Combined toxicity of dissolved mercury with copper, lead and cadmium on embryogenesis and early larval growth of the Paracentrotus lividus sea-urchin

The individual and combined toxicity of dissolved mercury, copper, lead and cadmium has been investigated by using the Paracentrotus lividus sea-urchi n embryo-larval bioassay. Embryogenesis success and early larval growth hav e been recorded after incubation of fertilised eggs in seawater, both with single metals and binary combinations of Hg with every other metal. For ind ividual metals the ranking of toxicity was Hg > Cu > Pb > Cd, with EC50 val ues of 21.9, 66.8, 509 and 9240 mug/l, respectively. Lowest observed effect concentrations (LOEC) for early larval growth were approximately three tim es lower than the EC50 values for Hg, Cu and Pb, and more than two orders o f magnitude lower for Cd, emphasizing the danger of underestimating toxicit y when only lethal effects are recorded. Marking & Dawson's additive indice s ranged from 0.10 to 0.19, indicating additive effects with a slight trend to synergism, which was statistically significant for the Hg-Pb combinatio n only. Hayes' additive indices were within the margins considered acceptab le to describe additive interactions.