elocation-id: e4056
Arsenic contamination in agricultural soils and irrigation water poses a significant threat to crop productivity and food security. In response to this problem, the present review aimed to analyze the use of immobilized nanomaterials as a technological alternative for the efficient removal of arsenic contamination in agricultural systems. Recent studies on the application of nanomaterials, such as zero-valent iron nanoparticles, nanoclays, and metal oxides, immobilized in polymeric, ceramic, or natural matrices, were collected and evaluated. The methodology consisted of a documentary and comparative analysis of scientific research published in peer-reviewed journals, considering the parameters of adsorption capacity, removal mechanisms, optimal conditions, and efficiency in the field. The results indicated that the immobilized nanomaterials have greater stability, regenerative capacity, and lower leaching risk compared to traditional methods. In addition, successful cases were documented in Mexico, where their implementation reduced the concentration of arsenic contamination in soils and irrigation water by up to 70%. It is concluded that the use of immobilized nanomaterials is a viable and sustainable strategy for agricultural decontamination; nevertheless, more studies on their environmental impact and cost-benefit are still required for their large-scale application.
immobilized nanomaterials, remediation of As, sustainable agriculture.
The presence of arsenic (As) in soils and irrigation water poses a critical threat to sustainable agriculture, crop quality, and public health. Regions such as Mexico, India, Bangladesh and Chile have reported high concentrations of As within the food security supply (Bhattacharya et al., 2010; Ruiz-Huerta et al., 2017). In addition, As is highly toxic and mobile in agricultural environments. For this reason, organizations such as the World Health Organization (WHO) and the Food and Agriculture Organization of the United Nations (FAO) have established permissible limits on water, soil, and food to reduce the associated risks.
In Mexico, the NOM-127-SSA-2021 and NOM-147-SEMARNAT/SSA1-2004 standards regulate the presence of As in drinking water and agricultural soils, establishing maximum values between 0.025 mg L-1 in water and 22 mg kg-1 in soils (Secretaría de Salud, 2022; SEMARNAT, 2007). Although there are traditional removal methods, such as coagulation, filtration, and ion exchange, they present limitations in efficiency and costs (Kumar et al., 2019).
Faced with this scenario, nanotechnology has emerged as a promising alternative, especially through the use of immobilized nanomaterials, which offer greater selectivity, stability, and efficiency in the adsorption of As. Therefore, this article presents a critical review of the use of immobilized nanomaterials in the remediation of soil and irrigation water contaminated with As, including case studies, mechanisms of action, technological comparisons, and their environmental assessment.
Arsenic in agricultural soils compromises ecosystem health and crop productivity (Ruíz-Huerta et al., 2017). In Mexican regions such as La Comarca Lagunera, the use of water contaminated with As has been shown to modify the pH, reduce the availability of essential nutrients, and affect the soil microbiota, decreasing the quality of the crops and increasing their toxicity by bioaccumulation (Osuna-Martínez et al., 2021).
As has both natural and anthropogenic origins. In its natural form, it is released by the erosion of arsenical minerals (arsenopyrite), volcanic activity, and the dissolution of minerals in aquifers rich in As. On the other hand, anthropogenic sources include the use of arsenical pesticides, contaminated fertilizers, irrigation with contaminated groundwater, mining activity, and industrial waste (Jiménez et al., 2023). Figure 1 summarizes these sources.
As directly interferes with agricultural soil dynamics, namely: microbiota, it inhibits beneficial bacteria and fungi, such as Rhizobium and Mycorrhizae, affecting nitrogen and phosphorus cycles, and reduces microbial biodiversity. Soil pH: in acidic soils, As has greater mobility and bioavailability; in alkaline soils, it can form complexes that immobilize nutrients. Essential nutrients: it competes with phosphorus and decreases the availability of iron (Fe), zinc (Zn) and manganese (Mn), altering metabolic processes, such as photosynthesis and protein synthesis (Singh and Srivastava, 2020; Beniwal et al., 2023).
