Relative potencies of individual polychlorinated naphthalenes to induce dioxin-like responses in fish and mammalian in vitro bioassays

A growing body of evidence suggests that polychlorinated naphthalenes (PCNs ) may be fairly widespread environmental contaminants. This may be cause fo r concern because exposure to PCNs has been linked to dioxin-like biologica l responses in a wide variety of species. This study used three in vitro bi oassays to characterize the dioxin-like potency of 18 individual PCN congen ers and 1 PCN metabolite. The PLHC-1 fish hepatoma cell bioassay was relati vely insensitive to PCNs. At the concentrations tested, only 1,4 di-CN and 2,4-dichloro-1-napthol caused significant induction of ethoxyresorufin O-de ethylase (EROD) activity in the PLHC-1 assay. In vitro EROD and luciferase assays using recombinant H4IIE rat hepatoma cells were more responsive to P CNs. Structure-activity relationships were observed both in terms of the de gree of chlorination and the positions of chlorine substitutions. Hexa-chlo rinated naphthalenes (CNs), exhibiting relative potencies (REPs) around 10( -3) (relative to TCDD), were the most potent congeners tested. Penta-CNs we re 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 s imilar 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 asso ciated with environmental samples.