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In the face of escalating soil contamination, this chapter meticulously examines the multifaceted strategies employed to mitigate metal/metalloid stress in crops, an imperative endeavor for maintaining agricultural productivity and ensuring food security. Central to the discussion is exploring advanced phytoremediation techniques alongside the strategic use of soil amendments, highlighting their efficacy in decontaminating metal/metalloid-laden soils. The narrative further extends to the crucial role of mycorrhizal fungi in enhancing plant resilience against metal/metalloid toxicity and the innovative application of genetic engineering and breeding techniques aimed at cultivating metal/metalloid-tolerant crop varieties. Moreover, the chapter sheds light on integrating cutting-edge soil remediation technologies, including electrokinetic and nanotechnology, showcasing their potential to revolutionize conventional remediation practices. The synthesis of these strategies underscores the importance of adopting an interdisciplinary approach, blending traditional methods with technological innovations to develop sustainable and effective solutions for metal/metalloid stress in agriculture. Additionally, the chapter emphasizes the need for robust policy frameworks and sophisticated monitoring tools to manage soil health comprehensively, advocating for a holistic strategy to safeguard agricultural landscapes against metal/metalloid contamination.
Suadi Food and Drug Authority (SFDA), Riyadh, Saudi Arabia
*Address all correspondence to: hmmotairy@sfda.gov.sa
1. Introduction to metal/metalloid stress in sustainable agriculture
The escalating incidence of soil contamination with metal/metalloids poses a formidable global challenge to sustainable agriculture and food security [1]. These contaminants, including lead (Pb), cadmium (Cd), mercury (Hg), arsenic (As), and aluminum (Al), emanate from various anthropogenic sources such as industrial discharges, pesticide use, and mining activities, accumulating in agricultural soils and consequently in the food chain, thereby impairing plant growth, reducing crop yield and quality, and threatening human health through bioaccumulation and biomagnification processes [2, 3].
The imperative for research in this domain stems from the dual need to ensure agricultural resilience and food safety in an era of burgeoning environmental stressors. Traditional remediation techniques often fail to address the scale and complexity of metal/metalloid pollution sustainably and cost-effectively. This underscores a critical gap in the existing literature and practice: developing and implementing innovative, eco-friendly strategies that can effectively mitigate metal and metalloid stress in crops while bolstering sustainable agricultural practices [4, 5].
This study endeavors to bridge this gap by exploring a holistic suite of strategies encompassing advanced phytoremediation techniques, genetic engineering, and the strategic application of soil amendments. The study aims to elucidate the efficacy of these approaches in detoxifying metal/metalloid-laden soils, enhancing plant resilience to metal toxicity, and ultimately fostering sustainable agricultural productivity. This research contributes to burgeoning environmental and sustainable agriculture by integrating cutting-edge soil remediation technologies with traditional agronomic practices. Moreover, it aligns with the pressing global mandate to safeguard agricultural landscapes against contamination and to ensure security of food in the face of environmental challenges [6, 7].
This chapter addresses these concerns by filling a significant gap in the current scientific discourse on soil decontamination and plant resilience mechanisms and proposing actionable insights for deploying these strategies at a scale. Consequently, it contributes to the foundational knowledge for developing robust policy frameworks and sophisticated monitoring tools to manage soil health comprehensively. This work advocates for a paradigm shift toward sustainable and resilient agricultural systems, as supported by the research of the authors in [4, 5].
2. Impact of metal/metalloid accumulation on crop yield and quality
Soil contamination with metals and metalloids significantly threatens agricultural productivity and food safety. These contaminants from industrial, agricultural, and natural sources accumulate in soils, leading to crop toxicity, diminished productivity, and heightened health risks along the food chain [1, 8].
Metal/metalloid accumulation impairs plant productivity by stunting growth, inhibiting seed germination rates, and reducing biomass through disrupted cell division and elongation [2, 3, 9]. These adverse effects stem from plant physiological and biochemical alterations [3].
Furthermore, metal/metalloid toxicity affects a plant’s reproductive capabilities, diminishing its ability to flower and bear fruit and impacting crop yield and quality. This reduction is linked to disruptions in photosynthesis, nutrient absorption, and enzyme activity [8, 10].
The absorption and translocation of metals/metalloids by plant roots can extend to the edible parts of crops (fruits and grains), affecting human and animal health throughout the food chain. The degree of translocation varies depending on the metal/metalloid type, plant species, and environmental conditions. For example, Typha domingensis primarily accumulates contaminants in its roots with minimal translocation to aerial parts, whereas hyperaccumulators have a translocation factor (TF) greater than 1, indicating efficient transport from roots to edible parts [7, 11]. Some metals also act as gerontogens, accelerating aging and increasing disease risks associated with aging in organisms [12, 13].
Consuming vegetables and fruits contaminated with metals such as Pb, Hg, Cd, and As is linked to severe health effects, including cancer and organ damage, particularly in developing regions where industrial and agricultural activities exacerbate soil contamination [14, 15, 16].
