EPA 820R24008
EPA Office of Science and Technology
December 2024
Method for Translating Selenium Tissue Criterion
Elements into Site-specific Water Column Criterion
Elements for California,
Version 2, December 2024
United States Environmental Protection Agency
1200 Pennsylvania Ave., NW
Washington, D.C. 20460
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Table of Contents
A. Introduction 4
B. Procedures 7
1.0 Site Definition 7
2.0 Determination of Community Present at Site 7
3.0 Target Species Selection 8
3.1 Food Web Modeling 8
3.2 Selection of TTF Values 12
3.3 Selection of Target Species 16
4.0 Selection of Translation Approach 16
5.0 Mechanistic Modeling Approach 16
5.1 Tissue Type Selection 16
5.2 Selection of TTFcompos,te Value 17
5.3 Selection of Conversion Factor Value 17
5.4 Data Collection for the Calculation of the EF 19
5.5 Chemical Analysis 23
5.6 Data Analysis for the Mechanistic Modeling Approach 23
6.0 Bioaccumulation Factor Approach 30
6.1 Additional Target Species Considerations for BAF - Exposure at the Site 30
6.2 Fish Tissue Type Selection 30
6.3 Sampling Plan 30
6.4 Chemical Analysis 33
6.5 Data Analysis for the Empirical BAF Approach 33
References: 35
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List of Acronyms and Abbreviations
AE
assimilation efficiency
BAF
bioaccumulation factor
°C
degrees Celsius
Cparticulate
concentration of selenium in particulate material
Cwater criterion element
translated site-specific water column criterion element
Ctissue criterion element
selenium fish tissue or bird egg criterion element
Cwater
concentration of total dissolved selenium in water
CF
conversion factor
CFR
Code of Federal Regulations
d
day
dw
dry weight
EF
enrichment factor
FAO
Food and Agriculture Organization
g
gram
IR
ingestion rate
ke
elimination rate constant
kg
kilogram
L
liter
m
meter
mg
milligram
ml
milliliter
Se
selenium
TTF
trophic transfer factor
I'l'j^oniposiie
composite trophic transfer factor
USEPA
United States Environmental Protection Agency
USGS
United States Geological Survey
WW
wet weight
Hg
microgram
|im
micrometer
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A. Introduction
This document describes the performance-based approach (PBA) methodology for
California's use in calculating site-specific water column criterion elements for the selenium
aquatic life and aquatic-dependent wildlife criterion as promulgated in the Environmental
Protection Agency's (EPA's) final rule, "Water Quality Standards; Establishment of a Numeric
Criterion for Selenium for the State of California."1 The PBA is a methodology that the State
may use to translate the bird and fish tissue criterion elements into water column criterion
elements on a site-specific basis. If the State follows the methodology as prescribed in the PBA,
it is not required to adopt and submit the outcomes that result from using the PBA to the EPA for
Clean Water Act (CWA) section 303(c) review in accordance with the procedures at 40 Code of
the Federal Regulations (CFR) part 131. If the State chooses to use the PBA, the State will
coordinate with the EPA at the beginning of the process. If the State calculates a site-specific
water column criterion element using another methodology, that criterion element must be
adopted by the State and submitted to the EPA for review under CWA section 303(c) in
accordance with the procedures at 40 CFR part 131.
As provided in this document, if the State uses this PBA, it will follow one of two
approaches to translate a fish tissue criterion element or bird egg criterion element into a water
column criterion element, either the mechanistic model approach or the empirical bioaccumulation
factor (BAF) approach. These two approaches are described by the EPA for the translation of
tissue criterion elements into water column criterion elements in Appendix K of 2021 Revision to:
Aquatic Life Ambient Water Quality Criterion for Selenium - Freshwater 2016 (USEPA 2021).
Given that these are well established approaches for translating concentrations between tissue
and water, the State of California will use these approaches for site-specific water column
criterion element translations if it does not wish to submit translation outcomes to the EPA for
review. The egg-ovary criterion element is the preferred fish tissue criterion element to be used
in either approach to translate to a water column criterion element for protection of aquatic life,
as the egg-ovary criterion element is most closely related to the toxicological effects of selenium
observed in fish. The bird egg criterion element will be translated into a water column criterion
element for the protection of aquatic-dependent wildlife, as birds are the most sensitive aquatic-
dependent wildlife taxa and the bird egg is most closely related to the toxicological effects of
selenium observed in birds. A sampling plan for the collection of data to be used for either the
mechanistic model or empirical BAF approach will consider the temporal, spatial, and
biogeochemical factors affecting water column, food web, and tissue selenium concentrations.
The EPA derived the national recommended CWA section 304(a) selenium water-column
criterion elements by modeling selenium bioaccumulation in aquatic systems. The EPA worked
with the United States Geological Survey (USGS) to derive a translation equation using a
mechanistic model of bioaccumulation previously published in peer-reviewed scientific literature
(Luoma et. al., 1992; Wang et. al, 1996; Luoma and Fisher, 1997; Schlekat et al. 2002; Wang
2002; Luoma and Rainbow 2005; Presser and Luoma 2006; Presser and Luoma 2010; Presser
2013). The mechanistic model approach is described in detail in Aquatic Life and Aquatic-
Dependent Wildlife Selenium Water Quality Criteria for Freshwaters of California (TSD)
(USEPA 2024) and 2021 Revision to: Aquatic Life Ambient Water Quality Criterion for
1 This final rule applies to certain waters of California in a manner consistent with the California Toxics Rule where
the protection of aquatic life and aquatic-dependent wildlife are designated uses. The final rule does not apply to
California waters where site-specific selenium criteria have been adopted, nor does it apply to California waters with
selenium criteria promulgated in the National Toxics Rule.
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Selenium - Freshwater 2016 (USEPA 2021). The EPA started with an equation that described
bioaccumulation of selenium in animal tissues by assuming that net bioaccumulation is a balance
between assimilation efficiency from diet, ingestion rate, rate of direct uptake in dissolved forms,
loss rate, and growth rate. This equation was then simplified as described in section 3.2.1 of
USEPA 2021. The growth rate factor was removed from the starting equation because high
consumption rates of selenium-contaminated food may counteract the selenium dilution that
occurs with the addition of body tissue during periods of fast growth. The factor accounting for
direct aqueous uptake of selenium was also removed from the starting equation because aqueous
exposure only accounts for a small proportion of selenium bioaccumulation by an organism
(USEPA 2021). The resulting mechanistic model equation can be used to derive a selenium
water column criterion element from fish egg-ovary or fish muscle criterion elements.
C
water criterion element ~
Cfish egg—ovary or muscle criterion element
TTFcomposite x EF X CF
(Equation 1)
Where:
Cwater criterion element
Cfish egg-°vary or muscle criterion element
YYp"composite —
EF
CF
translated site-specific water column criterion
element (total dissolved |ig/L),
fish egg-ovary or muscle tissue criterion element
(mg/kg dw),
composite trophic transfer factor (TTF) is the
product of the species-specific trophic transfer
factor (TTF) values for selenium in each trophic
level of the food web of the target fish or bird
species (no units of measurement),
enrichment factor is the proportional
bioconcentration of total dissolved selenium at the
base of the aquatic food web (L/g),
conversion factor is the species-specific proportion
of selenium in fish eggs, fish ovaries, or fish muscle
relative to the concentration of selenium in the
whole-body of the fish (no units of measurement, not
needed if starting with the whole-body fish tissue
criterion element or bird egg criterion element).
A conversion factor is not needed when translating from either the bird egg or fish tissue
whole-body criterion elements into a site-specific water column criterion element (because the
conversion factor is only used to convert a fish muscle or fish egg-ovary value into a
proportional fish whole-body value) so Equation 2 can be used for translations from the bird egg
or fish tissue whole-body criterion elements:
C
water criterion element ~
Cbird egg or fish whole-body criterion element
j'TFcornVosite x EF
(Equation 2)
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Where:
Cwater criterion element = translated site-specific water column criterion
element (total dissolved |ig/L),
Cbird egg or fish whole-body criterion element bird egg or fish whole-body tissue criterion element
(mg/kg dw),
TTfcomposite _ composite trophic transfer factor (TTF) is the
product of the species-specific trophic transfer
factor (TTF) values for selenium in each trophic
level of the food web of the target fish or bird
species (no units of measurement),
EF = enrichment factor is the proportional
bioconcentration of total dissolved selenium at the
base of the aquatic food web (L/g).
