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.
Highlights
Soil contamination by heavy metals and metalloids is a problem that all countries in the world are facing
It is estimated that the number of sites with soil contaminated by heavy metals and metalloids is around five million [2], and anthropological activities are usually the origin of this pollution
Toxicology The heavy metals and metalloids accumulate in the environment where anthropogenic sources increase the background quantity, and this effect becomes risky when the natural concentrations are such that they cause damage to living organisms
Summary
Soil contamination by heavy metals and metalloids is a problem that all countries in the world are facing. This review is focused on the removal of heavy metals, analyzing: (1) the toxicity effects of these pollutants on living organisms; (2) the legislation in force in some developed countries; and (3) the main remediation processes for contaminated soils. 3. Toxicology The heavy metals and metalloids accumulate in the environment where anthropogenic sources increase the background quantity, and this effect becomes risky when the natural concentrations are such that they cause damage to living organisms. Toxicology The heavy metals and metalloids accumulate in the environment where anthropogenic sources increase the background quantity, and this effect becomes risky when the natural concentrations are such that they cause damage to living organisms Their toxicity is relevant at low concentrations, as demonstrated by the limit concentrations imposed by legislative acts (Table 2). It is important to evaluate the diffusion of toxic elements in soil
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