EPA822-R-16-001
                                       January 2016
Development of National Bioaccumulation Factors:
          Supplemental Information for
    EPA's 2015 Human Health Criteria Update
          U.S. Environmental Protection Agency
                   Off ice of Water
            Office of Science and Technology
                   Washington, DC

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Contents

Figures	iii
Tables	iii
1.   Purpose	1
2.   Summary	1
3.   Chemical Procedure Classification	3
4.   Baseline BAFs	4
  4.1    Kow Method	4
  4.2    BAF Method	5
  4.3    BCF Method	6
5.   National BAFs	6
6.   Supporting Procedures	7
  6.1    Kow	7
  6.2    Food Chain Multiplier	7
  6.3    Fraction Freely Dissolved	7
  6.4    Lipid Content	8
  6.5    Species Trophic Level	9
7.   Examples	9
  7.1    Kow Method: Endrin	9
  7.2    BAF and BCF  Methods: Fluorene	10
    7.2.1    BAF Method	10
    7.2.2    BCF Method	11
References	13

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Figures

Figure 1. Framework for Selecting Methods for Deriving National BAFs (Source: USEPA 2003a,
Figure 3-1, p. 3-2)	2
Tables

Table 1. Food Chain Multipliers for Trophic Levels 2, 3, and 4 (Source: USEPA 2003a, Table 4-
6, p. 4-39)	8

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                                                        IV

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1. Purpose

This document describes the procedures and calculations EPA used to compute the national
bioaccumulation factors (BAFs) that were, in turn, used to calculate the Agency's updated
national recommended water quality criteria for human health for 94 chemicals (USEPA 2015).
For a scientific discussion of and rationale for using these methods, see EPA's 2000
Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health
(2000 Methodology), Technical Support Document Volume 2: Development of National Support
Factors (TSD), and EPA's final 94 criteria documents that describe the development of each
chemical-specific bioaccumulation factor included in the 2015 update on the National
Recommended Water Quality Criteria - Human Health Criteria  Table webpage (USEPA 2000;
USEPA 2003a; USEPA 2015).

2. Summary

EPA searched  peer-reviewed journal articles, federal and state reports, and databases to obtain
input variables—including species-level lipid content, trophic level (TL), degree of ionization and
metabolism of the chemical, and chemical-specific octanol-water coefficient (Kow)—to calculate
BAFs  used to update 94 national recommended human health criteria. EPA used data from the
searches to classify each chemical, using the decision framework presented in Figure 3-1 of
EPA's TSD (reproduced as Figure 1 in  this document) to derive the most appropriate BAFs
according to EPA's 2000 Methodology  and its TSD (USEPA 2000; USEPA 2003a).

EPA documented source information and reviewed and confirmed the derivation of each value.
In addition, quality control checks of data calculations and data entries were performed and any
errors found were corrected before BAF values were finalized. BAFs were rounded in
accordance with EPA's 2000 Methodology and quality control checks were performed to ensure
that the significant digits for each result were correct (USEPA 2000). The procedures followed
for calculating national  BAF values were documented in each of the 94 criteria documents.

The remainder of this document is organized into sections 3 through 7 and a list of references.
Section 3, Chemical Procedure Classification, provides details about the procedure decision
framework used to classify each chemical. Section 4, Baseline BAFs, presents the basic
equations used for computing baseline BAFs. Section 5, National BAFs, provides the basic
equations used for computing national  BAFs as a function of final baseline BAFs. The basic
equations in sections 4 and 5 are supported by additional methods and steps for establishing
the Kow, food chain multiplier (FCM), fraction freely dissolved (ffd), lipid content, and trophic
levels (TLs), which are  summarized in section 6, Supporting Procedures. Section 7, Examples,
provides numerical examples that demonstrate the approach to estimate baseline and national
BAFs for the chemicals endrin and fluorene.

