A critical review on various remediation approaches for heavy metal contaminants removal from contaminated soils

Highlights

• Impact of heavy metal toxicity towards the environment and human health.

• Physical, chemical, and bioremediation approaches were used for contaminated soils.

• Land filling, soil cleaning and solidification methods are well-established.

• Treatability studies are crucial in the selection of soil sanitation techniques.

• Future prospect and challenges of remediation would provide insights for readers.

Abstract

Heavy metal pollution remains a global environmental challenge that poses a significant threat to human life. Various methods have been explored to eliminate heavy metal pollutants from the environment. However, most methods are constrained by high expenses, processing duration, geological problems, and political issues. The immobilization of metals, phytoextraction, and biological methods have proven practical in treating metal contaminants from the soil. This review focuses on the general status of heavy metal contamination of soils, including the excessive heavy metal concentrations in crops. The assessment of the recent advanced technologies and future challenges were reviewed. Molecular and genetic mechanisms that allow microbes and plants to collect and tolerate heavy metals were elaborated. Tremendous efforts to remediate contaminated soils have generated several challenges, including the need for remediation methodologies, degrees of soil contamination, site conditions, widespread adoptions and various possibilities occurring at different stages of remediation are discussed in detail.

Introduction

Owing to the fast industrialization and overpopulation during the last few decades, there has been a massive increase in xenobiotic components including metals in the environment (Qin et al., 2020). The excessive entry of these components into the environment leads to human and environmental health issues. Even at low concentrations, heavy metals affect plants, soil, humans, plants, and animals, because these metal wastes are generally toxic in nature (Priya and Nagan, 2015; Elizabeth Rani et al., 2021). Due to various pollution exposures into the environment, the air, water, and land get contaminated. Air pollution can impact the quality of soil and water resources significantly (ECCC, 2013). Soil pollution occurs when pollutants, such as heavy metals, hydrocarbons, and pesticides, are released or disposed of. By contaminating precipitation and falling into water and soil habitats, air pollution can have an impact on the quality of soil and water bodies (Manisalidis et al., 2020). Water pollution can contribute to soil pollution and vice versa (Ahmed and Sulaiman, 2001; Lu et al., 2015). Harmful substances from wastewater can permeate into the soil from the water bodies. These may impose serious consequences on human health and the environment (Ashbolt, 2015). Subsequently, there are many new blooming advances to the recycling/re-use of wastewater. This effluent must be cleaned and recycled according to the most basic requirements, such as usability, recycling and cost. This is a major concern for developing nations (Jawed et al., 2020).

Wastewater usually contains toxins, such as cleansers, pesticides, prepared nourishment, drugs, and, organic/inorganic toxins (e.g. heavy metals and organic or inorganic salts). The improper disposal of wastewater into the environment contaminates the soil. The spectrum of nonbiodegradable heavy metals, such as chromium (Cr), cadmium (Cd), lead (Pb), mercury (Hg), iron (Fe), arsenic (As) and selenium (Se), brings exceptional prosperity but also frequent issues. There is also an insistent need for these metals to be separated from wastewater to make wastewater reusable. Traditional innovations remain accessible for effective remediation, for example, substance precipitation, surface adsorption (Jawed et al., 2020), film filtration (Chen et al., 2018; Naghdali et al., 2019), particle trade, photocatalysis, and flocculation. In all these methods, the most capable method to remove heavy metals from wastewater is the adsorption on nanomaterials because other methods do not adequately remove such heavy metals and their cut-off emphasis has pursued appropriate clearing (Hasan et al., 2018; Meepho et al., 2018). This would decrease the accumulation of waste metals into the soil underneath.

It is therefore vital to deploy advanced and site-specific remediation technologies that can effectively and safely remediate soils polluted by heavy metals (Ok et al., 2020). In the last several decades, different soil remediation technologies have been implemented (Murtaza et al., 2014; Sabir et al., 2015; Khan et al., 2021). These methods focus on decreasing the maximum and/or bioavailable heavy metal concentrations in the soil and their possible mechanisms in the food supply chain (Bhargava et al., 2012; Hou et al., 2020). Traditional methods for remediating heavy metals from polluted soils are based on physical, chemical, and biological methods that can be used to remediate contaminated soil in conjunction with each other. The majority of these methods, despite their high performance, are expensive, environmentally harmful, and time-consuming (Ahmed et al., 2021). Financial and technological effects and challenges have made soil clean-up a difficult job. The realistic application of these traditional methods to remediate soils poses many limitations and a certain degree of threats.

This present review examines the various technologies currently available for heavy metal remediation in terms of mechanisms, advantages, drawbacks, applicability, and costs. This review examines the methods for treating heavy metal-contaminated soils using physicochemical, biological, and techniques that combine these approaches, as well as the potential toxicity of metals after treatment, the interaction of metals with soil constituents, the difficulties of using this modification for site remediation, and potential opportunities. This review has also focused on remediation strategies for soils polluted with heavy metals, which include essential things required to properly remediate contaminated soils. This includes particular approaches that are implemented and being used at various locations. This paper explores the origins and risks of heavy metals in the soil and addresses methods and influencers for microbial remediation thereby this offers a valuable guide for restoring the health of the soil ecosystem. The data are used to determine the most useful remedial technology for the treatment of contaminated soils. This study will be of great use to industrial site owners who are tainted by long-term historical waste. This study has also focused on farmers with soils that are currently polluted with metal and are interested in improving the quality of their goods, or to urban gardeners who intend to improve the quality of the land.