RP8 Ecotoxicology of Agrochemicals and Pharmaceuticals
Thursday, 17 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(VIL-1117-725879) Effects of three fungicides on fathead minnow ovarian steroid synthesis in vitro.

Villeneuve, D.¹, Makynen, E.¹, Ankley, G.¹, ¹ U.S. EPA Mid-Continent Ecology Division, Duluth, MN, USA

ABSTRACT- A number of conazole and heterocyclic amine fungicides that depress fungal growth by inhibiting 14-demethylase, a cytochrome P450 that plays a key role in ergosterol biosynthesis, also have potential to disrupt the vertebrate endocrine system through effects on enzymes involved in steroid synthesis and/or metabolism. Three of these compounds, prochloraz (PRO), fenarimol (FEN), and ketoconazole (KTZ), were recently evaluated in a short-term fathead minnow reproduction test and were shown to affect spawning success to various degrees. The purpose of this study was to help define the mechanisms through which these three fungicides elicited their effect on fathead minnow reproduction using a series of in vitro bioassays relevant to steroid biosynthesis. All three chemicals inhibited in vitro testosterone (T) production in fathead minnow ovary tissue, with KTZ causing significant inhibition at concentrations greater than 3.3 g/L (6.2 nM), and PRO and FEN causing significant inhibition at 0.3-1.0 mg/L (0.9-2.6 M). In addition to reduced in vitro estradiol production concomitant with reduced T synthesis, all three chemicals were shown to inhibit aromatase activity in both brain and ovary tissue homogenates exposed in vitro, with PRO and KTZ causing significant inhibition at concentrations greater than 1.0 M, and FEN causing inhibition at concentrations greater than 75 M. Additional in vitro exposures with selective addition of steroid precursors were used to help identify the specific steroidogenic enzymes affected by each chemical. Results of this study help to establish important linkages between mechanisms of action at the biochemical level and ecologically relevant outcomes. Such linkages should help strengthen the use of mechanism-specific biomarkers and in vitro assays in ecological risk assessments related to endocrine disrupting chemicals. The contents of this abstract do not necessarily reflect U.S. EPA policy.

Key words: steroidogenesis, endocrine disruption, Pimephales promelas, aromatase