The nano-paradox: addressing nanotoxicity for sustainable agriculture, circular economy and SDGs

Abstract

Engineered nanomaterials (ENMs) have aroused extensive interest in agricultural, industrial, and medical applications. The integration of ENMs into the agricultural systems aligns with the principles of United Nations’ sustainable development goals (SDGs), circular economy (CE) and bio-economy (BE) principles. This approach offers excellent opportunities to enhance productivity and address global climate change challenges. The revelation of the adverse effects of nanomaterials (NMs) on various organisms and ecosystems, however, has fueled the debate on ‘Nano-paradox’ leading to emergence of a new research domain ‘Nanotoxicology’. ENMs have shown different interactions with biological and environmental systems as compared to their bulk counterparts. They bioaccumulate in organisms, soils, and other environmental matrices, move through food chains and reach higher trophic levels including humans ultimately resulting in oxidative stress and cellular damage. Understanding nano-bio interactions, the mechanism of gene- and cytotoxicity, and associated potential hazards, is therefore, essential to mitigate their toxicological outputs. This review comprehensively examines the cyto- and genotoxicity mechanisms of ENMs in biological systems, covering aspects such as their entry, uptake, cellular responses, dynamic interactions in biological environments their long-term effects and environmental risk assessment (ERA). It also discusses toxicological assessment methods, regulatory policies, strategies for toxicity management/mitigation and future research directions in nanotechnology, all within the context of SDGs, CE, promoting resource efficiency and sustainability. Navigating the nano-paradox involves balancing the benefits of nanomaterials with concerns about nanotoxicity. Prioritizing thorough research on above facets can ensure sustainability and safety, enabling responsible harnessing of nanotechnology’s transformative potential in various applications including mitigating global climate change and enhancing agricultural productivity.

Graphical abstract

Introduction

The transition from a ‘produce-consume-discard’ linear economy to a regenerative, closed-loop circular economy (CE) is gaining momentum. According to the World Economic Forum (WEF), the restorative CE system, based on the principles of sustainability, minimizes waste and optimizes resource utilization by design, playing a crucial role in achieving multiple Sustainable Development Goals (SDGs) and the 2030 Agenda set by the United Nations [1, 2]. While the CE is projected to generate $4.5 trillion in economic growth by 2030, the Food and Agriculture Organization (FAO) estimates that by 2050, a global population of 9.3 billion will require a 60% increase in food production [3]. According to the Global Agricultural Productivity Report, developing nations will need to double their production, with cereal production alone expected to rise by nearly one billion tons by 2050 [4]. Further SDG2: Zero Hunger focuses on sustainable agriculture, particularly through target 2.4, which promotes resilient farming practices to enhance productivity, and adaptation to changing climates to ensure food security. It thrives on eco-friendly farming techniques, rejuvenating the soil system by reducing synthetic inputs, improving product quality, and supporting long-term productivity and food supply while preserving the multi-functionality of natural ecosystems [5]. To feed a burgeoning global population and achieve SDG2 by eradicating hunger, it is essential to integrate innovative technologies, combining techno- and ecocentric approaches with sustainable food production systems [6]. The innovations will help mitigate eroded soils, declining agricultural yields, shifting climate patterns, and the emergence of pests and pathogens, thereby, supporting the agricultural CE.

Among emerging technologies, nanotechnology has demonstrated significant potential in advancing SDGs, sustainable agriculture and supporting a circular economy [2, 7,8,9,10]. By integrating nanotechnology, agriculture practices can become more sustainable and resource-efficient, reducing inputs such as water, fertilizers, and pesticides while increasing productivity. Nanomaterials offer innovative solutions for soil and water remediation, efficient nutrient delivery systems, early disease forecasting and precision agriculture. Moreover, nanotechnology supports CE principles by promoting the reuse of resources such as recycling plant waste as organic fertilizer, optimizing production processes, minimizing waste generation such as debris and rejuvenating natural ecosystems. This convergence of nanotechnology with SDGs and CE principles highlights its pivotal role in improving agricultural productivity while addressing major global challenges like climate change, food security, and environmental degradation [11].

Nanomaterials (NMs) are characterized by unique properties at the nanoscale, typically ranging from 1 to 100 nm. They encompass various classes such as metallic, organic (polymers and dendrimers), carbon and composite nanomaterials and can be engineered (ENMs) to possess tailored and tunable properties such as enhanced conductivity, improved drug delivery, and increased catalytic activity and absorption [12]. Manufactured nano-objects (MNOs) or ENMs exhibit diverse applications across multiple sectors including electronics, energy, food, textiles environment and medicine. In agriculture, ENMs are utilized in nano-enabled agrochemicals such as fungicides, pesticides, herbicides, fertilizers, alongwith nano-carriers for enhanced nutrient delivery. Additionally, nanotechnology supports precision farming through nano-sensors for sensitive and stable detection and amplification [13, 14], energy harvesting nano-generators, and energy devices in the industrial sector [15]. The triboelectric nanogenerator (TENG) has gained significant attention for its ability to generate electricity based on the coupling effect of electrostatic induction and triboelectrification [16], with plant based TENG models expected to contribute to clean energy generation [13]. The Indian Farmers Fertilizer Cooperative Limited (IFFCO) has recently introduced the world's first Nano Urea Liquid, demonstrating the role of nanotechnology in enhancing crop productivity [17]. A compiled list of nano-enabled agricultural products worldwide underscores their growing adoption. The Nanotechnology Product Database (ENMD) currently lists 10,881 nano-based products used in various industries with involvement of 3690 companies in 68 countries (https://product.statnano.com/). Owing to the above applications, the European Union has recognized nanotechnology as the ‘Key enabling technology’ [18] to meet the global food and energy demands.

