LAUSR

The toxicity of a commercial formulation of the fungicide chlorothalonil in sensitive stages of the native amphibian Rhinella arenarum (Ra) was assessed by means continuous treatments from embryo and larval development and 24-h pulse exposures evaluating acute and chronic lethal and sublethal effects and stage-dependent sensitivity. A risk assessment of chlorothalonil in Ra development also was performed. The results of continuous exposure in embryos showed a significant toxicity increase with exposure time, whereas sensitivity of larvae remained relatively constant through time (24 and 504-h LC50 = 0.86 and 0.04 mg L−1, and 0.37 and 0.34 mg L−1 for embryos and larvae respectively). Embryos exhibited several sublethal effects, such as delayed development, tail/axial flexures, edemas, and behavioral alterations. The 96-h NOEC values for lethal and sublethal effects were 0.025 and 0.01 mg L−1 respectively, so the 96-h Teratogenic Index was 2.5, which indicates the severe teratogenic potential of the fungicide. For 24-h pulse exposure experiments, S.21 and S.23 were the most sensitive stages for lethality (504-h NOEC = 0.05 mg L−1), whereas earlier stages exhibited severe morphological alterations. The results obtained in this study and the ecological risk evaluation highlight the severe toxicity of chlorothalonil threatening the continuity of Ra populations.