We are improving our website to help you find what you're looking for. During this transition some URLs may change. Learn more...

Models for Pesticide Risk Assessment

When EPA assesses the risk of a pesticide to human health or the environment, it considers the toxicity of the pesticide as well as the amount of pesticide to which a person or the environments may be exposed. In assessing exposure, scientists frequently use mathematical models to predict pesticide concentrations in food, water, residential, and occupational environments.

On this page:

Aquatic Models

OPP uses aquatic models to estimate pesticide concentrations in food, water, non-target organisms, residential and occupational environments. These estimated concentrations are used to assess exposure to aquatic organisms, humans, and the environment. More information about water models.

Surface Water Models

SWCC (Surface Water Concentration Calculator)

The Surface Water Concentration Calculator (SWCC) estimates pesticide concentrations in water bodies that result from pesticide applications to land. The SWCC is designed to simulate the environmental concentration of a pesticide in the water column and sediment and is used for regulatory purposes by the USEPA Office of Pesticide Programs (OPP). The SWCC uses PRZM version 5.0+ (PRZM5) and the Variable Volume Water Body Model (VVWM), replacing the older PE5 shell (last updated November 2006), which used PRZM3 (Carousel et al., 2005) and EXAMS (Burns, 2003). This updated model will improve users' interactions with the program and facilitate maintenance and operation of the software.

Top of Page


PFAM is an aquatic model used to estimate surface water exposure from the use of pesticides in flooded fields. In comparison to the current Tier 1 rice model, PFAM allows for more advanced evaluation of pesticide use on flooded agricultural areas such as rice paddies and cranberry bogs. The advanced capabilities of PFAM include accounting for water and pest management practices and for degradation in soil and aquatic environments, as well as for post processing of discharged paddy waters to a stream, index reservoir, farm pond, or other user-defined receiving water.

Top of Page

FIRST (FQPA Index Reservoir Screening Tool)

FIRST is a surface water model that is used to assess exposure to pesticides in drinking water.

FIRST Version 1.0
FIRST Version 1.1.1

Top of Page


KABAM is used to estimate potential bioaccumulation of hydrophobic organic pesticides in freshwater aquatic food webs and subsequent risks to mammals and birds via consumption of contaminated aquatic prey.

Tier I Rice Model

Tier I Rice Model is an aquatic model used to estimate surface water exposure from the use of pesticides in rice paddies.

Ground Water Models


PRZM-GW (Pesticide Root Zone Model for GroundWater) is used as a screening-level and refined tool for risk assessment purposes. In general, PRZM-GW provides conservative estimates of pesticide concentrations in groundwater, but it also allows for region specific scenario development in cases where refined drinking water assessments are needed.

Top of Page

SCIGROW (Screening Concentration In GROund Water)

SCIGROW is an aquatic model used to estimate pesticide concentrations in ground water.

Other Models

EXPRESS (EXAMS - PRZM Exposure Simulation Shell)

EXPRESS is designed to facilitate a rapid and consistent assessment of aquatic pesticide exposure on a variety of crops. EXPRESS is a joint project of the USEPA Office of Pesticide Programs' Environmental Fate and Effects Division (OPP/EFED) and the USEPA Office of Research and Development (ORD). View EXPRESS (EXAMS - PRZM Exposure Simulation Shell).


SWAMP is a probabilistic model that estimates the probability, magnitude, and certainty of the risk to aquatic organisms from exposure to pesticides. Information for this model is available in EPA's Web archive. Search EPA Archive

Top of Page

Additional Information Related to Water Models

Top of Page

Terrestrial Models

OPP uses terrestrial models to estimate pesticide concentrations on avian and mammalian food items and exposure and risk to terrestrial organisms from pesticide use.

MCnest (Markov Chain Nest Productivity Model )

MCnest integrates existing toxicity information from three standardized avian toxicity tests with information on species life history and the timing of pesticide applications relative to the timing of avian breeding seasons, to quantitatively estimate the impact of pesticide-use scenarios on the annual reproductive success of bird populations. View information about MCnest.

Top of Page

SIP (Screening Imbibition Program)

SIP is used by OPP to provide an upper bound estimate of exposure of birds and mammals to pesticides through drinking water alone.

STIR (Screening Tool for Inhalation Risk)

STIR is used by OPP to estimate inhalation-type exposure based on pesticide-specific information.

Top of Page

T-REX (Terrestrial Residue Exposure)

T-REX is used by OPP to estimate pesticide concentration on avian and mammalian food items.

  • T-REX Version 1.5.2 Executable (XLSM)(10 pp, 585 K, June 2013)
    • 6/6/2013, v. 1.5.2 Seeding rate inputs were corrected to accurately reflect data from Becker and Ratnayake, 2011. Comment sheet was removed from the model due to lack of functionality.
  • User Guide
    • User Guide Version 1.5 remains current

Top of Page

TIM (Terrestrial Investigation Model)

TIM is used by OPP to derive quantitative estimates of the probability (or likelihood) and magnitude of mortality to birds (of the same species) exposed to the simulated pesticide.

