Aquatic Life Criterion - Selenium

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What is selenium?

Selenium is a naturally occurring element present in sedimentary rocks, shales, coal and phosphate deposits and soils. There are around 40 known selenium-containing minerals but all are rare and generally occur together with sulfides of metals such as copper, zinc and lead.

Where does selenium enter surface water?

Selenium can be released into water resources by natural sources via weathering and by anthropogenic sources, such as surface mining, coal-fired power plants, and irrigated agriculture.

How does selenium affect aquatic life?

Selenium is a nutritionally essential element for animals in small amounts, but toxic at higher concentrations. Selenium bioaccumulates in the aquatic food chain and chronic exposure in fish and aquatic invertebrates can cause reproductive impairments (e.g., larval deformity or mortality). Selenium can also adversely affect juvenile growth and mortality.

Selenium is also toxic to water fowl and other birds that consume aquatic organisms containing excessive levels of selenium.

Final Aquatic Life Ambient Water Quality Final Criterion for Selenium- Freshwater 2016

EPA’s water quality criterion for selenium provides recommendations to states and tribes authorized to establish water quality standards under the Clean Water Act. This final criterion includes information to help states to develop site specific criteria that account for differing local conditions.

Draft Aquatic Life Chronic Criterion for Selenium in Freshwater

EPA updated the recommended aquatic life water quality chronic criterion for selenium in freshwater on June 30, 2016.  Below is the draft criterion that was released for public comment in July 2015.

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.

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