As bioaccumulates in edible crops, affecting their nutritional value and generating toxicological risks in living beings. Its absorption depends on the physiological characteristics of the crop. Table 1 details the most affected crops and their associated risks, including rice, wheat, maize and vegetables.
Beyond its toxicity, As deteriorates the nutritional quality of food by altering plant metabolism.
It competes with phosphorus and reduces the availability of Fe, Zn and Mn, affecting growth and nutritional content (Beniwal et al., 2023).
It affects the synthesis of proteins, sugars, and antioxidants, which deteriorates the energy value, flavor, and quality of the food (Huerta and Hernández, 2012; Ruíz-Huerta et al., 2017; Upadhyay et al., 2019; Beniwal et al., 2023).
It reduces intestinal absorption of minerals, increasing the risk of anemia, immunodeficiencies and bone diseases (Camacho et al., 2011; Singh and Srivastava, 2020).
Studies in Bangladesh, India, Argentina, Mexico and other countries show that the As present in soils and irrigation water has caused severe effects on crops and public health. Table 2 summarizes these cases, showing their geographical distribution, crops involved, and health consequences, such as hydroarsenicism, cancers and nutritional deficiencies (Bhattacharya et al., 2010; Alarcón Herrera et al., 2020).
As in agricultural systems not only compromises crop yields, but also decreases their nutritional value, puts public health at risk, and limits food security in rural areas.
The use of immobilized nanomaterials has emerged as an innovative strategy in agricultural remediation, offering efficient and sustainable solutions to remove As in soils and irrigation water. Their integration into solid matrices improves stability, facilitates recovery, and allows controlled application in the field.
Nanoparticles (NPs) of zero-valent iron (nZVI) have been used for the decontamination of water from both heavy metals and chlorinated organic compounds, due to their high reactivity and adsorption capacity. The immobilization of these NPs in solid matrices, such as polymers or inorganic supports, improves their stability and facilitates their application in agricultural environments.
Findings such as those by Qu et al. (2019) showed that nZVI immobilized in a chitosan matrix were effective in reducing hexavalent chromium (Cr(VI)) in contaminated soils, achieving a significant decrease in Cr(VI) concentration in a short period (Qu et al., 2019). At the same time, in China, the application of immobilized nZVIs in agricultural soils contaminated with As resulted in a 70% reduction in the concentration of As available, improving soil quality and crop safety.
Nanoclays, such as montmorillonite, bentonite, and other smectic clays, have been used for soil remediation due to their high specific surface area and cation exchange capacity, properties suitable for adsorbing pollutants and improving the physical properties of the soil. Their immobilization in organic or inorganic matrices allows for more controlled and efficient application (Almasri et al., 2018; Baigorria et al., 2021).
In this sense, the incorporation of nanoclays in soils contaminated with organochlorine pesticides showed an 85% reduction in the concentration of these compounds, in addition to improving water retention and soil structure. In addition, in Spain, the application of immobilized nanoclays in grape-growing soils contaminated with copper led to a 60% decrease in the concentration of available copper, promoting the recovery of the soil microbiota and the health of the vines.
Nanocomposites of metal oxides, such as zinc oxide (ZnO) and magnesium oxide (MgO), possess antimicrobial and contaminant-adsorption properties. Their immobilization in polymeric or ceramic matrices makes it possible to use them in the remediation of soils and agricultural water (Gao et al., 2021). The application of ZnO nanocomposites immobilized in an alginate matrix showed efficacy in the removal of pathogenic bacteria and the adsorption of heavy metals in irrigation water (Gao et al., 2021).
In Mexico, the use of ceramic filters impregnated with metal oxide nanocomposites allowed the purification of irrigation water with water quality problems. In regions such as Coahuila and Durango, the implementation of irrigation water remediation technologies has shown positive results. The use of iron oxides, such as Fe3O4 or Fe2O3, immobilized in filtration systems has significantly reduced the levels of As in water for the irrigation of corn and wheat crops (Morales et al., 2012).
