TOXICITY EFFECTS OF COPPER(II) ON THE MARINE DINOFLAGELLATE-AMPHIDINIUM CARTERAE - INFLUENCE OF METAL SPECIATION

The influence of copper(II) concentration and speciation on the growth of Amphidinium carlerae in batch culture in a modified ESAW medium wa s evaluated by two different experimental designs: (i) copper(II) was added to the cultures 2 h after cell inoculation and (ii) copper( II) had a 24 h pre-equilibration period in the medium before cell inoculat ion. To complement the biological data, the following information on t he chemical/biological system was obtained: (a) computational speciati on of the culture medium under chemical equilibrium conditions: (b) to tal and electrochemically labile copper concentrations in the culture medium during the toxicity experiments; and (c) cellular levels of cop per. The labile fraction of copper was measured by potentiometric ship ping analysis (PSA) at a deposition potential (E(d)) of -0.3 V. At thi s E(d) the dissociation of Cu-EDTA complexes was negligible. In both k inds of experiments the effects of copper were more evident after 4 da ys than after 7 or 10 days of exposure. When compared with situation ( ii) pronounced toxic effects were observed under situation (i): (1) A carterae growth rate was affected at lower copper concentration and in a more acute way: (2) the cells were exposed to significantly higher levels of labile copper (2- to 3-fold more than in situation (ii) for 13.4 mu M total copper) and (3) after 2 h of exposure to the metal the copper sorbed by the cells was about 2-fold higher. These results pro vide evidence for the importance of kinetic parameters in toxicity stu dies. Experimental copper lability together with speciation calculatio ns provided additional evidence that the bioavailable copper and its c ellular toxicity are directly related to the labile metal concentratio n This is higher than but directly proportional to the initial free me tal concentration in the medium as was experimentally verified. PSA-de rived copper lability provided a reasonable indicator of metal bioavai lability to A. carterae in this synthetic seawater medium. A first res ponse of A. carterae to copper toxicity is the release of the metal du e to re-equilibration between copper bound to the cell surface and to the ligands in the medium and/or efflux. A different mechanism must su bsequently be activated, allowing growth despite the relatively high c ellular levels of copper observed.