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                                      COLLECT & REVIEW }

                                     ^-^^^L^^J
^
t
Nonionic Organic

                                     CLASSIfV CHEMICAL
                                        OF CONCERN
                                       Ionic Organic

^
r
Inorganic &
Organometallic
Low/
Unknown
High


                                                                 1

Figure 1. Framework for Selecting Methods for Deriving National BAFs (Source: USE PA
2003a, Figure 3-1, p. 3-2)

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3. Chemical Procedure Classification

As explained in each of the updated 94 criteria documents (USEPA 2015), EPA used the
decision framework presented in its TSD to identify procedures to derive national TL-specific
BAFs for each chemical based on that chemical's properties (e.g., ionization and
hydrophobicity), metabolism, and biomagnification potential (see Figure 1) (USEPA 2003a).

EPA followed the guidelines provided in section 5.5 of the TSD to assess the occurrence of
cationic and anionic forms of the chemicals at typical environmental pH ranges. As explained  in
section 5.5, when a significant fraction of the total chemical concentration is expected to be
present as the ionized species in water, procedures for deriving the national  BAF rely on
empirical (measured) methods (i.e., procedures #5 and #6 in Figure 1) (USEPA 2003a).

When an insignificant fraction of the total chemical is expected to be present as the ionized
species (i.e., the chemical exists essentially in the neutral form), the national BAF is derived
following procedures established for nonionic organic chemicals (e.g., procedures #1  through #4
in Figure 1) (USEPA 2003a). To evaluate whether ionization was negligible,  EPA reviewed
dissociation constant (pKa) information provided in Hazardous Substances Data Bank (HSDB)
sources referenced in the individual criteria documents (USEPA 2015).

For chemicals for which ionization was determined to be  negligible at typical environmental pH
ranges, EPA followed the steps in section 3.2.3 of the TSD to determine the  procedures for
deriving the national BAFs for nonionic organic chemicals (USEPA 2003a). EPA evaluated the
log Kow values provided in the Agency for Toxic Substances and Disease Registry (ATSDR) and
HSDB sources referenced in the individual criteria documents to determine whether chemicals
should be classified as moderate-high hydrophobic (i.e., log Kow^_4) or low hydrophobic (i.e.,
log Kow < 4). Those chemicals were further evaluated to determine whether metabolism was
low/unknown or high; sources of information found on the metabolism of the chemicals are
referenced  in the individual criteria documents.

For organic chemicals for which ionization was determined not to be negligible at typical
environmental pH ranges and for the inorganic chemical included in the 2015 criteria update
(i.e.,  cyanide), EPA followed the guidelines  in section 3.2.1 of the TSD to evaluate the
biomagnification potential of the chemicals (USEPA 2003a). The ATSDR, HSDB, and EPA
sources used for the evaluations are referenced in the individual criteria documents.

The characteristics of each chemical used to derive national TL-specific BAFs are documented
in section 4.4.2 of each criteria document.

Following this decision  framework, EPA selected the method that provided BAF estimates for all
three TLs (TL2-TL4) in the following priority:

   1.  BAF estimates using the BAF method (i.e., based on field-measured  BAFs), if possible.
   2.  BAF estimates using the bioconcentration factor (BCF) method if (a) the BAF method did
       not produce estimates for all three TLs, and (b) the BCF method produced national-level
       BAF estimates for all three TLs.
   3.  BAF estimates using the Kow method if (a) procedure #1 or #3 was applicable (see
       Figure 1), and (b) the BAF and BCF methods did  not produce BAF estimates for all three
      TLs.

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If the procedure called for the BAF method but there were fewer than three TL estimates and
the Kow method did not apply, EPA estimated the BAF for the reported TLs by using a geometric
mean when there were two BAFs and using the single estimate when only one was available.
EPA did not mix values from  the BAF and BCF methods. If the BAF method did not have
sufficient reliable data for any TLs, EPA used the BCF method estimates in the same manner. If
none of these methods provided sufficient data or were appropriate for the procedure, EPA
used the BCF from the previously recommended 2002/2003 criteria (USEPA 2002a; USEPA
2003b).

4. Baseline BAFs

Three methods for computing baseline BAFs ((Baseline BAF)-n_n) are described in this section:
Kow, BAF, and BCF methods. Refer to section 3 to determine the applicability of each method to
a particular chemical. In  particular, note that the Kow method applies to chemicals that fall under
procedure #1 or procedure #3 and does not apply to chemicals that are highly metabolized or
have significant ionization. Also, including an FCM in  the equations is applicable to chemicals
that fall under procedure #1 using the Kow and BCF methods, or procedure #6 using the BCF
method. For other chemicals, the FCM can be dropped from the equations in this section (or
equivalently set to 1.0).