Metal/metalloid exposure can also induce premature senescence in harvested crops, adversely affecting their shelf life and marketability by accelerating tissue deterioration through oxidative stress. This impacts the economic value of agricultural produce and raises significant health concerns [17]. Furthermore, crops cultivated in metal-contaminated soils may require specialized storage conditions to mitigate further contamination risks during storage [16].
Addressing metal/metalloid pollution is crucial for ensuring the quality and safety of agricultural products, underscoring the need for effective soil decontamination strategies.
3. Comprehensive strategies for mitigating metal/metalloid stress in crops
Addressing metal/metalloid contamination in agricultural settings requires a comprehensive, multifaceted approach that integrates various remediation strategies. The selection of these strategies is influenced by factors such as the types of metals/metalloids present, the extent of contamination, soil properties, and the cost-effectiveness of the methods. Tailoring a combination of methodologies to meet each site’s specific conditions and challenges is essential for optimizing decontamination outcomes.
3.1 Advanced phytoremediation techniques for soil decontamination
Phytoremediation is a leading eco-friendly technique to mitigate metal/metalloid stress in agricultural lands. This strategy involves using plants with exceptional abilities to absorb, stabilize, and detoxify metals/metalloids, thereby rejuvenating contaminated soils. Among these, hyperaccumulators play a critical role due to their unique capacity to absorb and sequester high concentrations of metals/metalloids in their tissues, making them instrumental in soil remediation efforts [4, 5, 6, 18, 19].
Hyperaccumulators are characterized by their ability to thrive in metal-contaminated environments, accumulating metals/metalloids to levels far exceeding those typically found in common plants. This trait makes them particularly effective for phytoextraction, where plant uptake removes metals from soils. Ongoing research is dedicated to identifying new hyperaccumulating species and enhancing the efficiency of these plants in remediation processes.
However, the use of natural hyperaccumulators is often limited by their slow growth rates and low biomass production. To overcome these challenges, researchers are exploring the potential of high-biomass non-hyperaccumulators and ensuring the use of non-edible plants to prevent metal/metalloid entry into the food chain [4, 18].
Phytoremediation, particularly when leveraging hyperaccumulators, offers a sustainable, cost-effective, and in-situ remediation strategy that contrasts sharply with traditional methods. It aligns with environmental sustainability goals and provides potential economic advantages when integrated into standard agricultural practices [6, 20].
Phytoremediation employs plants to address soil contamination in various ways:
3.1.1 Phytoextraction
Phytoextraction, a core strategy within the phytoremediation spectrum, leverages the natural capabilities of plants to absorb, translocate, and sequester metals/metalloids from contaminated soils into their biomass (Figure 1). This environmentally friendly remediation method offers a sustainable and economically viable alternative to traditional soil cleanup methods, contributing significantly to the restoration of soil health and agricultural productivity.
Figure 1.
The phytoextraction process illustrates how hyperaccumulator plants can uptake and accumulate metal/metalloids from contaminated soil. The roots absorb contaminants, translocated to the shoots, and stored in the leaves.
The efficacy of phytoextraction largely depends on the plant’s ability to uptake metals/metalloids, move them to the aerial parts, and accumulate them in harvestable tissues. The root system plays a crucial role in metal uptake, influenced by the availability of metals in the soil, the presence of root exudates that modify metal bioavailability, and the expression of specific metal transporter proteins [21].
Selecting appropriate plant species is critical for effective phytoextraction. Hyperaccumulators, which can concentrate metals/metalloids in their tissues at levels 100–1000 times greater than typical plants, are particularly suitable for this process. However, their slow growth rate and low biomass output can restrict their practical use. Consequently, research increasingly focuses on high-biomass, non-hyperaccumulator plants that still exhibit significant metal accumulation capabilities [21].
Strategic cultivation of hyperaccumulator plants is essential for removing metals/metalloids from soils. Advances in genetic engineering can potentially enhance these plants’ efficiency by enabling them to express genes that improve metal uptake, translocation, and sequestration [22].
Despite its potential, phytoextraction faces challenges such as the slow removal rate of metals, potential food chain contamination, and the need for safe disposal of contaminated plant biomass. To optimize the phytoextraction process, overcoming these challenges requires a multidisciplinary approach that integrates plant physiology, soil science, and environmental engineering.
3.1.2 Phytostabilization
Phytostabilization offers a practical approach for managing soils contaminated with metals/metalloids, particularly where complete pollutant removal is impractical. By immobilizing contaminants within the soil matrix, phytostabilization prevents their migration to groundwater and entry into the food chain, making it an effective strategy for in-situ soil remediation.
The principal mechanisms of phytostabilization include the adsorption of contaminants onto plant roots, precipitation within the rhizosphere, and metal complexation with root exudates. These processes effectively reduce the bioavailability and mobility of pollutants, thereby mitigating their ecological and health impacts. The success of this method depends significantly on the choice of plant species, which must have a robust tolerance to the toxic effects of metals/metalloids, an extensive root system, and the ability to thrive in contaminated environments [23].
Non-edible plants are preferred in phytostabilization to avoid transferring contaminants into the food chain. Enhancing this method’s effectiveness often involves integrating soil amendments such as biochar or phosphate fertilizers, which help immobilize metals and improve soil quality [24].
