Mw. Hornung et al., TOXIC EQUIVALENCY FACTORS OF POLYBROMINATED DIBENZO-P-DIOXIN, DIBENZOFURAN, BIPHENYL, AND POLYHALOGENATED DIPHENYL ETHER CONGENERS BASED ONRAINBOW-TROUT EARLY-LIFE STAGE MORTALITY, Toxicology and applied pharmacology, 140(2), 1996, pp. 227-234
Polybrominated and polychlorinated biphenyls (PBBs/PCBs), dibenzo-p-di
oxins (PBDDs/PCDDs), dibenzofurans (PBDFs/PCDFs), and diphenyl ethers
(PBDEs/PCDEs) are persistent, lipophilic environmental contaminants th
at may pose a risk to fish early life stage survival. To determine thi
s potential risk, a rainbow trout early life stage mortality bioassay
was used in which the potency of individual polybrominated chemicals w
as compared to the potency of the most potent polychlorinated chemical
in these classes, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Followi
ng injection of newly fertilized rainbow trout eggs, fish-specific tox
ic equivalency factors (TEFs) were calculated as the molar ratio of TC
DD LD50 to brominated compound LD50. Signs of toxicity were identical
to those produced by polychlorinated TCDD-like chemicals and included
yolk sac edema, pericardial edema, multifocal hemorrhages, reduced gro
wth, and craniofacial malformations. Polybrominated dibenzo-p-dioxins,
dibenzofurans, and biphenyls exhibited decreased potency with increas
ed bromine substitution. Only 2,3,7,8-TBDD was more potent than 2,3,7,
8-TCDD, whereas other polybrominated dibenzo-p-dioxins were equipotent
or less potent than identically substituted polychlorinated dibenzo-p
-dioxins in this assay. Although two PBDF congeners were equipotent to
identically substituted PCDFs, 2,3,7,8-TBDF was 9-fold more potent th
an 2,3,7,8-TCDF. Both 3,3',4,4'-TBB and 3,3',4,4',5,5'-HxBB were 10-fo
ld more potent than identically substituted polychlorinated biphenyls.
The halogenated diphenyl ethers and di-ortho polybrominated biphenyls
were inactive in this assay. Thus, in this in vivo assay the polybrom
inated and polychlorinated TCDD-like chemicals were not always equally
potent. To assess the risk posed by mixtures of these chemicals to fe
ral fish populations, fish-specific TEFs for both polybrominated and p
olychlorinated chemicals should be used. (C) 1996 Academic Press, Inc.