Amidst the remarkable applications and practical benefits of ENMs, however, there is a growing concern regarding nanotoxicity and potential toxicological consequences of ENMs on plants, human health, and the environment [19, 20]. The safety aspect of nanotechnology has drawn significant attention, primarily due to the release of ENMs into the environment during their production, recycling, and disposal as emphasized by Alimi et al. [21]. The paradox with ENMs lies in their dual nature, offering valuable applications while posing toxicity risks. While their properties such as small size, increased surface area, and high reactivity make them useful for drug delivery, agrochemicals, pollution control, and catalysis, these also raise concerns when they penetrate cells and tissues potentially causing cellular damage. Extensive use of ENMs has led to alarming consequences on plants and environment prompting rigorous research and risk–benefit analysis to ensure safe use of nanotechnology [19, 20]. Consequently, a specialized research domain known as ‘nanotoxicology’ has emerged to examine the interactions between ENMs and biological as well as environmental systems [22].

Nanotoxicology evaluates the genotoxicity and cytotoxicity of ENMs and their environmental risk assessment (ERA), holding great significance in assessing safety and potential hazards associated with ENM usage [19, 23, 24]. Genotoxicity refers to ENMs’ capacity to induce DNA damage resulting in chromosomal aberrations and mutations, while cytotoxicity pertains to their ability to induce cell death or impair cellular function. ENMs engage with biological systems triggering detrimental effects such as oxidative stress and cellular dysfunction [25]. They have been observed to alter mitotic index (MI), penetrate cell walls, and disrupt cellular growth [26, 27]. In the environmental context, ENMs may interact with environmental metrices and co-occuring contaminants, potentially increasing ecological risks [24, 28, 29]. Evidence suggests that nanoparticles act as sinks for the organic and inorganic co-contaminants and amplify toxicity in the target organisms [30]. Therefore, understanding ENMs induced genotoxic and cytotoxic effects and their ERA is essential for developing safer nanotechnology applications [19, 31].

ERA involves identifying hazards, evaluating exposure routes, characterizing dose–response relationships, assessing bioaccumulation, understanding interactions and determining risks to ecosystems for taking informed regulatory decisions to foster sustainable management practices [32, 33]. Studies have shown that exposure conditions and environmental persistence of ENMs are key factors influencing their long-term toxicological outcomes [34,35,36,37], underscoring the need for comprehensive risk assessments. Despite extensive nanotoxicology research at cellular and molecular levels using in vitro and in vivo model systems, clear guidelines for documenting and mitigating the adverse effects of ENMs remain insufficient [38]. The Registration, Evaluation, Authorization and Restriction of Chemicals (REACH, EC 1907/2006) act [39], applicable to ENMs from Jan 1, 2020 [33] and the Toxic Substances Control Act (TSCA) in the United States, however, regulate ENM safety, requiring manufacturers to report and assess potential risks before market entry [40]. Enhancing risk assessment needs integrating laboratory research with field studies and computational modelling. Insights from toxicology and environmental chemistry can further refine hazard evaluations to promote responsible nanotechnological applications.

This review comprehensively analyzes published reports on the genotoxicity, cytotoxicity and environmental risk assessment of various ENMs including metallic, polymeric, carbon and composite nanomaterials. By collating experimental studies conducted both in vitro and in vivo, we aim to elucidate underlying mechanisms, identify key factors influencing nanotoxicity and address gaps in standard testing procedures and risk assessment. Furthermore, exploring how ENMs align with CE goals requires balancing their potential benefits with associated risks (Fig. 1). Navigating this nano-paradox is crucial for the responsible, sustainable and safe use of nanotechnology’s transformative potential in sustainable agriculture in line with the SDGs and CE principles.

