Fachgebiet Bodenchemie mit Pedologie, Institut für Bodenkunde und Standortslehre, Universität Hohenheim, 70593, Stuttgart, Germany.
Fachgebiet Biogeophysik, Institut für Bodenkunde und Standortslehre, Universität Hohenheim, 70593, Stuttgart, Germany.
Environ Pollut. 2021 Nov 1;288:117738. doi: 10.1016/j.envpol.2021.117738. Epub 2021 Jul 9.
Soil and groundwater contamination with potentially toxic elements (PTEs) including cadmium (Cd) and copper (Cu) has become a serious problem for ecosystem functioning. Silicon (Si) may precipitate these metals as silicates, and may also form, at undersaturation of silicates, 'Si-contaminant compounds', i.e. particles of polymerized silica with PTEs incorporated or adsorbed by inner-sphere complexes. While the formation of these compounds in aqueous solution has been proven, their formation in soil remains unclear yet. Therefore, we conducted column experiments with a topsoil horizon artificially contaminated with Cd or Cu solutions (10 mM) in the presence (10 mM) and absence of monomeric Si, and monitored the elemental composition of the eluates during 12 irrigation steps with artificial rainwater by microwave-plasma atomic emission spectrometry, the size and charge of the particles eluted by dynamic light scattering and phase analysis light scattering, and determined the spatial distribution of total and exchangeable Cd and Cu in soil after the experiments. When Si was previously applied to soil, significantly larger particles (up to > 200 nm) in the eluates indicated Si polymerization and formation of Si-contaminant compounds. However, Cd and Cu concentrations were very low (<0.4 μM), pointing to efficient retardation in soil. In any variant, the particles formed were slightly negatively charged (-11 mV). The molar metal:Si ratios in the eluates and significant correlations between the amounts of Si and metals in soil extracted by NHNO pointed to the formation of Si-contaminant compounds, too. More Cu than Cd was retained in soil, and significantly more in the presence of Si, but less Cu than Cd was in exchangeable form. While particularly Cu formed Si-contaminant compounds, which reduced the concentration of Cu ions, the Si-contaminant-compound particles in the eluates remained very small, thus potentially susceptible to particulate export from soil into the groundwater.
土壤和地下水受到潜在有毒元素（PTEs）如镉（Cd）和铜（Cu）的污染已经成为生态系统功能的严重问题。硅（Si）可能会将这些金属沉淀为硅酸盐，并且在硅酸盐不饱和的情况下，也可能形成“Si-污染物化合物”，即含有 PTEs 的聚合硅颗粒或通过内球络合物吸附的 PTEs。虽然已经证明这些化合物在水溶液中的形成，但它们在土壤中的形成仍然不清楚。因此，我们进行了柱实验，在存在（10 mM）和不存在（10 mM）单体 Si 的情况下，用人工 Cd 或 Cu 溶液（10 mM）污染表土层，并在 12 次人工雨水灌溉步骤中用微波等离子体原子发射光谱监测洗脱液中的元素组成，用动态光散射和相分析光散射监测洗脱液中颗粒的大小和电荷，并在实验后测定土壤中总交换态 Cd 和 Cu 的空间分布。当 Si 预先应用于土壤时，洗脱液中粒径明显较大（高达>200nm）表明 Si 聚合和 Si-污染物化合物的形成。然而，Cd 和 Cu 浓度非常低（<0.4 μM），表明在土壤中具有高效的阻滞作用。在任何情况下，形成的颗粒带轻微负电荷（-11 mV）。洗脱液中金属：Si 的摩尔比以及 NHNO 提取的土壤中 Si 和金属的量之间的显著相关性也表明了 Si-污染物化合物的形成。与没有 Si 时相比，更多的 Cu 被保留在土壤中，且有 Si 时更多，但可交换态的 Cu 比 Cd 少。虽然特别的是 Cu 形成了降低 Cu 离子浓度的 Si-污染物化合物，但洗脱液中的 Si-污染物化合物颗粒仍然非常小，因此可能容易从土壤中颗粒态输出到地下水。
