Distribution and Relationship of Uranium and Radium Along an Allochthonously Dominated Wetland Gradient Mohammad Nassour • Arndt Weiske • Jo ¨rg Schaller • Carsten Brackhage • E. Gert Dudel Received: 22 August 2014 / Accepted: 28 November 2014 / Published online: 30 December 2014 Ó Springer Science+Business Media New York 2014 Abstract Uranium mining may pose a large threat for freshwater ecosystems, caused by elevated concentrations of metals/radionuclides in drainage water. Important pollutants of such waters are uranium (U) and radium (Ra), because of their impact due to both radio- as well as chemo-toxicity. Despite the comprehensive knowledge about specific ele- ment speciation as well as fixation processes, less is known about the retention of U and Ra at a higher level of com- plexity (within allochthonous ecosystems as predominant for low order streams). Consequently, we investigated the dis- tribution and retention potential of allochthonous ecosys- tems regarding U and Ra as well as changing U/Ra ratios. We found U predominantly transported over long distances, whereas Ra mainly precipitates immediately after reaching the surface, i.e. in the spring area. Although high U accu- mulation in organic rich sediments is found, still high transport rates are detected. Low overall fixation of U within the allochthonously dominated wetland results in an U transport over long distances. Consequently, large areas are affected by U mining activities and its post-mining impact, with U being more relevant compared to Ra. Former and current uranium mining poses a high risk for freshwater ecosystems due to the input of potentially toxic elements/radionuclides and even direct radiation. From dumps, tailings and other associated contaminated sites radionuclides drain into surface and groundwater even long after decommissioning of mining (Jakubick and Kahnt 2002). Uranium concentrations of up to 500 lgL -1 have been observed in such waters (Meinrath et al. 1999), whereas the radioactivity in these waters is mainly related to uranium (U) and radium (Ra). More important even as a potential health risk for humans is the specific chemo- toxicity of U (Schott et al. 2005). Based on this knowledge more strict exposure guidelines for U have been adopted internationally within the last years. The World Health Organization (WHO 2004) recommends an intake of sol- uble U compounds of not more than 0.5 lg per kg body weight per day and a drinking water limit of 30 lgL -1 . Regarding these rather conservative guidelines, it is important to know the distribution/transport potential and contamination of ecosystems for both elements. Uranium transported in the water pathway occurs in dissolved form not only at low pH values (predominantly as uranyl cation) but also in a neutral to alkaline media (e.g., as calcium-carbonate complexes) (Mkandawire et al. 2005). Further, it may also be complexed with organic compounds like humic and fulvic acids as part of dissolved organic carbon (DOC), and it may be fixed to colloids particularly during transport within allochthonously domi- nated freshwater systems (Franke et al. 2000). Radium however occurs predominantly as RaSO 4 , which is insol- uble (Langmuir and Riese 1985). In this form it can be transported only partially associated to small particles (Benes et al. 1983). An exception would be a high saline milieu where radium may also occur in dissolved form (Lauria et al. 2004). Uranium and radium may accumulate Electronic supplementary material The online version of this article (doi:10.1007/s00244-014-0117-4) contains supplementary material, which is available to authorized users. M. Nassour Á A. Weiske Á J. Schaller Á C. Brackhage Á E. Gert Dudel Institute of General Ecology and Environmental Protection, Technische Universita ¨t Dresden, 01062 Dresden, Germany Present Address: J. Schaller (&) Environmental Geochemistry, University Bayreuth, Universita ¨tsstrasse 30, 95447 Bayreuth, Germany e-mail: joerg.schaller@uni-bayreuth.de 123 Arch Environ Contam Toxicol (2015) 68:317–322 DOI 10.1007/s00244-014-0117-4