## 1 Introduction  
Human activities have generated enormous amounts of pollutants through diverse activities, for instance, agriculture, industrialization, and urbanization [1]. The variety of pollutants is diverse, from agrochemical compounds, nitrogen, and phosphorus to chemical wastes, halogenated compounds, potential toxic metals, radionuclides, plastics, and microplastics, among others, affecting air, water, and soil [2]. Heavy metals (HMs) are among the most abundant pollutants in soil [3]; these elements are well known for their potential toxicity, persistence, and bioaccumulative nature. Their natural source includes weathering of metal-bearing rocks and volcanic eruptions, while anthropogenic sources include mining and various industrial and agricultural activities [4]. These contaminants affect not only the environment but also interacting living organisms, i.e., plants, animals, and microorganisms [4]. Of special concern is the accumulation of toxic chemicals in edible plants or animals. Consequently, this accumulation transfers these compounds to humans or air and water via eutrophication, soil structure degradation, and altered microbial dynamics, affecting environmental quality productivity [5, 6]. To overcome the concerns mentioned above, biotechnological strategies have been researched, i.e., bioaugmentation, biostimulation, and phytoremediation, which reduce the generation of by-products during the remotion of contaminants and enhance the complete mineralization of the pollutants. Besides, these biotechnologies reduce the cost of operation and maintenance [7,8]. Phytoremediation uses plants to degrade or extract pollutants from an environment and is based on evolutionary traits developed by plants to deal with environmental challenges, especially ionic homeostasis in the rhizosphere and in plant cells [9]. The establishment of plants in contaminated soil produces ecological and economical benefits in many ways: (a) phytostabilization; (b) phytoextraction of precious metals like Hg, Ag, and Ni; (c) sustainable land management; and (d) improvement of soil utility and fertility [10,11]. Plant strategies in phytoremediation include phytofiltration, phytostabilization, phytoextraction, phytovolatilization, and phytodegradation. Table 1 summarizes the different techniques of soil phytoremediation. The most important part of phytoremediation is the identification and establishment of metal-tolerant and metal accumulator plants. After that, different modifications and improvements are made until the creation of never-before-seen developments, such as the design and use of genetically modified plants [9] or the synthesis and use of nanomaterials to phytoremediate polluted sites [17,18]. Phytoremediation has been used extensively around the world [9]; the benefits of this biotechnology are numerous regarding the simplicity of its application, the cost of application and maintenance, and the fact that it is considered friendly to the environment compared to other chemical or physical techniques. However, the economic feasibility of this technology can be limited by several factors, mainly time-consuming processes, contaminant specificity, limited metabolic-detoxtifying capacity, extreme or variable climatological conditions, seasonal variability, and root-limiting growth [19]. In addition, the long-term act of phytoremediation increases the risk of incorporating toxic compounds into the trophic chain. During recent decades, the integration of biomass (polluted or not) into energy production processes has been evaluated to increase economic and environmental benefits. This coupling can help remove the economic restrains of phytoremediation and decrease the remobilization of metals. The valorization of derived phytoproducts from phytoremediation residual biomass such as bioethanol, biodiesel, biogas, and heat would not only help satisfy the global energy demand but also provide an alternative for fostering a biobased economy for sustainable development [20]. Grzegorska et al.