Fig. 1

Agricultural Nanotechnology as a mediator between Circular Economy and Sustainable Development Goals (SDGs). a The figure shows three concentric circles. The innermost circle represents the circular economy, with five components where colour intensity indicates action direction—lighter shades for decrease/minimization, darker for increase/maximzation. Encircling this, agricultural nanotechnology serves as the middle layer, linking the circular economy to the outermost layer, which represents the SDGs, divided into three sections, each with specific components. b Shown on the two pans of the balance is nanotechnology supported CE and SDGs and nanotoxicity where the latter gets counter-productive to the former, highlighting the importance of mitigating nanotoxicity

Entry and transport of engineered nanomaterials into biological systems

The entry and transport of ENMs in plants are influenced by their unique structural features such as the cellulose cell wall, cuticular layer, and stomata. Unlike animal cells, which are primarily bounded by a lipid bilayer, plant cells have an additional rigid cell wall that affects the mechanisms of ENM uptake. ENMs can enter plants through foliage, roots, or seed priming methods [41, 42] (Fig. 2). During agricultural applications, nanoparticles are typically sprayed onto leaves, where they are absorbed through the cuticle or stomata. The waxy cuticle, composed of wax, cutin, and pectin, although serves as a barrier but the hydrophilic and lipophilic channels allow the diffusion of nanoparticles below 5 nm. Additionally, nanoparticles may enter leaves via the stomatal pathway and accumulate in the epidermis and vascular tissue [43]. Stomatal entry facilitates ENM transport through apoplastic and symplastic routes into the plant’s vascular system. ENMs sized between 10 and 50 nm follow transport through adjascent cell cytoplasm (symplastic route), while larger ENMs (50–200 nm) move between cells (apoplastic route). Once internalized, ENMs travel with sugar flow through phloem sieve tubes, leading to bidirectional transport and accumulation in various organs. The apoplastic route, offering the least resistance is preferred for many water nutrients and non-essential metal complexes. Factors such as application methods, ENMs size, concentration and climate affect their adsorption after foliar application. Leaf morphology, chemical composition, presence of trichomes, leaf exudates and waxes influence ENMs trapping on leaf surfaces [44]. For instance, gold nanostructures (30–80 nm) applied via aerosol to watermelon plants showed cellular uptake through stomatal openings, and translocation from leaf to root via the phloem, as quantified by ICP-MS. Similarly, Ag ENMs have been reported to enter lettuce leaf through stomata [45]. ZnO ENMs also traverse the wheat leaf epidermis through stomata, subsequently releasing Zn ions in the apoplast, where both Zn ions and ZnO ENMs are taken up by the mesophyll cells [46]. Nanoparticle accumulation and transport are influenced by shape, application method, and plant tissue characteristics [47].

Fig. 2

Mechanisms of NPs entry into plants. Exposure via foliage and roots. Blue and red dotted lines represent the symplastic and apoplastic transport pathways of NPs

For root uptake, ENMs first adsorb to root surfaces, where negatively charged substances such as mucus and/or organic acids released by root hairs attract mostly positively charged nanoparticles. Lateral root formation creates new interfaces for nanoparticle absorption, and ENMs enter root tissues through small pores, endocytosis, or by binding with transport proteins. ENMs typically ranging from 3 to 5 nm in diameter enter plant roots via osmotic pressure, capillary forces, or direct passage through epidermal cells. Once inside, they move through extracellular spaces to the central vascular cylinder, primarily via the apoplastic pathway, and then cross the casparian strip barrier symplastically by binding to carrier proteins on endodermal cell membranes. Internalized ENMs travel between cells through plasmodesmata, reaching the xylem for transport to shoots and eventually returning to roots via the phloem. Within plants, ENMs localize in the epidermal cell wall, cortical cell cytoplasm, and nuclei, affecting nutrient absorption. Seeds also absorb ENMs through intercellular spaces and diffusion in cotyledons [44]. Studies indicate that nanoparticles infiltrate cells via hydrophilic pathways and endocytosis, with carbon-based nanoparticles specifically absorbed by root cells. Likewise, seed priming facilitates the penetration of nanoparticles into plant cells.

Negatively charged carbon-dotted ENMs (CDENMs) were translocated via both symplastic and apoplastic pathways, while positively charged CDENMs primarily followed the apoplastic pathway in cotton and cucumber. Root-supplied CDENMs showed higher leaf fluorescence than positively charged CDENMs, indicating that negatively charged ENMs have higher translocation efficiency from root to shoot [48]. Poly lactic-co-glycolic acid (PLGA) polymeric ENMs were absorbed through roots, stomatal openings and vascular tissues in Vitis vinifera L. [49], while poly (lactide-co-glycolide) b-poly (ethylene glycol) methyl ether ENMs translocated via the apoplastic route in rice [50]. Proteinoid polymer ENMs moved from roots to leaves through the protoxylem and casparian strips in Solanum lycopersicum and Lactuca sativa [51]. Composite ENMs (PAA-nCeO₂ and Cs-nCeO₂) dissolved under the influence of root exudates, releasing Ce³⁺ ions that formed complexes and traveled upward along vascular bundles, eventually accumulating in leaf veins. Intact composite ENMs also entered roots via casparian strip gaps at lateral roots and roots tips, later moving upward and accumulating in the leaf blade [52].

