Accumulation and toxicity ol Cd, Zn, Ag, and Hg in four marine phytopiankters

Abstract

Accumulation and toxicity of Cd, Zn, Ag, and Hg were measured in the diatom Thalassiosira pseudonana, the chlorophyte Dunaliella tertiolecta, the coccolithophore Emiliania huxleyi, and the cyanophyte Oscillatoria woronichinii. Bioaccumulation of the metals was measured over a wide (up to 105) range of metal concentrations, using .gamma.-emitting radioisotope of each metal. Metal content of cells was related to total external metal concentration in all cases, in accordance with Freundlich adsorption isotherms. Dead cells accumulated metals comparably to living cells, indicating that the initial association of metal with the cell is governed by adsorption. Volume/volume concentration factors computed at equilibrium ranged from 3 .times. 102 for Cd in T. pseudonana to 9.5 .times. 104 for Hg in E. huxleyi. Metal toxicity, as measured by depression of cell division rate, could generally be described as an exponential function of the log of the external (or cellular) metal concentration, consistent with the concept of cell thresholds of safe metal accomodation. Regression analyses of the data were used to calculate median-effective concentration (EC50) and non-effective concentration (EC0) metal concentrations for each alga/metal combination. Expressed on a cellular metal basis, Hg was usually the most toxic, but there was no clear trend for other metals for all species. Algal species can have markedly different surface affinities for metals. The most resistant species to Zn, Ag and Hg was D. tertiolecta. Enhanced metal tolerance in D. tertiolecta was partly attributable to metal exclusion. These data may provide a basis for predicting the toxicity of other metals to algae from metal concentration factors in the cells.