Ew. Zabel et al., INTERACTIONS OF POLYCHLORINATED DIBENZO-P-DIOXIN, DIBENZOFURAN, AND BIPHENYL CONGENERS FOR PRODUCING RAINBOW-TROUT EARLY-LIFE STAGE MORTALITY, Toxicology and applied pharmacology, 134(2), 1995, pp. 204-213
Fish-specific toxic equivalency factors (TEFs), which relate the toxic
potency of polyhalogenated aromatic hydrocarbons (PHAHs) to 2,3,7,8-t
etrachlorodibenzo-p-dioxin (TCDD) based on the endpoint of early life
stage mortality, have been used in assessing the risk to fish early Li
fe stage survival of complex mixtures of PHAHs in feral fish eggs, Use
of TEFs assumes that PHAH congeners act additively. However, this has
not been unequivocally determined. Isobolograms and a probit model we
re used to assess the validity of the additivity assumption by determi
ning the significance of interactions between pairs of polychlorinated
dibenzo-p-dioxin (PCDD), dibenzofuran (PCDF), and biphenyl (PCB) cong
eners when injected into newly fertilized rainbow trout eggs in ratios
bracketing those found in feral lake trout eggs from the Great Lakes,
The majority of congener pairs tested acted additively in causing rai
nbow trout early life stage mortality: [1,2,3,7,8-pentachlorodibenzo-p
-dioxin (1,2,3,7,8-PCDD)/TCDD]; [2,3, 4,7,8-pentachlorodibenzofuran (2
,3,4,7,8-PCDF)1,2,3,7,8-PCDD]; (2,3,4,7,8-PCDF/TCDD), (2,3,7,8-tetrach
lorodibenzofuran/2,3,4,7,8-PCDF); [3,3',4,4'-tetrachlorobiphenyl (PCB
77)/ 3,3',4,4',5-pentachlorobiphenyl (PCB 126)1; [2,3,3',4,4'-pentachl
orobiphenyl (PCB 105)/TCDD]; (2,2',4,4',5,5'-hexachlorobiphenyl/TCDD);
(PCB 105/PCB 126); and (2,3',4,4',5-pentachlorobiphenyl/PCB 126). The
only pairs showing evidence of a statistically significant interactio
n that deviated from additivity were (TCDD/PCB 77) and (TCDD/PCB 126).
Taken together, these results suggest that the use of fish-specific T
EFs to determine TCDD equivalents contributed by individual congeners
in a fish egg sample and then adding these TCDD equivalents to determi
ne the total amount contributed by all congeners may not exactly predi
ct the mortality risk posed to fish early life stages by the mixture o
f TCDD-like congeners in the eggs. However, the relatively small devia
tions from additivity in the rainbow trout sac fry mortality test (1-
to 4-fold) are less than traditional uncertainty factors used in nonca
ncer risk assessments (10-fold/factor) and are not sufficient to warra
nt a change away from the additivity assumption in assessing the risk
to fish early life stage mortality posed by TCDD and related compounds
in eggs. (C) 1995 Academic Press, Inc.