# Improvement of Arsenic Phytoextraction Using Indigenous Bacteria and Mobilizing Agents
## 1 Introduction  
Nowadays, human activities that cause direct or indirect release of organic and inorganic pollutants into the environment affect almost every aspect of modern society, from the process industry to transportation to agricultural practices, to name a few. These practices, too often accompanied by incorrect waste-disposal policies without adequate recovery of resources [1, 2], end up having increasingly significant effects on the ecosystem and human health [3]. The need to contain these problems as much as possible has led to the development of a wide range of physicochemical and biological approaches for the recovery of contaminated water [4, 5, 6, 7] and soils [8, 9, 10, 11]. Arsenic (As) is among the most toxic inorganic pollutants and is unfortunately a very widespread problem as it is commonly involved in electronics (as a semiconductor), in the metallurgical industry (to improve hardness and thermal resistance in metal alloys, as well as in gold and lead mining) and in the pharmaceutical and agricultural sectors (some of its compounds are used as pesticides) [12]. Apart from its toxicity, which makes this contaminant particularly dangerous for human health in case of direct contact [13], arsenic can be assimilated through the foodchain and from drinking water, with consequent bioaccumulation and occasional biomagnification [14], causing neurotoxicity and cardiovascular diseases [15; 16] and, even worse, carcinogenic effects [17]. Arsenic retention in the soil is related to soil properties, such as pH, organic matter content [18], clay minerals and redox conditions. Metal speciation strongly influences its mobility and bioavailability: As(III) and As(V) are the most important and common inorganic forms and also the most toxic in soil [19]. Exposure to arsenic negatively affects almost all body systems in humans [20]; for this reason, arsenic is one of WHO's 10 chemicals of major public health concern [21]. Along the same lines, Italian legislation limits the concentration of As in public, private and residential green land to 20 mg/kg [22]. In the case of soils contaminated by As or other potentially toxic metals, some technical limitations considerably reduce the range of possible intervention options [11]: to date, soil excavation and landfilling, as well as soil washing/flushing with stabilization/inertization, are still the most common solutions. As a potential alternative, the use of ElectroKinetic Remediation Technology (EKRT) is a promising in situ approach [23]. However, in recent years, the growing sensitivity towards environmental issues has highlighted an aspect rarely taken into consideration, namely, that most of the remediation activities have an environmental impact in themselves, as they require the use of chemical products or processes which require the consumption of raw materials and energy [24]. To avoid compromising the sustainability of approaches [24] and even the generation of harmful side effects [25], an increasing number of technologies aim to provide nature-based solutions (NBSs) [26]. Approaches of this type are generally more ecological and sustainable, as they aim not only to eliminate or reduce contamination but also to minimize the environmental impacts (emissions, energy consumption, waste production, etc.) and create synergies between different sectors and activities (protection of ecosystems and the promotion of a circular economy, climate change mitigation and resilience) [27]. Among NBS remediation measures, phytoremediation certainly occupies a leading position. It includes a variety of remediation technologies that employ plant species to remove organic and inorganic contaminants from soil and other environmental matrices (sediments, water) [28; 29; 30]. Their low cost, simplicity of operation and environmental benefits [31; 32] are just some of the advantages offered by these phyto-technologies, and their overall sustainability and effectiveness can be further increased when used in combination with other approaches [33; 34].