3.1.3 Phytovolatilization
Phytovolatilization utilizes the unique capabilities of certain plants to absorb contaminants from soil or water and release them into the atmosphere. This method is particularly suited for dealing with volatile organic compounds and metal/metalloids that can be transformed into less harmful volatile forms.
In phytovolatilization, plants take up contaminants through their roots, transport them to aerial parts, and release them as gases through transpiration. This process involves enzymatic reactions that convert metals like Hg and selenium (Se) into volatile forms such as elemental mercury vapor and dimethylselenide [25].
While offering a sustainable means of remediating contaminated sites, phytovolatilization requires careful selection of plant species with high transpiration rates and specialized enzymatic systems capable of converting contaminants into gaseous forms. Challenges include potential air quality impacts and the need for strategies to manage the released contaminants effectively [26].
By refining these sections, the manuscript will present a more polished, comprehensive, and scholarly discussion of phytoremediation strategies suitable for publication in a high-quality academic journal. Each strategy is contextualized within its practical application, challenges, and future research directions, providing a robust overview of contemporary approaches to managing metal/metalloid stress in crops.
3.2 Utilizing soil amendments and conditioners to mitigate metal/metalloid stress
3.2.1 Organic matter addition
Adding organic matter to soils contaminated with metals/metalloids is a well-established strategy for mitigating metal/metalloid stress in crops. Organic amendments such as compost, biochar, and manure can immobilize metals/metalloids, reducing their bioavailability to plants and decreasing the potential for uptake and accumulation in edible plant parts [4, 27, 28, 29].
These amendments enhance soil structure, increase water-holding capacity, and boost nutrient content, promoting healthier plant growth even in contaminated environments. Furthermore, they stimulate microbial activity in the soil, which is crucial in stabilizing and further immobilizing metals/metalloids [27, 28].
The strategic application of organic amendments improves soil properties and facilitates a conducive environment for microbial proliferation. This contributes significantly to detoxifying and rejuvenating metal/metalloid-contaminated soils, fostering sustainable agricultural practices [30].
3.2.2 Assisted phytoremediation
Assisted phytoremediation is a promising strategy for mitigating metal/metalloid stress in crops. This approach involves adding agents to the soil to enhance plants’ ability to remediate metal/metalloid contamination. These agents can include plant growth-promoting bacteria (PGPB), organic amendments like compost and biochar, and symbiotic fungi such as arbuscular mycorrhizal fungi (AMF), a type of fungi that form a mutualistic relationship with the roots of plants [25, 31, 32, 33, 34, 35].
Plant growth-promoting bacteria (PGPB) can enhance phytoremediation by promoting plant growth and health, thereby increasing the plant’s capacity to tolerate and accumulate metal/metalloids [25]. These bacteria can also directly bind to metal/metalloids, reducing their bioavailability and toxicity to plants.
Organic amendments like compost and biochar can immobilize metal/metalloids in the soil, reducing their bioavailability and plant uptake [33, 35]. These amendments can also improve soil health and fertility, promoting plant growth and metal/metalloid stress resilience. For instance, a study found that compost was constructed with a lower bioavailability of metal/metalloids, providing theoretical and technical support for the application of compost in metal/metalloid-polluted soils [32].
Biochar, recognized for its carbon-rich composition derived from biomass, exhibits a high surface area and abundant binding sites, making it an effective material for metal/metalloid remediation. This characteristic not only facilitates the immobilization of metal/metalloids, thereby preventing their uptake by plants and leaching into groundwater but also contributes to enhancing soil fertility. Applying biochar in contaminated soils is a significant sink for metal/metalloids, leveraging its adsorption capabilities to reduce the bioavailability and mobility of these pollutants. This dual function of biochar underscores its potential as a sustainable solution for soil remediation while improving soil health [27, 36, 37].
Arbuscular mycorrhizal fungi (AMF) form symbiotic relationships with plant roots, which make it easier for plants to take in nutrients and make them more resistant to abiotic stress factors like metal/metalloid contamination [33, 35]. These fungi can extend their hyphae into the soil, accessing a larger volume of soil than the plant roots alone. This allows them to capture nutrients with low mobility, such as phosphorus (P) and zinc (Zn), making them available to plants. In the context of metal/metalloid stress, AMF can help to immobilize metal/metalloids in the root zone, reducing their uptake and toxicity to plants [35].
In addition to these biological and organic amendments, assisted phytoremediation can also involve chemical amendments to alter soil properties and reduce metal/metalloid bioavailability. For instance, lime can be used to adjust soil pH, influencing the solubility and bioavailability of metal/metalloids [34].
3.2.3 Lime and pH adjustment
Soil pH profoundly influences the bioavailability of metals/metalloids, affecting their solubility and the extent of their binding to soil particles. Adjusting soil pH, typically by adding lime, can significantly alter the chemical forms of metals/metalloids, making them less available to plants [4, 38, 39, 40].
