Naylor C, Davison W, Motelica-Heino M, Van Den Berg G A, Van Der Heijdt L M
IENS, ES, Lancaster University, Lancaster LA1 4YQ, UK.
Sci Total Environ. 2006 Mar 15;357(1-3):208-20. doi: 10.1016/j.scitotenv.2005.04.034. Epub 2005 Jun 4.
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.
金属硫化物的不溶性被认为限制了硫化沉积物中痕量金属的生物有效性。然而，如果非平衡条件很重要，那么金属的有效性可能比简单的热力学计算结果所显示的要高。为了研究硫化淡水沉积物中铜、镍和锌可能的动态供应情况，采用薄膜扩散梯度技术（DGT）对它们以及铁、锰和硫化物进行了测量。DGT测量的是沉积物中溶质响应局部溶质汇向溶液的供应情况。在沉积物表面观察到了锰、铜、锌和镍的释放，这归因于锰氧化物还原溶解的供应。铜和镍的同时可提取金属（SEM）深度剖面比酸挥发性硫化物（AVS）或铁的剖面更紧密地跟随锰的剖面形状，这再次与锰氧化物的供应情况一致。对均质沉积物微宇宙的溶解度计算表明，铁、铜、镍和锌的硫化物处于过饱和状态，但DGT测量表明，痕量金属和硫化物都有大量从固相供应到孔隙水中。通过DGT测量的孔隙水中金属的比率与它们从铁和锰氧化物中的释放情况一致，这表明供应与去除过程一样，决定了孔隙水中的准稳态浓度。这些观察结果表明，痕量金属与硫化物接触时，不会立即以不溶性、惰性形式结合。这对沉积物中金属过程的建模以及某些生物群的吸收都有影响。
