Acute and Subchronic Toxicity of Arsenite and Zinc to Tadpoles of Rhinella arenarum Both Alone and in Combination

Abstract

The current study evaluated acute and subchronic toxicity of arsenite (As³⁺) and zinc (Zn²⁺) to stage 25 tadpoles of Rhinella arenarum in both single and joint laboratory exposures. LC50 values obtained for As³⁺ were elevated and remained within the range of 46 to 50 mg/L of As³⁺ between 4 and 17 d of exposure. Growth of tadpoles was completely inhibited with 30 mg/L of As³⁺, demonstrating the presence of ecologically relevant sublethal effects at concentrations lower than those resulting in lethality. With respect to Zn²⁺, a 96-h LC50 value of 2.49 mg/L was calculated in soft water. Contrary to results obtained for As³⁺, LC50 values of Zn²⁺ gradually decreased with increasing exposure duration, from 2.49 mg/L at 96 h to 1.30 mg/L after 21 d. In joint exposures to both metals, the type of interaction observed between As³⁺ and Zn²⁺ was concentration dependent. Lethal effects of As³⁺ were mitigated, unaffected, or potentiated by 0.01, 0.1, and 1–2 mg/L of Zn²⁺, respectively. However, although 0.01 mg/L of Zn²⁺ significantly reduced lethality of As³⁺-exposed tadpoles, the same concentration of Zn²⁺ did not help to reverse the stunt growth of these animals. Further studies need to examine which are the lowest concentrations As³⁺ required to reduce growth and whether Zn²⁺ serves to antagonize growth effects in this range of concentrations.

Acknowledgements

Funding for this work was provided by the “Consejo Nacional de Investigaciones Científicas y Técnicas” (CONICET PIP 5324) and the “Agencia Nacional de Promoción Científica y Técnica” (PICT 14375).

Julie Céline Brodeur and Jorge Herkovits are staff researchers of the “Consejo Nacional de Investigaciones Científicas y Técnicas” (CONICET), Argentina.

Current address for Cynthia Melina Asorey is Facultad de Ciencias del Mar, Universidad Católica del Norte, Larrondo 1281, Coquimbo, Chile.