Metals tend to form insoluble phosphates and carbonates at higher pH levels, whereas they are more likely to exist in bioavailable ionic forms at lower pH levels. However, the effectiveness of pH adjustment strategies can vary depending on the specific metal/metalloids involved and the initial soil conditions [38, 41].
It is essential to tailor pH adjustment strategies to the specific soil characteristics and metal/metalloid contamination types present, as their effectiveness can differ significantly under different environmental conditions [4, 38, 41].
3.3 Enhancing crop resilience to metal/metalloids through mycorrhizal fungi symbiosis
The symbiotic relationships between AMF and plants enhance resilience against metal/metalloid stress. This mutualistic interaction is pivotal for improving plant performance under contaminated conditions through enhanced nutrient uptake, reduced metal toxicity, and facilitated phytostabilization.
3.3.1 Symbiotic relationships
As a symbiotic relationship, the mutualistic relationship between mycorrhizal fungi and plants is vital in improving plant resistance to metal/metalloids. Most plant species, including most crops, are associated with mycorrhizal fungi, and these symbioses can improve plant performance through enhanced soil nutrient uptake [42]. The relationship between mycorrhizal fungi and plants, specifically AMF, plays a crucial role in alleviating the adverse effects of metal/metalloid stress on crops. These fungi can enhance plant performance, improve phytoremediation of metal/metalloids, and induce responses in plants that help ease the effects of metal/metalloids [42, 43, 44, 45, 46].
The AMF is particularly influential in improving the phytoremediation of metal/metalloids, such as, Cd, Pb, and Cr; these fungi can reduce the toxicity of these elements in contaminated environments, thus preventing their bioavailability and environmental migration in the soil [43].
The AMF-assisted alleviation of metal/metalloids phytotoxicity is a cost-effective and environment-friendly strategy; it can induce both molecular and physiological responses in plants that help mitigate the effects of metal/metalloids [44].
Fungi are often found in metal/metalloid-polluted soils; most plants form symbiotic relationships [45]. They can play an essential role in plant growth in metal-contaminated soils by acting as bio-alleviators and/or biofertilizers [46].
3.3.2 Improved nutrient uptake
The role of AMF in promoting nutrient absorption in metal-contaminated soils is critical to improving plant growth and health. This natural symbiotic relationship presents a promising solution for reducing metal/metalloid stress in crops and can be a crucial aspect of sustainable agricultural practices in contaminated environments [33, 44, 47, 48, 49, 50, 51].
The AMF enhances plant nutrient uptake, particularly in soils contaminated with metal/metalloids. These fungi establish symbiotic associations with plant roots by extending their hyphal networks into the soil, enhancing the surface area available for nutrient uptake. This symbiosis is especially beneficial in metal-contaminated soils, where nutrient availability may be compromised [46, 49, 50].
The AMF improves the uptake of essential nutrients such as nitrogen, P, and potassium (K) and micronutrients like Zn and Cu, which are often less mobile in the soil [50]. Doing so supports better plant growth and health, even under the stress of metal/metalloid contamination [44, 47, 48, 49]. The fungi’s ability to bind metal/metalloids can also reduce the toxicity of these metals to the plant, further aiding in nutrient uptake and overall plant performance [44, 51].
3.3.3 Facilitation of metal/metalloids phytostabilization
Moreover, AMF can alter the rhizosphere’s chemistry, leading to the immobilization or chelation of metal/metalloids, thus reducing their bioavailability to plants [44, 52]. This mechanism protects the plant from metal toxicity and minimizes the translocation of metals to the edible parts of crops, therefore minimizing the potential health hazards linked to the consumption of vegetables tainted with metals [33, 44].
4. Innovations in soil remediation technologies for metal/metalloid removal
4.1 Electrokinetic remediation
Electrokinetic remediation (EKR) is an advanced technology used to clean contaminated soil and groundwater, and it is especially effective in addressing soil metal/metalloid contamination. This versatile approach utilizes electrical currents to mobilize and extract a broad spectrum of metal/metalloids, making it a crucial component in the suite of modern soil decontamination techniques.
EKR is particularly adept at treating fine-grained soils with low permeability, where conventional remediation methods struggle to achieve efficiency. The technology operates on principles including electromigration, electroosmosis, and electrophoresis, which collectively enable the movement of contaminants toward strategically placed electrodes in the soil [53, 54, 55].
Recent enhancements in EKR involve nanotechnology, which involves developing nanoelectrodes and nanoscale amendments, significantly improving the efficiency and selectivity of metal/metalloid extraction from soils [20].
4.1.1 Mechanisms and applications
The primary mechanism of EKR, electromigration, facilitates the movement of charged metal ions through the soil toward oppositely charged electrodes. This movement is supported by electroosmosis—the migration of water and solutes toward the cathode-and electrophoresis, the transport of charged particles through a fluid under a uniform electric field [55, 56].
Recent innovations such as interval power breaking have been adopted to enhance EKR’s efficacy. This technique, which involves alternating cycles of power-on and power-off, improves the desorption and migration of ions, significantly increasing the removal efficiency of contaminants like Cd from soils [53]. Furthermore, introducing organic acids as facilitators has bolstered the solubilization and extraction of metal/metalloids, enhancing the overall effectiveness of the EKR process [57].