The State will use these equations to derive site-specific water column criterion elements
when using the mechanistic model approach. When the State derives a site-specific water column
criterion element for the protection of aquatic life, it will translate from the fish whole-body,
muscle, or egg-ovary tissue criterion element to determine an appropriate water column criterion
element using either Equation 1 (muscle or egg-ovary) or Equation 2 (whole-body). When the
State is using the mechanistic model approach to determine a water column criterion element that
is protective of the aquatic-dependent wildlife use, it will translate from the bird egg criterion
element using Equation 2.
Alternatively, the State may use the BAF approach described in Appendix K of USEPA
2021 to translate tissue criterion elements into site-specific water column criterion elements. If
so, the state will use Equation 3 and Equation 4 below to translate a fish tissue or bird egg
criterion element to a water column criterion element. Equation 3 will be used to calculate a
bioaccumulation factor by dividing the concentration of selenium in either fish or bird tissue by
the concentration of selenium in the water column.
C
BAF = ¦ tlssue
r
water (Equation 3)
Where:
BAF = bioaccumulation factor for selenium derived from site-specific field-
collected samples of tissue and water (L/g)
Ctissue = concentration of selenium in field-collected fish tissue or bird egg (|ig/g
dw)
Cwater = ambient concentration of selenium in field-collected water (total
dissolved |ig/L)
The site-specific BAF will then be used in Equation 4 with the appropriate criterion
element (fish egg-ovary, fish whole-body, fish muscle, or bird egg) that matches the tissue type
collected to derive the BAF, to calculate a site-specific water column criterion element (Cwater
criterion element)!
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r —
°water criterion element
Ctissue criterion element
(Equation 4)
BAF
Where:
criterion element
criterion element
translated site-specific water column criterion element (|ig/L)
tissue criterion element (jug/g dw)
bioaccumulation factor derived from site-specific field-collected
samples of tissue and water (L/g)
BAF
B. Procedures
1.0 Site Definition
The State will provide a clear definition of the site for which the site-specific water
column criterion element applies, including a description of the site boundaries and rationale for
the determination of the site boundaries. The site will be defined on the basis of expected
changes in selenium's biological availability and/or toxicity due to physical and chemical
variability of the site water and variability in the aquatic community. A number of factors could
be considered when defining a site, including hydrodynamics, water chemistry, and physical
habitat. Natural breaks in these elements, such as the confluence of one river with another, can
be used to determine boundaries of a site. The presence of a community with a unique taxonomic
composition may also justify a designation as a distinct site (i.e., assemblage that is distinct from
another site or presence of a rare, unique, or ecologically significant species such as a threatened
or endangered species). If a selenium discharge from a point source or non-point source is part of
a site, the site boundaries will reflect the magnitude and geographic extent of contamination
based on the influence of the discharge. As selenium bioaccumulation is largely dependent on
site-specific conditions (e.g., EF and food web structure), the PBA described in this document is
appropriate for single water bodies or water body segments. In contrast, if the State decides to set
site-specific water column criterion elements for larger areas, the State must derive and adopt
site-specific water column criterion elements for the EPA's review in accordance with the CWA
and the EPA's implementing regulations at 40 CFR part 131 (not using the PBA).
2.0 Determination of Community Present at Site
After the State has defined the boundaries of the site, the State will determine what
aquatic and aquatic-dependent species are present at the site, and whether the site includes the
habitat of any threatened or endangered species. The State will first evaluate scientific
publications and the State's monitoring data to determine what species, including threatened and
endangered species, are present at the site and whether the site may include the habitat of any
threatened or endangered species. If monitoring data or scientific publications are not available,
then the State will contact local resource agencies to see if they have information regarding the
fish and bird species present or reasonably expected to be present. If no information is available,
the State will perform appropriate fish (e.g., seining, electrofishing, and gillnets) and bird (e.g.,
point count surveys and nest monitoring) monitoring to determine the aquatic and aquatic-
dependent species present at the site. Fish sampling will be conducted both in the spring and fall
season. If sampling is not possible in the spring due to unsafe spring run-off flows, sampling will
be conducted in late spring or early summer once it is safe to conduct monitoring activities. Bird
monitoring will be conducted during the breeding season (typically April to August).
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The site-specific standards setting process should be reflective of the existing and
potential future beneficial uses at the site and the characteristics of the aquatic life and aquatic-
dependent wildlife present or reasonably expected to be present at the site, including threatened
and endangered species. If the State finds that fish are not present at the site and are not expected
to be present, then the State cannot use the PBA to determine a site-specific water column
criterion element for the aquatic life designated use. Instead, the State must either use the water
column criterion elements of the statewide criterion for the site or derive and adopt a site-specific
water column criterion element for the EPA's review in accordance with the CWA and the
EPA's implementing regulations at 40 CFR part 131.
3.0 Target Species Selection
The State will target the fish species with the greatest bioaccumulation potential from the
genera Acipenser, Lepomis, Scilmo, and Oncorhynchus for sampling or for modeling to develop
the site-specific water column criterion element. If no fish species from these genera are present
at the site, then the species with the greatest bioaccumulation potential will be targeted for
sampling or modeling. If all fish species at the site have similar bioaccumulation potential, then
the State will target the species that is most sensitive to selenium. The State will target the bird
species with the greatest bioaccumulation potential.
If the selected target species at the site is a threatened or endangered species, the State
will use the mechanistic model approach to derive the site-specific water column criterion
element. If sufficient information is not available and not able to be collected for the mechanistic
model approach for the target threatened and endangered species, then the State will sample a
closely related (e.g., order or closer) surrogate species with a similar dietary composition and
bioaccumulative potential for use in the BAF model.
3.1 Food Web Modeling
As a species is primarily exposed to selenium through its diet, quantifying the dietary
composition of each potential target species will help determine the bioaccumulation potential of
each fish and bird species present at that site. The State will begin by defining the diets of all fish
species in the genera Acipenser, Lepomis, Scilmo, and Oncorhynchus (or all fish species if no
species are present from Acipenser, Lepomis, Scilmo, and Oncorhynchus) present at the site and
all bird species present during the breeding season at the site by reviewing the relevant state and
scientific literature. In addition, if anadromous salmonids are present, the diet of the juvenile
anadromous salmonids, rather than adults, will be evaluated.
Dietary compositions of many fish and bird species are defined in the CWA section
304(a) recommended selenium criterion document (USEPA 2021) and the TSD (USEPA 2024)
for the California selenium criterion final rule. The State may also use publicly available
databases such as NatureServe (http://www.natureserve.org) and FishBase
(http://www.fishbase.org) to estimate the dietary composition of the fish species present at the
site. FishBase is a relational database developed at the World Fish Center in collaboration with
the Food and Agriculture Organization of the United Nations (FAO) and many other partners.
The State may use publicly available databases, such as North America Birds Online
(https://birdsna.org) to quantify the dietary composition of bird species present at the site. The
North America Birds Online database was developed by the Cornell Lab of Ornithology in
collaboration with the American Ornithological Society and is available through member
subscription. The Handbook of Freshwater Fishery Biology, volumes 1, 2, and 3 (Carlander
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1969-1997) and the Wildlife Exposure Factors Handbook, volumes I and II (USEPA 1993) may
also be consulted for diet information.
Once an average diet for each fish species in the genera Acipenser, Lepomis, Salmo, and
Oncorhynchus (or all fish species if these genera are not present at the site) and bird species
present at the site during the breeding season are identified and quantified, the State will
calculate the composite trophic transfer factor (' TTpcomposite) for each fish and bird species. For
sites that include threatened or endangered species, rather than using an average diet for each fish
or bird species, the State may use a dietary estimate within the species' range that reflects a
greater proportion of consumption of prey items with high selenium bioaccumulation potential.
Bioaccumulation of selenium from one trophic level to the next is quantified by a trophic transfer
factor {TTF). A TTF is a single value that represents the proportional concentration of selenium
in the tissue of an organism relative to the concentration of selenium in the food it consumes.
The parameter TTFcomposite quantitatively represents all dietary pathways of selenium exposure for
a particular fish or bird species within an aquatic system. The parameter is derived from species-
specific TTF values representing the food web characteristics of the aquatic system and the
proportion of each species consumed. The State will calculate a TTFcomposite utilizing Equation 5
and, if needed, Equation 6.
When more than one species is consumed at the same trophic level, the State will calculate the
TTF for that trophic level as the weighted average of the TTFs of all species consumed using
Equation 6. Examples of how a TTFcomposite will be calculated by the State are presented in
Figures 1 and 2.
(Equation 5)
Where:
the product of all TTF values at all trophic levels,
the TTF value of the highest trophic level.
(Equation 6)
Where:
the trophic transfer factor of the ith species at a particular trophic level
the proportion of the ith species consumed.