EPA used field-measured BAFs and laboratory-measured BCFs available from peer-reviewed,
publicly available databases  to develop baseline BAFs  (Arnot and Gobas 2006; Environment
Canada 2006). BAF and BCF values from additional peer-reviewed sources also were collected
and evaluated. If measurement units were not provided, the data from those sources were
considered "unverified."  Those values were recorded  but, ultimately, not used to calculate BAFs
for use in revising the 94 criteria. The chemicals for which additional sources were used to
calculate baseline BAFs are  listed below:
   •   1,4-Dichlorobenzene (Calamari et al. 1982)
   •   2,4,5-TP (Kenaga 1980; USEPA 1995)
   •  2,4-D (Wang etal. 1994)
   •  Benzo(a)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, chrysene,
      dibenzo(a,h)anthracene, indeno(1,2,3-cd)pyrene—Field-measured BAF for
      benzo(a)pyrene, an index polycyclic aromatic hydrocarbon (PAH), was used as a
      surrogate for estimating BAFs for other PAHs. This approach is consistent with
      conclusions of Neff (2002) that benzo(a)pyrene is a good indicator of the presence of
      pyrogenic PAHs in the environment and that these types of PAHs are expected to
      concentrate in organisms such as fish and shellfish as does benzo(a)pyrene.
   •  Cyanide (USEPA 2003b)
   •  Dinitrophenols (USEPA 2002b)


4.1   Kow Method
The Kow method of computing baseline BAFs is applicable to chemicals that fall under
procedures #1 and #3. It is a function of Kow and an appropriate FCM. One baseline BAF can be
calculated for each  combination of chemical and TL to which the Kow method applies. As
described in section 5.4 of the TSD, this method is used for each nonionic, moderate-to-highly
hydrophobic chemical with metabolism that is considered negligible or is unknown (USEPA

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2003a). In this method, the Kow is assumed to be equal to the baseline BCF, and thus the
organic carbon and lipid normalization procedures are not needed. To account for
biomagnification, the Kow value is multiplied by an appropriate FCM. The Kow method baseline
BAF equation is shown below (USEPA 2003a, p. 5-23):

                         (Baseline BAF)TLn =  Kow • (FCM)TLn

where:

   (Baseline BAF)Ti_ n   =   baseline BAF for TL "n" (L/kg-lipid)
   FCM              =   FCM for TL "n"
                      =   n-octanol-water partition coefficient
For chemicals that fall under procedure #3 (log Kow < 4), the FCM can be dropped from the
equation (or equivalently set to 1.0). See section 6.1, Kow, and section 6.2, Food Chain
Multiplier, for information on how the Kowand FCM were determined. See section 7.1, Kow
Method: Endrin, for an example of how to apply the Kow method for computing both baseline and
national BAFs for endrin.

4,2    BAF
The BAF method is applicable to all chemicals. In the BAF method, a baseline BAF is calculated
for each field sample BAF as shown in the equation below (USEPA 2003a, p. 5-1):

                           (Baseline BAF)j  =


where:

    (Baseline BAF)i =   baseline BAF for field sample i (L/kg-lipid)
    BAFj'          =   total BAF from field sample (i.e., total concentration of chemical in
                      tissue / total concentration of chemical in water [L/kg-tissue])
    ffd             =   fraction of the total concentration of chemical in water that is freely
                      dissolved
    ft              =   fraction of tissue that is  lipid

Multiple (Baseline BAF)i are averaged to a (Baseline BAF)-n_n by using the following procedure:

       1.  Compute the geometric mean across each chemical, computation method,  TL, and
          species to compute a set of "species-mean baseline BAFs."
       2.  Compute the geometric mean across each chemical, computation method,  and TL to
          compute a set of "trophic level-mean baseline BAFs" using the results from the
          previous step.

See section 6.3, Fraction Freely Dissolved, for information on computing the fraction of the total
concentration of chemical  in water that is freely dissolved, and section  6.4, Lipid Content, for
information on estimating the fraction of tissue that is lipid. See  section 7.2.1, BAF Method, for
an example of how to apply the BAF method to fluorene.

