

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As a follow-up to the NHEXAS studies, researchers from the EPA Office of
Research Development's National Exposure Research Laboratory (NERL)
held a workshop to discuss and document the lessons learned during the
NHEXAS studies. Investigators from EPA, other federal agencies, research
organizations, and universities who carried out the NHEXAS studies
participated in the workshop. Extensive interviews were conducted before
the workshop with key individuals from each organization to serve as a basis
of discussion. Successful strategies and areas for improvement in project
leadership, study design, survey operations, field sampling, analytical
laboratories, database creation, and quality assurance were recorded along
with recommendations for future studies.

The data from the three NHEXAS studies, including questionnaire and diary
responses, results of chemical measurements on the subject's blood, urine,
and residential environment, and results from the measurement of quality
control samples have been made publicly available. These data are available
through NERL's Human Exposure Database System at
http://www.epa.gov/heds/ or http://oaspub.epa.gov/heds/hedsstart.

Results and	General household characteristics and activities were examined using data

Implications from the Region 5 study to identify key factors that influence levels of
residential exposure to contaminants (Bonanno et. al., 2001). Volatile
organic compounds (VOCs) in the residences were associated with the
storage of gas-powered devices in the home or attached garage, the use of
mothballs, and the presence of carpets. Metals were linked to chipped paint,
window replacement, and smoking. Construction and cleaning activities in
the home were associated with higher levels of particles in the air and on the
floor or carpet and of one VOC in indoor air. These results indicate that
residential characteristics and activities can be used as predictors of the
presence of VOCs and metals in residences.

A statistical model was constructed by Clayton and colleagues (2002) to
examine anticipated relationships between exposure measurements and
environmental concentrations of arsenic and lead, biomarkers (blood, urine),
and questionnaire responses in the Region 5 study. Significant but weak
associations were found among the concentrations, exposures, and doses for
these chemicals. Relationships between the questionnaire data and the
various concentration, exposure, and biomarker measurements were also
generally weak. The authors suggest several ways to optimize the design of
future exposure assessment studies based on the model results.

Distributions of pesticide measurements and associations between these
measurements were summarized for the Minnesota Children's Pesticide
Exposure Study by Clayton et al. (in press, 2002). Partial aggregate
exposures, for the inhalation and ingestion routes only, were also estimated

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using these data. Personal air exposures were closely related to indoor air
concentrations for chlorpyrifos, malathion, and diazinon, while personal air
atrazine and diazinon levels were more closely related to outdoor air levels
(due largely to the very low levels measured indoors). The ingestion route
was more important than the inhalation route as a contributor to estimates of
aggregate chlorpyrifos exposure. However, the urinary metabolite of
chlorpyrifos exhibited a stronger association with air measurements than
with the dietary measurements.

Aggregate exposure to chlorpyrifos that was estimated using measurement
and questionnaire data from adults participating in the Maryland NHEXAS
study (Pang et. al., 2002). Exposure from inhalation of indoor air accounted
for most of the aggregate daily chlorpyrifos exposure. Concentrations in
indoor air and carpet dust, and corresponding exposure rates, were highly
correlated. The results suggest that analysis of aggregate exposure estimates,
based on direct measurements, can help to better determine the accuracy of
pesticide exposure and risk assessments.

These NHEXAS studies demonstrated that large scale exposure studies can
be efficiently and effectively conducted to produce high-quality, high-
quantity exposure data that can be use to reduce human risks to environmental
contaminants. Overall lessons learned from the NHEXAS studies, as
documented by Leovic et. al. (2002), include:

•	large-scale population-based exposure studies can be planned, designed,
coordinated, resourced, and implemented;

•	aggregate exposures to selected contaminants can be characterized through
the collection of relevant exposure samples and corresponding
information;

•	diverse members of the scientific community (including federal agencies,
universities, regions, states, communities, and contractors) can work
together efficiently and effectively to plan and conduct studies of this type;

•	the rate of successful sample collection and analysis was high in most
media;

•	cooperative agreements can be appropriate funding mechanisms to support
research;

•	the extensive documentation (e.g., protocols, methods, designs, and
databases) developed and evaluated for NHEXAS will be useful for
designing and conducting future studies; and

•	results from these studies will be useful for addressing many current
science issues and for developing future hypotheses.

