Emerging micropollutants: risks, regulatory trends, and adsorption based-magnetic nanotechnology solutions

Highlights

• Emerging micropollutants (EMPs) are posing a significant risk to human and environmental health and are detectable in analytical technique advancements.
• Magnetic and metal oxide nanomaterials provide a major and affordable alternative for the clean-up of EMPs along with their higher adsorption capabilities.

1 Introduction

The recent development of new technologies and the improvement of instrumental sensitivity has led to the identification of new classes of substances, named as emerging micropollutants (EMPs) (Zheng et al., 2025; Ratchnashree et al., 2023). The term ‘emerging’ is referred to a group of chemical substances that are detected in the environment, particularly in soil, surface water, groundwater, and the atmosphere, and they are not currently (or have only recently been) regulated (Sharma et al., 2025; Ruan et al., 2023). EMPs (Emerging micropollutants) constitute a wider group of synthetic and naturally occurring chemicals present in the environment, generally at trace concentration levels, ranging from picograms per liter (pg/L) to nanograms per liter (ng/L), which are causing growing concern due to their adverse effects on ecosystems and human health (Vasantha Raman et al., 2023; Dubey et al., 2023). Common groups of EMPs may include pharmaceutical and personal care products (PPCPs), per- and poly-fluoroalkyl substances (PFAS), surfactants, industrial chemicals, plasticizers, new pesticides, nanomaterials, and biological toxins (Kumar S. et al., 2025). These contaminants exhibit long-term persistence, capacity for further transformation and ability to undergo long-range transport, leading to their appearance even in regions far from their original sources, including remote areas (Scopetani et al., 2023). EMPs can enter the aquatic environment through various pathways including agricultural practices and run-off, landfill leachate, industrial activities, and direct discharge of treated or raw wastewater from and industrial wastewater treatment plants (WWTPs) (Haider Naqvi et al., 2023; Ayub et al., 2023; Jadaa and Mohammed, 2023; Jampílek and Králľová, 2025).

Though they have proven effective, traditional water treatment techniques including microbial degradation and enhanced oxidation processes are sometimes hampered by their high costs, intricate operations, and energy-intensive procedures (Kikanme et al., 2024). To clean-up EMPs from contaminated waters, there is a rising demand for alternative, more sustainable treatment techniques than conventional systems (Khajvand et al., 2022; Babaniyi et al., 2023; Ogundele et al., 2023).

The increasing complexity and diversity of pollutants in water systems necessitate the adoption of advanced technologies capable of selectively targeting and removing these compounds. In this context, nanomaterials represent a new Frontier in environmental remediation, offering unprecedented control at the molecular level (Kumar A. et al., 2025; Singh and Saxena, 2022; Karnwal et al., 2024). Their potential to be tailor-made means that particular treatment processes can be designed to deal with specific contaminants, including PFAS, pharmaceuticals, endocrine-disrupting chemicals, and heavy metals (Ben Dassi and Chamam, 2025; Dey et al., 2025). For the technologies to be sustainable and eco-friendly, there is a need to design processes for selective contaminant removal from the nanoparticles and to use efficient nanomaterial recovery and regeneration systems (Ayyadurai and Ragavendran, 2025; Aziz et al., 2025). In addition, application of metallic nanomaterials to adsorption processes is a highly promising route (Babaniyi et al., 2023; Ogundele et al., 2023; Sable et al., 2024). Adsorption as a process employs both physical and chemical forces in capturing and removing pollutants with strong efficiency potential for scaling up and integration into existing water treatment plants (Kumar S. et al., 2025; Singh et al., 2025).

Lastly, the confluence of water treatment and nanotechnology signals a paradigm shift towards next-generation clean-up methods wherein precision, efficiency, and sustainability are in delicate balance to address the global challenge of water pollution. The integration of such cutting-edge materials and methods is not only a technological advancement but also a necessary evolution to safeguard water resources for future generations. An in-depth review of the significant methods of synthesizing metal nanoparticles (MNPs), i.e., chemical, physical, and biological routes, is essential in order to understand their application in wastewater treatment (Chauhan et al., 2022; Li Q. et al., 2024). The review targets the application of MNPs due to their superior performance over other approaches in the removal of pollutants such as heavy metals, antibiotics, and pesticides. Compared to conventional treatment methods such as microbial degradation or oxidative advanced processes the use of MNPs offers a simpler yet efficient option. Their high surface area and catalytic properties make them uniquely capable of capturing and accumulating contaminants through physicochemical processes of adsorption (Ahmed et al., 2022; Kumar and Singh, 2025). Adsorption by metallic nanoparticles is one such trusted alternative to expensive and complex conventional treatment processes involving multiple processes such as microbial degradation, oxidation etc. The potential of MNPs for environmentally friendly and efficient water purification makes research in this field an imperative. While green nanotechnology offers valuable prospects for environmental remediation, further studies are essential to address the safety, regeneration, and long-term environmental impacts of MNPs. Therefore, this review aims to explore the synthesis methods, functional properties, and specific advantages of MNPs in wastewater treatment, with a particular attention to their feasibility, effectiveness, and ecological compatibility.

2 Review methodology

This review includes published research from the year 2014–2025, extracted from databases such as Web of Science, Google Scholar, ResearchGate, Scopus, and PubMed. Selection of papers included within relevance to the subject:

The application of nanotechnology in addressing EMPs presents both promising opportunities and notable concerns. One of the most explored treatment strategies involves adsorption-based techniques, which have shown significant potential for removing various pollutants. Comparative studies have been conducted to evaluate the efficiency of different nanomaterials in eliminating these contaminants, highlighting variations in their performance. Despite encouraging laboratory results, the real-world applicability of these technologies remains a challenge due to factors such as scalability, cost, and environmental safety. Additionally, limitations in nanotechnology solutions, including potential toxicity and long-term stability, must be carefully considered. From an environmental and sustainability standpoint, it is essential to balance the benefits of nanotechnology with its potential ecological risks to ensure responsible and effective implementation.

Numerous peer-reviewed studies were systematically screened for relevance to nanotechnology-based micropollutant removal, primarily adopting an adsorption technology and real-world applicability search strategy. Along with the keyword queries such as “Nanomaterials,” “Adsorption,” “Emerging Micropollutants,” and “Wastewater Treatment,” relevant studies were identified through a screening of the full manuscripts. The comparative analysis highlighted the pollutants associated with different wastes, including pharmaceuticals, pesticides, microplastics, plasticizers, surfactants, and flame retardants. In addition, nanotechnology-based solutions had been evaluated against actual implementation, taking into consideration cost, scalability, environmental risk, and regulatory constraints.

3 Advancing nanotechnology in wastewater treatment

The application of nanoparticles in water purification, especially for the removal of emerging micropollutants, offers a significant advantage over conventional methods due to their enhanced surface reactivity, tunable porosity, and superior adsorption efficiency. The fast emergence of micropollutants in wastewater, such as pharmaceuticals and pesticides, and industrial chemicals, has led to the need for efficient treatment technologies. Nanotechnology has been regarded as a revolutionary approach as it provides the highest surface area, with tunable chemical properties and multifunctional properties that enable various interactions with contaminants. A mechanistic classification of nanomaterials provides a clearer picture of their performance, shortcomings, and potential for real-world applications than simply mentioning generic “high efficiency.”

