Toxicidade de três inseticidas em um vertebrado não alvo, usando como modelo Physalaemus gracilis (Anura: Leptodactylidae)

Abstract

Agrochemicals used in agriculture has been a growing concern in developing countries due to the non-point pollution of different compartments such as the aquatic environment. Physalaemus gracilis (Anura: Leptodactylidae), popularly known as chorona frog, is a species of amphibian widely distributed in southern Brazil, Uruguay, Paraguay and Argentina and found in water sources close to agroecosystems. The aim of this study was to evaluate the toxicity of chlorpyrifos, cypermethrin and fipronil commercial formulation in P. gracilis. To evaluate the lethal and sublethal effects of chlorpyrifos commercial formulation, acute and chronic toxicity assays were performed in P. gracilis, and to evaluate the sublethal effects of cypermethrin and fipronil commercial formulation, chronic assay were performed. To obtain the larvae, total spawnings were collected in the wild with less than 24 hours of oviposition. Toxicity assays were initiated when larvae reached stage 25 of Gosner (1960). Acute assay had a duration of 96 h and chronic assay 168 h. Ten larvae were placed in a glass container containing 500 mL solution of different concentrations of the insecticide, with 6 replicates, totaling 60 larvae for each treatment. Control was carried out in the same design, without addition of the insecticide in the water. The sublethal effects observed were changes in swimming activity, oral morphology and biochemical biomarkers for chlorpyrifos. Only biochemical biomarkers were determined for cypermethrin and fipronil. The biomarkers determined were: AChE, BChE, SOD, CAT, GST, NPSH, carbonyl protein and TBARS. LC50 of chlorpyrifos for larvae of P. gracilis was 893,59μg.L-1. For chlorpyrifos, larvae showed reduced mobility and spasms and morphological abnormalities were found in the mouth and intestine. There was a reduction in AChE activity and an increase in the activity of CAT, SOD, GST and, in the NPSH and carbonyl protein levels. For cypermethrin there was hormetic effect for AChE activity. Inhibition of BChE and CAT and increase of SOD and GST occurred. To fipronil, there was inhibition of AChE, BChE and SOD, and increase of CAT and GST. Carbonyl protein levels increased for cypermethrin and fipronil. In this study P. gracilis was sensitive to concentrations that are environmentally relevant or that can be found in its natural habitat. The three insecticides showed potential of neurotoxic effect and induction of oxidative stress for the species. The effects on biochemical biomarkers of P. gracilis indicate that it is possible to use them for the purpose of monitoring the toxicity of pesticides in amphibians and to prevent irreversible effects on their population and ecosystem.