&EPA
      ORP
National Exposure Research Laboratory
Pesticide  Exposure
   Responsible and Safe Pesticide Use
                                                         REGIONAL TRANSPORT
                                                 DRY
                                               DEPOSITION
Pesticides in the Environment
Pesticides are important for keeping American agriculture productive, free from pest infestations and disease,
and economically viable. Many pesticides are also toxic to wildlife and consumers, so EPA and industry
work together to  write careful instructions for their safe and responsible use. In creating these instructions
- the pesticide "label" - industry first studies the chemistry and toxicology of their products in the laboratory
and submits the data to EPA. EPA then has the responsibility to use the data to predict how much chemical
would escape into natural ecosystems, and how long the chemical would remain in food chains and natural
reservoirs.  "Exposure" is  then combined with toxicological "effects" data, the likelihood of accidental
damage to ecosystems is evaluated, and the pesticide "label" is written to minimize these dangers and risks.

From the Laboratory to Fields and Streams in the Agricultural Landscape
Pesticides  are used throughout the  country, so
using a pesticide experimentally in one or a few
areas does  not tell  us enough  about how it will
behave when subject to the vagaries of wind, sun
and rain in  other areas. For this, an understanding
of environmental processes - the basic chemical
and physical mechanisms of pesticide transport
and degradation in the real world - is needed. This
knowledge  has accumulated over the past five
decades, and, although much remains to be done,
serves as the basis for the laboratory experiments
required of industry, and the means by which EPA
predicts the environmental behavior of pesticides
allowed into general use. The implications of our
knowledge  of processes are captured by  creating
and testing mathematical expressions that describe
the interaction of chemistry and environment. This
mathematics is then molded into computer algorithms, which are imbedded in a larger computerized
"decision-support system" that serves the information needs of the risk assessor. When making safety
decisions, the uncertainties in models, errors in chemical data, year-to-year changes in weather patterns, and
the range of soils, slopes, and cropping practices used by farmers all enter into the probabilistic and uncertain
nature of the risk equation.

Research Objectives
Ecological risk assessment of pesticides relies on "fate and transport" models that make direct use of industry
study results to predict exposure. These models,  developed from basic physical and chemical process
sciences, are tested in "validation" studies so their uncertainties can be known. By design, they capture the
uncertainties of weather and the heterogeneous soils of farmers' fields in probabilistic exposure estimates,
and so require high-quality nation-wide databases of climate, soil properties, and farming practices.
                                           WITH-
                                          DRAWAL
                                           FROM
                                          WELLS
                                         "T
                                                    ^GROUND-WATER
                                                      DISCHARGE
                                              RECHARGE  TO STREAMS
                                               FROM
                                              STREAMS
                                                                 SEEPAGE
                                        ENTRY
                                       THROUGH
                                        WELLS

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SAMSON Stations and State Parts of MLRA
Research  Summary
This  research  has  developed  models  of  the
atmospheric drift of pesticides (AgDisp), pesticide
persistence, runoff, and erosion in agricultural fields
(PRZA4), transport and fate in aquatic environments
(EXAMS), and food chain contamination (BASS). The
models  have  been  tested  by  comparing  their
predictions to real-world studies where one or another
of the model processes is most important, so that each
part of the model can be critically evaluated. In this
way the process algorithms have been continually
strengthened overtime.  Many  of these studies have
been  published  in the  scientific  literature and
summarized in the models' user manuals. The models,
their manuals,  the computer  source  codes, and
supporting databases are available at EPA's Center
for Exposure Assessment Modeling (CEAM) web site at   http://www.epa.gov/ceampubl/ceamhome.htm.
A national-scale database is currently being developed to provide a unified, high-quality single source of
input environmental data for all the models. The State divisions of Major Land Resource Areas (MLRA)
were chosen as a fundamental mapping unit, to facilitate access to soils and agricultural land use data from
the National Resources Inventory of the United States Department of Agriculture. The database includes
solar radiation data from the National Weather Service's SAMSON (Solar and Meteorological Surface
Observation Network) project,  hourly rainfall, wind, and weather data, and evaporation data developed as
a combination of weather observations and FAO (Food and Agricultural Organization of the United Nations)
standardized methods for estimating crop water requirements. This database includes 239 U.S. stations,
giving 30 years of data for comparable high-quality studies throughout the country..

Participants
ORD/NERL/ERD, Athens: Craig Barber, Sandra Bird, Lawrence Burns*, Lourdes Prieto, Luis Suarez
       * contact for more information: burns.lawrence(giepa.gov

Selected Publications from this Research
Teske,M.E.,Bird, S.L., Esterly, D.M., Curbishley,T.B., Ray, S.L., and Perry, S.G. 2002. AgDrift: Amodel
       for estimating near-field spray drift from aerial applications. Environm. Toxicol. Chem. (in press).
Burns,  L.A.  2001.  Probabilistic  Aquatic  Exposure  Assessment for  Pesticides.  I:  Foundations.
       EPA/600/R-01/071.  U.S. Environmental  Protection  Agency, National  Exposure Research
       Laboratory, Ecosystems Research Division, Athens, Georgia. 43 pp.
Burns, L.A. 2000. Exposure Analysis Modeling System (EXAMS): User Manual and System Documentation.
       EPA/600/R-00/081.  U.S. Environmental  Protection  Agency, National  Exposure Research
       Laboratory, Ecosystems Research Division, Athens, Georgia. 197 pp.
Burns, L.A. 1995. PIRANHA - A computer-based system for chemical risk assessment, pp. 305-315 In: M.
       L. Leng, E.M.K. Leovey, and P.L. Zubkoff (Eds.) Agrochemical Environmental Fate: State of the
       Art. CRC Press, Boca Raton.
Burns, L. A. 1983. Fate of chemicals in aquatic systems: process models and computer codes, pp. 25-40 In:
       R.L. Swann and A. Eschenroeder (Eds.) Fate of Chemicals in the Environment: Compartmental and
       Multimedia Models for Predictions (ACS Symposium Series 225). American Chemical Society,
       Washington, D.C.

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