Carbon-based nanomaterials, such as carbon nanotubes (CNTs), graphene oxide (GO), and activated carbon composites, have been extensively investigated due to their strong adsorption capabilities. These materials interact with pollutants through л-л stacking, hydrogen bonding, and electrostatic interactions, mechanisms particularly effective for aromatic compounds present in many pharmaceuticals and pesticides., graphene-oxide-based materials have exhibited greater than 90% removal of diclofenac at neutral pH, while carboxyl-functionalized CNTs have realized 85%–95% removal of atrazine in batch studies (Liu et al., 2022; Singh et al., 2023). With their high adsorption potential and modifiability of surface groups, nanocarbon materials face regeneration difficulties and possible issues of nanofragment release into treated water, thus being considered a key impediment toward upscaling. Metal and metal-oxide NPs-TiO₂, ZnO, Fe₃O₄, and CO₂-provide adsorption functionalities coupled with catalytic or photocatalytic degradation. These nanoparticles can remove pollutants through surface adsorption, redox reactions, and photocatalysis under UV or visible light.

Under UV light, TiO₂ nanoparticles offered a mineralization rate of diclofenac up to 90% in 60 min, whereas adsorption capacities of 150 mg/g were noted by Fe₃O₄ nanoparticles for some antibiotics (Ahmed et al., 2021; Khan et al., 2024). The combination of the adsorption properties with photocatalysis presents certain advantages; however, nanoparticle aggregation, toxic by-product formation, and an expensive synthesis process present a barrier to larger-scale use. It is thus suggested that future studies concentrate on eco-friendly green synthesis methods, along with the reduction of toxic intermediates. Hybrid nanocomposites like magnetic biochar, metal-organic frameworks (MOFs), and silica-graphene composites have been developed for synergistic removal of pollutants. Those materials operate via adsorption coupled with catalytic degradation, often surpassing the synthetic ability of single-component systems. For example, magnetic biochar was able to remove more than 96% of bisphenol A, while MOFs show an extraordinary adsorption capacity of up to 473 mg g−¹ for tetracycline (Quan et al., 2019; Liu et al., 2019). If the concern is efficiency, these hybrids, indeed, guarantee that. However, their potential for reuse and for magnetic separation facilitate easy recoveries from the medium. The environmental stability of these materials and the enormous costs of their manufacturing pose great threats to their use, so the emphasis has shifted towards designs that are stable and also economically friendly for large-scale wastewater treatment. Nanoparticle-biology hybrids represent a very recent area of study in wastewater treatment that involve the coupling of nanoparticles with microbial systems to facilitate the degradation of contaminants. Nano-enzymes or magnetic nanoparticles are used for supporting microbial consortia to enhance electron transfer and increase pollutant bioavailability, thereby speeding up degradation. Studies show that these Fe₃O₃-microbe-facilitated degradation systems improve degradation of phenol by 50% compared to microbial treatment alone (Jiang et al., 2024). Apart from being eco-friendly, they also offer an excellent selective removal of contaminants. Maintaining stability at the nano-bio interface and mitigating potential nanotoxic effects on microorganisms remain, however, key research gaps. Future studies should focus on optimization of interface chemistry and long-term stability of these hybrid systems for ensuring reliable performance.

Collectively, these advances illustrate the versatility of nanomaterials in wastewater treatment. Carbon-based nanomaterials excel in adsorption, metal oxides provide catalytic activity, hybrid composites integrate multiple mechanisms, and nano-bio systems introduce environmentally compatible, targeted degradation. Despite promising laboratory results, several challenges including scalability, environmental stability, material recovery, and potential toxicity must be addressed to translate these technologies into practical applications. Addressing these gaps represents a critical direction for future research, aiming to develop sustainable, high-performance nanomaterial-based wastewater treatment strategies. Below a Table showing nanomaterials with micropollutants and their removal efficiency in advance wastewater treatment is reported.

4 Comparative analysis: limitations and real-world challenges of nano-technology based remediation

Nanomaterials represent powerful alternatives to conventional treatment methods being endowed with adsorption power and surface reactivity.

4.1 Comparison of nanomaterials-based technology and conventional methods

They still are a constraint in actual implementation because of high initial cost, uncertain ecotoxicity, and a lack of regulatory policies. Table 1 provides a comparative analysis between conventional methods and their nanotechnology-based alternatives aiming to highlight the major advantages and limitations of each. The incorporation of nanomaterials enhances the conventional processes in terms of adsorption capacity, photocatalytic efficiency and reusability.

TABLE 1. Comparative overview between conventional water treatment methods and their nanotechnology-based alternatives.

However, in addition to the lack of large-scale synthesis methods, nanomaterials encountered hindered large-scale deployment representing a novelty in public acceptance. Yet, the scientific literature is devoid of long-term field studies, and fragmented regulations stand as further roadblocks to development in wastewater infrastructure, especially in developing countries.

4.2 Environmental and economic impact assessment

Nanoparticle-based solutions, while effective, present several economic and environmental challenges. From a cost perspective, nanoparticles are significantly more expensive-up to 5 to 10 times-compared to traditional adsorbents like activated carbon, which limits their feasibility for large-scale applications (Gadel Hak et al., 2023). Additionally, many nanoparticle synthesis methods demand high-temperature processes exceeding 500 °C, leading to increased energy consumption, higher operational costs, and larger carbon footprint (Wang et al., 2024). Another critical concern is waste generation; nanoparticles often become contaminated with metals during use, making their safe disposal difficult due to their persistent and resistant nature (Sable et al., 2024; Kumar M. K. et al., 2025; De Luca et al., 2023). These factors collectively highlight the need for more cost-effective, energy-efficient, and environmentally responsible approaches in nanomaterial development.

4.3 Problems of implementation in the real world

Despite their promising capabilities, nanoparticle-based techniques for removing EMPs face significant practical and societal challenges. One major limitation is the lack of pilot-scale testing, as most research remains confined to laboratory conditions without real-world validation (Hussain et al., 2023). Furthermore, actual wastewater systems are complex and contain a multitude of competing contaminants, which can hinder the effectiveness of nanoparticle adsorption (Altaf et al., 2022). Public and regulatory acceptance also poses a barrier, largely due to uncertainties regarding the long-term impacts of engineered nanomaterials on both human health and the environment (Dhumal et al., 2025; Dou et al., 2012; Wang et al., 2012). A particular concern is the persistence of nanoparticles in aquatic systems, as their stability makes post-treatment removal difficult and raises environmental safety issues (Edo et al., 2025; Fernandes, 20212; Fernandes et al., 2019; Shatkin, 2017). These limitations underscore the need for more comprehensive research, transparent risk assessments, and the development of safer, scalable technologies.

5 Conventional technologies for EMPs removal WWTPs

The current methods for remediating EMPs operate through various mechanisms and offer specific advantages, yet each also presents significant limitations that hinder widespread adoption (Altaf et al., 2022). For example, electro-kinetic remediation is both cost-effective and efficient, particularly in fine-grained or heterogeneous soils (Han et al., 2021). However, it suffers from drawbacks like high energy usage, poor mass transfer, and incomplete removal of organic pollutants bonded to clay particles or microorganisms. Similarly, microbial bioremediation is low-cost, environmentally friendly, and capable of rapid adaptation through genetic mutation, but its effectiveness is often constrained by a dependence on specific environmental conditions (Hofman-Caris and Hofman, 2019).

