Sorption of Cadmium and its Effect on Growth and the Utilization of Inorganic Carbon and Phosphorus of Two Freshwater Diatoms

Abstract

Cadmium was rapidly sorbed by Asterionella formosa and Fragilaria crotonensis during the first 5–10 min of exposure (0.05 to ~9 μg Cd∙L−1), followed by a hyperbolic increase in the cellular cadmium content as a function of time. Results obtained from experiments conducted in the light and dark, experiments using live and dead populations, and cellular site location studies imply that the sorption of cadmium by A. formosa is partially an active process, but for F. crotonensis it appears to be passive. Populations of A. formosa exhibited a corresponding decrease in the growth rate as the ambient cadmium concentration was increased from ~2 to ~9 μg∙L−1. In contrast, the growth rate of F. crotonensis was unaffected at levels ranging from ~0.05 to ~9 μg Cd∙L−1. The utilization of inorganic carbon by A. formosa was unaffected at ~4 μg Cd∙L−1, but reduced 45% at ~9 μg Cd∙L−1. The utilization rates of carbon and phosphorus by F. crotonensis were reduced at the lower cadmium concentrations and enhanced at the highest. Key words: cadmium, toxicity, sorption, diatom, Asterionella formosa, Fragilaria crotonensis