Metal stoichiometry in predicting Cd and Cu toxicity to a freshwater green alga Chlamydomonas reinhardtii

In this study. we quantified the accumulation and toxicity of cadmium and copper in a freshwater green alga, Chlamydomonas reinhardtii, under different phosphate conditions. The accumulated Cd and Cu concentrations increased significantly with increasing ambient P concentrations and free metal ion concentrations. The metal:P ratio remained independent of the ambient P concentration. For the three pulse-amplitude-modulated parameters. the median inhibition concentrations were 1.5-1.6 x and 2.0 x higher, but the medium inhibition cellular quota was 2.2 x and 1.2x lower for cells maintained at 0.1 mu M P than for cells maintained at 10 mu M P for Cd and Cu, respectively. Furthermore, the difference in metal toxicity decreased (for Cd) or disappeared (for Cu) when the toxicity was expressed by the metal:P ratio in the cells, indicating that the stoichiometry of metals and P can be better used to predict the toxicity of metals. It is necessary to consider the stoichiometry of metals in predicting metal toxicity in phytoplankton. (c) 2005 Elsevier Ltd. All rights reserved.