Effects of chelators on the acute toxicity and bioavailability of aluminium to Tetrahymena pyriformis

The acute toxic effects of aluminium (Al) to the ciliated protozoa Tetrahymena pyriformis GL (TP) were investigated after a short exposure of 9 h, a time which normally allowed three generations of T. pyriformis in control culture to be obtained. Al was administered under the soluble forms of three salts (AlCl3, Al(NO3)(3), Al-2(SO4)(3)) and the fine particles of an insoluble salt (Al2O3), with or without chelators (humic acids, citric acid, EDTA). A significant and a dose-dependent inhibition of the growth rate and of the motility was observed with TP exposed to Al compounds. The IC50 values of Al were ranked between 10 and 15 mu g Al/ml, whatever the soluble Al salt may be; it was increased to 495 mu g Al/ml with Al2O3. The Al chelates of citrate and EDTA did not significantly modify the toxicity of Al to TP. Furthermore, an increased and unexpected toxicity of Al was observed with Al humate chelates. This phenomena can be explained by the stimulation of the phagocytosis rate of TP by the particles of organic humic matter, which consequently induced a rapid increase of the amount of Al ingested by TP. Moreover, these toxicological results were confirmed by the intracellular quantification of Al by atomic absorption spectrometry and by the localization of Al in TP by an ultrastructural analysis, performed with an electron microscopy and a X-ray probe. (C) 2000 Elsevier Science B.V. All rights reserved.