Page 856 - The Toxicology of Fishes

836 The Toxicology of Fishes

TABLE 21.1
Toxic Equivalency Factors (TEFs) for Halogenated
Aromatic Hydrocarbon Dioxin-Like Potency in Fish
Compound TEF

2,3,7,8-TCDD 1
1,2,3,7,8-PeCDD 1
1,2,3,4,7,8-HxCDD 0.5
1,2,3,6,7,8-HxCDD 0.01
1,2,3,7,8,9-HxCDD 0.01
1,2,3,4,6,7,8-HpCDD 0.001
OCDD <0.0001
2,3,7,8-TCDF 0.05
1,2,3,7,8-PeCDF 0.05
2,3,4,7,8-PeCDF 0.5
1,2,3,4,7,8-HxCDF 0.1
1,2,3,6,7,8-HxCDF 0.1
1,2,3,7,8,9-HxCDF 0.1
2,3,4,6,7,8-HxCDF 0.1
1,2,3,4,6,7,8-HpCDF 0.01
1,2,3,4,7,8,9-HpCDF 0.01
OCDF 0.0001
3,4,4′,5-TCB (PCB-81) 0.0005
3,3′,4,4′-TCB (PCB-77) 0.0001
3,3′,4,4′,5-PeCB (PCB-126) 0.005
3,3′,4,4′,5,5′-HxCB (PCB-169) 0.00005
Note: World Health Organization ecological risk values
can be found in van den Berg, M. et al., Environ.
Health Perspect., 106(12), 775–792, 1998.

potency factors of AhR agonists that are specific to an endpoint, life stage, and species, whereas TEFs
are more generic potency estimates that are used for ecological risk assessments (van den Berg et al.,
1998). A TEF is defined as the TCDD ED (effective dose in which 50% of test organisms show a
50
response) or TCDD LD (effective dose in which 50% of test organisms are killed) divided by the ED 50
50
or LD of the individual congener. For example, the fish-specific TEF for PCB 126 based on early-life-
50
stage mortality in rainbow trout (Zabel et al., 1995a) is derived as follows:
PCB 126 TEF = 374 pg/g wet egg (TCDD LD 50 = . 0 005
74,0000 pg/g wet egg (PCB 126 LD 50 )

The concentration of a congener in an organism is multiplied by its respective TEF to determine the
TEQ concentration contributed by that congener. TEQ concentrations for all the individual congeners
in an organism are then added to calculate the total TEQ concentration contributed by the entire mixture
of PCB, PCDD, and PCDF congeners present in the organism. To assess risk, this total TEQ concentration
is compared to the administered dose or concentration of TCDD in the organism, determined in controlled
laboratory studies, to cause toxicity.
Using lake trout as an example, early-life-stage mortality due to contamination of eggs with dioxin-
like PCBs, PCDDs, and PCDFs can be evaluated by calculating the total concentration of TEQs in eggs
(TEQ ). The TEQ for a mixture of n congeners equals the sum of the TEQ values for each congener
egg
egg
egg
(pg TEQ per g wet egg), which is the product of the concentration of the congener in the egg (C ; pg
egg
congener per g wet egg) multiplied by the fish-specific TEF of the congener (pg TEQ per pg congener),
where i is a specific congener:
TEQ = ∑(C ) (TEF) i
egg
egg i