4.1.2 Challenges and innovations in EKR
Despite its many advantages, EKR faces challenges, including pH fluctuations within the soil that can impact the mobility and speciation of metals and metalloids. Acid generation at the anode and base formation at the cathode can create pH gradients that may precipitate metals near the electrodes, thereby reducing their mobility and extraction efficiency [55].
Innovative solutions, such as chelating agents and surfactants, have been explored to mitigate these issues by enhancing metal mobility and preventing precipitation. These adjustments help maintain a consistent soil environment conducive to effective metal/metalloid removal [58].
Additionally, ongoing advancements focus on improving the energy efficiency of EKR by integrating renewable energy sources and optimizing electrode configurations. For instance, the application of pulsed electric fields has significantly reduced energy consumption during the remediation process, thus minimizing this technology’s environmental footprint [59].
4.2 Nanotechnology
Nanotechnology offers a versatile approach to mitigating metal/metalloid pollution in soil and water environments. By developing specialized nanomaterials and nanosensors, this technology provides efficient, selective, and environmentally friendly solutions for remediating contaminated sites.
4.2.1 Nanomaterials for soil remediation
Nanotechnology harnesses nanomaterials’ unique properties to immobilize or effectively remove metal/metalloids from contaminated soils. Notably, nanoscale zero-valent iron particles are employed due to their high reactivity in degrading various pollutants, including metal/metalloids. These particles are engineered to target specific contaminants, enhancing soil quality and offering a sustainable soil remediation method [60].
Other nanomaterials, such as titanium dioxide (TiO2) and carbon-based nanoparticles, have significantly succeeded in adsorbing and transforming pollutants. This capability is crucial for mitigating the adverse impacts of agricultural practices on soil health, marking a significant advancement in soil remediation [60].
4.2.2 Nanosensors for water remediation
In the context of treating metal/metalloid-contaminated water, nanosensors play a critical role. Due to their high surface area and excellent adsorption properties, these devices can effectively detect metal/metalloids. Nanosensors are tailored with specific nanomaterials to enhance their sensitivity and selectivity toward target metal/metalloid ions, making them invaluable in monitoring and managing water quality [60].
4.2.3 Nano-adsorbents
The application of nano-adsorbents in water remediation is a prominent use of nanotechnology. Iron oxide nanoparticles (Fe2O3) and various metal sulfides have been extensively researched for their capacity to remove divalent metal ions, such as copper (Cu), nickel (Ni), and cobalt (Co), from water. These nano-adsorbents are preferred due to their high adsorption capacity and effectiveness across a broad pH range, making them highly effective in water remediation scenarios [61, 62].
4.2.4 Challenges and future directions
While nanotechnology provides innovative solutions for remediation, it is essential to consider the potential risks associated with deploying nanomaterials in environmental settings. Understanding nanoparticles’ behavior, movement, and potential hazards are crucial for ensuring nanotechnology applications’ long-term safety and viability in soil and water decontamination [60, 63].
Future research should focus on developing strategies to mitigate the ecological risks associated with nanomaterials. This includes enhancing their biocompatibility and degradability to prevent adverse environmental impacts.
Table 1 synthesizes critical aspects such as mechanism, efficacy, applications, and challenges of each technology, drawn from an extensive review of current literature. By juxtaposing these methodologies, the table serves as a crucial reference point for researchers and practitioners alike, facilitating an informed selection of remediation strategies based on specific environmental conditions and contamination profiles.
Remediation technology
Mechanism
Efficacy
Applications
Challenges
References
Phytoremediation
Utilization of plants to absorb, stabilize, and detoxify metal/metalloids from the soil
Varies by plant species and metal type
Soil decontamination, especially for agricultural lands
Slow growth rate of hyperaccumulators, potential food chain contamination
Comparative overview of soil remediation technologies for metal/metalloid stress mitigation in crops. The table presents a detailed comparison of various remediation methods, highlighting their mechanisms of action, overall efficacy, practical applications, and associated challenges.
5. Advanced tools for monitoring and assessing soil metal/metalloid contamination
5.1 Remote sensing and geographic information systems
Remote sensing (RS), gathering information about an object or phenomenon from a distance, typically using aircraft or satellite-based sensors, and geographical information systems (GIS) have emerged as indispensable tools in monitoring and strategically managing metal/metalloid stress in agriculture. By offering detailed insights into contamination levels and their spatial distribution, RS and GIS enhance the development, implementation, and evaluation of targeted mitigation strategies [64, 65].
5.1.1 Applications and advantages
RS technology facilitates the early detection of physiological alterations in crops attributable to metal/metalloid exposure, thereby allowing for targeted mitigation measures [64]. Concurrently, GIS’s spatial analytical capabilities are pivotal in identifying contamination hotspots and assessing the spread of metal/metalloids within agricultural landscapes, which is crucial for formulating and monitoring effective mitigation strategies [65].