The advanced oxidation processes (AOPs) are highly effective at breaking down persistent organic pollutants into simpler, more stable substances with minimal sludge production (Paliwal et al., 2012). Nonetheless, concerns over the human health risks posed by hydrogen peroxide (Lama et al., 2022), along with the high costs, substantial energy and chemical demands, and the formation of intermediate by-products, limit their practical use. Membrane filtration offers another approach, known for its compact footprint, reduced sludge generation, and strong performance in removing microcontaminants in an eco-friendly manner. However, its application at large scale is challenged by the high energy requirements, the production of concentrated waste, and the frequent need for membrane replacement (Saravanan et al., 2021).

A variety of technologies-such as advanced oxidation, microbial degradation, and enzymatic catalysis-have been explored to mitigate EMP contamination. While each has proven effective in specific contexts, their broader implementation is limited by prohibitive costs. In contrast, adsorption and biosorption techniques stand out as cost-effective alternatives, especially when employing waste materials for pollutant removal (Krishnan et al., 2023; Sen, 2023).

The current remediation technologies for emerging micropollutants are shown in Table 2. EMPs, including pharmaceuticals, pesticides, and endocrine-disrupting compounds, represent a growing concern in wastewater treatment due to their persistence and harmful effects on ecosystems and human health. Several conventional remediation technologies have been developed to address EMPs, each with distinct mechanisms, benefits, and limitations. Table 2 summarizes the key remediation strategies currently used, including electro-kinetic remediation, microbial bioremediation, advanced oxidation processes, and membrane filtration systems.

TABLE 2. Conventional remediation technologies used for EMPs.

While each of these technologies offers unique advantages, their limitations necessitate the exploration of more integrated and effective solutions. One promising direction is the development of hybrid systems, particularly membrano-nano composites, where metallic nanoparticles (MNPs) are embedded into or combined with membrane matrices. These systems have shown improved contaminant adsorption, enhanced reactivity, and reduced fouling, thereby overcoming some of the key shortcomings of standalone membrane and adsorption systems.

For example, incorporating silver, titanium dioxide, or zero-valent iron nanoparticles into polymeric membranes can significantly enhance antimicrobial activity, permeability, and selectivity. Moreover, such hybrid approaches align with environmentally sustainable goals while improving efficiency in removing a broader range of micropollutants.

Therefore, while the conventional approaches summarized in Table 3 provide foundational insights into current practices, the focus of this review will shift toward emerging nanotechnology-enhanced solutions, particularly the use of metallic nanoparticles, to evaluate their potential in overcoming existing limitations in EMP remediation.

TABLE 3. Nanomaterials with micropollutants and their removal efficiency.

6 Overview of emerging micropollutants

EMPs encompass a broad spectrum of organic and inorganic contaminants that enter aquatic environments through domestic, agricultural, and industrial sources (Gebru and Werkneh, 2024). Among these, Pharmaceuticals and Personal Care Products (PPCPs) represent a particularly concerning subgroup due to their chemical complexity, biological activity, and persistence in the environment (Shah, 2024). Common PPCPs include antibiotics, analgesics, hormones, antiepileptics, fragrances, and sunscreen agents. These compounds are typically present in trace concentrations (ng/L to μg/L), yet they can induce endocrine disruption, antibiotic resistance, and bioaccumulation even at such low levels (Chakraborty et al., 2023; Rehman et al., 2024). The challenge in removing PPCPs from water lies in their low biodegradability and structural diversity, which limit the efficiency of conventional wastewater treatment technologies (Ethiraj and Samuel, 2024; Demaria et al., 2025; Suleiman et al., 2025). As a result, many of these substances pass through treatment plants intact or only partially degraded, eventually entering surface and groundwater systems and posing a long-term risk to ecosystems and public health (Chauhan et al., 2025; Singh et al., 2025; Jayasekara et al., 2025).

Given these limitations, advanced nanomaterials, such as functionalized nanoparticles, nanocomposites, and carbon-based nanomaterials, have emerged as a promising solution for PPCP removal. Their high surface surface-to-volume ratio, tailorable surface properties, and nanoscale reactivity enable the selective adsorption and degradation of complex pollutants that conventional methods cannot address (Rasheed et al., 2020; Ogbeh et al., 2025). In particular, nanomaterials can be engineered with specific surface functionalities to target PPCPs through hydrogen bonding, π-π interactions. or electrostatic attraction. making the process efficient and adaptable (Ojha et al., 2021; Rani et al., 2025; Ali et al., 2019; Padhiary et al., 2025).

Moreover, these technologies offer the added advantage of regeneration and reuse, enhancing their sustainability for long-term water treatment applications. Their integration into hybrid systems (e.g., membrane-nano composites or photocatalytic reactors) is opening new frontiers in environmental remediation-enabling real-time, decentralized, and high-efficiency solutions for emerging pollutants. The urgent need to mitigate the ecological and health risks posed by PPCPs underscores the importance of transitioning toward next-generation water treatment strategies, where nanotechnology plays a pivotal role in achieving safer and cleaner water systems. As illustrated in Figure 1, the adsorption of EMPs depends on both environmental parameters and the physicochemical properties of materials whose surface chemistry and hydrophobicity influence their interaction with various contaminants. In particular, the properties of microplastic, such as particle size, surface area, surface chemistry, and hydrophobicity, are highlighted because they strongly affect adsorption efficiency and interactions with other pollutants.

6.1 Microplastics

MPs have become a pressing concern due to their widespread presence in aquatic environments, which has required stringent regulations and innovative treatment methods (Yang et al., 2022). In fact, WWTPs have long been recognized as a potentially significant source of MPs pollution in aquatic environments due to their polydisperse and degradation-resistant properties of MPs along with their capacity to pass through treatment processes. Several studies (Bilal et al., 2020) have reported the adverse effects of MPs on biota which include disturbances in feeding, mobility and reproduction that can lead to lethal or sub-lethal effects. Moreover, MPs can also contain toxic pollutants, such as heavy metals or endocrine-disrupting chemicals, increasing their bioavailability and toxicity, and affecting development and reproduction in humans and other species.

6.2 Pharmaceuticals and personal care products (PPCPs)

Pharmaceuticals and personal care products have become a major class of emerging micropollutants as they are continuously found in water bodies potentially adversely impacting ecosystems and human health. To tackle this problem, a wide variety of different treatment technologies have been developed and extensively studied, including physical processes such as membrane filtration and adsorption, biological processes using microbial degradation and enzymatic activity, and chemical methods that include AOPs and coagulation-flocculation techniques. While the effectiveness of these methods has been conventionally demonstrated, their various inefficiencies, including incomplete removals, energy-consuming operations, and the generation of secondary pollutants, call for new ideas.

