Toxicity of nickel, copper, and selenium in medaka embryos (oryzias latipes): a comparative study

The indispensability of biometals nickel, copper, and selenium in pharmaceutical, agricultural, and other industrial applications, coupled with their release from mining processes, has made them potent environmental contaminants, especially when present in aquatic ecosystems at levels above the essential range. The toxicity of these biometals in fish embryogenesis, including their toxicity levels, was studied using medaka embryos. Test solutions (0.001-10 ppm) of the biometals, along with an isotonic solution as a control, were introduced into the embryos using a nanosecond pulsed electric field application. The exposed embryos were cultured at 25 ± 1°C and microscopically observed daily for 14 days in an isotonic solution. Developmental abnormalities and toxicity were observed during the 14-day observation period. All biometals caused some abnormalities in developing embryos at all concentrations. Major abnormalities included delayed development; deformities such as curvature of bones or spines; abnormal formation of the hearts, eyes, and circulatory systems; and mortality. The toxicity of the biometals was significantly different (p < 0.05) from that of the control. Gene expression analysis revealed that 4747, 1961, and 1952 genes were affected by copper, nickel, and selenium, respectively. Copper affected the highest number of genes and caused the highest toxicity. These results indicate that nickel, copper, and selenium can cause toxicity in developing fish embryos at concentrations ranging from 0.01 ppb to 10 ppm. Therefore, there is a need to constantly monitor the levels of these biometals, particularly in aquatic ecosystems, to preserve aquatic life.