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.

Can Soil Improvers (Biochar, Compost, Insect Frass, Lime, and Zeolite) Achieve Phytostabilization of Potentially Toxic Elements in Heavily Contaminated Soil with the Use of Purslane (Portulaca oleracea)?

“…Also, Zn was found in compost (203 mg kg −1 ) and frass (70 mg kg −1 )-the four treatments of which (compost and frass at 2% and 4%) were found with increased Zn extractability. Although added Pb and Zn concentrations were low compared to the very high initial contents in soil, it is known that newly introduced metals are much more mobile than those deposited in soils over long periods of time [61]. Thus, these impurities may have caused the recorded increased DTPA extractability of Pb and Zn.…”

Use of diffusive gradients in thin-film technique to predict the mobility and transfer of nutrients and toxic elements from agricultural soil to crops—an overview of recent studies

“…At low concentrations, these PTEs can help some cellular functions in plants, as well as pigment biosynthesis, enzyme activities, photosynthesis, sugar metabolism, respiration, nitrogen fixation, and other functions, but even these elements become toxic at increased concentrations, affecting plant growth (Rashid et al 2023 ). Other PTEs such as Cd, Pb, As, Hg, and Sb are non-essential and highly toxic even at low concentrations and affect biota, and finally human health (Briffa et al 2020 ; Senila et al 2022 ; Thalassinos et al 2023 ).…”

Bioavailability of Cd in Plantago weldenii and Sonchus oleraceus Plants: The Effects of a Humic and Fulvic Acids-Based Biostimulant

“…Soil deterioration due to the accumulation of potentially toxic elements (PTEs) is a threat to both crop production and the environment [1,2], while PTEs have become a great concern to food security and human health due to their high toxicity, stability, and non-biodegradability [3][4][5]. Among these PTEs, cadmium (Cd) is one of the most important pollutants, being a hazardous and carcinogenic element even at low concentrations [6].…”

“…These organic substances may alleviate the mobility of PTEs by forming chelating bonds and stable organometallic complexes with metallic ions in mineral structures, thereby mitigating accumulation by plants and transfer in the trophic chain [19]. Usage of HMWOAs has been reported to minimize the total concentrations of Pb and Cd [3]. However, Evangelou et al [28] indicated the use of humic acids as an alternative chelating agent, as they can increase the solubility of cationic metals and absorption by roots.…”