File: ABSTRACT.TXT


                      EXPRESS Software System Abstract

  

               Center for Exposure Assessment Modeling (CEAM)
       National Exposure Research Lab - Ecosystems Research Division
                  Office of Research and Development (ORD)
              U.S. Environmental Protection Agency (U.S. EPA)
                          960 College Station Road
                         Athens, Georgia 30605-2700

                                706/355-8400



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SUMMARY

The Environmental fate and Effects Division (EFED) of the Office of
Pesticides Programs (OPP) currently uses linked Pesticide Root Zone Model
(PRZM) and Exposure Analysis Modeling System (EXAMS) models for a refined
(Tier II) estimation of pesticide concentrations in surface waters for
drinking water and aquatic exposure assessments. The PRZM is a one-
dimensional, dynamic, compartmental model that can be used to simulate
chemical movement in unsaturated soil systems within and immediately below
the plant root zone. EXAMS contains a set of process modules that link
fundamental chemical properties to the limnological parameters that control
the kinetics of fate and transport in aquatic systems. Multiple-year
pesticide concentrations in the water column are extracted from the
PRZM/EXAMS simulation as the annual daily peak, maximum annual 96-hour
average, maximum annual 21-day average, maximum annual 60-day average, and
annual average. The upper 10th percentile concentrations(except annual
average) are used to compare against ecotoxicological and human health levels
of concern (LOC). 

The standard PRZM-EXAMS runoff modeling scenario is based on
unique dimensions of fields draining into water bodies for drinking water
and aquatic exposure assessments. The PRZM model (v. 3.12.2, released
May 2005) is linked to two subordinate models (PRZM and VADOFT), which
combine different root zone and vadose zone characteristics into a single
simulation to predict pesticide transport and transformation down through the
crop root and unsaturated zone for site-specific situations. Each PRZM
modeling scenario represents a unique combination of climatic conditions,
crop specific management practices, soil specific properties, site specific
hydrology, and pesticide specific application and dissipation processes.
Daily edge-of-field loadings of pesticides dissolved in runoff waters and
sorbed to entrained sediment, as predicted by PRZM, are discharged
into a standard water body simulated by the EXAMS model. The EXAMS model
accounts for volatilization, sorption, hydrolysis, biodegradation, and
photolysis of the pesticide. 

EXPRESS (EXAMS - PRZM Exposure Simulation Shell) is designed to facilitate a
rapid and consistent assessment of aquatic pesticide exposure on a variety of
crops. EXPRESS is a joint endeavor of the USEPA Office of Pesticide Programs
(OPP) and the USEPA Office of Research and Development (ORD). The first
draft of the software was developed by OPP/EFED via contract. OPP retains
responsibility for development and maintenance of the crop-specific modeling
scenarios. ORD continues development,maintenance and public availability of the
Express software and its constituent models. EXPRESS has not yet,
be it noted, been certified by OPP for routine use in regulatory analyses.
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