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4.3    BCF Method
The BCF method is applicable to all chemicals. In the BCF method, a baseline BAF is
calculated for each laboratory-measured BCF as shown in the equation below (USEPA 2003a,
p. 5-19):

                      (Baseline BAF); = (FCM)TLn •


where:

   (Baseline BAF)i =   baseline BAF for laboratory sample i (L/kg-lipid)
   FCM           =   FCM for TL associated with species from laboratory measurement
   BCF-r'         =   total BCF from laboratory measure (i.e., total concentration of chemical
                      in tissue / total concentration of chemical in water [L/kg-tissue])
   ffd             =   fraction of the total concentration of chemical in water that is freely
                      dissolved
   ft              =   fraction of tissue that is lipid

For chemicals that fall under procedures #1 and #6 and when the log Kow is greater than or
equal to 4, the species must be assigned to a particular TL (i.e., 2, 3, or 4)  and the appropriate
FCM selected. For other cases, the FCM can be dropped from the equation (or equivalently set
to 1.0).

Multiple (Baseline BAF)i are averaged to a  (Baseline BAF)-n_n by using the  same procedure as
described in section 4.2, BAF Method.  See section 6.3, Fraction Freely Dissolved, for
information on computing the fraction of the total concentration of chemical in water that is freely
dissolved, and section 6.4, Lipid Content, for information on estimating the fraction of tissue that
is lipid. See section 7.2.2,  BCF Method, for an example of  how to apply the BCF method to
fluorene.

5. National BAFs

Final baseline BAFs are used to compute national BAFs. EPA's TSD presents the formula for
computing national TL-specific BAFs as follows (USEPA 2003a, p. 6-1):

            National BAF(TLn) = [(Final Baseline BAF)TLn •  (f,)TLn +  1] • (ffd)

where:

   National BAF          =  national BAF (L/kg-tissue)
   (Final Baseline BAF)-n_n =  mean baseline BAF for TL  "n" (L/kg-lipid)
   VL n)                  =  fraction of tissue that is lipid in aquatic organisms at TL "n"
   ffd                    =  fraction of the total concentration of chemical in water that is
                            freely dissolved

To derive national BAFs, EPA  uses national default values of lipid fraction  (ft) that are specific to
each TL.  The national default values of lipid fraction for TLs 2, 3, and 4 are:

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   ft(TL2)    =   0.019
   ft(TL3)    =   0.026
   ft(TL4)    =   0.030

These values reflect consumption-weighted mean values of the lipid fraction of aquatic
organisms that are commonly consumed throughout the United States. See section 6.2 of
EPA's TSD for a description of the technical basis of EPA's national default values for lipid
fraction  (USEPA2003a).

See section 6.3, Fraction Freely Dissolved, for information on computing the fraction of the total
concentration of chemical in water that is freely dissolved. See section 7, Examples, for
examples of calculated national BAFs.

6. Supporting Procedures

This section discusses selected supporting procedures used to calculate baseline and national
BAFs, including KoW, FCM, ffd, lipid content, and species TL.

b.l    KOW
KOW values were selected from ATSDR or HSDB sources with preference given to ATSDR. An
average log Kow was computed if a range or multiple values was reported from the selected
source.  The Kow values that were used are provided in the BAF Calculation Table.xlsx
spreadsheet, on the Chemical-Level Reference tab.

6.2    Food Chain Multiplier
For chemicals that fall under procedure #1 and either the Kow method or the BCF method is
being applied, or that fall under procedure #6 and the BCF method is being used, the FCM is
selected from Table 4-6 in the TSD (reproduced as Table 1 in this document) using the
chemical's Log Kow and linear interpolation (USEPA 2003a, p. 4-39). Chemicals with a Log Kow
less than 4 have an FCM equal to 1.0. The calculated FCMs for each chemical are provided in
the BAF Calculation Table.xlsx spreadsheet, on the Chemical-Level Reference tab.

