Population growth responses of Tetrahymena shanghaiensis in exposure to rare earth elements.

This article presents the population growth responses of Tetrahymena shanghaiensis s1 in exposure to rare earth elements (REEs). Both the light REEs (La, Sm) and the heavy REEs (Y, Gd) were investigated with 24- and 96-hr population growth assays to evaluate their aquatic toxicity. Four end points, cell count, frequency of neutral red (NR) uptake, total protein, and nucleic acid content were employed in the 24-h assay, and a population growth curve was plotted in the 96-h assay. The results of 24- and 96-h assays suggest a dual effect of REEs on T. shanghaiensis of the stimulated growth at low concentrations and the toxicity at higher ones. In the promoted growth of T. shanghaiensis, however, the cell density increased with an increased growth rate and the protein and nucleic acid content per 10(4) cells undertook no remarkable changes, which suggests possible cell growth control by REE.