The pharmaceutical and personal care products (PPCPs), including hormones, antibiotics, lipid regulators, beta blockers, non-steroidal anti-inflammatory drugs, antidepressant, anticonvulsants, antineoplastics among pharmaceuticals and fragrances, preservatives, disinfectants and sunscreen agents among personal care products, are EPs which might pose potential hazards to environment and health. These pollutants are becoming ubiquitous in the environments because they cannot be fully removed by the conventional WWTPs due to their toxic and recalcitrant properties. Thus, their presence has received increasing attention in recent years, resulting in great concern on their occurrence, transformation, fate and risk in the environment, and regulatories (Dey et al., 2019; Ziylan-Yavas et al., 2022; Han et al., 2024; Jiang et al., 2025; Kim et al., 2024; Rückbeil et al., 2025; Satyam and Patra, 2024).

6.3 Plasticizers

Plasticizers, such as bisphenol A (BPA) and phthalates, are generally added to materials to increase their softness and flexibility (Fasano and Cirillo, 2018). However, because these compounds are not completely removed by conventional wastewater treatment processes, they increasingly are being recognized as persistent environmental pollutants. Most often, plasticizers persist in treated effluents and sometimes in sewage sludge, thus posing a dual threat of environmental contamination and potential problems with sludge reuse in agriculture or landfills. They propensity to leach from plastic products and enter aquatic systems increases their impact, contributing to serious health issues such as endocrine disruption, reproductive abnormalities, and an increased risk of cancers (Godswill and Godspel, 2019). Given these challenges, considerable efforts have been to develop nanoparticle-based techniques to increase the removal efficiency of plasticizer from wastewater. Among these, adsorption techniques using engineered nanoparticles have shown impressive performance due to the high surface area of the nanoparticles, easily tunable surface functionalities, and strong affinity for both hydrophobic and hydrophilic pollutants (Raeisi et al., 2017). Examples include nanoparticle carbon-based materials (such as carbon nanotubes and graphene oxide), metal oxides (like titanium dioxide and iron oxide), and functionalized polymers that have been widely investigated for selective adsorption of plasticizers from complex aqueous matrices (Yin and Hakkarainen, 2011; Yin et al., 2014).

6.4 Surfactants

Among the most common organic contaminants found in wastewater, surfactants are the main constituents of cleaning agents and detergents and various industrial products. They are amphiphilic chemicals and thus exhibit hydrophilic and hydrophobic properties, which give them the characteristic tendency to reduce surface tension and thereby increase cleaning effectiveness. However, their structural diversity, from anionic to cationic, including nonionic and zwitterionic forms, significantly challenges conventional treatment methods, since each class displays unique chemical behaviors and persistence in aquatic environments. Although their structures are tailored for rapid biodegradation, intermediate surfactants degradation products often maintain or exceed the toxicity of the parent compounds, hence the environmental and health risks associated with this class of compounds (Knepper and Berna, 2003). The exploration of eco-friendly substitutes and their harmful effects on aquatic organisms is the focus of ongoing research. Regulations have begun to focus more on safety and biodegradability of surfactants in consumer goods.

Numerous articles have been published on the adverse effect of surfactants on the environment, wildlife and humans (Human & Environmental Risk Assessment (HERA) Project, 2002; Human & Environmental Risk Assessment (HERA) Project, 2013).

6.5 Flame retardants

Flame retardants are a group of various chemicals added to plastics, textiles, and electronic materials to reduce their flammability and slow the spread of fire. Although they play a crucial role in improving fire safety, their widespread use has raised concerns about their persistence, bioaccumulation, and adverse impacts on environmental and health issues. Flame retardants, of which BFRs represent a prominent group, including polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCD), have been pointed out as an emerging micro pollution given their widespread occurrence in water, soil, and air (Ward et al., 2008; Fromme et al., 2016; GadelHak et al., 2023; Gai et al., 2014). Conventional wastewater treatment processes, such as coagulation, sedimentation, and biological processes, are generally ineffective at removing flame retardants due to their low water solubility and high chemical stability. Advanced treatment processes, such as, AOPs, and membrane filtration, have shown promise but are often inhibited by high operational costs and incomplete removal. Regulatory approaches to mitigate the environmental and health challenges resulting from the use of flame retardants and other EMPs are matched with the development of potentially greener alternatives and innovative treatment technologies, such as nanoparticle-based systems. Such recent developments point to a way forward in efforts to reduce risks from flame retardants while enabling the safe reuse and management of water resources.

6.6 Pesticides

Among the most commonly used agricultural pesticides in agriculture are herbicides, insecticides, and fungicides, all intended to protect crops and improve productivity. Although essential to modern agricultural methods, the excessive and non-selective use of these pesticides has made them one of the most significant emerging micropollutants in water systems. Due to their chemical stability, pesticides often persist in the environment and can reach aquatic ecosystems through agricultural runoff, leaching, and improper disposal. Their occurrence in water poses serious risks for human health, biodiversity, and ecological balances (Mehta, 2023). Many pesticides are designed to resist degradation and remain effective for long periods. This persistence allows them to be transported through soil and water, contaminating groundwater, rivers, and lakes. For example, organochlorine pesticides such as DDT can persist in the environment for decades (Kadiru et al., 2022). The synthesis of magnetite-impregnated functionalized MWCNTs MWCNT–OH–Mag and MWCNT–COOH–Mag for 2,4-D and atrazine adsorptions under optimal pH conditions-enhanced improved adsorption performance, stability, and quick adsorption. The high adsorption capacity combined with rapid adsorption kinetics makes the materials reusable for the adsorption of contaminants from wastewater (Pereira et al., 2023) Currently, there is a strong emphasis on the development of environmentally friendly pesticides and integrated pest management strategies. This shift is driven by a growing awareness of EMPs and their potential risks. Research and regulatory frameworks have intensified in response, with governments around the world focusing on stricter regulations, advanced treatment technologies, and safer alternatives to reduce the impact of these substances. Effectively addressing the challenges posed by EMPs requires a holistic approach that integrates technological innovation, legislative action, and public education. Table 4 provides an overview of the main EMP categories, representative examples, and their reported human health effects according to recent studies.

TABLE 4. Shows a comprehensive discussion EMPs and their impacts on human health.

Traditional wastewater treatment methods, such as coagulation-flocculation, sedimentation, filtration, and activated sludge systems, are not as effective at removing organic pollutants. For instance, the removal efficiency of pharmaceuticals and personal care products (PPCPs) ranges between 20% and 90%, depending on the compound and the process. Hormones such as estradiol and 17α-ethinylestradiol exhibit rather moderate removal efficiencies (from ∼50 to 80%) with conventional systems, and some antibiotics, e.g., amoxicillin and sulfamethoxazole, are removed very poorly (30%–60%).

Similarly, surfactants such as alkyl benzene sulphonic acid (LAS) exhibit efficiencies of 50%–80%, resulting in significant residues in treated water. Flame retardants and pesticides also exhibit removal efficiencies generally below 50%, depending on the property of the chemical being tested. These inefficiencies demonstrate the ability of pollutants to persist and make it mandatory to develop modern remediation technologies. The combined treatment of sewage and industrial effluent tends to improve the efficiency of organic pollutants’ removal processes due to the high organic concentrations in industrial effluents. The immediate occurrence of wastewater leads to surface runoff from industrial effluents, resulting in varying wastewater outputs at different times of operation. In this context, the construction of a specialized remediation treatment facility is essential and indispensable.

