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.