For example, in Guanajuato, Mexico, the use of natural zeolites has helped improve the quality of irrigation water in areas affected by contamination with different heavy metals; this method has allowed farmers to reduce the levels of heavy metals in crops, thus ensuring greater food security (Armienta et al., 2020).
Immobilized TiO2 NPs are known for their photocatalytic properties, used for the degradation of organic pollutants in water and soil (Yu et al., 2013). The immobilization of TiO2 NPs in solid supports prevents their dispersion in the environment and facilitates their recovery. One study reported that TiO2 immobilized in silica spheres was effective in the degradation of pesticides in irrigation water, achieving a removal of 90% of contaminants under solar irradiation (Yu et al., 2013).
The removal of As in soils and irrigation water by nanomaterials occurs through various physicochemical mechanisms that depend on the composition, structure, and functionalization of the materials. The interaction between As and nanomaterials determines their adsorption efficiency, influenced by pH, As concentration, competition with other ions, and the stability of the nanomaterial in the agricultural environment. The main mechanisms of adsorption of As by nanomaterials include the following.
It involves the substitution of arsenical ions on the surface of the nanomaterial (eg., functionalized iron oxides), common in modified zeolites and nanoclays.
It is the formation of strong stable or coordinated covalent bonds, especially in nZVI (Fe0) and some metal oxides, such as Fe3O4 and MnO2. nZVI acts mainly by reducing As+3 to insoluble forms and chemisorption on iron oxides formed in situ.
It attracts arsenical species with opposite charge, depends on pH, and is common in nanocomposites functionalized with amino groups, such as nanoclays with organic modifications and nanoparticles doped with biopolymers. In the case of nanoclays such as montmorillonite, it retains As+5 by ion exchange with anions such as phosphate or sulfate.
In the case of immobilized TiO2 NPs, they oxidize As+3 to As+5 and promote its subsequent adsorption on the active surface, degrading associated organic compounds, which facilitates the adsorption of As by light-assisted oxidation.
In porous matrices, such as ceramic or polymeric supports, that increase As retention by diffusion and retention in internal channels.
Figure 2 is a schematic representation of the main physicochemical adsorption mechanisms involved in the removal of As by immobilized nanomaterials: chemisorption in TiO2 NPs, electrostatic adsorption in nanoclays, ion exchange in clays, and oxidation processes in the presence of Fe NPs. The structures reflect interactions at the molecular level typical of each system.
These mechanisms together allow the immobilized nanomaterials to overcome the technical limitations of traditional methods; the efficiency depends on the type of nanomaterial, the arsenical species (As+3 or As+5), pH, ionic competence, or environmental conditions. Unlike methods such as coagulation, ion exchange, or phytoremediation, immobilized nanomaterials have greater efficiency (approximately 95%), less waste generation, and a potential for reuse and regeneration. Table 3)presents some materials that overcome the technical and environmental limitations of traditional technologies.
Various nanomaterials have been used effectively to remove heavy metals from water and soils in several regions of the country. In Durango, NPs of oxides and activated carbon filters have been used, with efficient results in the adsorption of As and Pb, reducing their solubility (García and Bonilla, 2015; Zhao et al., 2020). In Guanajuato, natural zeolite filters have been shown to have a high capacity to trap As and Hg in their pores (Sridhar and Adeyemo, 2009; Morales et al., 2012).
Likewise, in Coahuila, biofilters combined with iron NPs have been developed to remove As and Cd through biological processes assisted by microorganisms (Finnegan and Chen, 2012; Wang et al., 2022). In Hidalgo, the use of activated carbon with NPs has shown high efficiency in removing Pb and Hg, improving the adsorbent properties of the system (Lui et al., 2021; García and Pérez, 2021).
