Efeitos ecotoxicológicos de metais na sobrevivência, desenvolvimento e comportamento de duas espécies endêmicas de anfíbios anuros neotropicais

Abstract

The contamination of aquatic ecosystems by metals is one of the main factors responsible for the decline and loss of amphibian populations worldwide. This study aimed to evaluate the ecotoxicological effects of the metal salts Copper Sulfate (CuSO4) and Cadmium Chloride (CdCl2) during the larval stage of Physalaemus nattereri and Rhinella diptycha, analyzing their impact on survival, morphology, development, and behavior. For P. nattereri, the LC50 values obtained in acute toxicity tests at 24, 48, 72, and 96 hours were 0.33, 0.25, 0.25, and 0.22 mg L⁻¹ for Cu, and 4.6, 4.33, 4.28, and 4.03 mg L⁻¹ for Cd, respectively. Acute toxicity tests showed an increase in mortality as metal concentrations and exposure time increased. During chronic exposure, P. nattereri tadpoles were resistant to Cu, with no mortality occurring, while Cd induced mortality at concentrations of 0.04 and 0.4 mg L⁻¹. No significant effects on growth and development were observed due to metal exposure. The results indicated that P. nattereri exhibits moderate sensitivity when compared to other amphibian species. Risk assessment showed a risk to amphibians, with maximum risk quotient (RQ) values of 75 for Cu and 972.2 for Cd, respectively. For the mixture of CuSO4 and CdCl2, the model that best fit the data was Concentration Addition (CA). The combination of the metal salts created a highly toxic mixture, causing synergism and representing a significant risk to the survival of P. nattereri tadpoles. For R. diptycha tadpoles, the LC50 value in acute toxicity tests at 96 hours of exposure was 0.49 mg L⁻¹ for CuSO4 and 1.09 mg L⁻¹ for CdCl2. We analyzed the probability distribution of distances traveled at each timestamp and the speed changes for each group. This analysis revealed that exposure of the tadpoles to CuSO4 and CdCl2 reduced their mobility capacity. This study highlighted the importance of understanding species-specific sensitivity as well as the sub-lethal effects of both metals on the development and morphology of P. nattereri and behavioral responses of R. diptycha. These results contribute to establishing a solid foundation for assessing the consequences of environmental contamination by these metals.