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Water: Selenium

Aquatic Life Criteria - Selenium

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Status of EPA Revisions to the Criteria

EPA is in the process of updating the acute and chronic freshwater ambient water quality criteria for selenium to reflect the latest scientific information. As a result, the currently recommended criteria for selenium may change substantially in the near future.

What is selenium?

Selenium is a naturally occurring element that is nutritionally essential, but it can be toxic to aquatic life (such as fish and invertebrates) where concentrations are excessive. It is also toxic to cormorants and other birds that consume aquatic organisms containing excessive levels of selenium.

Where does selenium come from?

Being a natural element, selenium can be found throughout the environment. Toxic levels of selenium in water bodies have mostly been related to irrigation of western soils that are naturally high in selenium, ash pond discharges from coal-fired power plants using coal that has selenium in it, petroleum refinery effluents, and runoff or discharges from certain mining activities. 

How does selenium affect aquatic life?

Selenium is a bioaccumulative pollutant. Aquatic life is exposed to selenium primarily through their diet. Risks stem from aquatic life eating food that is contaminated with selenium rather than from direct exposure to selenium in the water. Although selenium bioaccumulates, that is, accumulates in tissues of aquatic organisms, it is not significantly biomagnified. Unlike mercury or PCBs, concentrations of selenium do not increase significantly in animals at each level of the food chain going from prey to predator.

For aquatic life, the toxic effects with the lowest thresholds are effects on the growth and survival of juvenile fish and effects on larval offspring of the adult fish that were exposed to excessive selenium. In the latter case, besides reducing survival, selenium causes skeletal deformities.

Note: EPA no longer updates this information, but it may be useful as a reference or resource.

2009 SETAC Pellston Workshop: Ecological Assessment of Selenium in the Aquatic Environment

EPA participated in a February 2009 workshop sponsored by the Society of Environmental Toxicology and Chemistry (SETAC) in Pensacola, Florida, USA. Workshop participants included nearly 50 individuals from business, academia, government, and nongovernmental organizations. To view a summary of the workshop including key findings visit http://www.setac.org/resource/resmgr/publications_and_resources/selsummary.pdf.

December 2004 DRAFT Selenium Criteria

EPA published a draft ambient water quality criterion for selenium. The criteria recommendations presented in the December 2004 criteria document are have not been finalized; draft criteria do not constitute EPA recommendations.

1999 National Recommended Ambient Water Quality Criteria for Selenium

1987 National Recommended Ambient Water Quality Criteria for Selenium

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