Retention of Radionuclides and Arsenic by Algae Downstream of U mining Tailings

Abstract

Abstract. Algae including cyanobacteria function as efficient temporary sinks in wetlands below uranium mining tailings and dumps. As far as investigated their accumulation potential exceeds in parts higher plants and soils, microphytic and epiphytic algae each being superior to macrophytic algae and vascular plants. The enrichment compared to the surrounding water is high. In the living biomass uranium can be accumulated up to 300 mg/kg dry matter (DM), Iead up to 250 mg/kg DM and arsenic even up to 4000 mg!kg DM. On average approx. half of the contamination is loosely adsorbed on the cell surfaces. The dimension of contaminant remobilization is yet unknown. lntroductionHeavy metals and arsenic are -with few exceptions -very efficient accumulated in algae and aquatic plants (literature overview see Vymazal 1994). In photoautotrophic algae and cyanobacteria enrichment up to several percent per gram dry matter can be expected due to relatively high surface/volume ratio, mucilage (metal complexing) sheaths (e.g. Yen et al. 2001), fast growth rates and the ability to store phosphate actively as polyphosphate at growth Iimitation caused by the Iack of other resources (Vymazal 1994; Franklin et al. 2000). A P like behavior of As and interactions with Uranium are assumed (Planas and Healy 1978; change in chemical speciation: Knauer et al. 1999; Meinrath et al.l999; Mkandawire and Dudel, this volume ).The specific performance of photoautotrophic algae or chemoautotrophic bacteria has so far been sparsely considered in field investigations. However, concentration factors resp. transfer factors for uranium and especially for radium have been calculated already decades ago (for summary see Williams 1990). B. J. Merkel et al. (eds.), Uranium in the Aquatic Environment

The removal of uranium from mining waste water using algal/microbial biomass

“…If the cells are growing, the number of available surface sites increases; in other words, the rate at which U ions are removed from solution is a function of growth rate. Dienemann et al (2002) characterized the U content of algae growing in wetlands in U mine effluents. They describe the algae as efficient, temporary sinks for U. Bioadsorption of up to 300 mg of U per kg dry matter (mass) led the authors to believe that algae might be useful in the removal of U from the waste stream.…”

Enrichment of Uranium in Particulate Matter during Litter Decomposition Affected byGammarus pulexL.

“…From dumps, tailings, and other remnants of uranium mining contaminants like uranium, other radionuclides and arsenic are discharged into surface and groundwater . Uranium concentrations of up to 500 μg L −1 in the water body have been observed − . In water, uranium is dissolved not only at low pH values (predominantly as uranyl cation) but also in a neutral to alkaline milieu (e.g., as calcium−carbonate complexes) .…”

Uranium, Mining and Hydrogeology

“…Algae sampled from the respective ponds usually contained more uranium than found in the water (Dienemann et al 2002).…”