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.

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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

PWC (Pesticide in Water Calculator)

The Pesticide in Water Calculator (PWC) is an updated version of the tool previously known as the Surface Water Concentration Calculator (SWCC). The tool’s name was changed to better reflect that the PWC can now simulate both surface water and ground water.  In addition, the PWC has an improved volatilization routine and more batch run capabilities.  PWC version 1.52 is the latest version approved for regulatory use.  It comprises a graphical user interface, a field model (PRZM version 5.02) and a water body model: (VVWM version 1.02).

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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.


PFAM is an aquatic model used to estimate surface water exposure from the use of pesticides in flooded fields. In comparison to the 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 user-defined receiving water. Although PFAM scenarios were developed mainly for applications of pesticides to rice paddies, in the future additional pesticide scenarios may be developed for other crops.

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.

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Archived Water Models Search EPA Archive

  • SWCC (Surface Water Concentration Calculator)
  • FIRST (FQPA Index Reservoir Screening Tool)
  • SCIGROW (Screening Concentration in Ground Water)
  • EXPRESS (EXAMS - PRZM Exposure Simulation Shell)

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Additional Information Related to Water Models

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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.


The Bee-REX model is a screening level tool that is intended for use in a Tier I risk assessment to assess exposures of bees to pesticides and to calculate risk quotients. This model is individual-based, and is not intended to assess exposures and effects at the colony-level (i.e., for honey bees).

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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.

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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.

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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

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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.  Download it free of charge from the Mathworks websiteExit 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.

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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.

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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 (AGDISPTM) 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.

AgDRIFT (Version 2.1.1) (ZIP)(1 pg, 12 MB)

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AGDISPTM (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. AGDISPTM 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.

AGDISP (version 8.26) (ZIP)(1 pg, 7 MB)

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

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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

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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)

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Indirect Dietary Residential Exposure Assessment Model (IDREAM)

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.

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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.

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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