Aquatic Life Criterion - Selenium
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 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 criterion includes information to help states to develop site specific criteria that account for differing local conditions.
In 2021, EPA identified that the following text was missing from the second sentence in footnote 4 in the criterion table: "When selenium inputs are increasing." Corrected footnote 4 now states: "4. Water column values are based on dissolved total selenium in water and are derived from fish tissue values via bioaccumulation modeling. When selenium inputs are increasing, water column values are the applicable criterion element in the absence of steady-state condition fish tissue data.” Footnotes 2 and 3 also reflect that footnote 4 was corrected.
- Fact Sheet: Final Selenium Criterion (pdf)
- Federal Register: 2016 Selenium Criterion (July 13, 2016)
- 2021 Revision Aquatic Life Ambient Water Quality Criterion for Selenium - Freshwater 2016 (pdf)
- Response to Public Comments: 2015 Draft Selenium Aquatic Life Criterion (pdf)
The Selenium Technical Support Materials (TSMs) provide implementation support for states and authorized tribes for the national recommended Clean Water Act (CWA) section 304(a) selenium aquatic life criterion for freshwater. The documents are related to (1) criterion adoption, (2) fish tissue monitoring, (3) assessing and listing waters under CWA section 303(d), and (4) NPDES permitting. The period to comment on these draft documents closed on January 3, 2022.
- Technical Support for Adopting and Implementing EPA’s 2016 Selenium Criterion in Water Quality Standards (pdf)
- Technical Support for Fish Tissue Monitoring for Implementation of EPA’s 2016 Selenium Criterion (pdf)
- Frequently Asked Questions: Implementing Water Quality Standards Based on EPA’s 2016 Recommended Selenium Criterion in Clean Water Act Section 402 NPDES Permits (pdf)
- Frequently Asked Questions (FAQs): Implementing the EPA's 2016 Selenium Criterion in Clean Water Act Sections 303(d) and 305(b) Assessment, Listing, and Total Maximum Daily Load (TMDL) Programs (pdf)