Remediation of Metal/Metalloid-Polluted Soils: A Short Review

Abstract

The contamination of soil by heavy metals and metalloids is a worldwide problem due to the accumulation of these compounds in the environment, endangering human health, plants, and animals. Heavy metals and metalloids are normally present in nature, but the rise of industrialization has led to concentrations higher than the admissible ones. They are non-biodegradable and toxic, even at very low concentrations. Residues accumulate in living beings and become dangerous every time they are assimilated and stored faster than they are metabolized. Thus, the potentially harmful effects are due to persistence in the environment, bioaccumulation in the organisms, and toxicity. The severity of the effect depends on the type of heavy metal or metalloid. Indeed, some heavy metals (e.g., Mn, Fe, Co, Ni) at very low concentrations are essential for living organisms, while others (e.g., Cd, Pb, and Hg) are nonessential and are toxic even in trace amounts. It is important to monitor the concentration of heavy metals and metalloids in the environment and adopt methods to remove them. For this purpose, various techniques have been developed over the years: physical remediation (e.g., washing, thermal desorption, solidification), chemical remediation (e.g., adsorption, catalysis, precipitation/solubilization, electrokinetic methods), biological remediation (e.g., biodegradation, phytoremediation, bioventing), and combined remediation (e.g., electrokinetic–microbial remediation; washing–microbial degradation). Some of these are well known and used on a large scale, while others are still at the research level. The main evaluation factors for the choice are contaminated site geology, contamination characteristics, cost, feasibility, and sustainability of the applied process, as well as the technology readiness level. This review aims to give a picture of the main techniques of heavy metal removal, also giving elements to assess their potential hazardousness due to their concentrations.

Nanotechnology in the Restoration of Polluted Soil

“…Metalloid pollution of soil is a global issue owing to the deposition of these chemicals in the environment, affecting human health, plants, and animals. Also, they are hazardous at any concentration, even at extremely low levels [ 9 , 106 ]. Besides, HMs/metalloids can have a major effect on the abundance, structure, and diversity of soil microbial communities, which can lead to a shift in ecosystem functioning [ 107 , 108 ].…”

“…In previous years, several remediation methods have been introduced for the reclamation of these metalloids from soil. However, successful remediation of sites contaminated by metalloids is hindered by the fact that these pollutants do not decompose on their own and that it is not always possible to extract all of the contaminated soil [ 9 ]. Therefore, chemical stabilization of metalloids in soils, through adsorption, surface precipitation, structural integration, or ion exchange, is a promising solution for such sites since it immobilizes contaminants in the soils, limiting their mobility, bioavailability, and bio-accessibility [ 109 ].…”

“…The advancements in nanotechnology open a window globally to remediate or restore polluted soil in an effective way [ 6 , 7 ]. It has been claimed that nanotechnology has great potential as an environmentally cleaner technology, including by alleviation of the toxicities of various metals/metalloids [ 8 , 9 ]. Besides, nanotechnology has been recognized as a potential method for the remediation of pollutants in a variety of environmental matrices, including soils [ 6 ].…”

“…In this context, soil remediation is one of the main domains where nanotechnological approaches have been widely used. The uses of NPs have been explored lately to remove contaminants in a variety of ways, including by adsorption, redox reactions, precipitation, and co-precipitation, all of which are aided by their enormous specific surface area [ 9 ].…”

Application of Technological Solutions for Bioremediation of Soils Contaminated with Heavy Metals

“…Common effectors are ethylenediaminetetraacetic acid, citric acid, diethylenetriaminepentaacetic acid, ethylene glycol tetraacetic acid, and others. Synthetic chelating compounds are considered more effective, but have a severe disadvantage of usemany soluble and mobile forms of metals [11][12][13].…”