An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Ecological Structure Activity Relationships (ECOSAR) Predictive Model

The Ecological Structure Activity Relationships (ECOSAR) Class Program is a computerized predictive system that estimates aquatic toxicity. The program estimates a chemical's acute (short-term) toxicity and chronic (long-term or delayed) toxicity to aquatic organisms, such as fish, aquatic invertebrates, and aquatic plants, by using computerized Structure Activity Relationships (SARs).

 Key characteristics of the program include:

  • Grouping of structurally similar organic chemicals with available experimental effect levels that are correlated with physicochemical properties in order to predict toxicity of new or untested industrial chemicals
  • Programming of a classification scheme  in order to identify the most representative class for new or untested chemicals
  • Continuous update of aquatic QSARs based on collected or submitted experimental studies from both public and confidential sources

ECOSAR software is available for free and is posted below as a downloadable software program without licensing requirements. Information on use and set-up is provided in the ECOSAR Operation Manual v2.0 and ECOSAR Methodology Document v2.0. Check out What's New in ECOSAR V2.0 to see updates from ECOSAR V1.11.

Download  ECOSAR V2.0(1 pg, 196 MB)

Permission is granted for individuals to download and use the software on their personal and business computers. Users may not alter, modify, merge, adapt, or prepare derivative works from the software.

Additional Disclaimers:

  • ECOSAR is maintained and developed as a stand-along program by EPA.  For users’ convenience when screening chemicals, ECOSAR has been included in the EPA EPISuite program and the OECD Toolbox. These software tools have been developed separately and have different maintenance schedules; the version of ECOSAR in these programs may not represent the most recent version provided on this website
  • Professional judgement is needed to determine adequacy and applicability of the predictions provided in ECOSAR.
  • The program should be used for screening-level assessments that aim for an analog-like approach to evaluate aquatic hazard in the absence of quality experimental data.
  • Chemicals that should not be profiled in ECOSAR include inorganic or organometallic chemicals and polymers and chemicals with a molecular weight greater than 1,000 g/mol.
  • ECOSAR does not account for the unique physical properties of nanomaterials which may contribute to novel mechanisms of toxicity.

EPA Technical Contact:

Cathy Fehrenbacher, U.S. EPA Risk
Assessment Division (7403M)
1200 Pennsylvania Ave., N.W.
Washington, DC 20460-0001
Phone: 202-564-8551
Fax: 202-564-9063

Tracy Wright, U.S. EPA
Risk Assessment Division (7403M)
1200 Pennsylvania Ave., N.W.
Washington, DC 20460-0001
Phone: 202-564-9929
Fax: 202-564-9063