BARBEAU, T.R.*; University of Florida: Decreased Gonadal Steroidogenesis and Increased Plasma Insulin-Like Growth Factor-1 in Frogs Exposed to Aquatic Nitrates

Contamination of aquatic ecosystems with anthropogenic sources of nitrates has become of increasing concern to researchers in the past few years. Aquatic nitrates in North America range from less than 1 to greater than 100 ppm, and globally can exceed 300 ppm from runoff of nitrogen-based fertilizers, unregulated livestock wastes, and improperly treated industrial and human waste. Frogs are especially at risk for exposure to nitrates because they occupy aquatic systems during egg, tadpole, and reproductive adult stages. Laboratory studies on tadpoles have shown altered growth rates, reduced feeding, and developmental abnormalities after exposure to nitrates between 2.5 to 500 ppm. No study has examined the impact of exposure to sublethal doses of nitrate on reproduction in adult frogs. Here I make the first report that aquatic exposure of adult, female Xenopus laevis to sublethal doses (110 and 219 ppm) of nitrates inhibits ovarian synthesis of testosterone and estrogen, and increases plasma insulin-like growth factor-1. These hormones are necessary for normal development, growth, and reproduction in amphibians and many other vertebrates. Endocrine disruption by nitrates raises new concerns for contamination of watersheds by anthropogenic sources of nitrates and its potential impacts on amphibian declines and deformations.