Use of the Bioaccumulation Factor to Screen Chemicals for Bioaccumulation
Potential
Jed Costanza, David G. Lynch, Robert S. Boethling, and Jon A. Arnot
1. Default Terms and Equations in BCFBAFTM
The following terms and values are used for predicting BAF values by the
BCFBAFTM v3.01 program. These values and terms were slightly modified from those
presented by Arnot and Gobas (2003) and Arnot et al. (2008). The BAF-QSAR model
represents the steady-state condition where the rate of chemical uptake into the fish is
equal to the rate of chemical elimination as:
BAF  1  LB  
k1    k D        LD  K OW
k 2  k E  kG  k M
The terms and units in this equation are:
LB - lipid fraction of the fish for each trophic level (unitless)
k1 - chemical uptake rate constant from water (L/kg/d)
 - bioavailable solute fraction of the total chemical concentration in the water,
i.e., only the dissolved fraction can permeate membranes of the respiratory
surface area (unitless)
kD - rate constant for chemical uptake from diet (kg/kg/d)
β - food web biomagnification factor (L/kg)
τ - food web trophic dilution factor (unitless)
LD - volumetric lipid fraction for primary producers (i.e., phytoplankton, algae) at
the base of the aquatic food web (unitless).
KOW - octanol/water partitioning coefficient (unitless) to represent chemical
partitioning from water into the primary producers at the base of the food web.
k2 - rate constant for chemical elimination at the gill surface (1/d)
kE - rate constant for fecal egestion (1/d)
kG - growth dilution rate constant (1/d)
kM - rate constant for whole body, primary metabolic biotransformation (1/d)
Fixed Values by Fish Trophic-Level (TL):
Upper TL
0.107
62.7
0.01
1.53
0.0000005
0.0000005
LB
β
LD
W (kg)
Xpoc
Xdoc
Middle TL
0.0685
30.1
0.01
0.184
0.0000005
0.0000005
Lower TL
0.0598
16.1
0.01
0.096
0.0000005
0.0000005
W is the fish weight (mass).
Xpoc is the assumed concentration of particulate organic carbon (POC) in water (kg/L).
Xdoc is the assumed concentration of dissolved organic carbon (DOC) in water (kg/L).
The remaining values are calculated using the following equations (see Appendix K of
BCFBAF™ Help file):
The bioavailable fraction of a chemical in water is estimated as:

1
1  0.35  X poc  K OW  0.08  X doc  K OW
Where the values of 0.35 (L/kg) [1] and 0.08 (L/kg) [2] are proportionality constants
characterizing the sorptive capacities of POC and DOC relative to octanol. When using
the assumed default values for Xpoc and Xdoc the equation simplifies to:

1
.
1  2.15  10 7  K OW
The rate constant for chemical uptake from water:
k1 
1

1  0.4
 0.01 
W
K OW 

The rate constant for chemical uptake from diet:
0.02  W 0.15  exp 0.06  T 
kD 
where T is temperature assumed to be 10 °C.
0.00000005  K OW  2
The rate constant for chemical elimination at the gill surface:
k2 
k1
LB  K OW
The rate constant for chemical elimination through fecal egestion:
k E  0.125  k D
The rate constant for chemical elimination through fish growth:
k G  0.000502  W 0.2
The food web trophic dilution factor:




0.0065


Upper TL   

 0.25
 k  0.25 
 0.0065 
 M 0.01

 





0.01


Middle TL   

 0.25
 k  0.03 
 0.01 
 M 0.01

 

