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Aquatic Life Criteria for Selenium
Questions and Answers
- What is selenium?
- Where does selenium come from?
- How does selenium affect aquatic life?
- Are there risks to humans?
- Are there risks to wildlife?
- What are EPA recommended water quality criteria?
- What is the action EPA is taking?
- Why is EPA publishing draft criteria revisions for selenium at this time?
- What are the draft numeric criteria for selenium?
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. An example of such mining activities is West Virginia mountaintop mining, where selenium-bearing overburden is exposed to weathering.
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.
Are there risks to humans?
Yes, although it is nutritionally essential, there can be risks to humans who drink water or eat fish or shellfish containing excessive amounts of selenium. The drinking water Maximum Contaminant Level (MCL) is 50 parts per billion. Drinking water systems are required to monitor to ensure that concentrations remain below the MCL.
Our existing 304(a) human health criterion, published in 1998, is 170 parts per billion to protect people who drink the water and consume fish or shellfish from a water body. The human health criterion is based on our allowable maximum dose of 350 micrograms per day for a 70 kilogram (or 154 pound) person.
The draft proposed aquatic life criterion, 7.9 parts per million as dry tissue weight, after being converted to wet tissue weight, corresponds to our fish tissue advisory for 16 meals per month. Today's action on the criteria for aquatic life does not change our human health criterion and fish advisory values.
The Food and Drug Administration's recommended minimum intake of selenium is 70 micrograms per day. You can find more information on the human health dietary needs and human health risks of selenium on at: www.epa.gov/safewater/dwh/c-ioc/selenium.html.
Are there risks to wildlife?
Selenium risks to birds that eat aquatic organisms have been observed in some locations, such as Kesterson Reservoir in California. Our draft aquatic life criterion was not derived to necessarily protect wildlife that consume fish or consume other aquatic organisms. The question of the appropriate concentration for protecting birds is complex and is outside the scope of this aquatic life criterion.
Nevertheless, we are working on two fronts to protect wildlife. First, in consultation with the U.S. Fish and Wildlife Service (USFWS), we are developing a general approach or methodology for deriving nationally-applicable pollutant criteria for protection of wildlife. Second, specifically for selenium, we are working with the USFWS and other federal agencies to develop criteria to protect wildlife within California. Both of those activities are separate from this notice, and in the initial phases of development. Eventually they would yield separate criteria values for protection of wildlife.
What are EPA recommended water quality criteria?
An EPA recommended water quality criterion is a level of a pollutant, or other measurable substance in water that, when met, will protect aquatic life and/or human health. Section 304(a) of the Clean Water Act (CWA) requires us to develop and publish, and, from time to time, revise, recommended water quality criteria to accurately reflect the latest scientific knowledge. Water quality criteria developed under section 304(a) provide guidance to states and tribes in adopting water quality criteria into their water quality standards under section 303(c). Once adopted by a state or tribe, the water quality standards then are a basis for developing regulatory controls on the discharge or release of pollutants and other alterations of water quality. Our section 304(a) criteria also provide a scientific basis for us to develop any necessary federal water quality regulations under section 303(c) of the CWA.
What is the action EPA is taking?
We are proposing draft, revised water quality criteria for selenium. We have updated the acute and chronic criteria for fresh and salt water using new scientific data and information. The new criteria should provide better protection for aquatic life in water bodies throughout the country.
Why is EPA publishing draft criteria revisions for selenium at this time?
The Clean Water Act (CWA) requires us to periodically review and update ambient water quality criteria to reflect the latest scientific knowledge on the effects of pollutants. Water quality criteria developed under the CWA are based solely on data and scientific judgments. They are our recommendations – guidance for states and authorized tribes to use in adopting water quality standards. They are not regulations and do not impose legally binding requirements on us, states, authorized Tribes, industry, or the public. This draft criterion results from more than six years of development, cooperation with other federal agencies, and a comprehensive peer review process.
What are the draft numeric criteria for selenium?
All concentrations are in µg/L except the tissue criterion, which is in µg/g.
| Acute | Chronic | |
|---|---|---|
| Freshwater | 258 / 417 formula | 7.9 Tissue |
| Saltwater | 127 | None |