6.3    Fraction Freely Dissolved
The fraction of the total concentration of chemical in water that is freely dissolved (ffd) is included
in both the BCF method and the national BAF equations. The equation used to compute ffd is
shown below (USEPA 2003a, p. 4-7):
                        ffd =
                              1 + POC  • Kow + DOC • 0.08 • Kow
where:

   POC     =   concentration of particulate organic carbon (POC) in water (kilograms of
               particulate organic carbon  per liter of water) (kg/L)
   DOC     =   concentration of dissolved  organic carbon (DOC) in water (kilograms of
               dissolved organic carbon per liter of water) (kg/L)
               n-octanol-water partition coefficient

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Table 1. Food Chain Multipliers for Trophic Levels 2, 3, and 4 (Source: USEPA 2003a, Table 4-
6, p. 4-39)
Log
Kow
4.0
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
5.0
5.1
5.2
5.3
5.4
5.5
5.6
Trophic
Level 2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Trophic Trophic Log Trophic Trophic Trophic Log Trophic Trophic Trophic
Levels Level 4 Kow Level 2 Levels Level 4 Kow Level 2 Levels Level 4
1.23 1.07 5.7 1 7.40 9.54 7.4 1 12.0 19.5
1.29 1.09 5.8 1 8.21 11.2 7.5 1 11.5 17.6
1.36 1.13 5.9 1 9.01 13.0 7.6 1 10.8 15.5
1.45 1.17 6.0 1 9.79 14.9 7.7 1 10.1 13.3
1.56 1.23 6.1 1 10.5 16.7 7.8 1 9.31 11.2
1.70 1.32 6.2 1 11.2 18.5 7.9 1 8.46 9.11
1.87 1.44 6.3 1 11.7 20.1 8.0 1 7.60 7.23
2.08 1.60 6.4 1 12.2 21.6 8.1 1 6.73 5.58
2.33 1.82 6.5 1 12.6 22.8 8.2 1 5.88 4.19
2.64 2.12 6.6 1 12.9 23.8 8.3 1 5.07 3.07
3.00 2.51 6.7 1 13.2 24.4 8.4 1 4.33 2.20
3.43 3.02 6.8 1 13.3 24.7 8.5 1 3.65 1.54
3.93 3.68 6.9 1 13.3 24.7 8.6 1 3.05 1.06
4.50 4.49 7.0 1 13.2 24.3 8.7 1 2.52 0.721
5.14 5.48 7.1 1 13.1 23.6 8.8 1 2.08 0.483
5.85 6.65 7.2 1 12.8 22.5 8.9 1 1.70 0.320
6.60 8.01 7.3 1 12.5 21.2 9.0 1 1.38 0.210
For deriving the national BAF ffd term, EPA uses national default DOC and POC values for
estimating a representative fraction of chemical that is freely dissolved in U.S. surface waters.
The national default values of DOC and POC are (USEPA 2003a, p. 6-2):
=  2.9x 1 0-6 kg/L [=2.9 mg/L]
=  0.5x 1 0-6 kg/L [= 0.5 mg/L]
   DOC
   POC

See section 6.3 of EPA's TSD for a description of the technical basis of EPA's national default
values for DOC and POC (USEPA 2003a).

The calculated ffd for each chemical is provided in the BAF Calculation Table. xlsx spreadsheet,
on the Chemical-Level Reference tab.

6.4    Lipid Content
The following hierarchical steps were used to select lipid content for baseline BAF calculation:

   1 .   Use measured values if provided.
   2.   Select a lipid content based on species from Tables 4-5 and 6-3 in the TSD (USEPA
       2003a, p. 4-37, 6-18).
   3.   Use an average species value from all studies in database with reported values.
   4.   Apply national lipid fractions based on assigned tropic level, as listed below:

       ft(TL2)   =  0.019
       ft(TL3)   =  0.026
       ft(TL4)   =  0.030

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Measured values, values in Tables 6-3 and 4-5 in the TSD, and database average species
values all were reported as lipid content (USEPA 2003a). To convert to a lipid fraction, the
values were multiplied by 0.01. No conversion was needed for national TL lipid fractions.

The selected lipid fraction for each BAF or BCF value is provided in the BAF Calculation
Table.xlsx spreadsheet, on the Baseline BAFs tab. To derive national BAFs, EPA uses national
default values of lipid fraction (ft) that are specific to each TL (see section 5, National BAFs).