7 Adsorption: a promising nanotechnology-based strategy for EMP remediation

Adsorption has gained considerable attention as an effective and versatile method for removing EMPs from wastewater. Its appeal lies in its simplicity, efficiency, and adaptability to a wide range of contaminants. When combined with nanotechnology, the adsorption process becomes even more effective due to the unique properties of nanomaterials such as high surface area, tunable porosity, and modifiable surface chemistry—that significantly improve adsorption performance (Alprol, 2024). This method holds great promise for the removal of persistent organic and inorganic compounds, often finding application in industries for product separation and wastewater treatment (Behera et al., 2021).

There are two main types of adsorption: physical and chemical, which differ in both mechanism and strength of interaction. In practical terms, physical adsorption relies on weaker interactions like Van der Waals forces and is often reversible. This makes it suitable for applications requiring regeneration and reusability of the adsorbent-such as magnetic nanoparticles. Chemical adsorption, or chemisorption, forms stronger, often irreversible bonds. This is especially useful when targeting stubborn or reactive pollutants that require more permanent capture (Nayak et al., 2024).

Nanomaterials can be engineered to exhibit one or both of these adsorption behaviors, depending on surface modifications and functionalization. For example, functionalized carbon nanotubes or metal oxide nanoparticles can selectively bind to heavy metals or pharmaceutical residues through surface-active groups, combining the advantages of high affinity and selective (Ibrahim et al., 2024). Moreover, hybrid nanostructures such as metal-organic frameworks (MOFs) or magnetic nanocomposites can be tailored to provide mutli-modal adsorption sites, further enhancing the efficiency of chemical adsorption or chemisorption at higher temperatures. It involves strong intermolecular forces with high activation energies and cannot be reversed. Figure 2 schematically illustrates the adsorption mechanism of nanomaterials used for EMPs followed by the desorption and reuse of MNPs. Chemisorption typically has a high heat of adsorption as it is accompanied by a chemical reaction (Kainth et al., 2024).

8 Synthesis of metal and metal oxide nanoparticles for adsorption systems

The synthesis of metal and metal oxide nanoparticles (MNPs) is fundamental for their effectiveness in environmental remediation, particularly in adsorption-based removal of EMPs. Various chemical, physical, and biological approaches have been developed, each offering different levels of control over nanoparticle properties such as size, morphology, crystallinity, and surface reactivity-key parameters in adsorption performance.

8.1 Chemical methods

Chemical synthesis remains one of the most widely used strategies for the production of inorganic nanoparticles (MNPs), which involves the reduction of metal precursors through organic or inorganic reducing agents (Ahmad I. et al., 2024). One such method is the sol-gel approach, which, for example, was used to synthesize titanium oxide nanoparticles by dissolving titanium chloride in an ice bath with urea. The resultanting TiO₂ nanoparticles, with size ranging from 200 to 1,000 nm, exhibited distinct diffraction peaks (101, 004, 200, 105, and 204) in XRD analysis, confirming their crystalline nature. The vibrational bands observed at 3,406 and 3,107 cm⁻¹ in the FTIR spectrum further confirmedtheir identity.

Silver nanoparticles have also been synthesized via chemical reduction using agents such as sodium borohydride. TEM revealed an average particle size of 24.3 nm, and XRD confirmed crystallinity with peaks at planes (111), (200), (220), (311), and (222) (Ahmad A. et al., 2024). Similarly, (Ali et al., 2024), reported the reduction of silver nitrate using sodium citrate and tannic acid, producing AgNPs with an average diameter of 30 nm.

The co-precipitation is another commonly used chemical method, valued for its simplicity, low cost, scalability (up to kilogram scale), and environmental compatibility (Petrecca et al., 2021). This approach typically involves the addition of a base or reducing agent to aqueous solutions of metal salts-such as chlorides, nitrates, or sulfates—at room or elevated temperatures in an inert atmosphere (Rahimi and Doostmohammadi, 2020; Ranoszek-Soliwoda et al., 2017). Variables including reagent concentration, type of base, pH, ionic strength, and surfactants can be tailored to influence nanoparticle size, shape, and composition (Sharma et al., 2024). However, nanoparticles synthesized via co-precipitation often exhibit high polydispersity and poor crystallinity, necessitating post-synthesis annealing to improve magnetic and structural properties (Gholami et al., 2024).

Hydrothermal synthesis is another effective technique in which aqueous metal salts are heated under high pressure in autoclaves, promoting the transformation of metal hydroxides into metal oxide nanoparticles (Iqbal et al., 2024). This method can also use alternative solvents such as ethylene glycol or diethylene glycol in solvothermal synthesis (Jiang et al., 2024). Parameters such as reagent concentration, temperature, and reaction time significantly influence the morphology and crystallinity of the particles (Albino, 2020). Despite its advantage in improving crystallinity, hydrothermal synthesis is limited by slow reaction kinetics and relatively long processing times, which often result in products with broader size distributions.

Among advanced methods, thermal decomposition of organometallic precursors offers precise control over nanoparticle size, shape, and composition (Lartigue et al., 2011; Muzzi et al., 2022). Herein, precursors (e.g., metal carbonyls, metal-acetylacetonates) are decomposed in high-boiling-point solvents (e.g., benzyl ether, 1-octadecene) assisted by surfactants like oleic acid or oleylamine (Hyeon, 2003; Park et al., 2005; Patra et al., 2025). Metal oxide nanoparticles can be produced directly from precursors containing cationic metals, while metal nanoparticles require subsequent oxidation steps for oxide formation (Lefebure et al., 2011). Growth models such as those proposed by LaMer and Dinegar (2002) and further refined by Kwon and Hyeon (2008), help explain nucleation and formation of monodisperse particles.

However, the chemical reduction method presents significant environmental concerns. The use of reducing agents such as sodium borohydride, sodium citrate, liquid paraffin, and oleylamine often leads to the generation of toxic byproducts, sometimes more hazardous than the pollutants involved (Talapin et al., 2001; Calero-DdelC et al., 2010; Tran et al., 2025; Vasantha Raman et al., 2023). These risks, combined with the additional disposal costs, reduce the overall sustainability of these approaches.

8.2 Physical methods

Several physical methods-including pyrolysis, ball milling, ultrasonication, laser ablation, lithography, and sputtering-have been employed for the synthesis of MNPs. Among these, laser ablation is considered an efficient, high-yield alternative to chemical synthesis due to its short processing time and the production of stable nanoparticles (Li et al., 2021). In this method, a high-energy laser pulse targets a solid surface, generating a low-flux plume that subsequently condenses into nanoparticles. For instance, (Li et al., 2014; Mohammed et al., 2021), successfully synthesized copper nanoparticles averaging 51 nm with semi-spherical morphology.

Spray laser pyrolysis has also been used to produce ZnO nanoparticles (10–25 nm) with a hexagonal wurtzite structure, confirmed by TEM analysis. Similarly, evaporation-condensation methods.

The utilization of laser ablation yielded spherical copper oxide nanoparticles between 3 and 40 nm in size (Singh et al., 2008). Laser ablation has also been employed for synthesizing colloidal silver and copper oxide nanoparticles (Kudhur et al., 2024).

Another effective physical approach is sputtering, or physical vapor deposition (PVD), in which high-energy ions collide with a metal target, ejecting atoms that deposit onto a substrate and condense into nanoparticles. This method allows for precise control over particle morphology and distribution (Manninen, 2015). Using this technique, (Pentimalli et al., 2015), synthesized platinum nanoparticles in a glycerol matrix, where particle sizes varied from 1.8 to 3.2 nm depending on argon pressure (1.0–9.0 Pa).

