Microcalorimetric investigation of the toxic action of Cd2+ on Rhizopus nigricans growth

The microcalorimetric bioassay for acute cellular toxicity is based on meta bolic heat production from cultured cells. Microcalorimetry is a quantitati ve, inexpensive, and versatile method for toxicology research. The biologic al response to toxicants is the inhibition of the heat production rate in c ells and toxicity is expressed as the concentration of toxicant that is 50% effective in this inhibition (IC50). In this paper, the effect of Cd2+ on Rhizopus nigricans growth was investigated at 25 degrees C. The relationshi p between growth rate constants (k) and concentration of Cd2+ (C) shows a l ogarithmic normal distribution, and described as k = 1.2742 X 10(61) exp[-1 .810 X 10(-3) (C + 283.0)(2)], and IC50 is 0.72 mu g/ml. These signals are readily obtained by an LKB 2277-204 heat conduction microcalorimeter. (C) 2 000 Elsevier Science B.V. All rights reserved.