Relative Potencies of Individual Polychlorinated Naphthalenes to Induce Dioxin-Like Responses in Fish and Mammalian In Vitro Bioassays

Abstract

A growing body of evidence suggests that polychlorinated naphthalenes (PCNs) may be fairly widespread environmental contaminants. This may be cause for concern because exposure to PCNs has been linked to dioxin-like biological responses in a wide variety of species. This study used three in vitro bioassays to characterize the dioxin-like potency of 18 individual PCN congeners and 1 PCN metabolite. The PLHC-1 fish hepatoma cell bioassay was relatively insensitive to PCNs. At the concentrations tested, only 1,4 di-CN and 2,4-dichloro-1-napthol caused significant induction of ethoxyresorufin O-deethylase (EROD) activity in the PLHC-1 assay. In vitro EROD and luciferase assays using recombinant H4IIE rat hepatoma cells were more responsive to PCNs. Structure-activity relationships were observed both in terms of the degree of chlorination and the positions of chlorine substitutions. Hexa-chlorinated naphthalenes (CNs), exhibiting relative potencies (REPs) around 10⁻³ (relative to TCDD), were the most potent congeners tested. Penta-CNs were also rather potent, yielding REPs between 10⁻³ and 10⁻⁷. Tetra-, tri-, di-, and mono-CNs were less active. REPs for the active congeners were similar to those for some PCBs. The relative potency estimates reported here contribute to an emerging body of information that will aid determination of the relative contribution of PCNs to the total dioxin-like activity associated with environmental samples.