Wi
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A1 Three tronhic levels (simnlek
7 7 'F composite ^ y 'j^TL2
XXpTL3
xtfTL2
Four tronhic levels (simple^:
rj-irj-ip composite rj-irj-ipTLA ^ rj-irj-ipTL?> ^ rj-irj-ijjTLl
TTpTL4
JJpTL3
TTJ7TL2
C) Three trophic levels (mix within trophic levels^:
ppp composite = TTFTL1 x ^fTpTL2 ^ WJ+ (p-pTL2 x
JJpTL3
Wl m ^
W2 ^
rri7r.
TTF'
I)) Three trophic levels (mix across tronhic levels^:
pppcomposite = (ffpTLl x wJ+ (p-pTLl x JJpTLl ^
W 1
XXpTU
w2
TTF^li
Four trophic levels (mix across trophic levels^:
TTF composite = ^ffpTLA ^ jjpTLl ^ WJ+ ^jpTU ^ ^JJpT.
jtfTL3
ttfTL2
JJPTL4
Figure 1. Example mathematical expressions of JTFcomposite representing different food-web
scenarios for fish species. TTFcomposite quantitatively represents the trophic transfer of selenium
through all dietary pathways of a targeted fish species. The mathematical expression of the food
web model is used to calculate a value for TTFcomposite using appropriate species-specific TTF
values and the proportions of each species consumed at each trophic level.
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A) Three trophic levels (simple):
_ -y "J^composite rj*j
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3.2 Selection of TTF Values
Once the State has determined the proper equation to calculate the TTFcomposite for a
species, the State will select proper TTFs to populate that equation. To select proper TTF values,
the State will first evaluate the list of TTFs below, from the CWA section 304(a) recommended
selenium criterion document (USEPA 2021) and TSD for the California selenium criterion final
rule (USEPA 2024), to see if there is a known TTF for the species included in the TTFcomposite
equation. Examples of TTFco"'pos'te calculations can be found in Appendix B section 3 of the
CWA section 304(a) recommended selenium criterion document (USEPA 2021) and Appendix
B of the TSD for the California selenium criterion rule (USEPA 2024). The State may use the
TTF values from these lists exclusively, or in conjunction with TTF values obtained from the
other sources specified below.
Table 1. EPA-Derived Trophic Transfer Factor (TTF) Values for Freshwater Aquatic
Invertebrates.
AE = Assimilation efficiency (%), IR = Ingestion rate (g/g-d;
), ke = Elimination rate constant (/d).
Common name
Scientific name
AE
IR
ke
TTF
Crustaceans
amphipod
Hyalella azteca
-
-
-
1.22
copepod
Copepods
0.520
0.420
0.155
1.41
crayfish
Astacidae
-
-
-
1.46
water flea
Daphnia magna
0.406
0.210
0.116
0.74
Insects
dragonfly
Anisoptera
-
-
-
1.97
damselfly
Coenagrionidae
-
-
-
2.88
mayfly
Centroptilum triangulifer
-
-
-
2.38
midge
Chironimidae
-
-
-
1.90
water boatman
Corixidae
-
-
-
1.48
Mollusks
Asian clama
Corbicula flaminea
0.550
0.050
0.006
4.58
zebra mussel
Dreissena polymorpha
0.260
0.400
0.026
4.00
Annelids
blackworm
Lumbricuius variegatus
0.165
0.067
0.009
1.29
Other
zooplankton
Zooplankton
-
-
-
1.89
a Not to be confused with Potamocorbula amurensis
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Table 2. EPA-Derived Trophic Transfer Factor (TTF) Values for Freshwater Fish.
AE = Assimilation efficiency (%), IR = Ingestion rate (g/g-cT
), ke = Elimination rate constant (/d).
Common name
Scientific name
AE
IR
ke
TTF
Cypriniformes
blacknose dace
Rhinichthys atratulus
-
-
-
0.71
bluehead sucker
Catostomus discobolus
-
-
-
1.04
longnose sucker
Catostomus catostomus
-
-
-
0.90
white sucker
Catostomus commersonii
-
-
-
1.11
flannelmouth sucker
Catostomus latipinnis
-
-
-
0.98
common carp
Cyprinus carpio
-
-
-
1.20
creek chub
Semotilus atromaculatus
-
-
-
1.06
fathead minnow
Pimephales promelas
-
-
-
1.57
red shiner
Cyprinella lutrensis
-
-
-
1.31
redside shiner
Richardsonius balteatus
-
-
-
1.08
sand shiner
Notropis stramineus
-
-
-
1.56
Cyprinodontiformes
western mosquitofish
Gambusia qfftnis
-
-
-
1.21
northern plains killifish
Fundulus kansae
-
-
-
1.27
Esociformes
northern pike
Esox lucius
-
-
-
1.78
Gasterosteiformes
brook stickleback
Culaea inconstans
-
-
-
1.79
Perciformes
black crappie
Pomoxis nigromacirfatus
-
-
-
2.67
bluegill
Lepomis macrochirus
-
-
-
1.03
green sunfish
Lepomis cyanellus
-
-
-
1.12
largemouth bass
Micropterus salmoides
-
-
-
1.39
smallmouth bass
Micropterus dolomieu
-
-
-
0.86
striped bass
Morone saxatilis
0.375
0.335
0.085
1.48
walleye
Sander vitreus
-
-
-
1.60
yellow perch
Perca fla\>escens
-
-
-
1.42
Salmoniformes
brook trout
Salvelinus fontinalis
-
-
-
0.88
brown trout
Salmo trutta
-
-
-
1.38
mountain whitefish
Prosopium williamsoni
-
-
-
1.38
cutthroat trout
Oncorhynchus clarkii
-
-
-
1.12
rainbow trout
Oncorhynchus mykiss
-
-
-
1.07
Scorpaeniformes
mottled sculpin
Cottus bairdi
-
-
-
1.38
sculpin
Cottus sp.
-
-
-
1.29
Siluriformes
black bullhead
Ameiurus melas
-
-
-
0.85
channel catfish
Ictalurus punctatus
-
-
-
0.68
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Table 3. EPA-Derived Trophic Transfer Factor (TTF) Values for Aquatic-Dependent
Birds.
Common name
Scientific name
TTF
Non-Migratory
American coot
Firfica americcma
1.89
red winged blackbird
Agelaius phoeniceus
0.86
Migratory
American avocet
Recurvirostra americcma
1.44
cinnamon teal
Anas cyanoptera
1.79
eared grebe
Podiceps nigricollis
2.00
gadwall
Anas strepera
1.78
pied billed grebe
Podilymbus podiceps
0.78
yellow headed blackbird
Xanthocephalus xanthocephalus
1.04
If the State cannot obtain required TTF values from Tables 1, 2, or 3, the State will derive
species-specific TTF values from existing data. The State will do this by determining the species-
specific physiological coefficients representing food ingestion rate (IR), selenium efflux rate (ke),
and selenium assimilation efficiency (AE) from the scientific literature to calculate a TTF value
using Equation 7 (Reinfelder et al. 1998):
AE x IR
lib =
(Equation 7)
Where:
TTF = species-specific trophic transfer factor
AE = species-specific assimilation efficiency
IR = species-specific ingestion rate (g/g-d)
ke = species-specific efflux rate constant (/d)
If TTF values are not available from the above tables or cannot be calculated because the
physiological coefficients are unavailable, the State will extrapolate a new TTF value from a
surrogate species with an empirically derived TTF value. The TTF for a surrogate species will
come either from Table 1, 2, or 3 above or from the peer-reviewed scientific literature. The
surrogate species considered should have a similar dietary composition and, if possible, be
taxonomically related (within the same order). If the lowest matching taxon of the species of
interest is common to more than one of the available TTF values, the median TTF from the
matching table entries or published scientific literature will be used. The use of taxonomic
hierarchies in this way utilizes evolutionary relationships to infer biological similarities among
organisms (Suter 1993).
If the State cannot derive a TTF using one of the procedures described above, the State
will derive species-specific TTF values by assessing the relationship between the selenium
concentration in the tissue of organisms and the selenium concentration in the food they consume
using paired measurements from published field studies. Species-specific TTF values should not
be derived using paired measurements from controlled laboratory experiments as these
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measurements will likely not accurately represent selenium bioaccumulation in organisms in the
field. The published studies that should be used will have paired organism and diet selenium
measurements that have been collected at the same aquatic site in the field. Preferably these pairs
will be collected concurrently. However, individual aquatic sites may have selenium loads and/or
bioaccumulation characteristics that require different relative collection time criteria to
accurately characterize selenium relationships. Therefore, data from published studies can be
used if the time between collections is less than one year. The State will define the TTF value for
any trophic level as:
rTLn
TTUTLtl ctissue
* * r ~ rTLn
Lfood
(Equation 8)
Where:
ttfTLu
pTLn
utissue
nTLn
cfood
= The trophic transfer factor of a given trophic level,
= The selenium concentration (mg/kg dw) in the tissues of the consumer
organism,
= The selenium concentration (mg/kg dw) in the consumer organism's food.
