EPA Multiple-Path Particle Dosimetry Model
EPA researchers, in collaboration with Applied Research Associates, Inc. (ARA), developed the EPA Multiple-Path Particle Dosimetry Model (MPPD) to modernize inhalation dosimetry in EPA human health risk assessments. The EPA MPPD model is used to translate inhalation particle exposures for prediction of internal dose in the respiratory tract.
The EPA formally introduced inhalation dosimetry modeling in its assessment workflows with its 1994 inhalation reference concentration and application of inhalation dosimetry methods. To support these methods, EPA developed the regional deposited dose ratio (RDDR) model for inhaled particles. Beginning in 2019, EPA developed the EPA MPPD Version 2.0, 2025 model to reflect advancements in dosimetry modeling.
The animal species coverage and prediction capability for the two models is not identical. The EPA MPPD v2.0 model provides deposition predictions for humans, rats, mice, rabbits, monkeys, and pigs; and incorporates clearance processes to predict retained dose in humans and rodents (rat and mice). The RDDR model only provides deposition predictions in humans, rats, mice, rabbits, guinea pigs and hamsters.
EPA MPPD Version 2.0, 2025
EPA announces availability of the EPA Multiple-Path Particle Dosimetry Model, Version 2.0, 2025 (pdf)
About the Model
The EPA MPPD v2.0 model translates the animal exposure scenario for inhaled particle exposure to a human equivalent concentration. Internal dose predictions can also be used to:
- evaluate human variability due to differences in age, sex, race, or disease states
- improve experimental design by informing doses for in vivo and in vitro studies
- perform in vitro to in vivo extrapolation (IVIVE) of studies.
Who Should Use the Tool
The primary audiences for the EPA MPPD v2.0 model are organizations and individuals developing risk assessments who have a desire to follow EPA’s guidance and practices. These include federal and state agencies, international organizations, industry, and others.
Users of the model should have some familiarity with dosimetry modeling. The technical support documentation with user’s guide provides important background information including an introduction to respiratory tract anatomy and physiology, principles of inhalation dosimetry, along with documentation about how the model was developed, and derivation procedures and guidance on important procedures and input parameter values.
Benefits of Using the Tool
There are several new features that the EPA MPPD v2.0 model provides. It predicts clearance and retention of particles in the respiratory tract for humans, rats, and mice, in addition to internal deposited dose. This feature is not available in previous EPA inhalation dosimetry models. This retained dose metric is especially important for characterizing chronic exposures.
The EPA MPPD v2.0 model now includes clearance in the nasal region, including nose to brain translocation of nanomaterials, for humans and rodents (rats and mice). EPA also updated the clearance rate for humans in the lower respiratory tract and developed new clearance rates in the lower respiratory tract for rats and mice.
The EPA MPPD v2.0 model provides the ability to customize human exposures to different particle sizes and distributions, including multi-modal distributions. The particle size range of predictions is also expanded.
EPA MPPD v2.0 model supports the ability to customize predictions for both hygroscopic and soluble particles when data are available, expanding the domain of physicochemical properties for which the model can be applied.
Finally, the EPA MPPD v2.0 model also offers a refined estimate of systemic dose and the ability to customize the prediction further with chemical specific information.
User Guide and Technical Support Documentation
The Technical Support Documentation and User’s Guide provide important background information including an introduction to respiratory tract anatomy and physiology, principles of inhalation dosimetry, and documentation of how the model was developed along with derivation procedures and guidance on important procedures and input parameter values. Included is a chapter devoted to use cases that illustrate, in step-by-step fashion, how to properly interact with input menus of the software and how to use the associated six Excel files to facilitate calculation of human equivalent concentration (HEC) values for different scenarios relevant for risk assessment. Users are encouraged to use the guide as it improves understanding of the modeling and ensures transparent and consistent deployment of the model.
The document can be downloaded here: EPA Multiple-Path Particle Dosimetry Model, Version 2.0, 2025 (pdf)
The six Excel files can be found here:
Accessing the Model and Technical Contact
EPA MPPD v2.0 requires a PC with a Windows operating system running Windows 7 (or newer). Minimal hardware requirements include a 1-Ghz processor, 1-GB RAM, a Direct-X compatible graphics card for PC , and at least 100 MB of free disk space prior to installation. No internet connection is required to operate the software. The EPA MPPD v2.0 model also requires the OpenJDK or Oracle v8 Java Runtime Environment (JRE) to operate.
Additionally, a text editor (e.g., Notepad, Word) and spreadsheet software (Excel) are needed to view report files and spreadsheets outside of the model.
How to Install
The OpenJDK 8 JRE virtual machine and its Java libraries are required for the successful operation of the EPA MPPD software. The OpenJDK8 JRE may be downloaded from: https://adoptopenjdk.net/releases.html. Download. From this site, users should select the OpenJDK 8 and HotSpot applications, and the appropriate .msi file based on their operating system. If using a 64-bit system, choose the x64 option; otherwise, choose the x86 option for older PCs.
After the OpenJDK 8 JRE virtual machine and its Java libraries are installed, users can load the EPA MPPD v2.0 installer package file. To load the file on a Microsoft Windows Based System:
- Go to https://store.ara.com/product/multiple-path-particle-dosimetry-model-mppd-v-epa/ and download the “EPA MPPD v2.0 2025.msi” installer file.
- Follow the installation instructions to place the necessary files and folders in the directory of your choice. Users may choose to create desktop shortcuts and Start menu items to quickly access and run EPA MPPD.
Chapter 1 of the technical documentation and user guide contains additional details on installation. For technical assistance, submit your question via the contact us link below.