Toxicity of Hg, Cu, Cd, and Cr on early developmental stages of Ciona intestinalis (Chordata, Ascidiacea) with potential application in marine water quality assessment

The toxicity of mercury, copper, cadmium and chromium on sperm viability, f ertilisation, embryogenesis and larval attachment of Ciona intestinalis was examined. Fertilisation rate (FR) showed a small decrease even at the high est metal concentration tested. The median effective concentrations (EC50) reducing rates of embryogenesis and larval attachment by 50% were 54 mug Hg /l (0.27 muM), 46 mug Cu/l (0.72 mug), 838 mug Cd/l (7.46 muM), 10,318 mug Cr/l (198 muM), and 35 mug Hg/l (0.18 muM), 34 yg Cu/l (0.54 muM) and 11,75 5 mug Cr/l (226 muM). respectively. Therefore, Hg is three times more toxic than Cu ton a molar basis), ca. 30 times more toxic than Cd and ca. 1000 t imes more toxic than Cr to early stages of C. intestinalis. Rates of larval attachment and embryogenesis were the most sensitive endpoints, although t he latter is more advisable for routine assessment of seawater quality beca use of its greater simplicity. In addition to bivalves and sea-urchins, asc idian embryos can provide biological criteria for seawater quality standard s taking into account the sensitivity of a chordate and contributing to the detection of harmful chemicals with no marked effect on the species curren tly in use in seawater quality bioassays. (C) 2001 Elsevier Science Ltd. Al l rights reserved.