If the species consumes multiple dietary items, then the will be determined using Equation 9.
Cfood (j-'prey 1 ^ ^l) (j-'prey 2 ^ ^2) (j^prey i ^ (Equation 9)
Where:
fTLn
cfood
C,
= The selenium concentration (mg/kg dw) of the consumer organism's food,
prey t = The selenium concentration (mg/kg dw) in the tissues of the ith prey
species
Wi = the proportion of the ith species consumed
Species-specific TTF values will be derived from such measurements by using a
combined median and regression approach. The State will use the median of the ratios calculated
using Equation 8 as the species-specific TTF value, but only if a positive direct relationship
between the paired measurements is confirmed by linear regression analysis. Using the median
of the individual ratios provides an estimate of central tendency for that relationship that is less
sensitive to potential bias from measurements taken from aquatic systems with very high or very
low selenium concentrations. The State will consider the relationship acceptable if a linear
regression of tissue selenium concentrations and food selenium concentrations resulted in both a
statistically significant fit of the slope (p-value < 0.05) and a positive slope (i.e., selenium
concentrations in the consumer increases with increasing selenium in food). A significant
positive linear regression confirms that the relationship between selenium in organisms and the
food they ingest is adequately represented by the available data. Outlier analysis may be
performed to make sure that all data included are appropriate for use in analyses. In addition, the
data may be transformed to better reflect the underlying distribution of the data.
If TTFs need to be calculated by performing additional studies, then the State will adopt
the site-specific water column criterion element and submit it for the EPA's review in
15
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accordance with the CWA and the EPA's implementing regulations at 40 CFR part 131 rather
than deriving it through the PB A.
3.3 Selection of Target Species
Once the State has quantified the dietary composition and determined the appropriate
species-specific TTFs, the State will calculate the composite TTFs for all fish species in the
genera Acipenser, Lepomis, Salmo, and Oncorhynchus present at the site (or all the fish species if
the genera Acipenser, Lepomis, Salmo, and Oncorhynchus are not present at the site) and bird
species present at a site in the breeding season, using Equation 5 and, if needed, Equation 6.
The State will then compare the composite TTFs for all fish species in the genera Acipenser,
Lepomis, Salmo, and Oncorhynchus (or all fish species if no species in these genera are present)
and all bird species present at the site in the breeding season and select the fish and bird species
with the greatest composite TTF (greatest bioaccumulation potential) to sample or model for the
site-specific water column criterion element.
If all fish species have similar composite TTF's, then the species with the lowest ECio
will be selected to sample or model for the site-specific water column criterion element. If the
ECio of a particular species is unavailable, sensitivity can be estimated from the ECio of a closely
related taxon.
The species with the highest composite TTF value will have the greatest bioaccumulation
potential if selenium exposure is relatively equal throughout the site. If the highest
bioaccumulator at a site is an anadromous salmonid, then the smolt stage of the fish species will
be modeled or sampled as a whole-body sample. Smolts will be sampled because adult fish will
not be exposed to selenium from the site through their diet due to their migratory behavior.
If the State decides to use the BAF translation approach and exposure is not equal
throughout the site, the State will sample the species with the highest TTFcomposite located in the
area of highest bioaccumulation potential (i.e., areas with lentic properties, longest residence
time). If the State is using the BAF approach and there is uncertainty in which species will be the
highest bioaccumulator, the State will sample multiple fish or bird species to determine which
has the highest selenium concentrations and use the species with the highest selenium
concentration to calculate the BAF.
4.0 Selection of Translation Approach
As stated previously, if the State chooses to use the PBA, the State will coordinate with
the EPA at the beginning of the PBA process. Once the State has defined a site and selected a
target species, the State will select which approach it will use to translate the tissue criterion
element to a water column criterion element at the site. To make this decision, the State will
evaluate what information it has available about the site and which approach is easier to
accomplish logistically. The State will not use an approach for which it cannot acquire the proper
data.
5.0 Mechanistic Modeling Approach
5.1 Tissue Type Selection
The State can translate from any of the fish tissue criterion elements or the bird egg
criterion element into a site-specific water column criterion element. As the fish egg-ovary
criterion element is most closely related to the toxicological effects of selenium observed in fish,
16
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the egg-ovary criterion element is the preferred fish tissue criterion element to be used to
translate to a water column element. The State will select which fish tissue criterion element it
will translate from based on what data are available for the translation (e.g., CFs).
5.2 Selection of TTFcomposite Value
The TTFcomposite for the target species determined in Section 4.0 will be used in the model
for the water column translation. The TTF calculated using methods in Sections 4.1 Food Web
Modeling and 4.2 Selection of TTF Values and the information from the CWA section 304(a)
recommended selenium criterion document (USEPA 2021), the TSD for the California selenium
criterion rule (USEPA 2024), and the scientific literature will be used for the mechanistic model
translation.
5.3 Selection of Conversion Factor Value
Once the State has determined the proper fish tissue criterion element to translate to the
water column criterion element for a site, the State will select the proper CF value to populate
Equation 1, if the State has selected the egg-ovary or muscle criterion element. To select a
proper CF value, the State will use known species-specific CF values in Table 4 or Table 5
(reproduced from USEPA 2021 CWA section 304(a) recommended selenium criterion
document). If a species-specific CF value is not available in Table 4 or Table 5 from USEPA
2021, a CF value from a closely related surrogate species (within the same order) will be used. If
the lowest matching taxon of the target species is common to more than one of the available CF
values, the median CF values from the matching table entries will be used. If the target species is
a threatened or endangered species, or the water body includes habitat for threatened or
endangered species, the State could use the highest CF from the lowest matching taxon rather
than the median of those CF values. If a CF value is not available for a closely related surrogate
species, then the State will conduct the translation from the whole-body criterion element.
The EPA derived species-specific CF values (Table 4) by using empirical measurements
of selenium concentrations in different tissues of the same fish. To derive whole body to egg-
ovary CF values, the EPA defined matched pairs of selenium measurements from the whole
body and from the eggs or ovaries measured from the same individual fish or from matched
composite samples. Egg-ovary concentration was defined as a measurement from either the eggs
or the ovaries. If multiple measurements from both eggs and ovaries of the same individual or
matched composite sample were available, the average value was used. CF values were
calculated using matched tissue measurements from all available sites and studies for a given
species. The EPA had sufficient egg-ovary and whole-body selenium measurements to directly
derive egg-ovary to whole body CF values for 13 species of fish. However, matched pairs of
selenium measurements in eggs and/or ovaries and muscle tissue, and matched pairs of selenium
measurements in muscle and whole body were also available. To derive CF values for additional
fish species, the EPA used either the additional paired egg-ovary/muscle and muscle/whole body
data or a taxonomic classification approach to estimate the CF. The EPA derived an additional
seven CF values by multiplying egg-ovary/muscle and muscle/whole body conversion factors.
For more details on CF values for fish see Section 3.2.2.2 and Appendix B in USEPA 2021
CWA section 304(a) recommended selenium criterion document. For the process of translating
the bird egg criterion element or fish whole-body criterion element to a water column
concentration, CF values are not necessary.
17
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Table 4. EPA-Derived Egg-Ovary to Whole Body Conversion Factor (CF) Values (USEPA
2021).
