Zinc protection against cadmium effect on estrual cycle of Wistar rat

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 LC(50) values for this metal from 24 to 168 h diminished from about 26 to 1.8 mg Ni(2+)/L, respectively, but from 96 h onward, the LC(50) varied very slightly. Although a noticeable difference among the LC(50) and LC(10) or LC(90) was observed at 24 h of exposure, these parameters tended to a similar value at 168 h of exposure while the confidence intervals of LC(50) 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 Ni(2+)/L; Zn: 0.5-130 mg Zn(2+)/L). As a general pattern, low Zn concentrations (0.5 mg Zn(2+)/L) did not have a clear-cut effect on Ni toxicity, higher Zn concentrations (2-20 mg Zn(2+)/L) enhanced Ni toxicity, and concentrations of 30 mg Zn(2+)/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.

Copper toxicity and copper-zinc interactions in amphibian embryos

The copper hazard was evaluated by means of a 7-day toxicity test with Bufo arenarum embryos. The LC50 and LC10 values from 24 to 168 h of exposure were approx. 0.085 and 0.05 mg Cu2+/1, respectively, while the LC90 resulted in 0.155 mg Cu2+/1 but in this case from 96 h onwards the LC90 diminished up to approx. 0.105 mg Cu2+/1. These data plotted as Toxicity Profiles (TOP) provide a better understanding of concentration and time-dependent thresholds. For instance, exposure threshold occurs within the first 24 h of treatment while for concentration thresholds LC10 and LC90 seem to be more meaningful than LC50 because the S.D. of this last value is overlapping those of LC10 and LC90 for most of the exposure period evaluated. Toxicity data corresponds to a pH of 6.8 which is normal for the maintaining media. Combined treatments of copper and zinc point out a beneficial effect of zinc proportional to the zinc concentration in the maintaining media, e.g. 100% of protection was achieved with 30 mg Zn2+/1 for a copper concentration exerting 90% of mortality. The presence of Cu2+ did not enhance Zn2+ toxicity. The results are discussed in terms of water quality criteria for wildlife and human health protection purposes.