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Model Report

Assessment Tools for the Evaluation of Risk

Last Revision Date: 11/16/2009 View as PDF
General Information Back to Top
Model Abbreviated Name:

ASTER
Model Extended Name:

Assessment Tools for the Evaluation of Risk
Model Overview/Abstract:
ASTER (Assessment Tools for the Evaluation of Risk) was developed by the U.S. EPA Mid-Continent Ecology Division, Duluth, MN to assist regulators in performing ecological risk assessments. ASTER is an integration of the ECOTOXicology Database (ECOTOX; www.epa.gov/ecotox) and QSAR (Quantitative Structure Activity Relationships), a structure activity based expert system. ASTER is designed to provide high quality data for discrete chemicals, when available in the associated databases and QSAR-based estimates when data are lacking. The QSAR system includes a database of measured physicochemical properties such as melting point, boiling point, vapor pressure, and water solubility as well as more than 56,000 molecular structures stored as SMILES (Simplified Molecular Input Line Entry System) strings for specific chemicals. ECOTOX is a comprehensive database, which provides information on adverse effects of single chemical stressors to ecologically relevant aquatic and terrestrial species. ECOTOX includes more than 500,000 test records covering more than 6,000 aquatic and terrestrial species and 10,000 chemicals.

Keywords: Risk assessment, QSAR, SAR, Modeling, Ecotoxicology, Toxicology, Biodegradation, Environmental persistence, Aquatic, Terrestrial, Physical/chemical property
Model Technical Contact Information:
Christine L. Russom
USEPA/ORD/NHEERL/MED
Russom.chris@epa.gov
218-529-5218
The model was developed by U.S. EPA, Office of Research and Development (ORD), National Health and Environmental Effects Research Laboratory (NHEERL), Mid-Continent Ecology Division (MED)-Duluth MN.
Model Homepage: http://www.epa.gov/med/Prods_Pubs/aster.htm
Substantive Changes from Prior Version: Version 2.0 has many substantial changes / upgrades from the previous version
  • System is available as a web-based application, available to EPA staff and their contractors/grantees with access to the Agency’s Intranet server
  • System can now search on chemical synonyms
  • 2-D depiction of chemical structure is provided for chemicals having structure information
  • Direct output of reports to MS Excel format
  • Geometric mean of species group data provided for a quick overview of potential toxicity of the chemical
  • Addition of new output parameters including Media Type, Measurement, Effect Percent, Response Site, Significance and Level of Significance
  • Report header row links to field definition and codes
  • Addition of new models for estimation of log P (KowWin) and biodegradation (BioWin)
  • Major modification of batch chemical processing; providing empirical as well as modeled toxicity data for the fathead minnow, and empirical data for comparative fish species
Plans for further model development: In FY 08 a hazard ranking module was added to allow for batch prioritization / ranking of large chemical lists

User Information Back to Top
Technical Requirements
Computer Hardware
Desktop PC
Compatible Operating Systems
Microsoft Windows 98, 2000, XP, NT4
Other Software Required to Run the Model
Web browser; IE version 5.0 or higher User must have access to EPA’s Intranet
Download Information
Application is a web-based expert system and models cannot be downloaded from system.
Using the Model
Basic Model Inputs
Models require a structure. There is a database of over 56,000 structures associated with ASTER, and if a user enters a CAS number or chemical name the system will search for a structure. If not located, user will be prompted that not all models will work without structure information. Users can enter structure via SMILES notation.
Basic Model Outputs
Output is either to a web-viewable report format with text, and tables; or an MS Excel format. Full citations are provided for any models / data cited within the report. Uncertainty associated with models is provided. Users can look at the details of how a value was estimated / predicted; and override any property / value that is used in the final report during the active session.
User Support
User's Guide Available?
User guide can be downloaded from the website http://www.epa.gov/med/Prods_Pubs/aster.htm
Availability of User Support
In addition to the online help from the ASTER webpage; ORD/NHEERL/MED maintains a user support help desk for this application (ecotox.support@epa.gov / T: 218-529-5225)
User Qualifications
Knowledge of toxicology and basic structure-activity modeling; interpretation of results;

Model Science Back to Top
Problem Identification
A major need within OPPTS are tools that can be used to prioritize and rank large chemical lists and estimate information where data gaps exist e.g., for endangered species. Research is being planned to address the following questions:
  • For chemicals that lack adequate data on toxicological and exposure potential (e.g., certain PMN and HPV chemicals, inert pesticide ingredients, antimicrobial pesticides), how can toxic potency be predicted efficiently and credibly?
  • How can predictions be used to make decisions as to whether or not empirical studies are required to further refine a risk assessment?
  • What species/taxonomic groups are underrepresented in existing data collections?
  • What chemicals of importance to the Agency are not represented in existing data sets?
Summary of Model Structure and Methods
Expert system is rule-based, using sub-structure fragments to identify mode of toxic action of the compound. QSARs are based on the mode of action identified by the system; although users can override the selected MOA.

Models and expert system were developed based on research summarized in: Russom, C.L., Bradbury, S.P., Broderius, S.J., Hammermeister, D.E., and Drummond, R.A. 1997. Predicting modes of toxic action from chemical structure: Acute toxicity in the fathead minnow (Pimephales promelas). Environ. Tox. Chem. 16(5):948–967.

Third-party software (ClogP, KowWin, BioWin, 2-D depiction applet) are run from dlls imbedded in the system.

Model Evaluation
Model validation for mode of action expert system and available QSAR models are provided in the publication:
Russom, C.L., Bradbury, S.P., Broderius, S.J., Hammermeister, D.E., and Drummond, R.A. 1997. Predicting modes of toxic action from chemical structure: Acute toxicity in the fathead minnow (Pimephales promelas). Environ. Tox. Chem. 16(5):948–967.

ASTER includes links to the homepage for third-party applications (ClogP, KowWin, and BioWin), providing an overview of model validation and related citations.

Key Limitations to Model Scope
  • Models require the chemical structure
  • Most models require that the chemical be an organic chemical
Case Studies
Russom, C.L., R.L. Breton, J.D. Walker, and S.P. Bradbury. 2003. An overview of the use of quantitative structure-activity relationships for ranking and prioritizing large chemical inventories for environmental risk assessments. Environmental Toxicology and Chemistry 22:1810-1821.

Bradbury, S.P., C.L. Russom, G.T. Ankley, T.W. Schultz, and J.D. Walker. 2003. Overview of data and conceptual approaches for derivation of quantitative structure-activity relationships for ecotoxicological effects of organic chemicals. Environmental Toxicology and Chemistry 22:1789-1798.

Russom, C.L., S.P. Bradbury, and A.R. Carlson. 1995. Use of knowledge bases and QSARs to estimate the relative ecological risk of agrichemicals: A problem formulation exercise. SAR QSAR Environ. Res. 4:83-95.

Moore, D.R.J., R.L. Breton, and D.B. MacDonald. 2003. A comparison of model performance for six quantitative structure–activity relationship packages that predict acute toxicity to fish. Environmental Toxicology and Chemistry 22:1799-1809.


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