Common name
Scientific name
CF
Std. Dev.a
Acipenseriformes
white sturgeon
Acipenser trcmsmontcmus
1.69
Cypriniformes
bluehead sucker
Catostomus discobolus
1.82
0.19
flannelmouth sucker
Catostomus latipinnis
1.41
0.20
white sucker
Catostomus commersonii
1.38
0.36
desert pupfish
Cyprinodon macularius
1.20
0.10
common carp
Cyprinus carpio
1.92
0.49
roundtail chub
Gila robusta
2.07
0.29
fathead minnow
Pimephales promelas
1.40
0.75
creek chub
Semotilus atromacirfatus
1.99
1.00
razorback sucker
Xyrauchen texanus
3.11
Esociformes
northern pike
Esox lucius
2.39
Perciformes
bluegill
Lepomis macrochirus
2.13
0.68
green sunfish
Lepomis cyamllus
1.45
0.23
smallmouth bass
Micropterus dolomieu
1.42
0.19
Salmoniformes
brook trout
Salve linus fontinalis
1.38
Dolly Varden
Salve limis malma
1.61
brown trout
Salmo trutta
1.45
1.8 lb
rainbow trout
Oncorhynchus mykiss
2.44
cutthroat trout
Oncorhynchus clarkii
1.96
2.03b
mountain whitefish
Prosopium williamsoni
7.39
a Standard deviation for CF values
br those species that had egg-ovary and whole body selenium
concentrations.
b The brown trout and cutthroat trout standard deviations for CF values of 1.81 and 2.03 are considerably
higher than the other standard deviations in this table. The brown trout data were taken from two studies,
Formation Environmental (2011) and Osmundson et al. (2007). ('!<' values for three of the four fish
samples from Osmundson et al. were four to six times greater than the median. Also, the Formation
Environmental data consisted of samples collected from natural streams and samples collected from a fish
hatchery. The CF values for the fish hatchery samples were four to seven times lower than the median
value. Although collectively, the data set meets the criteria for including the brown trout CF, the CF
values for Osmundson et al. and Formation Environmental hatchery samples may be anomalously high
and low, respectively. Excluding these potentially anomalous data reduces the brown trout standard
deviation to 0.47. The cutthroat trout ('!•' values are from two sources (Formation Environmental 2012
and Hardy 2005). The reason for the higher variability in the cutthroat trout ('!•' values is due to the
relatively higher CF values in the hatchery fish from the Formation study. The standard deviation for
cutthroat trout drops to 0.62 if the hatchery fish are excluded. See Appendix B of (USEPA 2021) for a
presentation of the data for both species.
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Table 5. EPA-Derived Muscle to Whole Body Conversion Factor (CF) Values (USEPA
2021).
Common name
Scientific name
Median ratio
Bluegill
Lepomis macrochirus
1.32
Bluehead sucker
Catostomus discobolus
1.23
Common carp
Cyprimts carpio
1.61
Flannelmouth sucker
Catostomus latipinnis
1.46
Green sunfish
Lepomis cycmellus
1.23
Roundtail chub
Gila robusta
1.05
Smallmouth bass
Micropterus dolomieu
1.23
White sucker
Catostomus commersonii
1.34
5.4 Data Collection for the Calculation of the EF
The parameter EF represents the proportional concentration of selenium in particulate
material relative to the concentration of total dissolved selenium in water and is calculated as the
ratio of the concentration of selenium in particulate material and the concentration of total
dissolved selenium in water. The EPA defines particulate material as the mixture of living and
non-living entities at the base of the aquatic food web, including phytoplankton, periphyton,
detritus, inorganic suspended material, biofilm, sediment and/or attached vascular plants (Presser
and Luoma 2010).
The EF varies more widely across aquatic systems than any other parameter in the
mechanistic model equation and is influenced by the source and form of selenium, water
residence time, the biogeochemical characteristics of the water body, and the type of particulate
matter (USEPA 2021). Because the EF can vary greatly between water bodies, this parameter
has the greatest potential to introduce uncertainty to the translation from a tissue criterion
element to a site-specific water column criterion element. The greatest reduction in uncertainty
when translating a tissue criterion element to a water column criterion element using the
mechanistic model is achieved when spatially and temporally coincident site-specific empirical
observations of dissolved and particulate selenium of sufficient quality and quantity are used to
accurately characterize the EF. Therefore, the State will either collect site-specific field data or
use appropriate site-specific data (see below) to calculate the EF.
The EF is calculated as the ratio of the concentration of selenium in particulate material
and the concentration of total dissolved selenium in water:
gp ^particulate
Cwater
(Equation 10)
Where:
Cparticulate
Cwater
EF
Concentration of selenium in particulate material (|ig/g dw)
Concentration of total dissolved selenium in water (|ig/L)
Enrichment Factor (L/g)
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The State will determine site-specific EFs by a) deriving an EF value from field
measurements at the site, or b) deriving an EF value from appropriately collected existing site
data, if the conditions at the site have not changed greatly since the EF data was collected (e.g.,
no significant new inputs of selenium such as new mine expansion or petroleum refining
facility). If conditions have greatly changed since the EF data was collected, the State will not
use the existing data and will collect new field data to derive the EF. If the State uses existing
data, it will follow the same temporal bounds determined in the data requirements of the USEPA
2021 selenium criterion (see Section 3.2.2.3 of the USEPA 2021) and will assure that at least
eight paired data points are available for the site. For large sites, the State may use more than
eight paired data points for the calculation, if eight will not sufficiently represent the variability
at the site and additional paired data points are available. The EPA used sites with selenium
measurements in particulate and water collected within 1 year of each other as inputs to the
EPA's model to derive national lotic and lentic water column criterion elements. The EPA's
analysis of particulate and water samples from a sample population of aquatic systems found that
samples taken within one year of each other, based on data availability, were appropriate in
deriving the national criterion (Figure 3.5 in USEPA 2021). However, site-specific EF values
using particulate and water samples that are as spatially and temporally coincident as possible are
considered the most robust. Therefore, to calculate the EF the State will use spatially and
temporally coincident samples or will collect particulate and water samples at the same time and
location; if coincident samples are not available or cannot be collected, the State will use existing
data from that location if the data were collected within one year of each other. The State will
use the most closely related spatially and temporally coincident water and particulate data to
determine EF values, to ensure the data represents the same conditions for both the water and
particulate samples.
Where the State decides to collect new data, at each site the State will decide which
particulate material(s) is most appropriate to sample for the site and sample that material(s) using
the methods listed below. If enough samples can be collected from algae and detritus (organic
media), then sediment will not be sampled or used. The State may sample multiple media for
particulate material and combine the EFs, if appropriate for the site. Consistent with the EPA's
national recommended selenium 304(a) criterion, the State will only use selenium particulate
concentrations from sediment if the majority of the other measurements are from algae or
detritus because sediment samples were found to have a significantly lower correlation to
selenium in water than algae or detritus (USEPA 2021). The EF for the site will not be
determined using data from sediment samples alone.
5.4.1 Particulate Sampling
Using the methods below, the State will ensure that enough particulate material is
collected to perform selenium analyses. The State will discuss with the analytical laboratory that
will be performing the selenium analysis what amount of particulate matter is needed to conduct
the selenium analysis. All samples will be labeled with site, date, material collected, and initials
of the sampler.
5.4.1.1 Periphyton Sampling
When selected as a medium to sample, periphyton will be collected during periods of
stable stream flow and will not be sampled for 3 weeks after a high, bottom-scouring stream
flow. The State will collect a small amount of periphyton from all substrate types and habitat
20
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types within the site where it is present. The proportion of periphyton collected from each
substrate/habitat type will correspond to the relative abundance of each habitat type in the site.
To collect periphyton, the State will follow the standard methods described in Revised
Protocols for Sampling Algal, Invertebrate, and Fish Communities as Part of the National
Water-Quality Assessment Program developed by USGS (Moulton et al. 2002). The methods in
the following sections of Moulton et al. 2002 will be used for sampling periphyton from rocks,
wood, plants, and sand/silt, respectively: section 4.3.1 sampling methods for epilithic habitats,
section 4.3.2 sampling method for epidendric habitats, section 4.3.3 sampling method for
epiphytic habitats, and section 4.3.4 sampling method for epipsammic/epipelic habitats. For each
of these methods, rinse water will be deionized water. These methods will be followed except for
the quantification of the area from which the periphyton was collected. The area does not need to
be quantified for selenium analysis. No preservative solutions will be added to these periphyton
samples. Rather samples will be stored on ice for transport from the field to the lab, where they
will be frozen at -20°C until analysis. Samples will be held no longer than 6 months before
analysis.
When periphyton is being sampled from non-wadeable rivers and streams, the State will
follow the protocols in sections 5.4, 5.4.1, and 5.4.2 of Concepts and Approaches for the
Bioassessment of Non-wadeable Stream and Rivers (Flotemersch et al. 2006). Samples will not
be preserved as described in these methods, but rather will be placed on ice for transport from the
field to the lab, where they will be frozen at -20°C. Samples will be held no longer than 6 months
before analysis.
5.4.1.2 Macroalgae Sampling
If the State is collecting macroalgae (filamentous algae), it will follow methods outlined
in Moulton et al. (2002) in section 4.4.2 macroalgae. Macroalgae samples will not have any
preservative solutions added to them, rather, they will be stored on ice for transport from the
field to the lab. Samples will then be frozen at -20°C until analysis. Samples will be held no
longer than 6 months before analysis.
5.4.1.3 Phytoplankton Sampling
Phytoplankton samples will be collected for large rivers and for lentic water bodies.
Whole water samples will be collected using either a subsurface grab or a depth/width-
integrating sampler. In productive waters, 1 liter of water will likely be sufficient, but 5 or more
liters of water may need to be collected from unproductive water bodies (Moulton et al. 2002).
