Department of Earth & Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada.
Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15, Natsushimacho, Yokosuka, Kanagawa, 2370061, Japan.
Sci Rep. 2020 Jun 26;10(1):10417. doi: 10.1038/s41598-020-67279-w.
Given the high surface reactivity of clay minerals, it is assumed that flocculation will lead to metal accumulation in marginal marine settings. However, the degree of metal sorption to clays is impacted by solution pH and ionic strength, and it remains unknown whether riverine clays indeed serve as a metal sink once they encounter seawater where pH and ionic strength markedly increase. Here, we conducted cadmium (Cd) adsorption experiments to three types of common clay minerals - kaolinite, illite and montmorillonite. We found that 20-30% of Cd from illite and montmorillonite surfaces were desorbed when transitioning from freshwater to seawater pH and ionic strength conditions, while kaolinite showed no discernible differences. Synchrotron X-ray adsorption spectroscopy confirmed that Cd release corresponded to a change in bonding from outer- to inner-sphere complexes when clays encountered seawater pH and ionic strength conditions. If other trace nutrients (such as Cu, Zn, Co) adsorbed onto riverine clay minerals behave in a similar manner to Cd, we speculate that their desorption in marginal marine settings should exert a significant impact on the productivity of the biosphere.
鉴于粘土矿物的高表面反应性，人们认为絮体的形成将导致金属在边缘海域的积累。然而，粘土对金属的吸附程度受溶液 pH 值和离子强度的影响，并且尚不清楚当河流中的粘土遇到 pH 值和离子强度显著增加的海水时，它们是否真的充当金属汇。在这里，我们用镉（Cd）吸附实验研究了三种常见的粘土矿物——高岭石、伊利石和蒙脱石。我们发现，当从淡水到海水 pH 值和离子强度条件转变时，伊利石和蒙脱石表面的 20-30%的 Cd 被解吸，而高岭石则没有明显差异。同步加速器 X 射线吸收光谱证实，当粘土遇到海水 pH 值和离子强度条件时，Cd 的释放与从外层到内层配合物的键合变化相对应。如果其他痕量营养素（如 Cu、Zn、Co）吸附在河流粘土矿物上的方式与 Cd 相似，我们推测它们在边缘海域的解吸应该会对生物圈的生产力产生重大影响。
