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Waste and Cleanup Risk Assessment

Ecotox Thresholds

EPA has developed software that calculates Ecotox Thresholds (ETs) for selected chemicals and can print out a table of ETs and their sources.

The ECOTOX (ECOTOXicology) database provides single chemical toxicity information for aquatic and terrestrial life. ECOTOX is a useful tool for examining impacts of chemicals on the environment. Peer-reviewed literature and independently-compiled data files provided by United States and international government agencies are the sources of information provided in the database. Information on the species, chemical, test methods, and results presented by the author(s) have been abstracted and entered into the database.

What are ETs

The Superfund program has initiated a project to develop media-specific benchmark values for those chemicals commonly found in surface water, sediment and soil samples at sites (values for soil are still being developed). The values are referred to as Ecotox Thresholds (ETs), and are defined as media-specific contaminant concentrations above which there is sufficient concern regarding adverse ecological effects to warrant further site investigation. ETs are designed to provide Superfund site managers with a tool to efficiently identify contaminants that may pose a threat to ecological receptors and focus further site activities on those contaminants and the media in which they are found. ETs are meant to be used for screening purposes only; they are not regulatory criteria, site-specific cleanup standards, or remediation goals. For those chemicals with the potential to bioaccumulate to toxic levels in upper trophic wildlife (e.g., methyl mercury, PCBs, DDT, dioxins, and lead), these benchmarks may not be low enough at some sites.

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Using ETs

The maximum concentration of each chemical at a site is compared to the medium-specific ET to evaluate whether further risk assessment for the chemical is warranted.

The ET software calculates site-specific ETs by adjusting for pH and hardness in surface water and total organic carbon in sediment. The software can also compare the site-specific ETs to the concentrations detected at the site.

The January 1996 ECO Update on ETs (EPA 540/F-95/038) describes, in detail, how to calculate and use ETs. This issue of ECO Update is available as a Portable Document Format (PDF) file.

To download the PDF version of the January 1996 ECO Update - click here (PDF) (12 pp, 123K, About PDF).

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