oEPA
www.epa.gov/ord
science   in   ACTION
BUILDING A SCIENTIFIC FOUNDATION FOR SOUND ENVIRONMENTAL DECISIONS
   EPA computer models predict exposures to arsenic that echo reality
   Overview
   Arsenic exists naturally in rocks, soil, water
   and air. People's activities such as burning
   coal, preserving wood and managing food
   crops also contribute to arsenic in the
   environment.

   The U.S. Environmental Protection Agency
   (EPA) has set the arsenic standard for
   drinking water at 10 parts per billion (less
   than one-tenth of a drop of water in a 53-
   gallon tub) to protect consumers served by
   public water systems from the effects of long-
   term, chronic exposure to arsenic. Along with
   protective limits for arsenic in drinking water,
   arsenic exposures  in occupational settings are
   well described, and safeguards and limits
   have also been established.

   However, exposure to arsenic among the
   general U.S. population from both food and
   water ingestion is not well-defined because
   the variables that impact people's exposures
   to contaminants are difficult to measure, or
   vary from person to person and community to
   community, including the types and  amounts
   of food  people eat, and water they drink.

   Purpose of Research
   A critical element of EPA's mission is to
   protect public health by managing risks from
   exposures to pollutants. To do this,  EPA relies
   on  science-based decision-making and
   innovative solutions.

   EPA scientists recently conducted research to
   improve EPA's capability to estimate
   exposures to arsenic via two  pathways
   (drinking water and ingesting food) for the
   general U.S. population.

   Approach
   Exposure estimates were developed  using
   state-of-the-science computer models to
   combine available high-quality data  on food
   people eat and water they drink with
                         estimates of arsenic residues in foods and
                         drinking water. The accuracy of the modeled
                         estimates was then evaluated by comparing
                         them against physical measurements from
                         large-scale field surveys. Model development
                         and evaluation were performed using large
                         high-quality data sets from the U.S. Food and
                         Drug Administration (FDA), Natural Resources
                         Defense Council (NRDC), Centers for Disease
                         Control and Prevention (CDC),  and EPA.

                         EPA scientists specializing in modeling
                         research used EPA's Stochastic Human
                         Exposure and  Dose Simulation  (SjHEDS)-
                         Dietary model in this research. SHEDS-
                         Dietary is a population-based model that
                         incorporates real-world food consumption and
                         chemical residue data, and applies advanced
                         statistical methods to simulate individual
                         exposures to chemicals over different time
                         periods (e.g., daily, yearly).

                         EPA's modeled  predictions were compared to
                         arsenic intake from foods consumed by
                         people participating in EPA's National Human
                         Exposure Assessment Survey (NHEXAS)
                         duplicate diet study, as well as urinary
                         biomarker measurements provided  by
                         participants in CDC's 2003-2004 National
                         Health and Nutrition Examination Survey
                         (NHANES).

                         To predict the dose from people's arsenic
                         consumption, SHEDS-Dietary estimates were
                         linked to the MENTOR-3P modeling system.
                         MENTOR-3P stands for Modeling ENvironment
                         for TOtal Risk with Physiologically Based
                         Pharmacokinetic Modeling for Populations.

                         Linking SHEDS' estimates of exposure and
                         ingestion, with MENTOR-3P's estimates of
                         internal dose,  allowed researchers to
                         understand the variability between and
                         among  individuals, and equipped EPA with the
                         ability to develop arsenic dose  predictions
         U.S. Environmental Protection Agency
         Office of Research and Development

-------
that could be compared to biomarkers
measured in urine.

Conclusions and Impact
In this study, EPA scientists were able to use
the models to accurately predict dietary
exposures to arsenic. The study's modeled
estimates of arsenic exposures and doses for
the general U.S. population  from food and
water were found  to compare favorably with
the physical measurements  and observations
from biomonitoring samples and dietary
studies.

Study results showed that the foods we eat
may be as or more important as sources of

The study is detailed in a November 2009
peer-reviewed journal article: Xue, J.,
Zartarian, V., Wang S-W, Liu, S.V.,
Georgopoulos P, 2009. Probabilistic Modeling
arsenic as the water we drink and cook with.
Food groups that have been reported to
contain arsenic include some fruits, fruit
juices, rice, beer, flour, corn, and wheat,
depending on the item and where it is grown.
The study found estimated arsenic exposures
from diet to be low — approximately one-fifth
the level set to protect consumers from the
effects of long-term, chronic exposure to
arsenic in drinking and cooking water alone.

This research strengthens EPA's capability to
accurately predict dietary exposures to
arsenic and other chemicals. It also expands
and enhances EPA's suite of predictive
modeling exposure assessment tools.
of Dietary Arsenic Exposure and Dose and
Evaluation with 2003-2004 NHANES Data.
Environ Health Perspectives, vol. 118, no. 3,
p. 345-350.
Technical Contact:
Roy Fortmann, Ph.D., Acting Director
Human Exposure and Atmospheric Sciences Division
National Exposure Research Laboratory (NERL)
Office of Research and Development
U.S. Environmental Protection Agency
fortmann. roy@epa. gov
Media Contact:
Emily Smith, Communications Director
National Exposure Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
smith, emily@epa.gov (919.541.5556)
                                                                                  May 2010
       U.S. Environmental Protection Agency
       Office of Research and Development

-------