An experimental study of algal uptake of U,Ba, V,Co and Ni from dilute solutions

Experiments in which two species of freshwater green algae, Ankistrodesmus sp. and Selenastrum, were cultured in dilute solutions of metals chelated with EDTA reveal massive uptake of U and Ba, but relatively minor uptake of Ni, Co and V. For 2-ppm metal-spiked TBIM culture media at pH 8.1–8.2 and growth durations of 3–21 days at 13–16°C, both species accumulate U and Ba at levels of 1000 to 10,000 ppm by dry weight, representing a concentration factor of up to 5000 times the aqueous metal solute concentration. Uptake was comparable for passage of 100-ml spiked culture media through algal mats over 100 min. For aqueous solute concentrations of 20 ppb Ba, Co, Ni and U the algae adsorbed 3000–4000 ppm U and Ba giving concentration factors up to 200,000. With 40 ppb U, the algae adsorbed 6000 ppm, representing a concentration factor of 150,000. Co and Ni in the algae were present at levels below analytical sensitivity. The Ba aqueous concentration was about equivalent to, and the U concentration 100 times natural marine water abundances. For 2-ppm Co-, Ni- and V-spiked culture media, algal uptake was 40–600 ppm Ni, 17 ppm Co and 12 ppm V, respectively.Given the abundance of algae in both fresh and marine waters, coupled with the known association of plankton with U-rich Black Sea muds, the experimental results may indicate that algae also play a significant role in mediating U and Ba uptake from the hydrosphere. The recorded levels of algal uptake for metals are ～1000 × (U), ～100 × (Ba), ～100 × (Ni), ～20 × (Co), and ～6 × (V), previously reported abundances for “typical” marine plants.