At the same time, in San Luis Potosí, good results have been reported in phytoremediation systems with carbon nanofilters, which allow the retention of As and Pb in combination with plants that absorb pollutants (López and Martínez, 2020; Zhao et al., 2020). In Sonora, nanoclays functionalized with amino groups have shown great capacity to reduce the availability of As and Pb in agricultural soils (Martínez et al., 2020).
Finally, in Querétaro, manganese oxides doped with iron NPs have been effective in stabilizing As and Cd in contaminated soils (Figure 3) (Ramírez et al., 2021). These applications have not only demonstrated technical efficiency, but have also contributed to improving environmental health and quality of life in rural communities exposed to high levels of As. In several cases, there has been a reduction in diseases associated with the consumption of contaminated water and an increase in farmers’ confidence in the safe use of water resources for their crops.
Historically, As in agricultural systems have been treated with conventional methods, such as chemical coagulation, activated carbon filtration, ion exchange, and phytoremediation. However, these approaches have significant limitations: low efficiency at low concentrations and difficulty in scaling in the field.
In contrast, immobilized nanomaterials offer key advantages: higher adsorption efficiency (up to 95%), low environmental impact, and possibly regeneration. Immobilized in supports such as biopolymers, zeolites, or biochar, they improve stability, reduce leaching, and facilitate recovery. Table 4 shows a comparison between traditional methods and immobilized nanomaterials considering efficiency, cost, and sustainability.
Despite their efficiency, the use of nanomaterials requires a comprehensive assessment to ensure their compatibility with the agricultural environment and consider the following sub-themes.
Nanomaterials based on biopolymers such as chitosan or cellulose are preferable, as they degrade naturally without leaving any lingering residues. Instead, metal nanoparticles can accumulate and alter soil structure in the long term.
Some nanoparticles (e.g., silver, Zn, or Ti oxides) have antimicrobial properties that can reduce beneficial soil populations, such as nitrogen-fixing bacteria or mycorrhizae. It is recommended to use natural supports to minimize their toxicity.
Unstabilized nanomaterials can migrate into nearby bodies of water. Their immobilization in solid matrices reduces this risk, keeping the material at the application site and preventing secondary contamination.
Although immobilized nanomaterials present techniques, they also involve ecological risks that must be considered before their large-scale application. One of the main ones is the alteration of the soil microbiota, since some nanomaterials, such as zinc and silver oxides, have antimicrobial properties that can reduce populations of beneficial microorganisms, such as nitrogen-fixing bacteria or mycorrhizae.
In addition, if not properly stabilized, nanomaterials can migrate into the environment, accumulate in sensitive areas, such as bodies of water or non-target plant roots, and modify essential soil processes. This mobility and environmental persistence could generate indirect ecotoxic effects on the food chain.
To minimize these risks, it is recommended to prioritize the use of biocompatible or biodegradable matrices, such as chitosan, cellulose, or alginate, which reduce toxicity and improve the retention of the nanomaterial at the application site. Likewise, post-application environmental monitoring protocols should be established, which include bioassays on soil microorganisms, leachate analysis, and evaluation of changes in soil physicochemical properties.
Finally, the use of nanomaterials in agricultural systems must be regulated by regulatory frameworks that ensure a safe, sustainable, and socially acceptable application, especially in regions with high environmental vulnerability.
Immobilized nanomaterials represent an innovative and effective technology for the removal of As in various water and soil matrices, with significant advantages over traditional methods in terms of efficiency, stability, selectivity, and environmental sustainability. Nevertheless, their large-scale application still faces challenges related to production costs, optimization according to soil or water type, and the evaluation of their ecological impact.
In addition, aspects such as biodegradability, interaction with soil microbiota, and leaching risk must be carefully analyzed to ensure safe and sustainable use. These materials have the potential to transform remediation strategies in agriculture, but their implementation must be accompanied by regulatory frameworks, environmental studies, and socio-economic strategies that ensure their responsible and effective adoption in the long term.
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