United States
Environmental Protection
.Agency
Office of Water
www.epa.gov
EPA 822-F-16-005
June 2016
Aquatic Life Ambient Water Quality Criterion for
Selenium in Freshwater 2016- Fact Sheet
Summary
EPA has published the final national chronic aquatic
life criterion for the pollutant selenium in fresh
water. The 2016 criterion document is the final
update of EPA's 1999 recommended national chronic
aquatic life criterion for selenium, developed per
Clean Water Act section 304(a). The 2016 criterion
reflects the latest scientific knowledge, which
indicates that selenium toxicity to aquatic life is
primarily based on organisms consuming selenium-
contaminated food rather than by being exposed
only to selenium dissolved in water. The final
criterion is expressed both in terms offish tissue
concentration (egg/ovary, whole body, muscle) and
water concentration (lentic, lotic).
EPA's water quality criterion for selenium provides
recommendations to states and tribes authorized to
establish water quality standards under the Clean
Water Act. The revised criteria document includes
information to help states to develop site specific
criteria that account for differing local conditions. In
addition, later this year EPA intends to release for
public comment draft technical support materials to
assist states in addressing implementation questions
such as fish tissue monitoring.
Background
EPA developed the 2016 national recommended
aquatic life criterion for selenium using the best
available science. In 2004, EPA published the first
draft of the updated selenium criterion using fish-
tissue concentrations. In 2009, EPA participated in an
expert workshop on selenium and in 2010
collaborated with the U.S. Geological Survey to
develop a selenium bioaccumulation model. As a
result, EPA then revised the 2004 draft criterion to
include egg-ovary tissue and water column
concentrations. In 2014, EPA released the draft
criterion for public comment and external peer
review. EPA revised the draft criterion accordingly
and in 2015 released the draft for a second round of
public comment. EPA has considered all public
comments and peer reviewer comments in the
development of the 2016 final criterion document.
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.
How Does Selenium Enter Surface Waters?
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).
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Selenium can also adversely affect juvenile growth
and mortality.
What are National Recommended Aquatic Life
Criteria?
Ambient water quality criteria for the protection of
aquatic life are numeric concentrations of pollutants
in surface waters that are protective of aquatic life
designated uses, with specific recommendations on
the duration and frequency of those concentrations.
Under Clean Water Act section 304(a), EPA is
directed to develop and publish water quality criteria
that reflect the latest scientific knowledge. Water
quality criteria are based on data and scientific
judgments about the relationship between pollutant
concentrations and potential environmental and
human health effects. EPA's recommended water
quality criteria are not rules, nor do they
automatically become part of a state's water quality
standards. States must adopt into their standards
Comparison of 2016 Selenium Criterion to 1999 Criteria.
water quality criteria that protect the designated
uses of the water bodies within their area. These can
include scientifically defensible site-specific criteria
that are different from EPA's national recommended
criteria, as long as the site-specific criteria are
protective of the designated use. Water quality
criteria are not effective under the Clean Water Act
until they have been adopted into state water quality
standards and approved by EPA.
How does the 2016 Criterion compare to the 1999
criteria?
The 2016 selenium criterion document recommends
that states and authorized tribes adopt a multi-media
criterion into their water quality standards. The
criterion has four elements and EPA recommends
that states includes all four elements in their
standards. The table below compares the 2016
criterion with the 1999 criteria.
Criterion
Version
2016 Selenium
Criterion
1999 Selenium
Criteria
Chronic
Egg-Ovary1
[mg/kg dw]
15.1
N/A
Whole
Body1
[mg/kg
dwj
8.5
N/A
Muscle1
[mg/kg
dw]
11.3
N/A
Water
Lentic1
[HE/L]
1.5
(30 day)
5
(4 day)
Water
Lotic1
[Hg/L]
3.1
(30 day)
5
(4 day)
Short-term
Water1
[ug/L]
Intermittent
exposure
equation
Acute
Equation
based on
water column
concentration
1A note on hierarchy of table: when fish egg/ovary concentrations are measured, the values supersede any whole-body, muscle, or water column elements except in
certain situations. Whole body or muscle measurements supersede any water column element when both fish tissue and water concentrations are measured, except in
certain situations. Water column values are derived from the egg & ovary concentrations via bioaccumulation modeling. Water column values are the applicable
criterion element in the absence offish tissue measurements, such as waters where fish have been extirpated or where physical habitat and/or flow regime cannot
sustain fish populations, or in waters with new discharges of selenium where steady state has not been achieved between water and fish tissue at the site.
2016 Criterion expression:
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EPA is recommending a national selenium criterion expressed as four elements (Figure 1). EPA recommends
that when implementing the criterion, the fish tissue elements take precedence over the water column
elements, except in certain circumstances. All elements are protective against chronic selenium effects, and
account for both short term and longer term exposure to selenium. Two elements are based on the
concentration of selenium in fish tissue (eggs and ovaries, and whole-body or muscle) and two elements are
based on the concentration of selenium in the water-column (two 30-day chronic values and an intermittent
value). Aquatic communities are expected to be protected by this chronic criterion from any potential acute
effects of selenium.
Figure 1
One
Criterion
Two
Media
Four
Elements
Fish Egg-Ovary
Fish Whole-Body
or Muscle
Water Column
Monthly
(Lenticor Lotic)
Water Column
Intermittent
(Lenticor Lotic)
How to View the Criteria Document and
Supporting Information
EPA has established an official public docket for this
action under Docket ID No. EPA-HQ-OW-2004-0019,
accessed at www.regulations.gov. You may also
download the document and supporting information
from EPA's aquatic life criteria website at:
www.epa.gov/wqc/aquatic-life-criterion-selenium
For more information, please contact Joe Beaman by
email at beaman.ioe@epa.gov
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