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Model Report

Tier 1 Rice Model for Estimating Pesticide Concentrations in Rice Paddies

Last Revision Date: 11/18/2009 View as PDF
General Information Back to Top
Model Abbreviated Name:

Tier 1 Rice Model
Model Extended Name:

Tier 1 Rice Model for Estimating Pesticide Concentrations in Rice Paddies
Model Overview/Abstract:
The Tier 1 Rice Model estimates screening level aquatic concentrations of pesticides in rice paddies. It is a simple pesticide soil:water partitioning model with default values for water volume, soil mass, and organic carbon. Pesticide degradation is not considered in the model.
Keywords: Rice Model, Screening Model,
Model Technical Contact Information:
Agency Contact:
Dirk Young, Ph.D.
Model Coordinator

Developer Contact
James A. Hetrick, Ph.D.
Senior Science Advisor

Model Homepage: http://www.epa.gov/oppefed1/models/water/index.htm#rice
Substantive Changes from Prior Version: Formalized calibration of soil mass. Refined the default organic matter content based on soil surveys.
Plans for further model development: Future model development will include pesticide degradation and hydrology.

User Information Back to Top
Technical Requirements
Computer Hardware
Calculations may be performed without a computer.
Compatible Operating Systems
Other Software Required to Run the Model
Download Information
Using the Model
Basic Model Inputs
Pesticide application rate
Pesticide soil:water partitioning coefficient (Kd or Koc)
Basic Model Outputs
A single estimate of pesticide concentration in water
User Support
User's Guide Available?
Other User Documents
User Guide includes theory, calibrations, and evaluations.
Availability of User Support
User Qualifications
Knowledge of general environmental modeling

Model Science Back to Top
Problem Identification
The Tier 1 rice model was developed to estimate environmental concentrations of pesticides used in rice paddies. These concentrations are used in the ecological and human health risk assessments to support review and registration of pesticides under FIFRA and FQPA.
Summary of Model Structure and Methods
The model is a simple soil:water partition equation. It was designed to serve as Tier 1 screening model for assessing pesticide exposure for pesticides used on rice.
Model Evaluation
Because the model is a screening-level exposure model, it has undergone an analysis to ensure the model predicted EECs are higher than measured pesticide concentrations in rice paddy studies. The default model parameters (water depth, sediment bulk density, porosity, and soil organic carbon content, and sediment interaction depths) were determined from typical literature values or by calibration. Model was evaluated by comparisons with 5 field studies and shown to be appropriately protective.
Key Limitations to Model Scope
Estimates only high-end concentrations. Does not consider degradation, management practices such as water-holding periods.
Case Studies
Model has been used in many pesticide registration documents.

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