John Wiley & Sons, Ltd.

Cross‐species comparison of relative potencies and relative sensitivities of fishes to dibenzo‐p‐dioxins, dibenzofurans, and polychlorinated biphenyls in vitro

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Dioxin‐like compounds (DLCs) of varying toxicities are found in complex mixtures. The toxic equivalency factor (TEF) approach was developed based on the potency of a DLC relative to the potency of TCDD to streamline risk assessment. One limitation of the TEF approach is uncertainty regarding differences in relative potency (ReP) of DLCs among different species. RePs among fishes are limited relative to RePs among birds and mammals, and TEFs for fishes are based entirely on the model species, rainbow trout (Oncorhynchus mykiss). An in vitro liver explant assay was utilized to characterize species‐specific responses with regard to up‐regulation of CYP1A transcript following exposure to six DLCs in rainbow trout, white sturgeon (Acipenser transmontanus), lake sturgeon (Acipenser fulvescens), and northern pike (Esox lucius). Differences in sensitivities were observed among species following exposure to DLCs. RePs developed from liver explants of rainbow trout were comparable to RePs developed from embryo‐toxicity assays. Differences in RePs between species with the least and greatest RePs were up to 40‐fold. To compare RePs among species, concentrations of DLCs in fish eggs in the Fraser River and in Lake Ontario were used to calculate toxic equivalents (TEQs) determined from TEFs or TCDD equivalents (TCDD‐EQs) determined from RePs. TEQs underestimated TCDD‐EQs for white sturgeon, lake sturgeon, and northern pike, indicating uncertainty in application of TEFs to diverse fishes. This article is protected by copyright. All rights reserved

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