Aificial pond microcosms with pond water, including phytoplankton, periphyton, macrophytes, and larval gray tree frogs (Hyla versicolor), were treated with atrazine to achieve final aqueous concentrations of 0, 20, 200, or 2, 000 μg/L. Dissolved oxygen concentrations (DO) decreased to approx. 20 to 40% of their preexposure values in the 200‐ and 2, 000‐μg/L treatment groups within 1 d of atrazine addition. Dissolved oxygen in these microcosms returned to control concentrations by 10 d after exposure but declined again to approximately 60 to 80% of control values at 21 d after exposure and remained depressed for the remainder of the study. In the 200‐ and 2, 000‐μg/L treatment groups, pH decreased similarly within 1 d of atrazine exposure and returned to control values within the following 16 d. The DO and pH did not differ significantly between the 0‐ and 20‐μg/L groups or the 200‐ and 2, 000‐μg/L groups. Frogs from the two higher atrazine concentration treatment groups were 5% shorter and had 10% lower body mass at metamorphosis than those from the control and low atrazine concentration groups. No difference in length or body mass at metamorphosis was detectable between the 0‐ and 20‐μg/L groups or between the 200‐ and 2, 000‐μg/L groups. Larval period was 5% longer in the 2, 000‐μg/L group than in the 200‐μg/L group but did not differ from controls in any treatment group. No significant treatment‐related differences were detected for survival rate. The decrease in amphibian length and weight at metamorphosis may indicate a reduction in fitness in wild populations of anurans exposed to atrazine at 200 to 2, 000 μg/L.

Abstract-Artificial pond microcosms with pond water, including phytoplankton, periphyton, macrophytes, and larval gray tree frogs (Hyla versicolor), were treated with atrazine to achieve final aqueous concentrations of 0, 20, 200, or 2,000 g/L. Dissolved oxygen concentrations (DO) decreased to approx. 20 to 40% of their preexposure values in the 200-and 2,000-g/L treatment groups within 1 d of atrazine addition. Dissolved oxygen in these microcosms returned to control concentrations by 10 d after exposure but declined again to approximately 60 to 80% of control values at 21 d after exposure and remained depressed for the remainder of the study. In the 200-and 2,000-g/L treatment groups, pH decreased similarly within 1 d of atrazine exposure and returned to control values within the following 16 d. The DO and pH did not differ significantly between the 0-and 20-g/L groups or the 200-and 2,000-g/L groups. Frogs from the two higher atrazine concentration treatment groups were 5% shorter and had 10% lower body mass at metamorphosis than those from the control and low atrazine concentration groups. No difference in length or body mass at metamorphosis was detectable between the 0-and 20-g/L groups or between the 200-and 2,000-g/L groups. Larval period was 5% longer in the 2,000-g/L group than in the 200-g/L group but did not differ from controls in any treatment group. No significant treatment-related differences were detected for survival rate. The decrease in amphibian length and weight at metamorphosis may indicate a reduction in fitness in wild populations of anurans exposed to atrazine at 200 to 2,000 g/L.