Figure 30.5. Relative response to induction 7 days after i.p. injection of PCB-77 (1.0 mg/kg) in three species of Hudson River (HR) fish collected near Poughkeepsie, NY, or from a hatchery (REF). EROD activity in PCB treated fish is expressed relative to control fish from the same sites injected with corn oil (C.O.) alone. * Indicates significantly different (P < 0.05) from control response.

between the two populations, suggesting that mechanisms other than differential uptake or efflux were responsible for variable susceptibilities. Furthermore, CYPlA-encoded ethoxyresorufin O-deethylase (EROD) activity was not significantly inducible by dermal administration of TCDD in adult killifish from Newark Bay. In contrast, dose-responsive induction of EROD activity, up to thirty-fold, was observed in killifish from Tuckerton Harbor.

Resistance to PCBs was also observed in killifish from Newark Bay and two sites in the main stem HR (Elskus et al., 1999). Environmentally-exposed adult killifish from Newark Bay and the HR exhibited ten-fold higher levels of total PCBs than those from reference sites. However, there were no site-related differences in measures of reproductive success including number of eggs deposited, embryo and larval survival, and larval length. Treatment of depurated adults from Newark Bay and a reference site with medium and high doses of an environmentally relevant mixture of PCBs did not result in site-or dose-related differences in hatching success, larval growth, or larval mortality. However, hepatic CYP1A expression was not inducible in adult fish from Newark Bay, but was not inducible in adults from the reference site. Furthermore, hepatic, gill, gut, and heart CYP1A expression was induced in larval offspring of reference site parents, but not in those of Newark Bay parents. This demonstrated that the resistant pheno-type in killifish from Newark Bay was heritable to at least the F1 generation and that modulated gene inducibility was not tissue-specific. Resistance to overt toxicity and CYPlAexpressionfrom PCBs and PAHs has also been observed in killifish from two other highly polluted locales, New Bedford Harbor, Massachusetts, (PCBs) (Nacci et al., 1999), and the Elizabeth River, Virginia (PAHs) (Meyer and Di Giulio, 2002), suggesting that resistance in fish may be a common occurrence in chronically exposed populations.

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