SRC's  Escosar Program

The structure-activity relationships (SARs) presented in this program are used to predict the aquatic toxicity of chemicals based on their similarity of structure to chemicals for which the aquatic toxicity has been previously measured. Most SAR calculations in the ECOSAR Class Program are based upon the octanol/water partition coefficient (Kow). Various surfactant SAR calculations are based upon the average length of carbon chains or the number of ethoxylate units.

SARs have been used by EPA since 1981 to predict the aquatic toxicity of new industrial chemicals in the absence of test data. The acute toxicity of a chemical to fish (both fresh and saltwater), water fleas (daphnids), and green algae has been the focus of the development of SARs, although for some chemical classes SARs are available for other effects (e.g, chronic toxicity and bioconcentration factor) and organisms (e.g., earthworms). SARs are developed for chemical classes based on measured test data that have been submitted by industry or they are developed by other sources for chemicals with similar structures, e.g., phenols. Using the measured aquatic toxicity values and estimated Kow values, regression equations can be developed for a class of chemicals. Toxicity values for new chemicals may then be calculated by inserting the estimated Kow into the regression equation and correcting the resultant value for the molecular weight of the compound.

To date, over 150 SARs have been developed for more than 50 chemical classes. These chemical classes range from the very large, e.g., neutral organics, to the very small, e.g., aromatic diazoniums. Some chemical classes have only one SAR, such as acid chlorides, for which only a fish 96-hour LC50 has been developed. The class with the greatest number of SARs is the neutral organics, which has SARs ranging from acute and chronic SARs for fish to a 14-day LC50 for earthworms in artificial soil.

The ECOSAR Class Program is a computerized version of the ECOSAR analysis procedures as currently practiced by the Office of Pollution Prevention and Toxics (OPPT). It has been developed within the regulatory constraints of the Toxic Substances Control Act (TSCA). It is a pragmatic approach to SAR as opposed to a theoretical approach.

The EPA Internet web-page for Ecosar is:
www.epa.gov/oppt/newchems/

This ECOSAR program is designed for the expert user. You are expected to have some knowledge of environmental toxicology and organic chemistry. It is menu-driven and contains various help functions to assist you. You cannot change any of the equations or data stored within the program or accidently erase any important information.

Example Entry / Results

The newest version of Ecosar runs under Windows (3.1, 95, 98, NT) making the estimation of soil adsorption coefficients more convenient and accurate. Methods for chemical structure input now support SMILES notations as well as chemical structures produced in popular chemical drawing programs.