The TIM executable and graphical user interface (GUI) should be unzipped and saved to the directory of the user's choosing. In order to run the GUI,  the Matlab Compiler Runtime (MCR) must be installed on the user's computer.  It can be downloaded free of charge from the ExitMathworks Exitwebsite.  The required version is the Windows 32-bit MCR for Matlab release 2012a. A full technical description of TIM v. 3.0 beta is provided in the manual (and associated appendices). User's guidance on running and parameterizing the model is provided in Appendix A.

Top of Page


TerrPlant is a Tier 1 model providing screening-level estimates of exposure to terrestrial plants from single pesticide applications.

T-HERPS (Terrestrial Herpetofaunal Exposure Residue Program Simulation)

T-HERPS is a simulation model that estimates exposure to terrestrial reptiles and amphibians from pesticide use.

Top of Page

Atmospheric Models

OPP uses atmospheric models to predict the deposition patterns of pesticides released into the atmosphere.


AgDRIFT® (version 2.1.1), a modified version of the AGricultural DISPersal (AGDISP®) model developed by the US Forest Service, was created under a Cooperative Research and Development Agreement between the EPA, the US Department of Agriculture's Forest Service, and the Spray Drift Task Force. The AgDRIFT® model has the capability to assess a variety of spray drift conditions from agricultural applications and off-site deposition of liquid formulation of pesticides. This model can be used in estimating downwind deposition of spray drift from aerial, ground boom and orchard/vineyard airblast applications.

Top of Page


AGDISP® (version 8.26) is a "first-principles" science-based model that predicts spray drift from application sites. The model was developed by the USDA Forest Service. AGDISP® was designed to optimize agricultural spraying operations and has detailed algorithms for characterizing the release, dispersion, and deposition over and downwind of the application area. This model can be used in estimating downwind deposition of spray drift from aerial and ground boom applications. In addition, it can be used in estimating downwind deposition of spray drift from forestry and adulticide/mosquitocide applications. The research version of AGDISP model can be obtained from Dr. Harold W. Thistle, USDA Forest Service.

PERFUM (Probabilistic Exposure and Risk Model for FUMigants)

PERFUM is used to calculate distributional exposure to soil fumigants emitted from treated agricultural fields. View information about PERFUMExit

Top of Page

SOFEA (SOil Fumigant Exposure Assessment)

SOFEA system is used to calculate exposure to bystanders who are in proximity to fileds treated with soil fumigants. View information in the archive about the 9/9/2004 FIFRA Scientific Advisory Committee. Search EPA Archive

FEMS (Fumigant Exposure Modeling System)

FEMS is used to calculate exposure to bystanders who are in proximity to fields treated with soil fumigants. View information in the archive about the 8/26/2004 FIFRA Scientific Advisory Committee meeting. Search EPA Archive

Top of Page

Health Effects Models

OPP uses health effects models to predict effects to humans from exposure to pesticides.

DEEM (Dietary Exposure Evaluation Model)/CALENDEXTM - FCID

DEEM provides dietary probabilistic assessments of dietary pesticide exposure. CALENDEXTM - FCID evaluates aggregated exposure that appropriately incorporates the probability of simultaneous exposures across multiple pathways.

CARES (Cumulative and Aggregate Risk Evaluation System)

Top of Page


The Indirect Dietary Residential Exposure Assessment Model (IDREAM) was developed to estimate acute and chronic indirect ingestion exposure that can result from use of disinfectants and sanitizers on kitchen surfaces in residential settings. It provides guidance for estimating these exposures where there may be inadvertent transfer of residue to edible items prepared on surfaces treated with these pesticides. View the IDREAM model.

LifeLineTM Version 4.3

LifeLine has been used to assess dietary, aggregate and cululative risks of pesticides. The current version is 5.0. View information about Lifeline softwareExit

OPHED (Occupational Pesticide Handler Exposure Data)

Describes data sources used in exposure and risk assessment of occupational pesticide handlers (i.e., mixer/loaders and applicators). Includes the "Occupational Pesticide Handler Unit Exposure Surrogate Reference Table". View information about OPHED.

Top of Page

OPPED (Occupational Pesticide Post-application Exposure Data)

Describes data sources used in assessment of occupational post-application exposures (e.g., harvesting, weeding, etc.). Includes "Science Advisory Council for Exposure, Policy 3". View information about OPPED.

REx (Residential Exposure Assessment)

This model has been replaced by CARES and the residential exposure standard operating procedure. Information about this model is available in the archive (FIFRA SAP meeting for 9/26/2003). Search EPA Archive Use REX SAP as your search term.

Top of Page

SHEDS (Stochastic Human Exposure and Dose Simulation Model)

SHEDS is a physically-based stochastic model developed to quantify exposure and dose of humans to multimedia, multipathway pollutants. View information in the archive about the 8/30/2002 FIFRA Scientific Advisory Committee meeting. Search EPA Archive

SWIMODEL (Swimmer Exposure Assessment Model)

SWIMODEL is a screening tool for conducting exposure assessment of pesticides found in indoor swimming pools and spas. View the SWIMODEL.

PBPK/PD (Physiologically-Based Pharmacokinetic/Pharmacodynamic)

View information in the archive about the 12/11/2003 FIFRA Scientific Advisory Committee meeting. Search EPA Archive

Top of Page