Cadmium accumulation in Scenedesmus vacuolatus under freshwater conditions

Cd accumulation in cultures of Scenedesmus vacuolatus, a freshwater alga, was investigated in water samples from freshwater systems (two hard- and one softwater system) and compared to accumulation from synthetic culture medium. The Cd accumulation in S. vacuolatus was compared to total, labile, and free Cd measured by various analytical methods. In the hardwater samples, Cd accumulation was similar to accumulation from the culture medium and approximately followed the free ion activity model. In the softwater system, Cd accumulation increased with increasing free and total Cd concentrations, but was lower than expected from the free Cd2+ concentrations compared to the other freshwaters and culture media. Cd accumulation in the various freshwaters was not simply related to labile and free Cd concentrations measured by several methods. From experiments using fulvic acid as a ligand in the culture medium, no influence on Cd accumulation other than by modifying the Cd speciation was detected. Modeling of the Cd uptake revealed that besides cation and proton competition, other factors such as dissolved organic carbon composition and the presence of colloids might reduce Cd accumulation in softwater systems.