Ball milling is a top-down mechanical process in which metal powders are ground to nanoscale through the transfer of energy from rotating balls. Parameters such as milling time, force, speed, and temperature significantly influence the nanoparticle characteristics (Konnerth et al., 2016). Although effective in producing uniformly sized nanoparticles, physical methods are often limited by high energy consumption and associated costs (Bramsiepe et al., 2012; Meierhofer and Fritsching, 2021).

8.3 Biological methods

Biological nanoparticle synthesis is gaining momentum as an eco-friendly and cost-effective alternative that reduces the toxic byproducts associated with chemical methods (Meierhofer and Fritsching, 2021). This approach uses microbial systems (bacteria and fungi) and plant-derived extracts as reducing and stabilizing agents.

Bacteria such as Pseudomonas sp. strain THG-LS1.4 has been used for biosynthesizing silver nanoparticles, with FE-TEM confirming sizes ranging from 10 to 40 nm and irregular shapes (Carrapico et al., 2023). Similarly, P. aeruginosa BS-161R produced spherical AgNPs with an average size of 13 nm (Abeer Mohammed, Abd Elhamid et al., 2022). Gold nanoparticles (15–30 nm) were also biosynthesized using Pseudomonas aeruginosa strain ATCC 90271 (Menon et al., 2017), while Geobacter sulfurreducens yielded AuNPs with an average diameter of 20 nm (Jimenez-Sandoval et al., 2023).

Despite promising results, bacterial synthesis has limitations, including the need for sterile conditions and the potential pathogenicity of some strains. As a result, the focus has increasingly shifted toward the use of plant extracts, rich in phytochemicals and capable of simultaneously reducing and stabilizing metal ions during nanoparticle formation (Chelike et al., 2024; Ali et al., 2021; Mehta et al., 2024). Figure 3 below shows nanoparticle synthesis methods that may involve chemical, physical, and biological pathways. The illustration was prepared using information from the review source (Arbab et al., 2021).

A strategic shift toward eco-design and life-cycle assessment (LCA)-based synthesis optimization will be essential to bridge the gap between lab innovation and real-world application. Additionally, the development of modular pilot-scale production systems that integrate green synthesis with post-processing for magnetic recovery or reuse will further enable nanotechnology to be viably integrated into advanced water treatment infrastructure.

The methods for synthesizing nanoparticles may involve chemical, physical, and biological pathways a summary of these methods is shown in Table 5. However, while many chemical methods prevail due to their scalability and precision, their environmental disadvantages serve to emphasize the need for greener alternatives.

TABLE 5. Comparison of physical, chemical and biological pathways involved in nanoparticles synthesis.

9 Sustainable environmental applications of magnetic nanotechnology

In line with the focus of this review on MNPs-technology-Based solutions, this section summarizes the practical applications of magnetic and metal oxide NPs for the remediation of EMPs. Rather than restating pollutants-specific cases discussed in previous sections, it highlighted how nanomaterials such as magnetic composites, nano-zero-valent, iron, and graphene-magnetic hybrids, serves as multi-functional platforms for the adsorption, catalysis, and separation. Their high surface area, magnetic recoverability, and reusability make them ideal for eco-friendly wastewater treatment systems. The effective removal of steroids, pesticides, antibiotics, and steroids from wastewater has been proven in the literature using metal and metal oxide nanoparticles (Kanan et al., 2022). Due to its sustainability and the wide variety of adsorbents that can be used, adsorption is therefore the method of choice.

9.1 Removal of pharmaceuticals

The distinctive properties of nanoparticles-such as their large surface area, high reactivity, and customizable functionalities make them highly effective for removing pharmaceutical contaminants from wastewater. Among these, Fe/N-CNT/beta-cyclodextrin nanoparticles demonstrated excellent performance in photocatalytic adsorption, with aspirin removal reaching 71.9%. This effectiveness was validated through various characterization techniques including UV-Vis spectroscopy, scanning electron microscopy (SEM), and Fourier Transform Infrared Spectroscopy (FTIR). Similarly, Ca(II)-doped chitosan/beta-cyclodextrin composites, characterized using UV-Vis, FTIR, Thermogravimetric-Differential Analysis (TGDA), SEM, and Energy-Dispersive X-ray (EDX), showed an outstanding removal efficiency of 99.09% for acetaminophen.

Further characterization using SEM, Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), UV-Vis spectroscopy, and X-ray Photoelectron Spectroscopy (XPS) indicated that the magnetic graphene oxide sponges (MGOS) had a maximum adsorption capacity of 473.0 mg/g for tetracycline. Furthermore, diclofenac treated with Cu-NPs exhibited a removal rate of 91.4%, as indicated by UV-Vis and XRD analysis. Photocatalytic degradation of cefixime using TiO2 nanoparticles achieved a removal efficiency of 90.0%, as supported by zeta potential analysis, FTIR, and UV-Vis spectroscopy (Islas-Flores et al., 2013; Praskova et al., 2014; Mphahlele et al., 2015; Liu et al., 2019; Rahman and Nasir, 2020).

These findings highlight the significant potential of metal and metal oxide nanoparticles to enhance chemical treatment methods for pharmaceutical pollutants in water. Their large specific surface area, high reactivity, and amenability to target specific contaminants make them ideal for multi-component pharmaceutical mixtures that are commonly found in wastewater. Advanced characterization methods enable a greater insight into removal mechanisms and nanoparticle interactions, supporting the optimization and real-world application of these technologies. Thus, nanoparticle-based solutions hold a future solution to pharmaceutical pollution in aquatic ecosystems, in the interest of public health and environmental sustainability.

9.2 Removal of MPs

The use of nanoparticle-based materials for the removal of microplastics (MPs) and related contaminants such as bisphenol A (BPA) from aquatic systems has emerged as a promising and efficient strategy. Due to their high adsorption capabilities, various metal and metal oxide nanoparticles have been employed for this purpose. For instance, chitosan-nanoscale zero-valent iron (nZVI) composites have demonstrated a BPA removal efficiency of 95.0%, as confirmed through characterization techniques like Fourier-Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). Similarly, magnetic biochar nanoparticles achieved a 96.3% BPA removal rate, as verified through X-ray Photoelectron Spectroscopy (XPS), XRD, TEM, FTIR, and Raman spectroscopy. Moreover, graphene aerogel embedded with magnetic iron oxide nanoparticles (IO-NPs) showed a remarkable BPA adsorption capacity of 353.8 mg/g, determined using SEM, XRD, FTIR, and Raman spectroscopy (Nizamuddin et al., 2019; Quan et al., 2019; Dehghani et al., 2020; Karri et al., 2020; He et al., 2020).

These studies underscore the effectiveness of nanoparticle-based materials in adsorbing and eliminating MPs and associated organic pollutants like BPA. The high surface area and tunable surface properties of nanoparticles enhance their ability to trap such contaminants efficiently (Quan et al., 2019). The activation potential of nanoparticles also contributes to improved selectivity and stronger binding with a variety of pollutants. Additionally, the application of advanced characterization techniques helps to thoroughly understand the interactions between nanoparticles and pollutants. This knowledge enables the optimization of these materials for broader environmental applications, supporting efforts to protect freshwater sources and mitigate the harmful impacts of plastic pollution on ecosystems and human health.