Water samples will be collected from the photic zone of the water body (likely in the 0.5
m to 1 m depth range). Water samples will be prefiltered through 53 |im mesh and then
phytoplankton will be collected on pre-weighed .65 |im polyvinylidene fluoride filters (Graves et
al. 2021). Filters will then be folded into quarters with filtered biomass inside and placed in a
plastic sampling bag. Samples will be placed on ice for transport from the field to the lab, where
the sample will be frozen between -25°C and -30°C until analysis.
If large volumes of water need to be collected to get a sample with sufficient mass (as
indicated by the lab processing the sample) for analysis or filtering of the water in the field is
impractical, unfiltered water samples will be transported on ice to the lab for processing. Large
quantities of water will be processed using a high volume, continuous centrifuge to concentrate
the phytoplankton in the water samples. That phytoplankton will then be freeze dried and sent for
selenium analysis.
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5.4.1.4 Sediment Sampling
The method in Section 4.3.4 of Moulton et al. 2002 for epipsammic/epipelic habitats will
also be used if sediment is sampled. Sediment will only be sampled from depositional zones or
habitats. Sediment will only be sampled in addition to another particulate material. No
preservative solutions will be added to these samples. Rather, samples will be stored on ice for
transport from the field to the lab, where they will be frozen at -20°C until analysis. Samples will
be held no longer than 6 months before analysis.
5.4.2 Water Sampling
The State will make the greatest effort to sample water concurrently with particulate
samples or use water data that was collected concurrently with particulate data. However, if
spatially and temporally coincident samples cannot be collected or are not available, the State
will use water measurements for the calculation of an EF that were collected within one year of
particulate material being collected. The State will use the most closely related spatially and
temporally coincident water and particulate data to determine EF values, to ensure the data
represents the same conditions for both the water and particulate samples.
Water samples will be collected using a peristaltic pump from mid-water column in
wadeable streams. If water is being sampled from a lake or non-wadeable stream, then a surface,
middle, and bottom water sample will be collected and composited.
Water samples that are collected will be filtered through a 0.45 |im syringe filter and
collected in a high-density polyethylene bottle. If large particulates are present, the water will
also be prefiltered through a 125 |im filter. 250 ml of water will be collected.
Water samples will be preserved with nitric acid to a pH of less than 2. Samples will be
transported on ice from the field to the lab and then stored at 4°C until processing.
5.4.3 Time of Year for Sampling
Particulate samples will be collected during the algae growing season only (likely limited
to spring and summer).
5.4.4 Location of Sampling and Number of Samples
The State will collect eight particulate samples within each site. Composite periphyton
samples will be composed of periphyton material from all periphyton habitats found throughout
the site. Other types of particulate material will be collected from randomly selected locations
within the site where that particulate material is located. The State will also collect eight water
samples.
If the water samples are being collected with periphyton samples, they will be collected
from randomly selected locations throughout the site. Otherwise, water samples will be collected
from the site where the particulate material is collected.
If a selenium discharge is present at the site, the State will make sure the sampling
locations capture areas of potentially high exposure, based on the physical, chemical, and
biological characteristics of the water body. For large sites, the State may collect more samples,
if eight will not sufficiently represent the variability at the site.
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5.5 Chemical Analysis
The State will use an EPA or other published method for chemical analysis of total
dissolved selenium in water samples. The State will measure selenium concentrations in
particulate materials using methods described in Appendix L of USEPA 2021 CWA section
304(a) recommended selenium criterion document or other published methods. The State will
also verify that the methods being used have method detection limits and quantitation limits
sufficiently sensitive to quantify the selenium concentration within the sample. The State will
report all particulate material concentrations as dry weight concentrations.
5.6 Data Analysis for the Mechanistic Modeling Approach
The State will calculate a site-specific water column criterion using the mechanistic
model approach by applying appropriate input values to Equation 1, if translating from the fish
egg-ovary criterion element or fish muscle criterion element, or Equation 2, if translating from
the fish whole-body criterion element or bird egg criterion element. The State will use the
TTFcompos'te previously calculated during the target species analysis in this calculation. The tissue
criterion element will either be the bird egg or one of the fish tissue criterion elements. If the
egg-ovary or fish muscle criterion element is being used, then the CF value included will be the
one selected or derived as described in section 5.3.
The EF value will be calculated using field collected data or appropriate existing site-
specific data and Equation 10. To calculate a site-specific EF value, the State will first calculate
the ratio of each individual particulate measurement and its associated water measurement (if
more than one water measurement is available for any given particulate measurement, the State
will use the median water measurement). If more than one ratio for any given category of
particulate material is available (e.g., more than one ratio of algae to water), the State will use the
median of the ratios to represent the EF for that particulate material. The State will then calculate
the geometric mean of the median ratios for each category of particulate material (e.g., algae,
periphyton, etc.) as the site EF value. If enough measurements can be collected from other
media, then sediment measurements will not be used to calculate the EF. If enough
measurements cannot be collected from other media, the State will only use sediment
measurements if the majority of the other measurements are from other organic particulate
material (algae, periphyton, phytoplankton or detritus).
Below are examples of calculations of site-specific water column criterion elements using
the mechanistic model approach.
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Example 1
Bluegill (Lepomis macrochirus) that consume mostly amphipods in a river:
Current water concentration (total dissolved |ig/L)
5.00
Current particulate concentration (mg/kg dw)
4.25
Trophic transfer factor for bluegill (TTFtl3)
1.03
Trophic transfer factor for amphipods (TTFtl2)
1.22
Egg-ovary to whole-body conversion factor for bluegill (CF)
2.13
Selenium egg-ovary criterion element (mg/kg dw)
15.1
„ „ Cparticulate
~ c
mg
-water
4.25
Ep = kgdw
5.00 |ig/L
= 0.85 L/ g
jy^pomp ° 8 ite _ jy^TL3 x jijipTU2
= 1.03 X 1.22
= 1.26
r
r _ uegg-ovary
^water criterion element
fTpcomposite x EF X CF
IS.l^dw
C _ kg
water criterion element t
1.26 x 0.85-x 2.13
= 6.62 [ig /L total dissolved selenium
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Example 2
Fathead minnow (Pimephales promelas) that consume mostly copepods in a river:
Current water concentration (total dissolved |ig/L)
5.00
Current particulate concentration (mg/kg dw)
4.25
Trophic transfer factor for fathead minnow (TTFtl3)
1.57
Trophic transfer factor for copepods (TTFtl2)
1.41
Egg-ovary to whole-body conversion factor for fathead minnow (CF)
1.40
Selenium egg-ovary criterion element (mg/kg dw)
15.1
„ „ Cparticulate
br —
c,
water
4.25^dw
EF = kg
TL2
5.00 |ig/L
= 0.85 L/g
TTFcomP°site = 'yypTLs x 'yyp
= 1.57 x 1.41
= 2.21
r
r _ uegg-ovary
c,
water criterion element jjpcomposite x EF X CF
mg
kg
IS.l^dw
water criterion element
2.21 x 0.85 L/g x 1.40
= 5.74 |ig/L total dissolved selenium
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Example 3
Bluegill (Lepomis macrochirus) that consume mostly aquatic insects in a lake:
Current water concentration (total dissolved |ig/L)
5.0
Current particulate concentration (mg/kg dw)
8.75
Trophic transfer factor for bluegill ( Til' " 3)
1.03
Trophic transfer factor for aquatic insects (median of Odonates, Water
boatman, Midges, and Mayflies) (TTFTL2)
2.14
Egg-ovary to whole-body conversion factor for bluegill (CF)
2.13
Selenium egg-ovary criterion element (mg/kg dw)
15.1
„ „ Cparticulate
br —
a
8.
