Field trials of phytomining and phytoremediation: A critical review of influencing factors and effects of additives

Plant-based technologies including phytomining, phytoextraction, phytodegradation, phytostabilization and phytovolatilization have drawn much attention during the last decade. To examine the feasibility of these nature-based solutions to accumulate, degrade, stabilize or volatize metal(loid)s and/or organic contaminants, an increasing number of field studies have been conducted. This review critically evaluates influencing factors in phytomining and phytoremediation approaches, including contaminant concentrations, fertilizer application and chelating agent addition, planting characteristics (e.g. plant density, seeding, cropping and harvesting methods), and soil properties (e.g. salinity, soil texture and soil pH). A proper trial design will assure the robustness of the results if these factors were taken into consideration seriously. We also summarized knowledge about additives used in field trials, especially biological waste-derived amendments such as biochar, compost, sewage sludge and manure. According to the literature reviewed, controversy remains whether these amendments can promote the plant performance. In addition, the utilization of microorganisms and transgenic plants in field trials, and the associated biosafety concerns such as horizontal gene transfer were discussed. Future research should examine the ecological risks associated with phytomining and phytoremediation (e.g. the secondary migration of contaminants due to improper handling of harvested plants). It is suggested that the results of field studies should guide commercial applications of phytomining and phytoremediation.