9.3 Removal of PPCPs

Nanoparticles are able to perform optimally in environmental remediation because they have a large surface area, are tunable, and thus reusable for the effective adsorption of PPCPs contaminants. For example, TiO₂ and ZnO nanoparticles have been shown to have photocatalytic activity leading to the adsorption and degradation of organic UV filters benzophenone and octinoxate by Ahmad A. et al. (2024). Carbon nanomaterials such as graphene oxide and activated carbon are able to adsorb the insect repellents like N,N-Diethyl-m-toluamide (DEET) effectively by π-π interaction and high surface area (Li J. et al., 2024). Similarly, silica nanoparticles and magnetite (Fe₃O₄) can capture aromatic fragrances and phthalates due to their functionalized surface and magnetic recoverability (Albino, 2020). Clay nanoparticles and nano-zero valent iron (nZVI) are highly efficient at adsorbing surfactants and sulfates contained in soaps and shampoos (Rahimi and Doostmohammadi, 2020). Al₂O₃ and CeO₂ metal oxides are used for the removal of paraben and phenolic preservatives, while silver nanoparticles (AgNPs) and zeolites remove triclosan and triclocarban disinfectants (Carrapico et al., 2023; Singh et al., 2008). However, despite these advantages in terms of selective adsorption and regenerability, some challenges remain: nanoparticles can be incredibly expensive and have a huge environmental impact. On this front, advances in environment-friendly synthesis and large-scale application can mitigate these problems and increase efficiency against various PPCP pollutants.

9.4 Removal of plasticizers

Nanoparticles are highly efficient adsorbents for toxic and carcinogenic plasticizers such as Bisphenol A (BPA) and Bisphenol A diglycidyl ether (BADGE), which are endocrine disruptors consequently having human and environmental implications. BPA removal through carbon-based nanomaterials of graphene oxide and MWCNTs occurred through adsorption at high capacities because of π-π stacking and hydrogen bonding interactions and thus removal mechanisms in water sources (Li Q. et al., 2024). Nano-zero valent iron (nZVI), and magnetic nanoparticles (such as Fe₃O₄) can adsorb contaminants while providing facile recovery due to their magnetic characteristics and surface activity (Rahimi and Doostmohammadi, 2020). Metal-organic frameworks (MOFs) and mesoporous silica nanoparticles exhibited target adsorption affinity to plasticizers by means of their tunable porosity and functionalized surfaces for contaminants (Bellusci et al., 2024). Although highly effective, their synthesis optimization for least environmental imprint and optimized capability becomes utmost to be a worthy answer to the challenges in plasticizers contamination.

9.5 Removal of surfactants

Nanoparticles could bring about an extremely effective surfactant remediation system, which are some of the major persistent contaminants found in landfills, sludge, and wastewater. Surfactants such as alkyl benzene sulfonic acid (anionic surfactants), quaternary ammonium compounds (cationic surfactants), alkylphenol polyethoxylates (nonionic surfactants), and amine oxides (amphoteric surfactants) usually degrade into byproducts that are toxic and can display estrogenic activities. Nanomaterials such as TiO₂, nZVI, graphene oxide, silica nanoparticles, and CNTs are useful, particularly in surfactant removal. These nanomaterials act through different adsorption processes: electrostatic interactions, ion exchange, and π-π stacking to capture and eliminate surfactants from water and soil samples. They utilize nanoproperties such as adsorption, high surface area, and reactivity for degradation and sequestration of such pollutants. Thus, the environment becomes cleaner and safer (Rahimi and Doostmohammadi, 2020; Sharma, et al., 2024).

9.6 Removal of flame retardants

Flame retardants such as the more recent brominated flame retardants DBDPE, TBB, and TBPH, along with organophosphorus flame retardants TDCIPP and TCEP, are considered hazardous to humans and the environment due to their persistence and toxicity. These chemicals can interfere with hormone regulation, affect sperm quality, developmental, and neurological functions. Therefore, there is a growing demand for new nanomaterials such as graphene oxide, Fe₃O₄ nanoparticles, biochar, and zeolites, among these emerging contaminants. Remediation mechanisms may include adsorption by means of hydrogen bonding, π-π stacking, and photocatalysis. These nanomaterials provide a sustainable and efficient mechanism to reduce the environmental load of flame retardants, consequently reducing their harmful impact on ecosystems and human health (Carrapico et al., 2023).

9.7 Removal of pesticides

Several nanomaterials have been investigated for use in removing pesticide residues from drinking water, agricultural runoff, and wastewater. Carbon-based nanomaterials such as graphene, with a high adsorption capacity of200–600 mg/g, are well known for their usefulness in water purification (Rosales et al., 2021). Their high-performance results from properties such as high surface area, reactivity, and variability. Nanoparticles are considered highly effective for pesticide removal. For example, aldrin removal was procured at about 95.0% using palladium/iron bimetallic nanoparticles, as witnessed by TEM and GC-MS analyses, with ZnO-chitosan nanoparticles achieving a 99.0% removal for permethrin. Raman spectroscopy, XRD, and SEM analysis revealed 99.9% removal of malathion and 93.7% of lindane using SDS-1-modified Al(OH)₂ nanoparticles. Beta-CD/MRGO composites removed 93.2% of dieldrin, confirmed through VSM, FTIR, SEM, GC-ECD, MSPE, and XRD. Silica-modified graphene also improved adsorption of organophosphorus pesticides (Moradi Dehaghi et al., 2014; Dehghani et al., 2017; Mahpishanian and Sereshti, 2017; Rosales et al., 2021; Narwal et al., 2023; Katyal et al., 2023).

Metal oxide nanomaterials like magnesium, cerium, and titanium oxides have also proven effective due to their strong adsorption ability (Zhang et al., 2024). Nanocrystalline cerium (IV) oxide, under suitable conditions, degraded parathion methyl into less harmful compounds (Moradi Dehaghi et al., 2014). The high surface area and reactivity of nanoparticles enhance pesticide adsorption, reducing contaminant levels in water (Narwal et al., 2023; Katyal et al., 2023). Functionalization further improves their selectivity and binding affinity. Advanced characterization techniques provide insights into these interactions, enabling material optimization. Thus, nanoparticle-based strategies offer a promising solution for minimizing pesticide pollution and protecting water quality and public health (Mahpishanian and Sereshti, 2017). Some recent Nanomaterials which are used in EMPs removal are reported in Table 6.

TABLE 6. Some recent Nanomaterials used in EMPs removal.