ENMs can enter the human body through three primary routes including ingestion, inhalation, and dermal penetration, each posing potential health risks [53, 54] (Fig. 3). When consumed via food or beverages, ENMs may be absorbed through the gastrointestinal tract, where their size and chemical composition influence their uptake and potential toxicity. For instance, titanium dioxide (TiO₂) ENMs, commonly found in the food additive E171, are widely used for their coloring and opacifying properties [55, 56]. Additionally, inorganic ENMs, such as titanium or zinc, are incorporated into antimicrobial food packaging materials to prevent bacterial contamination, though their unintentional release into food has been reported [57, 58]. Once ingested, these ENMs can interact with the gut lining and potentially enter the bloodstream via endocytosis, transcytosis, passage through villous gaps and paracellular uptakes [59]. Another significant route of entry for ENMs is through the respiratory system. When ENMs are inhaled, they can deposit in different regions of the respiratory tract depending on their size. Larger particles tend to remain in the upper respiratory tract, while smaller particles can reach the alveoli. Once deposited, these particles can cause various toxic effects due to prolonged interaction with pulmonary cells. Subsequently, inhaled ENMs can also enter the bloodstream, leading to systemic exposure and potential health risks [60, 61]. In highly polluted urban environments, diesel black carbon and engineered ENMs like silica are common airborne contaminants [62]. Beyond anthropogenic sources, naturally occurring ENMs derived from volcanic activity, rock weathering, and forest fires, which release silica, iron, and carbon ENMs may also present potential risks to human health [63, 64]. Moreover, certain ENMs can penetrate the skin, particularly when present in cosmetics, gaining access through hair follicles or damaged skin. The extent of dermal absorption depends on ENM characteristics and skin integrity [65, 66]. Interestingly, it has been observed that ENMs around 4 nm in diameter are capable of penetrating intact skin, whereas ENMs larger than 45 nm are restricted to permeating only damaged skin [67]. Zinc oxide nanoparticles (ZnO), commonly used in sunscreens, can be absorbed through human skin and enter systemic circulation, as evidenced by their detection in blood and urine following exposure [68]. Similarly, silver (Ag) and gold (Au) nanoparticles, used in dermo-cosmetic formulations and medical applications, penetrate the skin but show limited systemic absorption, with Ag ENMs potentially causing localized inflammation in the skin [69, 70]. Generally, five most plausible mechanisms have been suggested for the entry of ENMs into the cells (Fig. 4).

Fig. 3

Mechanisms of NPs entry into human body. Cyan blue and red dotted lines represent the ingestion and inhalation routes of NPs uptake

Fig. 4

Transport of engineered nanomaterials into cells

Direct diffusion

Small-sized ENMs traverse the cell membrane through direct diffusion, a passive process driven by the concentration gradient of ENMs across the membrane and dependent on various factors like shape, charge, size, hydrophobicity, as well as the composition of both the ENMs and membrane [43]. The passage of ENMs across the plasma membrane, depends on membrane characteristics such as lipid fluidity, composition, and embedded molecules [71]. Understanding this entry mechanism is crucial for understanding ENM-cell interactions and their potential biological effects.

Endocytosis

ENMs interact with the plasma membrane or extracellular matrix and enter cells via endocytosis, forming vesicles that transport them to intracellular compartments. Endocytosis varies by cell type and involved molecules, and includes phagocytosis, clathrin-mediated, caveolin-mediated, clathrin/caveolae-independent, and micropinocytosis [26]. Cellular uptake depends on ENM properties such as size, shape and charge. In Nicotiana tabacum cv. Bright Yellow (BY-2) cell suspensions, single-walled carbon nanotubes (500 nm), crossed the cell wall and membrane via fluid-phase endocytosis [72]. Likewise, mono- and polydispersed poly (lactic-co-glycolic) acid (PLGA) ENMs were internalized primarily through clathrin-independent pathways. The cell wall plays a crucial role in ENM size selection, more so than the plasma membrane [73]. Its 5–20 nm apoplast diameter restricts ENM uptake, translocation, and accumulation influenced by transpiration rate, cell wall composition, mucilage, stomatal openings and symbiotic associations. Experimental studies show that carbon-based ENMs and nanotubes are taken up by the root cells of Catharanthus roseus via endocytosis [72]. Additionally, trojan and corona protein interactions contribute to ENM accumulation and toxicity inside cells [74].

Channels, aquaporins, and membrane transporter proteins

The translocation of ENMs is also mediated by membrane transporter proteins and channel based on their affinity for the transporters. These proteins facilitate ENM entry by forming complexes with them [75, 76]. In tomato seeds and wheat seedlings, multi-walled carbon nanotubes penetrate the seed coat by creating pores. However, ENM passage is restricted by small pore size, low open probability, and limited selectivity [77]. Aquaporins have been identified as key mediators of nanomaterial entry into seed coat cells [41], along with other transporter proteins that facilitate ENM uptake.

Plasmodesmata

In some cases, plasmodesmata enable the invasion of NMs into the cells. It has been suggested that ENMs smaller than 14–40 nm can pass through plasmodesmata and enter the cells as demonstrated in the transport of Ag ENMs in Arabidopsis thaliana [78], gold ENMs in woody poplar (Populus deltoides X nigra) [79] and ZnO-ENMs (8 nm diameter) in Brassica species [80], amongst many other nanoparticles.

