Removal of Technetium from Solution by Algal Flagellate Euglena gracilis

Abstract

Based on limited data for the removal of radioactive (99)Tc by freshwater phytoplankton, it has been thought that phytoplankton are unsuitable for remediation of (99)Tc-contaminated waters. This work sought to verify the validity of this assumption by studying the removal of (99)TcO(4)(-) by freshwater and brackish water phytoplankton. The phytoplankton used were Euglena gracilis, Chlamydomonas pulsatilla, Chlorella vulgaris, and Spirulina platensis. Each of them was incubated for 63 d, and the removal of (99)Tc from solution was periodically determined. Significant removal of (99)Tc was observed only for E. gracilis, and the maximum removal was 70% of the total (99)Tc added. The killed cells of E. gracilis, however, removed hardly any (99)Tc. When E. gracilis cells were washed with fresh culture medium, only 13% of the total (99)Tc was desorbed. These results suggested that intracellular uptake of (99)Tc by E. gracilis occurred. These results are the first documented example of significant removal of (99)Tc by planktonic microalgae.

Environmental conditions for the formation of insoluble Tc in water ponds located above paddy fields

“…2), indicating the involvement of bacteria in the formation of insoluble Tc. In fact, various bacteria species have been reported to possess the ability to reduce and to precipitate the pertechnetate anion (Khijniak et al, 2003;Lloyd, 2003), and some species of gram-negative bacteria have been found to be responsible for the formation of insoluble Tc in the water pond of flooded paddy fields (Ishii and Uchida, 2005). In this study, the presence of Tc-accumulating bacteria in the microcosm sample was also confirmed (Fig.…”

“…from the surface of drifting brown sea weed and confirmed the bacterial capability of removing Tc(VII) aerobically. Ishii and Uchida (2007) found that aerobic phytoplankton Euglena gracilis removes Tc from aqueous solutions. Results of the present experiments also suggested that aerobic Tc-accumulating bacteria could be present in paddy fields, and their ability must be reconfirmed.…”