Abstract

Exposure to environmental pollutants contributes to the global decline of amphibians. Amphibian embryos are unique models for studying the effects of various toxic agents on developmental processes. Some of the most detrimental toxic agents are heavy metals, the study of which is a priority in ecotoxicology. Copper is a microelement required in many biological systems, but it can be toxic at concentrations higher than normal physiological range. The purpose of the present study was to analyze the toxic effect of high concentrations of Cu (10, 25, and 50 mg/L) on Bufo bufo embryos. The present study shows that short-term (48 h) toxicity test can fail to register toxicological effect of Cu, whereas long-term toxicity test demonstrates that all analyzed concentrations are lethal to common toad embryos. Early stages of development (stages 4-8, Gosner 1960) are shown to be rather tolerant to copper, even at high concentrations. Effects of copper begin to manifest themselves at the blastula stage (stages 8-9, Gosner, 1960). The present study also shows that initial egg density affects copper-related mortality rate of embryos. If egg density is high, copper-related mortality rate is sometimes decreased, possibly because jelly coats of eggs bind great amounts of dissolved copper. It is also shown that clutches can differ in sensitivity to different copper concentrations. Taken together, our data demonstrate that the conditions of the experiment (such as the initial egg density) and individual sensitivity of clutches to the toxic agent considerably contribute to the results of the ecotoxicological experiment.