Production of root exudates or organic matter

The roots of certain plant species like A. thaliana, and Glycine max secrete exudates or organic compounds that regulate ENM uptake and toxicity in the soil [43]. It has been demonstrated in A. thaliana seedlings exposed to TiO₂ (5 nm) complexed with Alizarian red S nano-conjugate, root-secreted mucilage forms a pectin hydrogel capsule that mediates ENM entry [81]. Moreover, the carbohydrates in mucilage can inhibit ENM toxicity in the rhizosphere or facilitate their uptake in various species. Once inside plant cells, ENMs are transported via symplastic and apoplastic pathways [82], with plasmodesmata serving as the primary channel for intercellular movement.

Genotoxicity of engineered nanomaterials

Genotoxicity refers to the ability of a substance to cause DNA damage leading to chromosomal aberrations and mutations [83,84,85,86]. When inert materials are reduced to the nano scale, their increased surface area enhances reactivity, allowing interactions within biological systems contributing to nanotoxicity. While significant progress has been made has been made in understanding the mechanisms of ENMs induced genotoxicity, much remains to be unraveled [87]. Nevertheless, many in vivo and in vitro studies of genotoxic effects provide important insights for mitigating nanotoxicity.

In vitro and in vivo assays for genotoxicity assessment

Both in vivo and in vitro studies are pivotal for evaluating the genotoxic potential of ENMs and understanding their mechanism. In vivo studies have been conducted in animal models like rodents and many plant species like Allium cepa, Vicia faba, Zea mays, Hordeum vulgare, Tradescantia sps, N. tabacum, Crepis cappillaris and Drimia indica [88] and are extremely important to validate the results of in vitro systems. Several assays have been widely used for genotoxicity assessment. The A. cepa test [89] documents chromosomal abnormalities in the root meristems of A. cepa and has been extensively used for genotoxicity studies [88]. The Ames test tests the potential genotoxic agents including ENMs to induce mutations in Salmonella typhimurium strains [90]. The mutagenicity of ENMs is measured in terms of the number of histidine-revertant colonies. It has been widely used to assess metal ENM genotoxicity in both in vivo and in vitro systems [91].

The Comet test is a sensitive technique that quantifies DNA damage by embedding cells in agarose gel and subjecting them to electrophoresis. The damaged DNA migrates forming a comet-like tail, whose extent of length and intensity indicates the damage. This assay has been used to assess the TiO₂ and ZnO ENMs induced DNA damage in A. cepa [92]. The micronucleus assay, on the other hand, evaluates ENMs induced chromosomal instability and damage by detecting micronuclei that are small, darkly stained extranuclear bodies containing whole or fragmented chromosomes in the cell. The presence of micronuclei indicates ENM-induced chromosomal instability and genotoxicity potential, while aneuploidy resulting from chromosome breaks has also been detected in many organisms [93]. These assays collectively provide valuable insights into ENM-induced genotoxicity and aid in risk assessment. The United States Environmental Protection Agency (EPA) ‘Gene-Tox’ program reviews standard genotoxicity tests encompassing gene mutations, chromosomal aberrations, and DNA damage in various plant species including A. thaliana, Tradescantia sps, Z. mays, G. max and H. vulgare [94].

Mechanism of genotoxicity

Direct and indirect genotoxicity

ENMs can induce DNA damage through diverse mechanisms [85]. The characteristic features of ENMs that facilitate their penetration into the nucleus and determine genotoxicity have been specified as their dimension, ion release and zeta potential [83]. Once they traverse the cell and nuclear membranes, ENMs engage with DNA structured in chromatin or chromosomes, depending upon the specific stage of the cell cycle. Direct genotoxicity results from physical interactions between ENMs with DNA [27] affecting base pairing, phosphorylation and leading to adducts production, strand breaks or alteration in DNA conformation, replication and transcription.

For instance, silver and titanium dioxide ENMs have been demonstrated to trigger DNA damage and strand breaks and endoreduplication in both in vivo and in vitro models [95, 96]. Further, it has been observed that the hydrophobicity and surface charge of ENMs significantly influences genotoxicity [97]. In indirect genotoxicity, ENMs interact mechanically or chemically with nuclear proteins involved in replication, transcription, mitotic spindle function, and cell cycle regulation.

Oxidative stress and reactive oxygen species (ROS) generation

The generation of ROS by ENMs is a critical factor influencing their biological activity. ROS, including superoxide anions (O₂⁻), hydrogen peroxide (H₂O₂), and hydroxyl radical (OH⁻), are typically produced as a result of ENM interactions with cellular components, and/or exposure to UV light, potentially causing oxidative stress [31, 84, 85, 98]. ROS influence cellular signaling pathways that regulate cell death, proliferation, and differentiation [99]. Excessive ROS production disrupts normal redox-regulated physiological functions, leading to impaired cell signaling, altered cell motility, reduced DNA repair capacity, lipid peroxidation, protein oxidation, DNA damage and cytotoxicity [102]. ENMs have been linked to oxidative damage, causing lesions, DNA strand breaks, and compromised cell cycle processes [101]. In plants, ROS acts as a ‘double-edged-sword’. While it plays an important role in signaling, excessive ROS can damage biomolecules and organelle structures. This may lead to protein oxidative carbonylation, lipid peroxidation, DNA/RNA breakage, membrane destruction and ultimately necrosis, apoptosis, or even mutagenesis [38, 85, 100]. The extent of ROS generation and resulting oxidative stress is influenced by ENM size, surface area, and chemical composition [103]. Understanding these interactions is crucial for developing safer nanomaterials and mitigating potential risks associated with ENM exposure.