EF =
water
8.75
5.00
= 1.75 L/g
TTFcomP°site = 'Y'YpTLS x rprppTL2
= 1.03 X2.14
= 2.20
r
r _ uegg-ovary
^water criterion element
YTFcomposite x EF X CF
mg
kg
IS.l^dw
^water criterion element ~ 2 2Q x 1 75 L/g X 2 13
= 1.84 |ig/L total dissolved selenium
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Example 4
Fathead minnow (Pimephalespromelas) that consume approximately % copepods and ]A aquatic
insects in a river:
Current water concentration (total dissolved |ig/L)
5.0
Current particulate concentration (mg/kg dw)
4.25
Trophic transfer factor for fathead minnow (TTl,ns)
1.57
Trophic transfer factor for copepods and aquatic insects (TIT'"2)
Copepods =1.41
Average of all aquatic insects = 2.14
i(TTFt xwt)
TTF?l2 =
= (1.41 x %) + (2.14 x i/3)
= 1.65
1.65
Egg-ovary to whole-body conversion factor for fathead minnow (CF)
1.40
Selenium egg-ovary criterion element (mg/kg dw)
15.1
„ „ Cparticulate
~ c
water
4.25 ££dw
EF= !«
5.00 |ig/L
= 0.85 L/g
TTFcomP°site = 'yypTLS x rprppTL2
= 1.57 x 1.65
= 2.59
r
r _ uegg-ovary
^water criterion element
YTFcomposite x EF X CF
mg
kg
IS.l^dw
r —
^water criterion element ^ 59 Q L/g X 1 40
= 4.90 |ig/L total dissolved selenium
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Example 5
Flathead chub (Platygobio gracilis) with a diet of approximately 80% aquatic insects and 20%
Current water concentration (total dissolved |ig/L)
5.0
Current particulate concentration (mg/kg dw)
4.25
Trophic transfer factor of flathead chub:
Lowest matching taxon is the family Cyprinidae. Therefore, the TTF value of
Cyprinidae is used (TTF^L3)
1.20
Trophic transfer factor for insects (T'/T'1L2)
Average of all aquatic insects = 2.14
2.14
Egg-ovary to whole-body conversion factor for flathead chub (species-specific
value not available, so median CF for family Cyprinidae is used). (CF)
1.95
Selenium egg-ovary criterion element (mg/kg dw)
15.1
„ „ Cparticulate
br —
a
water
4.25^dw
EF = kg
5.00 |ig/L
= 0.85 L/g
TTFcomposite = [TTpTL3 x jjpTL.2 x + [JJpTLS x
Where:
wi = Proportion of fathead chub diet from insects; and
W2 = Proportion of fathead chub diet from algae
TTFcomposite = ^ 20 X 2.14 X 0.8] + [1.20 X 0.2]
= 2.29
r
r °egg-ovary
water criterion element ~ jjpcomposite x EF X CF
IS.l^dw
r kg
uwater criterion element
2.29 x 0.85 L/g x 1.95
= 3.98 |ig/L total dissolved selenium
28
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Example 6
Largemouth bass {Micropterus salmoides) that consume mostly Western mosquitofish
Gambusia affinis) that consume approximately 3/4 insects and ]A crustaceans in a
arge river
Current water concentration (total dissolved |ig/L)
5.0
Current particulate concentration (mg/kg dw)
4.25
Trophic transfer factor of largemouth bass (TTFTi¥)
1.39
Trophic transfer factor of Western mosquitofish (I"/T'lls)
1.21
Trophic transfer factor for insects and crustaceans (TIT'"2)
Median all Insects - 2.14
Median all Crustaceans - 1.41
Z('/"/7';//2w,)
ttF112 =
= (2.14 X 0.75) +(1.41 X 0.25)
= 1.96
1.96
Egg-ovary to whole-body conversion factor for largemouth bass (species-
specific value not available, so median CF for genus Micropterus is used) (CF)
1.42
Selenium egg-ovary criterion element (mg/kg dw)
15.1
r
°particulate
EF=~c
water
4.25 ?®dw
EF= !«
5.00 |ig/L
= 0.85 L/g
TTFcomP°site = rJirJTpTL4 x rprjvpTL3>/ rprppTL2
= 1.39 x l.21x 1.96
= 3.30
r
r _ uegg-ovary
^water criterion element
c,
water criterion element
YTFcomposite x EF X CF
mg
kg
IS.l^dw
3.30 x 0.85 L/g x 1.42
= 3.79 |ig/L total dissolved selenium
29
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6.0 Bioaccumulation Factor Approach
6.1 Additional Target Species Considerations for BAF - Exposure at the Site
The State will consider differences in exposure at the site when selecting which fish and
bird species will be sampled for the BAF approach. In order to fully assess which species has the
greatest bioaccumulation potential, selenium exposure at the site, in addition to diet, will be
considered when selecting a target species. The State will make the greatest effort to target
species in the genera Acipenser, Lepomis, Salmo, and Oncorhynchus (or all the fish species if the
genera Acipenser, Lepomis, Salmo, and Oncorhynchus are not present at the site) for sampling
that feed in areas with sediment and flow characteristics that will lead to the greatest selenium
bioaccumulation potential. Therefore, if the site is a lotic site but has areas that have lentic
properties, the State will target a species for sampling that utilizes these lentic locations for
feeding, as selenium has the potential to bioaccumulate more in lentic areas.
6.2 Fish Tissue Type Selection
When the State is using the BAF approach to derive a site-specific water column criterion
element to protect the aquatic life designated use, the State will collect fish egg samples, if
available and practical, as egg concentrations have the strongest correlation to toxicity effects
compared to all the tissue types. If egg samples are not available or impractical to collect, then
the State will collect whole-body or muscle samples.
Fish egg samples will be collected when the State can sample the fish at the appropriate
time of the year and when the fish is large enough to easily sample eggs. The State will contact
local fish biologists to determine the spawning time periods for their target fish species and will
then collect egg samples from those target fish species in the pre-spawn time period, when the
eggs are mature but the fish have not yet released their eggs.
If the State is not able to collect egg samples during this pre-spawn period either due to
resource limitations or safety concerns due to high flows during spring snow melt, the State will
instead collect whole-body or muscle samples of fish. If the State is collecting whole-body or
muscle tissue samples, the State will contact local fish biologists to determine the spawning time
period for the target fish species. They will make sure that for whole-body or muscle samples,
the fish are collected outside of that spawning period and also not collected directly post spawn
(~ 1 month after spawning) to avoid collecting fish tissue that is depurated of selenium, since
selenium is transferred to fish eggs during egg development. If a small asynchronous spawning
species is being sampled where it is difficult to identify one specific spawning period and
difficult to sample eggs, the State will collect whole-body samples of fish (with eggs, if present)
and perform the BAF translation from the whole-body tissue criterion element.
6.3 Sampling Plan
6.3.1 Fish Tissue Sampling
The State will collect composite egg, whole-body or muscle samples. Those composite
samples will be at least 20 g ww, unless impractical due to fish size or limited number of fish at a
location. In those instances, the State will discuss with the analytical laboratory that will be
performing the selenium analysis what mass of tissue is needed to conduct the selenium analysis
and related QA/QC protocols and collect that mass. For the composites, the fish tissue will be
from fish that are all the same species. If whole-body or muscle tissue is being collected, the fish
30
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will all be similar in size such that the smallest individual is no less the 75% of the total length of
the largest individual. All samples will also be collected within a week of each other.
For egg samples, gravid females will be collected using appropriate fish collection
techniques for the water body (e.g., seines, hoop nets, electrofishing, angling etc.). The State will
make sure that they are not sampling any undersized juveniles. Once the fish are collected, they
will be carefully observed for signs of physical damage, mortality, or other sources of stress. If a
fish is showing signs of physical damage, mortality, or other sources of stress, the sign of stress
will be documented, and no eggs will be collected from the fish. Since any handling of the fish
will remove the protective body layer of slime, fish will be handled as little as possible using dip
nets and soft material gloves.
Adult fish for egg collection will be held in live wells until the eggs are sampled. Egg
collection tools will all be cleaned and dried before use. Female fish will be randomly selected
from the live well and the area around the urogenital opening will be dried with paper towels.
The length and weight of the female fish will be measured and recorded. The eggs will then be
expressed from the fish by applying gentle pressure to the lower half of the fish from behind the
pectoral fins and along the fish towards the anus. This application of pressure will be repeated
until all the eggs have been expressed. Eggs will be collected in pre-cleaned steel bowls and
stored in a cool place. Eggs will be examined to make sure that they are free of fecal matter,
urine, and blood. Any eggs that have other substances attached will be discarded using a clean
plastic pipette. Samples will be transferred to resealable plastic bags and placed on ice for
transport back to the lab where eggs will be weighed to the nearest gram using a top-loading
digital scale, composited, and frozen (-20°C) for storage (if not analyzed immediately) and
shipped for laboratory percent moisture and selenium analysis when appropriate (Janz and
Muscatello 2008). All samples will be labeled with site, date, fish species sampled, material
collected, and initials of the sampler. Samples will be frozen at -20°C in plastic, borosilicate
glass, quartz or PTFE bottles. Sample will be held for a maximum of 6 months.
For whole-body samples, fish (male or female) will be collected using appropriate fish
collection techniques for the water body and sacrificed using an overdose of tricaine
methanesulphonate (MS-222). The length, weight, species, and sex of whole fish samples will be
measured and recorded as each fish is collected. Fish will then be individually wrapped in extra
heavy-duty aluminum foil. Spines on fish will be sheared to minimize punctures in the aluminum
foil packaging (Stober 1991). Each individual fish will be placed into a waterproof plastic bag
and sealed. All samples will be labeled with site, date, fish species sampled, material collected,
and initials of the sampler. Once packaged, samples will be immediately placed on ice for
transport back to the lab. In the lab, samples will be composited and frozen at -20°C (if not
immediately analyzed) until selenium and percent moisture analysis. Samples will be held for no
longer than 6 months.