10 Recovery and regeneration of nanoparticles

To prevent potential downstream environmental impacts, nano-adsorbents must be removed from the water after adsorbing micropollutants. In addition, these recovered nano-adsorbents should be regenerated and reused in other processes to support sustainable development goals (Nzilu et al., 2023). Efficient, easy-to-use, fast, economical, and energy-saving methods are essential for nano-adsorbents recovery (Gul et al., 2024). Magnetic nanoparticles can be extracted using an external magnetic field, while filtration and centrifugation facilitate their recovery (Dhiman et al., 2021). Several dehydrating agents, including ultrapure water, HCI, H₃SO₄, H₃PO₄, NaOH, and NaCl, have been evaluated for their effectiveness. Among these, hydrochloric acid demonstrated the highest performance, with removal efficiencies ranging from 60% to 86% for various adsorbents, such as plant-based biochar (Ahammad et al., 2021). Conversely, adsorbed pollutants could not be effectively removed using water or sodium chloride. The study also revealed that although increasing the HCl concentration initially increased the desorption efficiency, excessively high concentrations could damage the adsorbent. Moreover, the desorption efficiency improved with increased contact time until equilibrium was reached (Chen et al., 2007; Conti et al., 2021; Wang et al., 2024).

For the adsorption process to be both technologically and commercially viable, regeneration is essential. The choice of regeneration technique depends largely on the nature and cost of the adsorbent. For instance, banana peel has been used as a bio-adsorbent for copper removal, with desorption rates up to 94% using 0.1 N sulfuric acid. Repeating this process up to seven times yielded consistent and efficient results. Other tested solvents -such as NaOH, CH₃COOH, distilled water, and tap water-achieved desorption rates less than 30% (De Gisi et al., 2016; Dehghani et al., 2023). In another study, chromium was removed from waste using stability-enhanced magnetic nanoparticles. Desorption was found to be effective under alkaline conditions using NaOH, and even after six regeneration cycles, the adsorption capacity decreased by only 9% (Kulkarni and Kaware, 2014).

Solvent washing has also proven effective for the recovery of various solutes. Notably, the use of non-thermal plasma instead of conventional electric heating has shown encouraging results in terms of energy-savings. MEA-impregnated silica has proven as a promising alternative for the efficient adsorption and desorption of carbon dioxide (Kulkarni and Kaware, 2014; Bao et al., 2024). A variety of techniques-or combinations thereof-have been used to develop nano-adsorbents with high adsorption capacity and selectivity for emerging micropollutants (Moreira et al., 2022). Factors such as the type of adsorbent and adsorbate, as well as stability and toxicity concerns, play a significant role in selecting an appropriate regeneration method.

To maintain the long-term performance of nano-adsorbents, thermal, chemical, and electrochemical methods are commonly used for media regeneration (Gómez-Pastora et al., 2014; Moreira et al., 2022). Regeneration is vital not only for environmental conservation but also for economic efficiency. A key issue in adsorption technologies is managing the disposal of spent adsorbents, and regeneration helps mitigate this problem by reducing the need for constant replacement and minimizing waste (Younas et al., 2021). Multiple regeneration strategies-such as solvent washing, thermal treatments, chemical regeneration, and electrochemical methods have been employed with varying success levels (Natarajan et al., 2022; Ahmadi et al., 2023). Figure 4 shows the scheme prepared based on the source (Hassan et al., 2020) about a procedure of regeneration and reuse of MPs, that includes treatment with acid or base followed by washing and reuse with a lower efficiency than the first cycle, respectively.

11 Challenges and perspectives: scalability, sustainability, and regulation

The review highlights the transformative potential of nanotechnology in addressing aquatic environmental contamination. Nanoparticles particularly metal and metal oxide nanomaterials have shown excellent efficacy in removing a wide range of pollutants, including pharmaceuticals, pesticides, plasticizers, surfactants, and flame retardants. Their large surface area, tunable reactivity, and easiness of functionalization make them ideal candidates for adsorption and degradation processes. Among them, green-synthesized nanoparticles stand out as cost-effective and environmentally friendly alternatives, offering sustainable synthesis routes using plant extracts and waste materials.

11.1 Challenges and perspectives

Despite their promise, several challenges must be addressed to translate laboratory success into field-scale implementation. Scaling up nanoparticle synthesis, particularly with eco-friendly and cost-effective methods, remains a bottleneck. Mass production without compromising the particles’ uniformity, functionality, and eco-safety is a critical obstacle. Moreover, the long-term environmental toxicity of nanoparticles post-application is not yet fully understood. Concerns include bioaccumulation, ecological disruption, and toxicity to non-target organisms, which require further toxicological and ecotoxicological assessment under real-world conditions. Furthermore, the absence of an explicit rule and a consistent set of verification criteria obviously hinders the safe laboratory studies for commercial applications. The scientific community is at the forefront of public trust; if these communities themselves begin to doubt the safety of nanotechnology, even that scant inch of acceptance will be more difficult to achieve. Eliminating barriers can only be achieved through open collaboration of barriers across disciplines, through accurate assessment of the nanoparticle lifecycle, and transparent dialogue between researchers, policymakers, industry, and the society at large. Regulatory frameworks for the use of nanomaterial in environmental applications are at different stages of maturity across regions:

European Union (EU): The EU has taken a relatively proactive stance with regulations such as REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals), which includes specific provisions for nanomaterials. The European Chemicals Agency (ECHA) has issued published guidelines for nanoparticle characterization, safety data sheets, and environmental risk assessments. However, implementation at the WWTP level remains limited, and standard monitoring methods for nanomaterials in effluents are still lacking.

United States (US): Regulatory progress is more fragmented. Agencies such as the EPA and FDA address nanomaterials under general chemical safety laws (e.g., TSCA), but no nanotechnology-specific mandates exist for wastewater treatment applications. Efforts remain largely voluntary or at the research funding level, such as through the National Nanotechnology Initiative (NNI).

Emerging Economies (e.g., India, Brazil, South Africa): Regulatory frameworks are nascent or absent. Although nanotechnology R&D is accelerating, regulations are often outpaced by innovation. Furthermore, infrastructure for nanoparticle monitoring, safety assessments, and workforce training is limited, making safe implementation difficult.

Additionally, legislation surrounding the use of nanomaterials in WWTPs is still evolving. While some countries have initiated frameworks for nanoparticle use in environmental remediation, a globally harmonized regulatory guideline is lacking, especially concerning nanoparticle disposal, fate, and monitoring in treabted water effluents.

11.2 Key message and future directions

Nanotechnology offers a promising path for next-generation water treatment, especially in tackling complex and trace-level micropollutants. Based on current research, the most promising nanomaterials include Fe₃O₄-based magnetic composites, green-synthesized TiO₂ and ZnO, carbon-based materials (GO, CNTs), and hybrid MOFs, many of which are currently at TRL 4–6, with pilot testing beginning in select regions.

A strategic roadmap to advance this field should include:

• Short-term (1–3 years): Standardization of green synthesis protocols, comprehensive life cycle and risk assessments, and improved nanoparticle recovery methods.
• Mid-term (3–6 years): Integration of nano-based systems into existing WWTPs, development of nano-enabled filtration membranes, and establishment of pilot-scale demonstrations.
• Long-term (6–10 years): Regulatory harmonization across regions, industrial-scale deployment, and creation of circular systems for nanoparticle regeneration and reuse.

In conclusion, advancing nanotechnology for environmental remediation demands interdisciplinary collaboration, responsible innovation, and evidence-based regulation. If these efforts align, nanoparticle-enabled water treatment can play a pivotal role in ensuring safe, sustainable, and resilient water systems globally.

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Footnotes

Edited by: Yawei Shi, Dalian Maritime University, China

Reviewed by: Ponnusami Venkatachalam, SASTRA University, India

Prerna Mehta, GD Rungta Educational Society, India