6.5   Species Trophic Level
TL assignment information was primarily obtained from the EPA 2014 NHANES Fish
Consumption Rate Report and Fishbase.org and used to determine TLs for organisms in the
BCF and BAF data sources (USEPA 2014; Froese and Pauly 2015). When no primary source
was available, an expert fishery biologist and an expert invertebrate zoologist provided TL
identifications. These experts checked all TL identifications for correctness and consistency.
The following university websites were consulted to inform the experts' review:

   •  Central Michigan University Zooplankton of the Great Lakes (McNaught 2015)
   •  Encyclopedia of Life (Encyclopedia of Life 2015)
   •  The Murray-Darling Freshwater Research Centre Australian Freshwater Invertebrates
      Guide (Murray-Darling Freshwater Research Centre 2013)
   •  University of Maine School of Marine Science (University of Maine 2015)
   •  University of Michigan Animal Diversity Web (Myers et al. 2015)

The results of this analysis are provided in the BAF Calculation Table.xlsx spreadsheet,  on the
Species-Level Reference tab.

7. Examples

This section presents examples that collectively demonstrate the Kow, BCF, and BAF methods
of deriving baseline and national BAFs. The reader can compare these examples to the
companion  BAF Calculation Table.xlsx spreadsheet.

7.1   Kow  Method: Endrin

The Log Kow for endrin from ATSDR ranges from 5.34 to 5.6 (see BAF Calculation Table.xlsx,
Chemical-Level Reference tab). Thus, an average Log Kow value of 5.47 was used (Kow = 10547).
Based on the FCMs presented in Table 1, the FCMs for TLs 3 and 4 were interpolated to be
5.637 and 6.299, respectively. The FCM forTL2 is 1.0. Multiplying the interpolated FCMs by
Kow yielded  values of 295,120.92, 1,663,596.64, and 1,858,966.69 L/kg as the baseline BAFs
for TLs 2, 3, and 4, respectively. The calculation of endrin's baseline BAF for TL 4 is shown
below:

                        (Baseline BAF)TL 4= Kow-(FCM)TL4

               (Baseline BAF)TL4 =  105-47 • 6.299 =  1,858,966.69 L/kg-lipid

Converting  the baseline BAF expressed on a L/kg-lipid content to a national BAF expressed on
a L/kg-tissue basis relies on the national default values of lipid fraction (ft) and fraction of the

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total concentration of chemical in water that is freely dissolved (ffd). The calculation of ffd for
endrin is shown below:

                                             1
                       ffd~ 1 + POC  Kow + DOC 0.08  Kow

            c  	 	 	 f\ QOOO
             fd ~ 1 + 0.5 x 10~6 • 10547 + 2.9 x 10~6 •  0.08 • 10547 ~ '

The ffd value is substituted into the national BAF equation along with the trophic-specific value
for ft. Continuing with the endrin example and TL 4 (f{(-n_4)=0.030), the national BAF is calculated
using the following equation:

          National BAF(TL4) = [(Final Baseline BAF)TL4  (f^)TL4 + 1] (ffd)

     National BAF(TL4) =  [1,858,966.69 • 0.030 + 1] • 0.8223 = 45,862.41 L/kg-tissue

The corresponding values for TLs 2 and 3 were computed as 4,611.98 and 35,570.31 L/kg-
tissue, respectively. Rounding the values to two significant figures yields national BAF values of
4,600, 36,000, and 46,000 L/kg-tissue for TLs 2, 3, and 4, respectively.

72   BAF and BCF           Fluorene

The Log Kow for fluorene from ATSDR is 4.18 (Kow = 10418) (see BAF Calculation Table.xlsx,
Chemical-Level Reference tab). Based on the FCMs presented in Table 1, the FCMs for TLs 3
and 4 were interpolated to be 1.346 and 1.122, respectively. The FCM forTL2 is 1.0.

The calculation of ffd for fluorene is shown below:


                       ffd= 1 + POC  Kow + DOC 0.08  Kow

                                        1
            ffd ~ 1 + 0.5 x 10-6 • 10418 + 2.9 x 10-6 •  0.08 • 10418 ~ 0'9890

The ffd term is part of the equations for the BAF method, BCF method, and the national BAF
equation. Calculations of fluorene's baseline and national BAFs using the BAF and BCF
methods for TL 2 are explained in the sections that follow.

