Evaluation of Nickel–Zinc Interactions by Means of Bioassays with Amphibian Embryos

The nickel hazard was evaluated by means of a 7-day toxicity test with Bufo arenarum embryos. The LC50 values for this metal from 24 to 168 h diminished from about 26 to 1.8 mg Ni2+/L, respectively, but from 96 h onward, the LC50 varied very slightly. Although a noticeable difference among the LC50 and LC10 or LC90 was observed at 24 h of exposure, these parameters tended to a similar value at 168 h of exposure while the confidence intervals of LC50 overlapped all other confidence interval values. These results, plotted as toxicity profile curves, are useful for determining time and concentration thresholds for Ni. Nickel–zinc interactions on B. arenarum embryos were evaluated by means of simultaneous treatments with both cations (Ni: 5–35 mg Ni2+/L; Zn: 0.5–130 mg Zn2+/L). As a general pattern, low Zn concentrations (0.5 mg Zn2+/L) did not have a clear-cut effect on Ni toxicity, higher Zn concentrations (2–20 mg Zn2+/L) enhanced Ni toxicity, and concentrations of 30 mg Zn2+/L and higher had a beneficial effect in most cases. The metal interaction studies provide a scientific basis for the establishment of water quality criteria for wildlife protection purposes.