Treatment with Ag₂CoFe₂O₄ ENMs in wheat induced hormesis in roots, while oxidative damage was evidenced by alterations in photosynthetic pigments and antioxidant enzyme activities (CAT, SOD, GPX, APX) due to ROS generation [104]. Ag ENMs resulted in significant reduction in root elongation, shoot/root fresh weights, chlorophyll, and carotenoids; increased H₂O₂ formation, lipid peroxidation, foliar proline, and ROS generation; decreased sugar content; and altered mitochondrial membrane potential in seedling roots in O. sativa [105], Spirodela polyrhiza [106], S. tuberosum [107]. Ag ENMs-Cit-L-Cys phytotoxicity has been demonstrated to be associated with ROS generation and oxidative stress in callus cultures of P. nigra [108] and Lemna [109]. Higher doses ≥ 200 mg L^− 1 of a commercial nanofertilizer Magnesium Aluminum oxide showed genotoxic effects [98]. Furthermore, carbon nanodots (CNDs) [110] also play a dual role in plants depending on their type and concentrations, for instance, while silver quantum dots reduce photosynthetic processes and gas exchange attributes, carbon nanodots show milder effects in A. thaliana [111]. Chen et al., [112] recorded higher toxicity of CNDs at 1000–2000 mg/L concentration in maize that was reflected in reduced shoot (72% and 38%), and root (68% and 57%) fresh weight, respectively. Their toxicity level depends on the source of biochar which involved different plant sources [112]. In addition, composite cobalt ferrite (CoFe₂O₄) ENMs also inhibit seed germination, reduce shoot growth, deteriorate photosynthetic pigments, increase antioxidant enzymes (CAT, APX, GPX) and enhance oxidative damage in wheat plants [113]. Another composite ENM (silver sulfide) reduced root growth and increased the production of MDA and H₂O₂ in wheat [114]. Similarly, copper chitosan ENMs (composite ENMs) also caused inhibitory effects on the seedling growth of maize [115]. Furthermore, polymeric ENMs (chitosan) at 90 ppm also caused toxicity in wheat by causing a severe reduction in germination rate, germination percentage, mean germination time, germination value and mean daily germination, seedling growth, shoot and root fresh weight.

Chromosomal aberrations (CAs)

Exposure to ENMs has been observed to result in CAs, including deletions, duplications, inversions, and translocations [116,117,118]. These aberrations arise from direct physical interactions between ENMs and DNA, as demonstrated in human cells. In A. cepa, while CuO and TiO₂ ENMs exposure resulted in a decrease in MI by 28% and 17% respectively, Al₂O₃ ENMs exposure increased the MI by 13% compared to untreated control onion roots. In wheat, Fe₂O₃ ENMs exhibited genotoxic and clastogenic effects, causing DNA damage and aberrations such as deconstructed metaphase, C-Metaphase, chromosomal loss, chromosomal fracture, polyploidy, deconstructed anaphase, lagging chromosome, fragment, polar deviation among others [84, 117]. NPK nano-fertilizer application on wheat led to significant mitotic aberrations in the root tips potentially disrupting normal cell function [119]. Similarly, CuO ENMs caused significant decrease in the mitotic index in the root tip cells of P. vulgaris when compared to the control [118]. ENMs-induced oxidative stress further amplifies CAs by impairing chromosome segregation [120]. Understanding the mechanisms underlying the ENM genotoxicity is important for assessment of associated risks and developing strategies for their mitigation. By elucidating the pathways of ENMs-induced DNA damage, oxidative stress, and CAs, the key targets for intervention can be identified to establish safer practices for ENM applications.

Cytotoxicity of engineered nanomaterials

ENM-induced cytotoxicity refers to the disruption of cellular structures and processes resulting from cellular interaction of the ENMs [22, 121, 122]. Cytotoxic assessments can be done using simple assays and studying the ENM-triggered pathways. Proposed mechanisms include the physicochemical properties of ENMs, high surface charge, generation of free radical species, fibrous structure, and surface chemistry among others [122].

