Toxicity and accumulation of selenite and selenate in the unicellular marine alga Cricosphaera elongata

Abstract

The toxicity and bioaccumulation of selenium in the 4+ and 6+ oxidation states were investigated in a marine unicellular alga Cricosphaera elongata in culture. Selenite was more toxic than selenate. Exponentially growing cells and cells in the stationary phase of C. elongata rapidly accumulated selenite (0.1 and 1.0 mg/L Na2SeO3) and selenate (0.1 and 1.0 mg/L Na2SeO4). Within the first two hours of contact, the amount of selenium taken up decreased sharply in exponentially growing cells, while cells in the stationary phase continued accumulating selenium until a plateau was reached. The presence of metabolic inhibitors such as KCN (potassium cyanide) or DCMU (3-(3,4-dichloro-phenyl)-1,1 dimethylurea) or glutaraldehyde did not modify the first phase of accumulation of selenite by C. elongata in the stationary phase, whereas further accumulation was inhibited. Possible mechanims of accumulation of selenium are discussed. In a series of long term experiments (14 or 31 d), intracellular partitioning of Se in C. elongata cells, exposed to selenite, was analysed; total, protein-bound and free cytosolic selenium concentrations increased with selenium concentration added to the culture medium (0.1 or 1 mg/L Na2SeO3) and with exposure time (at 0.1 mg/L Na2SeO3) from 14 d or 31 d. Most of the selenium was associated with proteins; these proteins may represent a form of storage or detoxication of selenium.