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

A recent ecological risk assessment of the herbicide atrazine found that th e ecosystems at greatest risk within North America are the streams, rivers, and reservoirs of the midwestern corn-growing regions. Habitats adjacent t o application areas could be exposed to high levels of atrazine during peri ods of amphibian activity such as breeding and migration. Because fertilize r application coincides both spatially and temporally with atrazine applica tion in agricultural areas, we tested the effects of atrazine and nitrate o n northern leopard free (Rana pipiens) larvae in the laboratory. Larvae wer e exposed to atrazine (0, 20, and 200 mug/L) and nitrate (0, 5, and 30 mg N O3-N/L) from first-feeding stage through metamorphosis in a factorial desig n. Atrazine concentrations in metamorphosed juveniles were approximately si x times the concentration in the water, indicating bioconcentration of atra zine 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 sl owed growth of larvae. Though this growth inhibition is statistically signi ficant, it is probably not biologically important when compared with natura l variation in the environment. Thus, concentrations of atrazine and nitrat e commonly found in the environment do not appear to pose a significant thr eat to R. pipiens larvae through direct toxicity.