Comparative toxicity of diuron on survival and growth of Pacific treefrog, bullfrog, red-legged frog, and African clawed frog embryos and tadpoles.

Abstract

The effects of the herbicide diuron on survival and growth of Pacific treefrog (Pseudacris regilla), bullfrog (Rana catesbeiana), red-legged frog (Rana aurora), and African clawed frog (Xenopus laevis) embryos and tadpoles were determined in static-renewal tests. P. regilla and X. laevis embryos had reduced growth and developed increased deformities in diuron concentrations over 20 mg/L. Hindlimb bud and forelimb development were retarded in R. aurora following 14 days exposure to diuron concentrations of > 7.6 mg/L. Mean 14-day LC50s for P. regilla and X. laevis tadpoles were 15.2 and 11.3 mg/L diuron, respectively. The 21-day LC50 for R. catesbeiana tadpoles was 12.7 mg/L diuron. The 14-day LC50 for R. aurora tadpoles was 22.2 mg/L. The lowest NOAELs calculated in embryo tests were 14.5 mg/L for P. regilla (10 days) and 7.6 mg/L diuron for X. laevis (4 days). The lowest NOAELs calculated in tadpole tests were: P. regilla, 14.5 mg/L (14 days); R. catesbeiana, 7.6 mg/L (21 days); R. aurora, 7.6 mg/L (14 days); and X. laevis, > 29.1 mg/L (14 days). Diuron concentrations having an effect on survival, growth, and malformation in the laboratory were much higher than those found in normal field spray situations; field studies would be needed to determine the hazard to amphibians in areas of localized pooling of recently applied herbicide in the environment.