5.1.2 GIS for strategy development
Geographic Information Systems (GIS), computer systems that capture, store, analyze, and display geographical data, play a critical role in strategy development and impact assessment by mapping metal/metalloid contamination patterns and evaluating the success of mitigation strategies over time. This information guides the refinement of interventions, ensuring their efficacy in reducing metal/metalloid stress [65]. Furthermore, integrating RS and GIS data with agronomic models predicts the impact of metal/metalloid stress on crop yields, thereby informing the optimization of agricultural practices to mitigate such stress [66]. Predictive analytics provided by RS and GIS enable a proactive approach to managing metal/metalloid contamination, facilitating the implementation of preventive measures before crops are adversely affected [67]. Table 2 offers a concise overview of case studies demonstrating their application. This table succinctly encapsulates the geographical areas investigated, pollutants assessed, methods utilized, key findings, and the impactful role of GIS in enhancing remediation strategies. It underscores the significance of RS and GIS in enabling precise, informed interventions for metal/metalloid contamination across diverse landscapes.
Geographic area
Pollutants
Remediation/assessment method
Key findings
Impact of using GIS
Reference
Fosu Lagoon, Ghana
Pb, Cu, Cd, Mn
Atomic Absorption Spectrometry
Seasonal variations in metal concentrations, sometimes exceeding WHO limits, highlight the need for dynamic monitoring and remediation strategies
Incorporating GIS could pinpoint contamination hotspots, optimize remediation efforts, and enhance phytoremediation strategies
Iran, with a focus on arid and semi-arid regions prone to dust storms
Dust particles are particularly interested in dust phenomena’s metal/metalloid content. The study does not specify metal/metalloid concentrations but emphasizes the environmental and health risks associated with metal/metalloid-laden dust
The study leverages a combination of remote sensing data, geographic information systems (GIS), and statistical methods to monitor and evaluate dust phenomena, including the spatial and temporal distribution of dust storms
Remote sensing and GIS are effective tools for the spatial and temporal analysis of dust storms. The study highlights the increasing trend in dust storm occurrences and the effectiveness of remote sensing technologies, particularly MODIS imagery, in monitoring these events
GIS and remote sensing technologies have significantly contributed to understanding the distribution and intensity of dust storms. They offer valuable insights into identifying the sources and migration patterns of dust, facilitating targeted remediation and mitigation strategies
The study employed RS and GIS techniques to assess soil degradation and the environmental risks of metal/metalloids. It employed Landsat ETM+ images and digital elevation models (DEMs) for spatial analysis
The region experiences significant soil degradation due to salinization, alkalization, compaction, and waterlogging. Most soils exhibited moderate to high degrees of degradation, with a notable chemical and physical degradation risk. Metal/metalloid analysis revealed varied levels of pollution across different geomorphological units, indicating a need for targeted remediation
GIS and remote sensing proved instrumental in mapping soil degradation and assessing metal/metalloid risks, providing a valuable tool for environmental management and the development of sustainable agricultural practices in the Nile Delta
Assessment through GIS and multivariate analysis (PCA and cluster analysis) along with the use of geoaccumulation index, contamination factor (CF), Improved Nemerow’s Pollution Index (Pn), and Potential Ecological Risk Index (PERI)
The study area exhibits varying degrees of soil metal/metalloid contamination, with certain regions displaying high levels of pollutants, indicating strong to extremely strong contamination in some samples. The application of GIS and multivariate statistical analysis highlighted the anthropogenic influence on metal/metalloid concentrations
GIS played a critical role in mapping the spatial distribution of metal/metalloid, aiding in the identification of contaminated zones, and facilitating the development of targeted remediation strategies
Northern slope of the Eastern Tianshan Mountains, Xinjiang, NW China
Zn, Cu, Cr, Pb, As, Hg
Geoaccumulation index, single-factor pollution index, potential ecological risk, and multivariate analysis were used to assess soil metal/metalloid pollution and health risks across commercial, industrial, and agricultural areas
Elevated Pb, As, and Hg levels were noted, surpassing Xinjiang soil background values by significant margins in various functional areas, indicating notable soil contamination. In contrast, average concentrations of Zn, Cu, and Cr were below these background values, suggesting lesser pollution concerns for these metals
GIS and remote sensing techniques provide a nuanced understanding of the spatial distribution of metal/metalloid contamination, pinpointing areas with heightened ecological risks. This spatial insight is crucial for targeted remediation efforts and policy planning
West side of Nile River, El-Minia governorate, Egypt
Cr, Co, Cu, Cd, Pb, Zn
The study utilized GIS and multivariate analysis, including Principal Component Analysis (PCA) and Contamination Factors (CF), to assess soil contamination levels. Soil samples were analyzed for metal/metalloid concentration using Inductively Coupled Plasma Mass Spectrometry (ICP-MS)
Significant contamination with metal/metalloid, notably Cd, Pb, and Zn, was observed. Approximately 70.7% of the area exhibited considerable metal/metalloid concentration, indicating moderate to high soil contamination. The assessment suggests that the misuse of low-quality water for irrigation and excessive use of mineral fertilizers are significant contributors to the contamination
