The goals of this effort are threefold. First, EPA will revise its freshwater acute criterion for selenium, which will build upon work conducted and proposed earlier under the Great Lakes Water Quality Initiative Guidance. Second, EPA will revise its freshwater chronic aquatic life criterion which, among other aspects, will incorporate new data on selenium effects under field conditions. Third, EPA plans to develop new guidelines that will facilitate the derivation of site-specific chronic aquatic life criteria for selenium. Background Selenium, a metalloid that is released to water from both natural and anthropogenic sources, can be highly toxic to aquatic life at relatively low concentrations.
Selenium is also an essential trace nutrient for many aquatic and terrestrial species.
Derivation of aquatic life criteria for selenium is complicated by its complex biogeochemistry in the aquatic environment. For example, multiple oxidation states of selenium often exist in ambient surface waters, each displaying different toxicological and chemical properties. Selenium can undergo rapid biotransformation between its inorganic and organic forms which also can affect its bioavailability and toxicity. Bioaccumulation of selenium in aquatic food webs further complicates the derivation of aquatic life criteria because both water and dietary exposures need to be considered. EPA's national aquatic life criteria for selenium were last published in 1987.