For muscle samples, fish (male or female) will be collected using appropriate fish
collection techniques for the water body and sacrificed using an overdose of MS-222. The
length, weight, species, and sex of the fish will be measured and recorded as each fish is
collected. Fish will then be individually wrapped in extra heavy-duty aluminum foil. Spines on
fish will be sheared to minimize punctures in the aluminum foil packaging (Stober 1991). Each
individual fish will be placed into a waterproof plastic bag and sealed. All samples will be
labeled with site, date, fish species sampled, material collected, and initials of the sampler. Once
packaged, samples will be immediately placed on ice for transport back to the lab. Once in the
lab, fish will be filleted according to methods in section 7.2.2 Processing Fish Samples in
31
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Guidance for Assessing Chemical Contaminant Data for Use in Fish Advisories: Volume 1 Fish
Sampling and Analysis (USEPA 2000). Samples will then be composited and frozen at -20°C
until selenium and percent moisture analysis. Samples will be held for no longer than 6 months.
6.3.2 Bird Egg Sampling
The State will sample individual bird eggs from a site by collecting one egg per clutch
(nest) after the clutch is complete. The State will collect eight bird egg samples for the target
species sampled at the site (Ohlendorf et al. 2008) to reduce the impact of sampling while still
attaining an estimate of variability across the site. If the site is small relative to the total foraging
area of the target species being sampled, the variability will likely be greater and a larger
sampling size may be required.
Egg samples should be free of debris (e.g., feathers and nest material) and fecal matter.
All egg samples will be labeled with site, date, species information, and initials of sampler and
placed in resealable plastic bag. The egg samples will be placed on ice for transport back to the
lab where the eggs will be measured for length and breadth (to the nearest 0.01 millimeter) and
weighed for total egg weight (to the nearest 0.07 gram). All egg samples will be stored in a
freezer at -20°C until selenium analysis (Evers 2009). Samples will be held for no longer than 6
months.
6.3.3 Water Sampling
The State will make the greatest effort to sample water concurrently with fish tissue and
bird egg samples or use water data that were collected concurrently with tissue data. However, if
temporally coincident samples are not available or cannot be collected, the State will use water
measurements that were collected within one year of the tissue material collected. The State will
use the most closely related temporally coincident water and tissue data to ensure the data
represents the same conditions for both the water and tissue samples.
Water samples will be collected using a peristaltic pump from mid-water column in
wadeable streams. If water is being sampled from a non-wadeable water body, then a surface,
middle, and bottom water sample will be collected and composited. Water samples that are
collected will be filtered through a 0.45 |im syringe filter and collected in high density
polyethylene bottle. If large particulates are present, the water will also be prefiltered through a
125 |im filter. 250 ml of water will be collected. Water samples will be preserved with nitric acid
to a pH less than 2. All samples will be labeled with site, date, material collected, and initials of
the sampler. Samples will be transported on ice from the field to the lab and then stored at 4°C
until processing. Samples will be held for no longer than 6 months.
6.3.4 Time of Year for Sampling
The State will determine what time of year to collect fish samples based on which tissue
type and fish species the State decides to sample. The State will contact local fish biologists to
determine the spawning period for target species at the site. If the State is collecting fish egg
samples, the State will collect them during the appropriate pre-spawn period for the target
species, which will be when the eggs are mature. Whole-body samples or muscle samples will be
collected outside of the spawning period and post-spawning period (at least a month after
spawning). For most fish species, this will likely be late summer or early fall. Fish will also not
be sampled during winter months. If the site has characteristics that will cause significant
temporal variability in selenium concentrations, the State will consider sampling in multiple
32
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seasons or multiple years. As the bird tissue criterion element is based on bird eggs, bird samples
will only be collected during the breeding season of the target species. The State will
concurrently collect water samples. If concurrent samples cannot be collected or are otherwise
not available, the State will use water samples collected within a year of fish and bird egg
samples. The State will use the most closely related temporally coincident water and tissue data
to ensure the data represents the same conditions for both the water and tissue samples.
6.3.5 Location of Sampling
Once the State has defined the site for the site-specific water column criterion element,
the State will identify locations from within the site that correspond to the target fish and bird
species feeding habitats, home ranges, and/or nesting areas. Locations within those areas will
then be randomly selected for sampling fish tissue and bird eggs. Water samples paired with bird
egg samples will be collected from random locations within the bird species aquatic feeding
habitat. Water samples paired with fish tissue samples will be collected from the same location
where the fish was sampled.
6.3.6 Number of Samples
The State will collect eight composite fish samples, composed of three fish (or more if
needed to have adequate tissue mass for chemical analysis) or eight bird egg samples (one egg
per nest after the clutch is complete) and eight water samples for the site (Hitt and Smith 2015,
BCMOE 2014). If the State is not able to find sufficient fish to create eight composites of three
fish, or that will result in negatively impacting the fish population at the site in question, then the
State will either create eight composites of two fish or sample eight individual fish (if they are of
sufficient size). For large sites, the State may collect more samples, if eight will not sufficiently
represent the variability at the site.
6.4 Chemical Analysis
The State will use an EPA or other published method for chemical analysis of total
dissolved selenium in water samples. The State will measure selenium concentrations in fish and
bird tissue using methods described in Appendix L of USEPA 2021 CWA section 304(a)
recommended selenium criterion document or other published methods. The State will also
verify that the methods being used have method detection limits and quantitation limits
sufficiently sensitive to quantify the selenium concentration within the sample. The State will
report all tissue concentrations as a dry weight concentration.
6.5 Data Analysis for the Empirical BAF Approach
Several considerations in the analysis of the available data to derive a BAF-based site-
specific criterion must be addressed in order to account for uncertainty and produce a defensible
outcome. First, if the State collected data from more than one species of fish or bird, it will
calculate the median BAF for each species using Equation 3. The State will select the species
(one fish species and one bird species) with the highest BAFs for the calculation of the water
column criterion element. Next, the State will use all paired water and fish samples or paired
water and bird egg samples to calculate BAFs for the selected species using Equation 3. A BAF
will be generated for each fish/water pair and bird/water pair. The State will then select the 80th
percentile of the distribution of calculated BAFs to derive the water column criterion element,
33
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using Equation 4, to ensure protection of sensitive and highly exposed species at the site. If the
target species is a surrogate for a threatened or endangered species, or the water body includes
the habitat of any threatened or endangered species, the State may select a higher percentile of
the distribution of calculated BAFs to use in deriving the water column criterion element. The
fish tissue criterion element used in Equation 4 will be for the same tissue type that was
collected to calculate the BAF.
Below is an example of the derivation of a site-specific water column criterion element
for a water body impacted by selenium where bluegill samples were collected (USEPA 2021).
Site-specific selenium egg concentration (bluegill; mg/kg dw)
22.0
Selenium egg/ovary criterion element (mg/kg, dw)
15.1
Ambient total dissolved selenium water column concentration (|ig/L)
4.0
Water column criterion element (total dissolved |ig/L)
X
Solve for the BAF:
Site — specific egg Se concentration
BAF =
Ambient dissolved selenium water column concentration
mg Se
AF = 22 ° kj = 5.5 kdSe'L
4.0
V-gSe " kg
Solve for site-specific water column criterion element:
Fish tissue criterion element
Water column criterion element =
15.1
BAF
mg Se
k cj
Water column criterion element = ;—= r = 2.75ugSe/L
r r kg Se • L nu '
3 ¦ 3 T
kg
Water column criterion element= 2.75 |ig/L total dissolved selenium.
Another factor that the State will consider is the impact of selenium inputs to downstream
waters where conditions for selenium bioaccumulation are more favorable (e.g., a selenium input
to a lotic system (e.g., river) that flows into a lentic receiving water (e.g., lake)). In such a
circumstance, the State will ensure that the site-specific water column criterion element for the
upstream site accounts for potential impacts on the downstream site, including any impacts to
threatened and endangered species in the downstream waters. The State may collect fish tissue
samples or bird egg samples from the downstream site to ground-truth the conditions at the
receiving water and help to determine if the selenium input from the upstream site is having an
impact to selenium concentrations in the fish tissue or bird eggs at the downstream site.
Finally, the State may consider revising the site-specific water column criterion element
if conditions at the site change (such as hydrodynamics) such that fish tissue or bird egg
concentrations increase despite constant water concentrations.
34
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