Specific recommendations for future studies were provided for seven topic
areas: project leadership, study design, survey operations, field sampling,
analytical laboratories, database issues, and quality assurance.

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The NHEXAS data sets have been made publicly-accessible on the internet
in formats which can be used by most commercial software packages. An
abstract describes each data set and document, and a data dictionary and
code table are also provided to define each data set. Extensive
documentation on how the studies were conducted, including quality
assurance documents and standard operating procedures for sample
collection and analysis, are also available. These features provide the user
with data in an easy-to-use format together with enough information to
evaluate the quality and potential uses of the data. These data are available
through NERL's Human Exposure Database System at
http://www.epa.gov/heds/ or http://oaspub.epa.gov/heds/hedsstart

The NHEXAS analysis projects were conducted under Contracts between
EPA's National Exposure Research Laboratory and Emory University,
Research Triangle Institute, and the University of Arizona. The Minnesota
Department of Health and the University of Minnesota participated in the
Minnesota Children's Pesticide exposure study.

This research has been published in the following manuscripts:

Bonanno, L.J., Freeman, N.C.G., Greenberg, M., Lioy, P.J. "Multivariate Analysis on
Levels of Selected Metals, Particulate Matter, VOC, and Household Characteristics
and Activities from the Midwestern States NHEXAS." JAppl Occup Environ Hyg
2001; 16(9):859-874.

Clayton, C., Pellizzari, E., Quackenboss, J. "National Human Exposure Assessment
Survey: Analysis of exposure pathways and routes for arsenic and lead in EPA
Region 5." J Expo Anal Environ Epidemiol. 2002 Jan; 12(1): 29-43.

Clayton, C.A, Pellizzari, E.D., Whitmore, R.W., Quackenboss, J.J. "Distributions,

associations, and partial aggregate exposure of pesticides and polynuclear aromatic
hydrocarbons in the Minnesota Children's Pesticide Exposure Study (MNCPES)." J
Expo Anal Environ Epidemiol. In press 2002.

Pang, Y., Macintosh, D.L., Camann, D.E., Ryan, P.B. "Analysis of Aggregate Exposure to
Chlorpyrifos in the NHEXAS-Maryland Investigation." Environ Health Perspect
2002 Mar; 110(3):235-240.

The results from the Lessons Learned workshop are summarized in:

Leovic, L., Sheldon, L., Thomas, K., Highsmith, R., Tulve, N., Robertson, G.,

Hammerstom, K., Quackenboss, J., Melnyk, L., Berry, M., Pellizari, E., Lebowitz,
M., Ryan, P.B. "Lessons Learned from the National Human Exposure Assessment
Survey (NHEXAS) Pilot Studies." Proceedings of the 12th Conference of the the
International Society of Exposure Analysis (ISEA).

The measurement and questionnaire databases, metadata, and study
documentation are available on the Human Exposure Database System
(HEDS) website at http://www.epa.gov/heds/

Future Research Future analyses of the NHEXAS data will be based on the projects included
in the Strategic Plan for Analysis of the NHEXAS Pilot Study (EPA 600/R-
00/049), which is available at

Research
Collaboration
and Publications

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http://www.epa.gov/nerl/research/nhexas/nhx_strat.htm

Contacts for Questions and inquiries on NERL's research to analyze the results of the

Additional	NHEXAS studies can be directed to:

Information	James j Quackenboss

US EPA, Office of Research and Development
National Exposure Research Laboratory
P.O. Box 93478
Las Vegas, NV 89193-3478

Phone: 702/798-2442

E-mail: quackenboss.james@epa.gov

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