Potential kinetic availability of metals in sulphidic freshwater sediments

IENS, ES, Lancaster University, Lancaster LA1 4YQ, UK.
Science of The Total Environment (Impact Factor: 4.1). 04/2006; 357(1-3):208-20. DOI: 10.1016/j.scitotenv.2005.04.034
Source: PubMed


The insolubility of metal sulphides is believed to limit the bioavailability of trace metals in sulphidic sediments. However, if non-equilibrium conditions are important, metals may be more available than simple thermodynamic calculations suggest. To investigate the possible dynamic supply of Cu, Ni and Zn in a sulphidic freshwater sediment, they were measured, along with iron, manganese and sulphide, by the technique of diffusive gradients in thin-films (DGT). DGT measures the supply of solute from sediment to solution in response to a local solute sink. Release of Mn, Cu, Zn and Ni was observed at the sediment surface and attributed to the supply from reductive dissolution of manganese oxides. The depth profile of simultaneously extractable metals (SEM) for Cu and Ni followed the shape of the Mn profile more closely than the profiles of either acid volatile sulphur (AVS) or Fe, again consistent with supply from Mn oxides. Solubility calculations for a mesocosm of homogenised sediment indicated supersaturation with respect to the sulphides of Fe, Cu, Ni and Zn, yet DGT measurements demonstrated a substantial supply of both trace metals and sulphide from the solid phase to the pore waters. Ratios of metals measured in pore waters by DGT were consistent with their release from iron and manganese oxides, indicating that supply, as much as removal processes, determines the pseudo-steady state concentrations in the pore waters. The observations suggest that trace metals are not immediately bound in an insoluble, inert form when they are in contact with sulphide. This has consequences for modelling metal processes in sediment, as well as for uptake by some biota.

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    • ") and undersaturation of albandite is generally observed in sulfidic porewater (Naylor et al. 2006). "
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    • "Unfortunately, without sampling using multiple DGT probes, R values cannot be determined; to date, experiments have only been performed on carefully homogenised sediments to enable comparison of the results of multiple probes. [23] However, there are several ways resupply effects can be minimised. A thicker diffusive layer will mean that the porewater concentration of sulfide is less likely to drop over the deployment time, so kinetic calculations of iron(II) and sulfide dynamics based on the results are more relevant. "
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    Environmental Chemistry 01/2009; 6(1). DOI:10.1071/EN08059 · 2.51 Impact Factor
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    • "At the 3 sampling sites, a DET and a DGT probe were inserted in situ and back to back in the sediments by a diver and 24 h later again removed. The preparation of the DET and DGT probes prior and posterior to sampling has been detailed previously (Leermakers et al., 2005; Naylor et al., 2006; Zhang et al., 1995). Briefly, before deployment, the DET and DGT probes were de-oxygenated by immersing them for 24 h in a container with metal free (using Chelex 100) NaCl (0.01 M) solution. "
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