GIS played a pivotal role in mapping the spatial distribution of metal/metalloid contamination, facilitating the identification of contaminated zones, and evaluating contamination levels across the study area. This spatial analysis aids in the formulation of targeted mitigation strategies to address soil contamination issues
Beni Amir Irrigated Perimeter, Tadla Plain, Morocco
Zn, Cr, Pb, Cu, Cd
Utilization of Geographic Information Systems (GIS), geoaccumulation index (Igeo), enrichment factor (EF), contamination factors (CF), and Pollution Load Index (PLI) for analyzing soil samples and assessing metal/metalloid contamination
The study area exhibits significant metal/metalloid contamination exceeding WHO and FAO limits, particularly around industrial areas and urban agglomerations. GIS was instrumental in revealing the spatial distribution and intensity of contamination
GIS technologies enabled precise mapping of contamination hotspots, illustrating the areas most affected by metal/metalloid pollution, which aids in targeted remediation efforts and environmental planning
Mollisol dairy farm in Dulbert Mongolian Autonomous County, Daqing City, Heilongjiang Province, China
As, Hg, Cd, Pb, Cr, Cu, Ni, Zn, Sb
GIS-based spatial analysis and pollution index method were used to evaluate soil, water, and manure contamination levels. The study applied inverse distance weighted interpolation for spatial distribution assessment
High contamination levels of As in soil indicate extreme contamination; moderate contamination levels of Ni in surface water and Sb in cow drinking water. The study underscores the significant environmental impact of metal/metalloid accumulation in soil and the potential risks to the food chain
GIS was crucial for visualizing the spatial distribution of contamination and optimizing sample collection. This technology facilitated a detailed understanding of the contamination patterns and helped prioritize areas for remediation efforts
The study utilized the Positive Matrix Factorization (PMF) model and Geographic Information Systems (GIS) to assess contamination levels and identify the sources of metal pollutants in surface soil samples from agricultural and recreational areas
High As, Sr., Mn, and Fe levels were noted, indicating significant soil contamination, which was further analyzed for source apportionment. The study distinguished between natural mineral dissolution and anthropogenic contributions from past mining activities and current agricultural practices
GIS played a critical role in mapping the spatial distribution of contaminants, allowing for detailed visualization of contamination hotspots and facilitating the effective targeting of remediation efforts
Illustrative case studies on applying remote sensing and geographic information systems in monitoring and mitigating metal/metalloid contamination. This table presents a curated selection of research efforts that leverage RS and GIS for enhanced understanding and management of metal/metalloid stress in various geographical contexts. It details the pollutants analyzed, the assessment or remediation methods applied, and the critical outcomes of these studies, highlighting GIS’s instrumental role in mapping contamination, identifying risk areas, and guiding remedial actions effectively.
5.2 Biosensors
Biosensors represent a significant advancement in detecting and monitoring environmental pollutants, including metal/metalloids and other hazardous substances. Their integration into environmental management strategies offers a real-time, sensitive, cost-effective approach to assessing and mitigating pollution.
5.2.1 Environmental monitoring
Biosensors represent a class of analytical instruments that integrate a biological sensing element with a physicochemical transducer. These devices are engineered to quantitatively detect and measure the concentration of various chemical entities, facilitating precise analytical assessments. In environmental monitoring, biosensors are particularly valuable for detecting pollutants at low concentrations, offering a rapid and specific response to various environmental contaminants [74, 75, 76, 77, 78, 79, 80, 81].
Metal/metalloids rank prominently among environmental pollutants, distinguished by their toxicity and enduring presence in ecosystems. Traditional methods for detecting metal/metalloids are often labor-intensive, time-consuming, and require sophisticated equipment. Biosensors, however, offer a promising alternative. For instance, microbial biosensors utilize microorganisms that exhibit specific responses to metal/metalloids, enabling the detection of pollutants like Hg, silver, Cu, and Cd [77]. These biosensors can provide real-time data on metal/metalloid concentrations, facilitating immediate decision-making and remediation actions [80].
5.2.2 Advancements and applications
Recent advancements in biosensor technology have significantly enhanced their application in environmental monitoring. Electrochemical biosensors, for example, have been developed to detect pesticides and metal/metalloids, leveraging the high sensitivity and specificity of electrochemical methods [82]. Integrating nanomaterials into biosensor designs has improved their performance, offering lower detection limits and faster response times [83].
Biosensors are particularly useful in monitoring soil and water quality. For instance, soil microbial fuel cell-based biosensors have emerged as a novel approach for real-time and rapid soil pollution monitoring [74, 84]. In water quality monitoring, biosensors can detect various pollutants, from metal/metalloids to organic compounds, ensuring drinking water’s safety and aquatic ecosystems’ health [78].
Despite their potential, biosensors’ application in environmental monitoring faces challenges, including field validation, developing more robust and versatile sensors, and integrating biosensors into comprehensive monitoring networks [75, 76]. Future research is expected to address these challenges, enhance biosensors’ sensitivity, selectivity, and portability, and expand their application to a broader range of environmental pollutants [81].
