Uptake, translocation, and transformation of silver nanoparticles in plants

Silver nanoparticles (AgNPs) have been globally applied in consumer products because of their antimicrobial properties. Broad applications inevitably release AgNPs into the natural environment. Moreover, AgNPs are produced naturally in soils. Plant uptake of AgNPs is the first step of their transfer along food chains, which ultimately raises concerns about human health. This review systematically summarizes the current knowledge on the uptake process of AgNPs in plants which is regulated by the physical properties of nanoparticles (e.g., size, surface coating, and morphology), environmental conditions (e.g., soil redox conditions, soil components, co-contaminants, and symbiotic microorganisms), and plant species (e.g., monocotyledon and dicotyledon). After internalization, AgNPs are translocated within plants and undergo biotransformation, including aggregation, oxidative dissolution, sulfidation, chlorination, and complexation with organic matter such as thiolates. Little is known about whether the internalized AgNPs and the transformed products will be accumulated in edible tissues of plants, which can raise the possibility of Ag to enter the food chains. Knowledge gaps about detailed mechanisms of transformation and translocation of AgNPs in planta still limit our understanding of Ag fate in plant-soil systems. This review intends to give a comprehensive assessment of the interaction between AgNPs and plants, highlighting that an integrated investigation of the full life cycle of AgNPs in plant-soil systems is needed to ensure safe application of nanoparticles.