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Water: Selenium

Aquatic Life Criterion - Selenium

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new icon Extension of Public Comment Period on External Peer Review Draft Aquatic Life Criterion for Selenium in Freshwater

EPA is extending the public comment period on a draft updated national recommended aquatic life criterion for the pollutant selenium. The public will be able to provide scientific views on the draft document until July 28, 2014. The draft document is an update to EPA’s 1999 chronic aquatic life criterion for selenium and reflects the latest scientific information, which indicates that selenium toxicity to aquatic life is primarily driven by organisms consuming selenium-contaminated food rather than by direct exposure to selenium dissolved in water. The external peer review draft criterion has four parts, including two fish tissue-based and two water column-based elements. EPA recommends that states and tribes adopt all four elements of the selenium criterion into water quality standards.

Following closure of the extended public comment period, the draft document will undergo an independent, contractor-led, external expert peer review. After considering public and expert peer review feedback, EPA will revise and publish the draft criterion document and subsequently again request public comment. Once finalized, EPA’s water quality criterion for selenium will provide recommendations to states and tribes authorized to establish water quality standards under the Clean Water Act.


What is selenium?

Selenium is a naturally occurring element that is nutritionally essential, but it can be toxic to aquatic life (such as fish) where concentrations are elevated. 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 primarily 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, except when the food web is primarily mollusk-based (i.e., the fish eat mostly clams or mussels).

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.

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