Toxic effects of pyrethroids in tadpoles of Physalaemus gracilis (Anura: Leptodactylidae).

Pyrethroid insecticides are one of the most commonly used pesticide groups, but these compounds have brought risks to non-target species, such as amphibians. This study evaluated the toxicological effects (mortality, swimming activity and oral morphology) caused to a South American species of anuran amphibian, Physalaemus gracilis, exposed to the pyrethroids cypermethrin and deltamethrin. Total spawnings of this anuran were collected in the natural environment and transported to the laboratory where they were kept under controlled conditions. Chronic assays were defined between 0.1 and 0.01 mg L-1 of cypermethrin, and 0.009 and 0.001 mg L-1 of deltamethrin. For cypermethrin, a further chronic toxicity test was performed at 0.05 and 2.0 mg L-1, with hatchlings at stages S.20-S.25. Cypermethrin and deltamethrin were lethal enough to kill over 70% of exposed tadpoles in 1 week at concentrations that can be found in nature (0.01-0.1 mg L-1). The exposure effects also influenced swimming activity and caused changes in oral morphology, which would make it difficult for the animals to survive in their natural habitat. Both pyrethroids presented a risk for P. gracilis, so they should be re-evaluated for non-target wild species.