Chapter 8 - Nanomaterial transformation in root–soil interface: a function of root exudate or microbial activity?

Abstract

Nanomaterials (NMs) are highly dynamic and reactive; various physical, chemical, or biological transformations may occur in the environment. These processes change the properties of NMs, thereby affecting the subsequent behavior, including transport in soil, uptake and translocation in the plant, and their toxicity to organisms. For example, some metal-based NMs such as nano-Ag, nano-Cu, and nano-ZnO may dissolve quickly in the environment. Acquisition of an evolving coating of environmental or biological molecules (called “corona”) on the surface of these NMs could occur, which either accelerates or slows the dissolution. The released metal ions can be accumulated by the plant directly or as complexes with other components from the environment. For other NMs such as nano-Au and nano-TiO2, their chemical structures are persistent in environment, but physical transformation such as aggregation, agglomeration, or corona formation may occur, which can modify their surface charge and chemistry and influence subsequent behavior and bioavailability. In terms of the agricultural application of NMs, the initially designed analyte function may be compromised due to these transformation processes that may occur both in the soil before the material interacts with the plant or at the nanoparticle–plant interface. Therefore a full understanding of the transformation mechanisms, processes, and drivers in the soil–plant system is essential for accurate MNs risk assessment, as well as safe and effective use of these materials in agriculture.