Simultaneous mitigation of arsenic and cadmium accumulation in rice grains by foliar inhibitor with ZIF-8@Ge-132

Simultaneous mitigation of Arsenic (As) and Cadmium (Cd) in rice grains is hardly achieved with conventional soil treatments due to their opposite chemical behaviors in paddy soils. This study evaluates the effectiveness of a novel foliar inhibitor with germanium (Ge) -modified zeolitic imidazolate framework (ZIF-8@Ge-132) in cooperative mitigation of As and Cd in rice grains in a As and Cd co-contaminated paddy field, and the effecting mechanisms are elucidated by a series of advanced techniques. The results showed that the grains inorganic As and Cd was remarkably decreased by 45 % and 66 % by the foliar spay of ZIF-8@Ge-132, respectively. ZIF-8@Ge-132 also reduced the As and Cd contents in rice tissues, except for Cd in leaves, where Cd content increased by 148 %. The image-based measurement of plant phenotypic traits and the elements of image analysis using Laser Ablation-ICP-MS (LA-ICP-MS) and Laser Scanning Confocal Microscopy (LSCM) revealed that the possible mechanisms for the reduction of As and Cd in rice grains were as follows: (i) the thickening of the xylem in roots significantly retarded As and Cd absorption by rice plants. (ii) co-accumulation of Ge and Cd in the leaf vascular system likely contributed to the high Cd retention in rice leaves. (iii) antagonistic effects of Zn suppressed the uptake and transport of As in roots/leaves, resulting a lower As accumulation in rice grains.