Sublethal effects of trace metals (Cd, Cr, Cu, Hg) on embryogenesis and larval settlement of the ascidian Ciona intestinalis.

Toxicity of Cadmium (Cd), Chromium (Cr), Copper (Cu), and Mercury (Hg) on the early developmental stages of Ciona intestinalis was investigated. Developmental defects of larvae after exposure of gametes throughout their development to the larval stage were assessed. Gamete exposure to increasing metal concentrations resulted in a significant decrease of the percentage of normally hatched larvae, showing median effective concentrations (EC50) of 721 microg/L (6.42 microM) for Cd, 12772 microg/L (226 microM) for Cr, 36.6 microg/L (0.576 microM) for Cu, and 44.7 microg/L (0.223 microM) for Hg. Larval attachment was significantly affected when gametes were exposed to the metals throughout development. The EC50 reducing larval attachment by 50% were 752 microg/L (6.7 microM) for Cd, 15026 microg/L (289 microM) for Cr, 67.8 microg/L (1.607 microM) for Cu, and 78.1 microg/L (0.389 microM) for Hg. Therefore, on a molar basis Hg is three times more toxic than Cu, 20-30 times more than Cd, and 700-1000 times more toxic than Cr, for both responses.