Toxicity of zinc sulphate for tadpoles of bullfrog (Lithobates catesbeianus): acute toxicity, chronic toxicity and hematological parameters

Abstract

The aim of this study was to evaluate the effect of zinc sulfate (ZnSO₄) on hematological parameters of bullfrog tadpoles, Lithobates catesbeianus, through acute and chronic toxicity tests. Although the toxicity of zinc for several species of fish has been studied, the toxicity of this metal is not well known to all aquatic organisms, especially for amphibians. The action of this metal ion on the respiratory system of fish occurs by precipitation of the mucus produced by the gills of fish that die by asphyxiation. The acute toxicity tests showed that LC50-96h (median lethal concentration) of zinc sulfate was 2.78 mg L^-1, level considered below that set by CONAMA. Chronic toxicity tests were performed on three concentrations: CL50-96h/100 (0.0278 mg ZnSO₄ L^-1), LC50-96h/10 (0.278 mg ZnSO₄ L^-1) and LC50-96h (2.78 mg ZnSO₄ L^-1) during 312 hours under semi-static, and a control group (without addition of zinc sulfate). Analyses of hematological parameters indicate the occurrence of changes, showing the possibility of chronic effects in tadpoles of L. catesbeianus, which should be better studied.