Ecosystems Research Division

EXAMS facilitates the development of aquatic ecosystem models for the rapid evaluation of the fate, transport, and exposure concentrations of synthetic organic chemicals, such as pesticides, industrial materials, and leachates from disposal sites. EXAMS includes an integrated database management system for the storage and management of information required by the software. EXAMS generates and summarizes data critical for ecological risk assessments.

At its core, the process models in EXAMS link the fundamental chemical properties of the substance in question to limnological parameters controlling the kinetics of aquatic fate and transport. Chemical properties are measured via laboratory methods, which in some cases (e.g., registered pesticides) are required by law to be studied and reported to regulatory agencies. Much of the required limnological data for EXAMS has been collected historically, so given a specific project at a certain site, data needs can often be met without undertaking an intensive field sampling program.

EXAMS has the capability to analyze long-term (steady-state), chronic chemical discharges, and short-term acute chemical releases from irregular discharges or weather-driven runoff and erosion in agriculture. EXAMS also performs full kinetic simulations that allow for monthly variation in the climatological parameters and alterations of chemical loadings on a daily time scale. EXAMS is generalizable in spatial dimension and in the number chemicals and chemical degradation byproducts, so the user controls the complexity of the environmental description and the number of chemicals to be investigated.

EXAMS has been used for analyses of exposure, defined as the expected environmental concentrations of synthetic chemicals and their transformation products. Exams can report acute (e.g., 96 hours) or chronic (21 days or longer) exposures (specific exposure intervals can be specified by the user). EXAMS has also been used to model the fate (spatial distribution of the chemical and its transformation products in aquatic ecosystems) of chemicals. EXAMS generates a sensitivity analysis to determine the relative importance of each transformation and transport process. Finally, EXAMS has been implemented to examine persistence, or the time required for natural purification of an affected ecosystem, via export and chemical degradation, once the release has terminated.

EXAMS is linked to the PRZM terrestrial model and the BASS bioaccumulation model.

For additional modeling information, please go to the EPA's Council on Regulatory Environmental Modeling (CREM) site. CREM promotes consistency and consensus within the Agency on mathematical modeling issues including model guidance, development, and application, and enhances both internal and external communications on modeling activities. The CREM is the Agency's central point to address modeling issues.

For information on models distributed by EPA's Center for Exposure Assessment Modeling (CEAM), please go to http://www.epa.gov/ceampubl/.

Back to Modeling at ERD