2
1




0.02


Lower TL   

 0.25
 k  0.016 
 0.02 
 M 0.01




0.5
The kM QSAR (see Section 7.2 of BCFBAF™ Help file) uses the following regression:
Log k M   0.30734215  Log K OW   0.0025643319  M w  1.53706847  1 Fi  ni
i
where Fi is a list of fragments provided in Appendix F of BCFBAF™ Help file and ni is
the number of times individual fragments occurs in the molecule.
2. Aqueous Chemical Concentration in the BAF Equation
The chemical concentration in fish at steady state as a function of the total chemical
concentration in water is:
(1)
Where kTotal is the sum of the first order elimination rate constants: k2, kE, kG and kM.
For a BAF based on total water concentration:
(2)
Substituting Eq. 1 into Eq. 2 yields:
(3)
Cwater total is divided out to get a BAF based on total water concentration, but  remains on
the right-hand side of the equation. The BAFs reported in the main paper are for total
water concentration. The default Arnot and Gobas BCF and BAF model predictions in
the BCFBAF model are those based on the total water concentration only and the
assumed default fractions of POC and DOC in the water column.
The dissolved concentration (Cwd) can be calculated from the total water concentration
and the bioavailable solute fraction ():
(4)
Substituting Eq 4 into Eq 1 yields:
(5)
For BAF based on dissolved water concentration:
(6)
Substituting Eq. 5 into Eq. 6 yields:
(7)
Cwd is divided out to get a BAF based on dissolved water concentrations,  is not on the
right-hand side of the equation.
3. Identity of 43 Persistent Organochlorines in Figure 2
CASRN
Name
038444-85-8
007012-37-5
038444-77-8
038444-93-8
036559-22-5
041464-39-5
041464-40-8
041464-43-1
033025-41-1
052663-58-8
032598-11-1
032690-93-0
052663-62-4
052663-60-2
065510-45-4
052663-61-3
038379-99-6
041464-51-1
038380-01-7
037680-73-2
032598-14-4
038380-03-9
031508-00-6
038380-05-1
038411-22-2
035065-28-2
052712-04-6
051908-16-8
038380-04-0
052663-63-5
035065-27-1
035065-30-6
038411-25-5
052663-70-4
052663-67-9
035065-29-3
052663-69-1
052663-68-0
035694-08-7
040186-71-8
052663-76-0
002385-85-5
2,3,4'-PCB
2,4,4'-PCB
2,4',6-PCB
2,2',3,3'-PCB
1,1'-Biphenyl, 2,2',3,4'-tetrachloro2,2',3,5'-PCB
2,2',4,5'-PCB
1,1'- Biphenyl, 2,3,3',4'- tetrachloro2,3,4,4'-PCB
1,1'- Biphenyl, 2,3,4',6- tetrachloro2,3',4',5-PCB
2,4,4',5-PCB
2,2',3,3',4-Pentachlorobiphenyl
2,2',3,3',6-PCB
2,2',3,4,4'-PCB
2,2',3,5,5'-PCB
2,2',3,5',6-PCB
2,2',3',4,5-PCB
2,2',4,4',5-PCB
2,4,5,2',5'-PCB
1,1'-Biphenyl, 2,3,3',4,4'-pentachloro2,3,3',4',6-PCB
2',3,4,4',5'-PCB
2,2',3,3',4,6'-PCB
2,3,6,2',3',6'-PCB
2,3,4,2',4',5'-PCB
2,2',3,4,5,5'-Hexachlorobiphenyl
1,1'-Biphenyl, 2,2',3,4',5,5'-hexachloro2,2',3,4',5',6-PCB
2,2',3,5,5',6-Hexachlorobiphenyl
2,4,5,2',4',5'-PCB
2,2',3,3',4,4',5-Heptachlorobiphenyl
1,1'-Biphenyl, 2,2',3,3',4,5,6'-heptachloro1,1'-Biphenyl, 2,2',3,3',4,5',6'-heptachloro1,1'-Biphenyl, 2,2',3,3',5,5',6-heptachloro2,2',3,4,4',5,5'-Heptachlorobiphenyl
2,2',3,4,4',5',6-Heptachlorobiphenyl
2,2',3,4',5,5',6-Heptachlorobiphenyl
2,2',3,3',4,4',5,5'-PCB
1,1'-Biphenyl, 2,2',3,3',4,5',6,6'-octachloro1,1'-Biphenyl, 2,2',3,4,4',5,5',6-octachloroMirex
039801-14-4
1,3,4-Metheno-1H-cyclobuta[cd]pentalene,
1,1a,2,2,3,3a,4,5,5,5a,5b-undecachlorooctahydro- (9CI)
1. Seth R, Mackay D, Muncke J. 1999. Estimating the Organic Carbon Partition
Coefficient and its Variability for Hydrophobic Chemicals. Environmental Science
and Technology 33(14): 2390-2394.
2. Burkhard LP. 2000. Estimating Dissolved Organic Carbon Partition Coefficients
for Nonionic Organic Chemicals. Environmental Science and Technology 34(22):
4663-4668.