7.2.1  BAF Method
One field sample was available for fluorene with a BAF of 79,432.8  L/kg for an amphipod
(Pontoporeia hoyi) (TL 2). No BAF samples were available for TLs 3 and 4. A  baseline BAF is
calculated for each field sample available. The fraction lipid  (fy) in this equation is determined as
described in section 6.4, Lipid Content. In this example, fy was not provided with the source
data and was estimated as 0.03 based on data from the TSD's Tables 4-5 and 6-3 (USEPA
2003a).The calculation of baseline BAF using the BAF method for fluorene is shown below:

                                             [BAFi   1  1
                          (Baseline BAF)} =  ——^ - 1  • —
                                             L ffd     J  *f

                                                                              10

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                              [79432.8
            (Baseline BAF); = [ Q       ~ l  '     = 2,677,062.70 L/kg-lipid
If multiple baseline BAFs were derived, they were averaged prior to computing the national BAF
by calculating a geometric mean first by species, then by TL. In this example forfluorene,
however, only one field sample was available.

Thus, the calculated baseline BAF above, the ffd value, and the national default trophic-specific
value for fraction lipid (ft) are substituted into the national BAF equation. Continuing with the
fluorene example and TL 2 (ft(-n_2)=0.019), the national BAF is calculated using the following
equation:

          National BAF(TL2) =  [(Final Baseline BAF)TL2  (f^)TL2 + 1] (ffd)

      National BAF(TL2) = [2,677,062.7 • 0.019 + 1] • 0.9890 = 50,307.82 L/kg-tissue

Rounding this value to two significant figures yields a national BAF value using the BAF method
of 50,000 L/kg-tissue for TL 2.

7.2.2   BCF Method
Twelve laboratory-derived BCF values were available for fluorene for six species at all three
TLs. Focusing on TL 2 for this example, six BCF values were available for two species: an
oligochaete (Lumbriculus variegatus) and a water flea (Daphnia magna). The oligochaete
laboratory-derived BCF values are 330, 380,  490, 405, and 500 L/kg. The water flea BCF value
is 506 L/kg. In the BCF method, a baseline BAF is calculated for each laboratory-measured
BCF value. Calculation of the baseline BAF using the BCF method forfluorene using the BCF
value of 330 L/kg is shown below:

                     (Baseline BAF)j = (FCM)TLn


                                 r 330      I   1
             (Baseline BAF); = 1 • [^^ - lj • — =  11,088.54 L/kg-lipid
The other oligochaete baseline BAF values calculated using the BCF method are 12,773.67,
16,480.96, 13,616.24, and 16,817.99 L/kg-lipid. The water flea baseline BAF value calculated
using the BCF method is 10,212.12 L/kg-lipid. Multiple (Baseline BAF)i are averaged to a
(Baseline BAF)-n_n by taking a geometric mean first by species, then by TL. For fluorene at TL 2,
a geometric mean of 13,983.01 L/kg-lipid was calculated for the oligochaete and only one water
flea baseline BCF value of 10,212.12 L/kg-lipid was available. The geometric mean of those two
values is 1 1,949.74 L/kg-lipid, which is the derived baseline BAF for fluorene TL 2 using the
BCF method. The corresponding values for TLs 3 and 4 were computed as 17,652.38 and
23,784.77 L/kg-lipid, respectively.

The calculated baseline BAF values above, the ffd value, and the national default trophic-specific
value for fraction lipid (ft) are substituted into the national BAF equation. Continuing with the
                                                                               11

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fluorene example and TL 2 (ft(TL2)=0.019), the national BAF is calculated using the following
equation:

          National BAF(TL2) = [(Final Baseline BAF)TL2 • (f^)rL2 + 1]' (ffd)

        National BAF(TL2)  =  [11,949.74  • 0.019 + 1] • 0.9890 = 225.55 L/kg-tissue

The corresponding values for TLs 3 and 4 were computed as 454.92 and 706.71 L/kg-tissue,
respectively. Rounding the values to two significant figures yields national BAF values using the
BCF method of 230, 450, and 710 L/kg-tissue for TLs 2, 3, and 4, respectively.
                                                                               12

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