Selenium Eco Risk Issues

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Selenium Eco Risk Issues
Ed Hanlon U.S. EPA/ORD/OSP Reagan
Building Washington DC hanlon.edward_at_epa.gov
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Selenium Aquatic life criteria overview
? EPA updated its national aquatic life criteria
for selenium in 1987. ? EPA is currently
working to revise national freshwater aquatic
life criteria for selenium ? 1987 criteria can
not be conveniently adjusted to account for
combined toxicity of different selenium forms or
other factors that might affect selenium
bioavailability, mostly due to lack of
appropriate data. ? New literature has
accumulated on the toxicity of different forms
of selenium to aquatic life.
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EPA plans to publish two products from its
selenium criteria revision effort
1) Revised freshwater acute and chronic Selenium
criterion (i.e., criterion maximum concentration
or CMC). ? will build upon previous work
conducted under Great Lakes Water Quality
Initiative Guidance (61Federal Register
58444-58449) which addressed the combined
toxicity of different selenium forms.
? final, peer reviewed acute and chronic
criterion is expected to be complete by
December 2001
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EPA plans to publish two products from its
selenium criteria revision effort (contd)
1) Guidelines for making site-specific
adjustments to the chronic criterion ? The
guidelines may be developed by reviewing
nationally available tissue residue data,
factoring in the bioaccumulation rates at the
specific site of concern. ? The guidelines are
very important because a single national
criterion has been criticized. ? final, peer
reviewed site-specific guidelines is expected to
be complete sometime after publication of the
acute and chronic criteria.
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Complex selenium biogeochemistry in the aquatic
environment greatly complicates the derivation of
aquatic life criteria
? Multiple oxidation states of selenium
compounds exist in ambient surface waters (e.g.,
selenate (Se6), selenite (Se4), elemental
selenium (Se0) and selenide (Se-2)), with each
displaying different toxicological and chemical
properties. ? Selenium can undergo
biotransformation between its inorganic and
organic forms which can affect its
bioavailability and toxicity.
? Bioaccumulation of selenium in aquatic food
webs complicates the derivation of aquatic life
criteria because both water and dietary
exposures need to be considered
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Report on the peer consultation workshop for
Selenium Aquatic Toxicity and Bioaccumulation
(EPA-822-R-98-007)
? released in September 1998 (EPA-822-R-98-007),
available at http//www.epa.gov/ost/selenium ?
peer consultation workshop held May 27-28, 1998
in Washington, D.C., involving experts in
selenium aquatic toxicology, geochemistry,
ecotoxicology, bioaccumulation, and
biochemistry. ? assessed state of the science
on several technical issues related to selenium
chronic toxicity and bioaccumulation in water,
tissue, and sediment. ? not a consensus
building exercise policy discussions not
entertained.
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Generally, but not necessarily universally,
accepted themes from peer consultation workshop
(doesnt necessarily reflect EPA views or policy)
Water Issues ? Most toxicologically important
forms of organoselenium dissolved in water are
protein or peptide-bound forms freely
dissolved seleno- amino acids were considered
less toxicologically important due to their
extremely low occurrence in water ? Available
data too sparse to support quantitative
relationships between selenium chronic toxicity
and water quality parameters. ? Extrapolation
of acute toxicity/water quality relationships
to chronic toxicity is highly uncertain.
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Generally, but not necessarily universally,
accepted themes from peer consultation workshop
(doesnt necessarily reflect EPA views or
policy)(continued)
Tissue Issues ? Most toxicologically important
forms of organoselenium are protein or
peptide-bound forms, although most measurements
have been made of total selenium. ? Reproductiv
e tissues in fish (ovaries, eggs) are the most
reliable tissue for correlating selenium tissue
residues to chronic effects, although need
additional residue-effects data. ? Poor
correlation between water concentrations and
tissue residues in higher trophic level aquatic
organisms, due to many factors including
varying patterns of historical loadings and
temporal asynchrony between water and tissue
concentrations.
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Generally, but not necessarily universally,
accepted themes from peer consultation workshop
(doesnt necessarily reflect EPA views or
policy)(continued)
Sediment Issues ? Sediments are the dominant
sink for selenium in aquatic ecosystems and
represent an important link and exposure source
to the benthic driven food web. ? Elemental and
organoselenium (in detritus) are dominant
selenium forms in aquatic sediments, although
most measurements have been made on total
selenium. ? Sediment toxicity data base is very
limited and does not support broad-based
quantitative relationships between toxicity and
sediment quality characteristics
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Generally, but not necessarily universally,
accepted themes from peer consultation workshop
(doesnt necessarily reflect EPA views or
policy)(continued)
Cross Cutting Issues ? Selenium residues in
fish and sediments in freshwater ecosystems
respond slowly to changes in selenium
concentrations in water (on the order of months
or years) while residues in lower trophic level
organisms (plankton) respond rapidly
(days) ? Type of water body (lentic vs. lotic)
can have a large effect on selenium cycling.
However, such water body types can be closely
interconnected.
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Generally, but not necessarily universally,
accepted themes from peer consultation workshop
(doesnt necessarily reflect EPA views or policy
Water Issues ? Most toxicologically important
forms of organoselenium dissolved in water are
protein or peptide-bound forms freely
dissolved seleno- amino acids were considered
less toxicologically important due to their
extremely low occurrence in water ? Available
data too sparse to support quantitative
relationships between selenium chronic toxicity
and water quality parameters. ? Extrapolation
of acute toxicity/water quality relationships
to chronic toxicity is highly uncertain.
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Recent Selenium References, some generated by EPA
? Selenium LC50 Calculations, Robert Pepin
312-886-1505 Selenium Acute Criterion (Aquatic
Life) Great Lakes, Keith Sappington
202-260-9898 ? Selenium Effects in Streams
Study Reports on Selenium Effects in
Experimental Streams, Keith Sappington
202-260-9898 ? National Freshwater Acute
Criteria for Selenium, Keith Sappington
202-260-9898 ? National Freshwater Chronic
Aquatic Life for Selenium and Site Specific
Criteria Guidelines, Keith Sappington,
202-260-9898 ? References available to EPA for
developing or revising aquatic life criteria for
Selenium. http//www.epa.gov/ostwater/standa
rds/criteria/selref.html
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Acute and Chronic Toxicity Workgroup Being Formed
? EPA is currently establishing a work group
that will be charged initially with revising the
acute freshwater criterion and subsequently
with revising the freshwater chronic criterion
and developing site-specific criteria
guidelines. ? As inputs to this workgroup, EPA
has sponsored additional acute toxicity
testing, has updated its literature review in
1998, is planning to publish new data on
selenium effects in experimental streams, and is
critically evaluating the tissue-
residue-effects data base for establishing
residue-based toxicological benchmarks for
selenium.
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Additional Information?
? For more information on EPAs revision of
selenium aquatic life criteria, consult
http//www.epa.gov/ost/selenium ? contact
Keith Sappington via e-mail at
sappington.keith_at_epa.gov