Abstract
Abstract. Benthic macro-invertebrate bioturbation can influence the remobilisation of uranium (U) initially associated with freshwater sediments, resulting in a high release of this pollutant through the overlying water column. Given the potential negative effects on aquatic biocenosis and the global ecological risk, it appears crucial to improve our current knowledge concerning the biogeochemical behaviour of U in sediments. The present study aimed to assess the biogeochemical modifications induced by Tubifex tubifex (Annelida, Clitellata, Tubificidae) bioturbation within the sediment in order to explain such a release of U. To reach this goal, U distribution between solid and solute phases of a reconstructed benthic system (i.e. in mesocosms) inhabited or not by T. tubifex worms was assessed in a 12-day laboratory experiment. Thanks notably to fine-resolution (mm-scale) measurements (e.g. "diffusive equilibrium in thin-films" DET gel probes for porewater, bioaccumulation in worms) of U and main chemical species (iron, sulfate, nitrate and nitrite), this work (i) confirmed that the removal of bottom sediment particles to the surface through the digestive tract of worms greatly favoured oxidative loss of U in the water column, and (ii) demonstrated that both U contamination and bioturbation of T. tubifex substantially influenced major microbial-driven biogeochemical reactions in sediments (e.g. stimulation of denitrification, sulfate reduction and iron dissolutive reduction). This study provides the first demonstration of biogeochemical modifications induced by bioturbation in freshwater U-contaminated sediments.
Highlights
Trace metal pollution of rivers, lakes and estuaries is a serious ecological problem in many industrialised areas worldwide
This study provides the first demonstration of biogeochemical modifications induced by bioturbation in freshwater U-contaminated sediments
The concentration of total U in the water column of contaminated aquaria, with and without T. tubifex worms, over time is presented in Fig. 1, with the apparent net accumulation rate of U in the water column as an inset
Summary
Trace metal pollution of rivers, lakes and estuaries is a serious ecological problem in many industrialised areas worldwide. Despite recent efforts to improve water quality, notably in most developed countries, many aquatic ecosystems are still threatened by pollution accumulated in sediments and groundwater. In this context, the case of uranium (U) released by mining extraction is of particular interest due to its complex biogeochemical behaviour and its potentially high ecotoxic risk for aquatic biocenosis. Whereas the natural geochemical background level of U in freshwater sediments is considered to be < 10 μg U g−1 (dry weight) (Kurnaz et al, 2007), much higher concentrations, up to several mg U g−1, have been measured in rivers and lakes close to former or operating mining sites (Neame et al, 1982; Hart et al, 1986; Lozano et al, 2002; Lottermoser and Ashley, 2006). The long-term storage capacity of such contaminated sediments depends on numerous geochemical and biological parameters affecting the solubility and the mobility of U.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
