Potentially Toxic Elements: A Review on Their Soil Behavior and Plant Attenuation Mechanisms against Their Toxicity

Abstract

The presence of potentially toxic elements (PTEs) can induce phytotoxicity and growth inhibition in plants. These elements are bioaccumulated and biomagnified in the food chain due to their high stability and resistance to biodegradation. The availability and mobility of PTEs in soil depend on certain physicochemical procedures. Many scientific studies on PTEs have provided valuable information about the processes, environmental fate, effects and remediation techniques. However, there is a need for gathering and presenting all up-to-the-date information concerning mechanisms and processes of PTE mobility in the soil-plant interface. More specifically, soil chemical reactions and processes need to be discussed under the light of PTE potential uptake by plants, as well as the physiological mechanisms at plant molecular level of PTE attenuation when plants are subjected to PTE stress. Thus, in this study we discuss the important soil processes that influence the bioavailability of PTEs for plant uptake. We also elucidate the mechanisms such as phytochelation and antioxidant defense through which plants can mitigate PTE toxicity, enhance their tolerance, and promote their survival in contaminated soils. Moreover, we discuss the major mechanisms of reactive oxygen species (ROS) production and the strategies for ROS scavenging which involve enzymes and non-enzymatic compounds that demonstrate antioxidant effects. In conclusion, this review provides a comprehensive understanding regarding PTE toxicity, utilization and transportability. It could be used by the scientific community and soil end-users towards a better understanding of the mechanisms that plants use to alleviate PTE toxicity, significantly affecting the potential use of plants in soil remediation programs and their capacity to grow in PTE-contaminated soils.