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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

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