Nanobubble-assisted phytoremediation of heavy metals and emerging contaminants: A critical review of mechanisms, microbiome interactions, and applications

Heavy metals and emerging contaminants are increasingly pervasive in soils and aquatic environments, which pose severe risks to ecosystems and public health. Phytoremediation is an attractive in situ remediation strategy for managing these pollutants, but its application is constrained by low remediation rates, limited plant tolerance to pollutants, and poor contaminant bioavailability. Over the past decade, nanobubble (NB) technology has gained attention as a feasible approach to address these bottlenecks. This review critically examines the applications of NBs in phytoremediation and its underlying mechanisms. Furthermore, the review delineates how NBs regulate redox conditions, enhance interfacial mass transfer and ion enrichment, and generate reactive oxygen species (ROS). Collectively, these processes govern contaminant speciation and transformation, plant stress responses, and rhizosphere microbial functions. The behavior and remediation outcomes of NBs are highly dependent on gas type, bubble stability, ionic strength, and dosage regime, which collectively determine whether NBs promote phytoextraction, phytostabilization, or contaminant degradation. We further synthesize recent studies on NB-mediated regulation of heavy metal and emerging contaminant bioavailability, plant physiological adaptation, and rhizosphere microbiome assembly in both soil-based and soilless systems. Recent advances in coupling NBs with amendment strategies are also critically discussed. Moreover, major challenges of NB transport and persistence in heterogeneous media, ecological risks associated with ROS and contaminant remobilization, and gene expression in plants are highlighted. This review provides mechanistic insights into NB-assisted phytoremediation and identifies research priorities for its scalable application.