Effects of atrazine and nitrate on northern leopard frog (Rana pipiens) larvae exposed in the laboratory from posthatch through metamorphosis

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Abstract
A ecent ecological rsk assessment of the herbicideatrazinefound that theecosystemsat greatest risk within North America are the streams, rivers, and reservoirs of the midwestern corn‐growing regions. Habitats adjacent to application areas could be exposed to high levels of atrazine during periods of amphibian activity such as breeding and migration. Because fertilizer application coincides both spatially and temporally with atrazine application in agricultural areas, we tested the effects of atrazine and nitrate on northern leopard frog (Rana pipiens) larvae in the laboratory. Larvae were exposed to atrazine (0, 20, and 200 μg/L) and nitrate (0, 5, and 30 mg NO3‐N/L) from first‐feeding stage through metamorphosis in a factorial design. Atrazine concentrations in metamorphosed juveniles were approximately six times the concentration in the water, indicating bioconcentration of atrazine by larvae. Atrazine, nitrate, and their interaction had no significant effect on development rate, percent metamorphosis, time to metamorphosis, percent survival, mass at metamorphosis, or hematocrit. However, nitrate slowed growth of larvae. Though this growth inhibition is statistically significant, it is probably not biologically important when compared with natural variation in the environment. Thus, concentrations of atrazine and nitrate commonly found in the environment do not appear to pose a significant threat to R. pipiens larvae through direct toxicity.