6. Crop improvement through breeding and biotechnological approaches for metal resistance
6.1 Traditional breeding for tolerance
Integrating traditional breeding techniques with molecular tools and recent biotechnological advancements offers a promising pathway toward developing crop varieties endowed with superior metal/metalloid stress tolerance. These innovative breeding strategies contribute to safeguarding food security and ensuring the safety of agricultural produce in regions plagued by metal/metalloid contamination. Notable works by the authors in [85, 86, 87] underscore the effectiveness of selecting and hybridizing plants bearing desirable traits, such as enhanced metal/metalloid tolerance. This approach has historically enhanced crop resilience to various environmental stresses, underscoring the enduring value of traditional breeding methodologies complemented by contemporary scientific advancements.
6.2 Molecular breeding and marker-assisted selection
Recent strides in molecular breeding, particularly marker-assisted selection (MAS), have significantly bolstered our ability to identify and select genes conferring metal tolerance. This approach, exemplified by the work of the authors in [86, 88], leverages high-throughput sequencing technologies for the rapid identification of Quantitative Trait Loci and candidate genes responsible for metal/metalloid tolerance. The precision of MAS in pinpointing genetic markers associated with desirable traits has revolutionized the breeding process, enabling the development of crop varieties tailored to thrive in contaminated soils.
6.3 Integration of biotechnological tools
The integration of CRISPR/Cas9 gene editing represents a pivotal advancement in crop improvement research. This technique allows for precise genetic modifications by directing the Cas9 enzyme to specific DNA sequences, facilitating targeted edits to enhance plant resilience to metal/metalloid stress.
The pioneering applications by the authors in [89, 90] demonstrate CRISPR/Cas9’s capability to modify genetic pathways for improved abiotic stress tolerance, significantly enhancing crop yield and quality on contaminated soils. This technology complements traditional breeding and provides a transformative approach to understanding and manipulating the genetic bases of metal resistance in plants.
This strategy promises to advance food security in metal-contaminated regions and open new research avenues for sustainable agriculture by merging CRISPR/Cas9 with existing breeding methods.
6.4 Genetic modification for enhanced uptake or exclusion
Genetic modification is a transformative approach within the spectrum of strategies to enhance metal/metalloid resistance in crops. This section has detailed the application of genetic engineering tools to develop transgenic plants with enhanced capabilities for either the uptake or exclusion of metal/metalloids, thereby addressing environmental metal/metalloid stress more effectively. Pioneering efforts by researchers in [91] and the insights provided by the authors [4] illustrate the potential of genetic interventions in augmenting the phytoremediation capacity of plants.
This section has outlined several key genetic strategies, including enhancing metal accumulation through gene manipulation in metal homeostasis and improving plant tolerance to oxidative stress via bolstering antioxidant defense systems. These enhancements not only facilitate the direct management of metal/metalloids in contaminated environments but also support the development of crops with intrinsic resistance to such stresses.
Moreover, integrating genetic modifications that enable plants to volatilize metal/metalloid-explored by the authors in [92], represents a significant advancement in phytoremediation technology. These capabilities, particularly the enhanced mercury volatilization discussed by the authors in [93], leverage natural plant detoxification pathways augmented with engineered enzymatic functions to transform toxic metal forms into less harmful states.
However, deploying genetically modified plants in environmental remediation is not without challenges. It necessitates a comprehensive evaluation of potential ecological impacts to ensure that the benefits of such plants in phytoextraction substantially outweigh any adverse effects on biodiversity and ecosystem health, a concern highlighted by the authors in [5].
In summary, genetic modification, as part of a broader integrated strategy involving traditional breeding and cutting-edge biotechnological tools, offers promising prospects for developing robust agricultural systems that thrive in metal-contaminated environments. This comprehensive approach aims to enhance crop resilience and productivity and contributes to the sustainable management of environmental pollutants through advanced phytoremediation techniques.
This chapter underscores the imperative for a holistic and integrated approach to alleviating metal/metalloid stress in agricultural ecosystems, seamlessly integrating traditional agronomic practices with the forefront of technological innovation. It accentuates the necessity of a diverse arsenal of strategies, from applying phytoremediation and soil amendments to leveraging genetic engineering to effectively combat metal/metalloid toxicity in crops. This chapter not only underscores the vital role of interdisciplinary research in forging resilient and sustainable agricultural methodologies but also calls for an expanded focus on refining and global dissemination of these remediation technologies. As we navigate the complexities of metal/metalloid contamination, it is incumbent upon the global research and farming communities to foster collaborative, cross-disciplinary endeavors. Such concerted efforts are essential to enhance the efficacy, scalability, and accessibility of these technologies, thereby fortifying agricultural productivity and ensuring global food security amidst escalating environmental challenges.
The views expressed in this paper are those of the author(s) and do not necessarily reflect those of the SFDA or its stakeholders. Guaranteeing the accuracy and validity of the data is the sole responsibility of the research author(s).
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Written By
Hany Almotairy
Submitted: 09 April 2024Reviewed: 26 April 2024Published: 21 May 2024
Open access peer-reviewed chapter
