Comparison of heavy metal accumulation by a bloom-forming cyanobacterium,Microcystis aeruginosa

Microcystis aeruginosa is the dominant species during cyanobacterial blooms in freshwater lakes.In the present study,we compared the bioaccumulation characteristics of cadmium(Cd) and zinc(Zn) in Microcystis cells.In short-term uptake tests,a rapid sorption of Cd and Zn occurred in the first few minutes,with a subsequent slower internalization process.No obvious difference was observed between Zn and Cd in terms of their short-term uptake kinetics.In efflux experiments,elimination of Zn from the cells was faster than that of Cd.In the 72-h exposure tests,the intracellular Cd concentrations increased with exposure time whereas the intracellular Zn concentrations always reached a plateau.The cellular Cd showed greater variation than the cellular Zn at various free Cd 2+ or Zn 2+ concentrations.The differences in Cd and Zn accumulation and elimination indicated that Microcystis cells had a higher bioaccumulation capacity for Cd than for Zn.In field studies,the bioconcentration factor(BCF) of Cd in lake-harvested Microcystis was more than 10 times higher than those of other metals.The results of the present study strongly suggested that the bloom-forming Microcystis may affect the Cd transportation and biogeochemical cycling in eutrophic freshwater ecosystems.