Water: Selenium
Science & TechnologySurface Water Standards & GuidanceWater Quality StandardsWater Quality CriteriaAquatic LifePollutantsSeleniumAquatic Life Criteria for Selenium - Draft CriteriaAquatic Life Criteria for Selenium - Draft Criteria
Fact Sheet; December 2004
We are proposing draft revised water quality criteria for selenium. These revised criteria reflect a new and improved approach to measuring this bioaccumulative pollutant in the aquatic environment. At this time, we seek scientific data, information, and views on the draft revised ambient water quality criteria, which will then be considered by us before issuance of new final criteria for selenium.
- Why we are developing draft revised criteria for selenium
- Improvements in the draft selenium criteria
- The proposed fish tissue chronic criterion value and what it means
- Protecting water-dependent wildlife from the harmful effects of selenium
- Additional Information
Why we are developing draft revised criteria for selenium
The Clean Water Act (CWA) requires us to periodically review and update ambient water quality criteria to reflect the latest scientific knowledge on the effects of pollutants. Water quality criteria developed under the CWA are based solely on data and scientific judgments. They are our recommendations – guidance for states and authorized tribes to use in adopting water quality standards. They are not regulations and do not impose legally binding requirements on us, states, authorized tribes, industry, or the public. These draft criteria result from more than six years of development, cooperation with other federal agencies, and a comprehensive peer review process.
We last reassessed all available toxicity data when it published its 1987 aquatic life criteria for selenium. Since then, much new scientific data has become available. The new data suggest that, while selenium occurs naturally and is nutritionally essential, it is toxic to both aquatic life and wildlife where concentrations are excessive. The draft revised criteria for selenium reflect not only the new data but also a better method for monitoring selenium based on its presence in fish tissue. The proposed revised criteria contain recommended safe levels for selenium exposure over the short-term and long-term and for both fresh water and salt water. A special monitoring trigger is also included.
Improvements in the draft selenium criteria
For the first time, due to the bioaccumulative properties of selenium, we are presenting one component of the criteria expressed as a concentration of the pollutant in fish tissue rather than a concentration in the water. This is the proposed draft freshwater aquatic life criterion for long-term effects (called the chronic criterion). Such a criterion allows us to better account for the bioaccumulative nature of selenium.
Different water bodies have different types of food chains and therefore different propensities for bioaccumulation of selenium. The draft fish tissue-based measure allows more consistent interpretation of monitoring data across the country because the tissue concentration is the most reliable indicator of selenium exposure and risk to fish under different environmental conditions.
For purposes of setting NPDES permit limitations, the tissue criterion can be translated to a water concentration by using a site-specific bioaccumulation factor – a ratio between the tissue concentration and the water concentration.
The proposed fish tissue chronic criterion value and what it means
The draft freshwater chronic criterion is expressed as a concentration in whole-body fish tissue of 7.91 µg/g, dry weight, and says if fish tissue samples exceed 5.85 µg/g during summer or fall, fish should be monitored during the winter to determine if selenium exceeds 7.91 µg/g. Because we do not have data directly applicable to deriving a chronic criterion for saltwater, a saltwater chronic criterion is not included in the draft document.
Protecting water-dependent wildlife from the harmful effects of selenium
EPA and the U.S. Fish and Wildlife Service agree that wildlife should be protected from the harmful effects of selenium and efforts have been initiated outside the scope of these draft revised aquatic life criteria. The two agencies are developing a general approach or methodology for deriving national pollutant criteria to protect wildlife and the agencies are working together to develop criteria to protect wildlife from toxic effects of selenium specifically within California.
Additional Information
You may download the draft document, titled Draft Aquatic Life Water Quality Criteria for Selenium - 2004 (PDF) (334 pp., 872 K; EPA 822-D-04-001).
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