ACUTE AND CHRONIC TOXICITY OF AMMONIUM-NITRATE FERTILIZER TO AMPHIBIANS FROM SOUTHERN ONTARIO

Increasing nitrate levels in surface and ground waters are of global c oncern. Effects of nitrates on human health are well documented, but e ffects on amphibians have received little attention. I exposed Bufo am ericanus (American toad), Pseudocris triseriata (chorus frog), Rana pi piens (leopard frog), and Rana clamitans (green frog) tadpoles to ammo nium nitrate fertilizer in water. In acute tests, mortality varied amo ng species (96-h LC50; 13.6-39.3 mg/L NO3-N) and significant weight lo ss occurred. In chronic tests (100 d; 0, 2.5, 5, 10 mg/L NO3-N) chorus frog and leopard frog tadpoles had significantly lower survivorship i n the 10-mg/L treatments, but green frog survivorship was not affected . Number of chorus frogs metamorphosing was significantly lower in the 10-mg/L treatment, but development time was not affected. In acute ex posures, reduced activity, weight loss, and physical abnormalities wer e observed. Toxic effects of ammonium nitrate occurred in all four spe cies at concentrations that are commonly exceeded in agricultural area s globally. Nitrate fertilizers may play a role in the apparent global amphibian decline.