In vitro and in vivo models for cytotoxicity assessment

ENM-induced cytotoxicity has been evaluated in both in vitro and in vivo models. In vitro models provide controlled experimental conditions to evaluate cytotoxic effects of ENMs on cellular processes, while in vivo models provide insights into hazards associated with ENMs in complex biological systems. Plant-based models have been used to evaluate systemic responses and organ-specific effects [123]. In vivo studies expose plants to ENMs through foliar application, root uptake, seed priming or hydroponic systems. Phytotoxicity manifests as growth inhibition, ROS generation, and cell death. Further, ENM bioaccumulation and translocation within various plant tissues can exacerbate anomalies as demonstrated in studies involving carbon nanotubes. Alternate strategies for assessing nanotoxicity include cost effective in silico approaches such as molecular docking, molecular dynamics simulations, and quantitative structure–activity relationship (QSAR) modeling for predictive analysis [124]. Computational models such as ‘Nanotox’ [125], and ‘Nano-QSTR’ [126] among others are widely used to minimize reliance on animal models for nanotoxicity testing. Additionally, in vivo plant models like A. cepa, S. polyrhiza, Lemna species, and green alga Chlorella species have been utilized for cytotoxicity studies [127].

Cytotoxicity mechanism

Once ENMs bind to cell membrane molecules, they enter the cells through various entry modes. Inside the cell, they often interact with organelles like mitochondria and chloroplast, interfering with the oxidative reduction process, and triggering an oxidative burst, that interferes with the electron transport chain elevating ROS in the cell [128]. The resulting ROS affects most cellular organelles, inducing membrane damage via lipid peroxidation, protein modification, and DNA damage [128].

Silver ions (Ag⁺) released after the oxidation of silver oxide ENMs accumulate in cellular compartments via diffusion or endocytosis, causing mitochondrial dysfunction. Furthermore, Ag-ENMs also generate ROS after interacting with the cell membrane, which eventually causes nucleic acid and protein damage, hindering cell proliferation and cell death. Excessive ROS can trigger necrosis and apoptosis [100]. In response to ROS generation, cells activate ROS scavenging mechanism or antioxidant mechanisms involving enzymatic (superoxide dismutase, guaiacol peroxidase, and catalase) and non-enzymatic (Ascorbate, glutathione, carotenoids, phenolics, and tocopherols) molecules to mitigate apoptosis. Several studies have demonstrated activation of antioxidant defense mechanisms in plants as a response to ENM exposure [129].

Cellular responses to engineered nanomaterials

ENMs can trigger various cellular responses, including intracellular localization and pathways that lead to cellular death. Entry and cellular uptake of ENMs has been elaborated in the previous section and endocytic pathways are the preferred routes for ENMs entry into cells. Once internalized, ENMs may accumulate in organelles including vacuoles, cytoplasmic vesicles, and endomembrane systems, including golgi bodies and endosomes as observed with gold ENMs in Arabidopsis. ENMs exposure can induce apoptotic-like cell death characterized by caspase-like activities and DNA fragmentation. Similarly, autophagy-related cell death has been linked to zinc oxide ENMs in A. thaliana [130]. Polystyrene ENMs have shown significant cytotoxicity in wheat protoplasts [131], with 20 nm amino-modified PS-ENMs (PS-20A) causing severe damage to membranes, chloroplasts, and mitochondria. The amino modification increases the severity of damage, induces enhanced ROS production, membrane permeability and LDH leakage more than carboxyl-modified PS-ENMs [131]. Similarly, high concentrations of CuO ENMs (250–2500 μg/L) severely disrupted cellular functions in phytoplankton diatom Thalassiosira weissflogii [132] and marine microalga Nannochloropsis oculata [133] causing cytotoxic, genotoxic, and mechanical damage, including growth inhibition, decreased photosynthetic efficiency, membrane integrity disturbance, increased ROS production, and cell death. Although plants lack an immune system comparable to animals, they respond to ENMs exposure by activating defense signaling pathways and producing defense-related molecules. For instance, ENMs exposure has been observed to result in ROS generation and upregulation of defense-related genes in Arabidopsis.

Factors affecting nanotoxicological outputs

The toxicological effects of ENMs are significantly influenced by their physicochemical properties, dose–response relationship, cell, and tissue specificity, interactions with cellular biomolecules, and synergistic effects (Fig. 5). Each of these factors will be discussed in the following sections.

Fig. 5

Factors affecting the toxicity of engineered nanomaterials including size, shape, chemical composition, surface charge, surface functionalization and dissolution

Physico-chemical properties of engineered nanomaterials

The physical (size and shape) and chemical (composition and charge) properties of ENMs significantly influence their interactions with cellular biomolecules and subsequent cytotoxicity.

Size, shape, and surface area

The size, shape, and surface area of the ENMs are the key determinants of their cellular interaction and toxicity. Smaller NMs (1–10 nm) can easily enter cells and organelles, and their endocytic uptake and reactivity gets enhanced due to a high surface area to volume ratio. Studies have shown that smaller ENMs exhibit greater cellular internalization and cytotoxicity. For instance, Au ENMs (< 6 nm) can pass through the nuclear pore, while ENMs larger than 10 nm penetrate the cell membrane but cannot traverse the nuclear membrane [134]. Similarly, the toxicity and size relationship of ENMs has been studied with silver and gold ENMs in many species. Smaller Ag ENMs (0.6–2 nm) exhibit greater toxicity than larger Ag ENMs (5 and 20 nm). In general, ENMs smaller than 5 nm penetrate cells via translocation or diffusion, whereas larger ENMs (> 5 nm) are internalized through phagocytosis.

