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EXAMS: Exposure Analysis Modeling System

The Exposure Analysis Modeling System (EXAMS) is an interactive modeling system that allows a user to specify and store the properties of chemicals and ecosystems, modify either via simple commands, and conduct rapid evaluations and error analyses of the probable aquatic fate of synthetic organic chemicals.

EXAMS simulates an aquatic ecosystem tracing the path and behaviour of a toxic pollutant. It has a database of toxic substances and a command-driven interface, which allows for the definition of new substances and for modifiation of the ecosystem definition.
Each water body may be constituted by up to 32 different segments, for each of which the balance of up to 28 different substances may be simulated. The basic phenomena taken into consideration are: accumulation, chemical and biological transformation, and transport. Environmental conditions may be constant (in the short or the long term) or varying monthly. It ma be use to conduct rapid evaluations and error analyses of the probable aquatic fate of synthetic organic chemicals.

EXAMS combines chemical loadings, transport, and transformation into a set of differential equations using the law of conservation of mass as an accounting principle. It accounts for all the chemical mass entering and leaving a system as the algebraic sum of external loadings, transport processes that export the compound from the system, and transformation processes within the system that convert the chemical to daughter products. The program produces output tables and simple graphics describing chemical exposure, fate, and persistence.

The EXAMS model system is available for microcomputer (DOS) systems


area: dynamics of natural ecosystem
objectives: simulation
description: acquatic ecosystems, ecotoxicology, mass balance, short-term, long term


The program is available at:

Center for Exposure Assessment Modeling (CEAM)
U.S. Environmental Protection Agency
Environmental Research Laboratory
College Station Road
Athens, Georgia 30613
(404) 546-3123 / (FTS) 250-3123
The model (fortran code and the documentation) can be downloaded at: EPA-CEAM EXAM Model information and at EXAM presentation of the WWW-Server for Ecological Modelling at the University of Kassel


Lawrence A. Burns, Ph. D.
Research Ecologist
Environmental Research laboratory
U.S. Environmental protection Agency
Athens, Georgia 30613 USA


  • User's guide for Exams.
  • Games, L. M. (1982) Field Validation of Exposure Analysis Modeling System (EXAMS) in a Flowing Stream In: Modeling the Fate of Chemicals in the Aquatic Environment, Ann Arbor Science, Ann Arbor, Mi 1982:325-346



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