Toxicity of six pesticides to common frog (Rana temporaria) tadpoles.

Amphibian species inhabiting agricultural areas may be exposed to pesticides during their aquatic larval phase. We tested the toxicity of six commonly used pesticides on Rana temporaria spawn and tadpoles. In acute tests, tadpoles were exposed to relatively high concentrations of azoxystrobin, cyanazine, esfenvalerate, MCPA ([4-chloro-2-methylphenoxy] acetic acid), permethrin, and pirimicarb for 72 h. Chronic exposure tests were performed from fertilization to metamorphosis with azoxystrobin, cyanazine, and permethrin at concentrations similar to those found in surface waters in agricultural areas in Sweden. The most lethal pesticides in the acute exposure were azoxystrobin, permethrin, and pirimicarb. Also, negative effects on the growth of the tadpoles were observed with azoxystrobin, cyanazine, and permethrin. The chronic exposure at lower pesticide concentrations did not result in increased mortality or impaired growth. However, we found a positive effect of permethrin on growth and size at metamorphosis. The results suggest that the examined pesticides can inflict strong negative effects at high concentrations but have no or relatively weak effects on R. temporaria spawn or tadpoles at concentrations found in Swedish surface waters.