Uptake and sedimentation of arsenic, nickel, and uranium from uranium mine-impacted water by chlamydomonas noctigama
The primary aim of the research summarized in this thesis was to confirm or refute that algae are involved in metal sedimentation from surface water, and whether this activity, if any, is enhanced by increased phosphorus availability. A small-scale laboratory-based experiment was devised to elucidate the role of the chlorophyte alga Chlamydomonas noctigama in the removal of arsenic, nickel and uranium from mine water. Results indicated that the presence of C. noctigama significantly enhanced the removal of these metals relative to treatments without cells. Metals were present in greater concentrations in particulate matter in treatments with cells compared to treatments without cells, and there was a corresponding decrease in the concentrations of dissolved metals. This leads to the conclusion that sedimentation was mainly biotically induced. Additional evidence of biotic involvement in metal removal from water by C. noctigama was obtained by using EDX spectroscopy and X-PEEM spectromicroscopy to observe complexation of arsenic, nickel and uranium to C. noctigama cells. Arsenic, the metal which was present at the lowest concentration in the DJX water, was present on scanned cells in low concentrations, and nickel and uranium, which were present at high concentrations in the DJX water, were present at higher concentrations. Examination of a single cell using X-PEEM spectromicroscopy showed uranium co-localized with carbon and phosphorus on the exterior of the cell. Crystalline particulate matter may have increased in the presence of cells. EDX spectroscopy showed that the crystalline particulate matter was possibly hydroxyapatite that contained various metals, including arsenic, nickel and uranium. EDX spectroscopy was used to determine the frequencies at which the cell-metal and particulate matter-metal associations occurred, and the relative concentrations of the metals associated with particulate matter. No correlation between metal removal and phosphorus concentration in the media, or between algal density and phosphorus concentration was observed. However, phosphorus concentrations were not growth-limiting in these experiments, and so the effect of phosphorus on abiotic precipitation of metals remains unclear. Results suggest two mechanisms by which C. noctigama may remove arsenic, nickel and uranium from solution: by direct sorption to the exterior of the cell, and by sorption to a cell product. An experiment using cells preserved in Lugol’s iodine (a common phytoplankton sample preservative) indiated that Lugol’s preserved samples could not be used to quantify metals using spectroscopy. Consequently, historical samples preserved with Lugol’s iodine cannot be analyzed by this method.
Uranium, Nickel, Arsenic, Water Quality, Chlamydomonas, Mining, Bioremediation
Master of Science (M.Sc.)