ENMs occur in various shapes including ellipsoids, spheres, sheets, cylinders, cubes, and rods. Their shape significantly influences their nano-bio interactions like cellular uptake, biodistribution, intracellular localization, deposition, and interactions with cellular components, even when their sizes and compositions are similar [135]. While spherical ENMs are prone to endocytosis, non-spherical ENMs are internalized more effectively. In BEAs-2ß cell cultures, hydroxyapatite ENMs in needle and plate shapes exhibited higher toxicity than rod and sphere shaped ENMs. The crystal structure of ENMs has also been reported to affect their toxicity [136]. For instance, anatase-like titanium dioxide ENMs (octahedral TiO₂ crystals of the same size) were nontoxic, whereas rutile-like ENMs (prism-shaped TiO₂ crystals) caused oxidative damage to DNA, lipid peroxidation, and the formation of micronuclei, indicating abnormal chromosome segregation during mitosis [137].

Surface charge and coating

The surface charge of NMs is one of the important surface characteristics that plays an important role in interaction with biological systems and nanotoxicity. The surface charge influences the stability of ENMs, interaction with the cell membrane, and cellular uptake. Zeta potential, which is affected by the surface charge of ENMs, plays an important role in their adsorption on the membranes and affects their toxicity [138]. The studies have reported a reduction in the toxicity of TiO₂ ENMs by introducing functional NH₂ or SH groups on their surfaces [139]. Positively charged ENMs are more toxic than neutral or negatively charged ENMs, due to their ability to freely pass through the cell membrane and their strong affinity to negatively charged DNA. Altering the charges of ENMs can regulate their localization and toxicity, enabling their effective application. Furthermore, the presence of surface coatings in the form of polymers or other biomolecules can modify their physiochemical properties affecting their biocompatibility, availability, functionality, and toxicity. Nanoparticle surface engineering is an upcoming domain of nanotechnology that is garnering a lot of interest recently for diverse applications [140].

Surface functionalization plays a pivotal role in determining NMs toxicity. By utilizing molecules such as proteins, peptides, aptamers, antibodies, and oligosaccharides, the physicochemical properties of ENMs including their electric, magnetic, optical properties, and chemical reactivity can be modified to induce cytotoxic effects. These modifications have the potential to increase the biocompatibility and uptake efficiency of ENMs which are the key determinants of their toxicity. A study involving Selenium ENMs with three different surface stabilizers namely Poly-L-lysine (PLL), polyvinylpyrrolidone (PVP), and polyacrylic acid (PAA), demonstrated varying levels of toxicity depending on the surface functionalization (PLL > PAA > PVP) [141].

Aggregation and dissolution

The aggregation and dissolution behaviors of ENMs influences their cellular interactions and toxicological properties. Aggregation refers to the clustering of ENMs, while dissolution indicates ionization of these particles to release ions. The uptake, properties, and interactions of ENMs change depending upon their presence individually or in aggregates. The solubility of ENMs is yet another determinant of their toxicity level. Most ENMs exhibit low solubility and form colloidal dispersions. For instance, the precipitation of silver ENMs reduces its toxicity while the oxidative dissolution process generates Ag⁺ ions, which increases their toxicity [142]. Additional parameters like size, shape, pH, surface chemistry, and charge influence the dissolution and precipitation of NMs, thereby, affecting nanotoxicity [143, 144].

Dose–response relationship

The dose–response relationship is a key factor in nanotoxicology and refers to the relationship between the concentration of NMs and the intensity of their cytotoxic effects. Studies have demonstrated that higher doses or concentrations of NMs produce greater nanotoxicity [9]. However, this relationship can exhibit non-linear behavior, where intermediate doses sometimes exhibiting different cytotoxicity than lower and higher concentrations. Advance methods like inductively coupled mass spectroscopy (ICP-MS) [145] and flow cytometry [146] have been used to provide more precise dosimetry by measuring their cellular uptake. Accurate quantification of ENMs dosage in cellular systems using advanced analytical methods and dosimetric devices by real-time sampling is recommended, as in situ dosimetric devices fail to measure the correct dosage due to the transient nature of ENMs, agglomeration and sedimentation [127, 147].

Cell and tissue type specificity

The cytotoxic effects of ENMs greatly vary depending on the specific cells or tissue exposed. The differences arise due to changes in metabolic characteristics, functionality, and defense mechanisms among cells. Further, specificity in signaling mechanism, gene expression, and cellular interactions within specific tissue types contributes to different responses towards nanotoxicity. For instance, studies have demonstrated that composition and size of ENMs along with the target cell type determine the degree of cytotoxicity [148] Further, the type of particles used also influence the nanotoxicity [149], therefore, it is important to consider both cell specific factors and ENMs characteristics for nanotoxicological assessments.

Synergistic and antagonistic effects and interactions

ENMs can interact with chemicals, biological factors, anti-microbial agents, and even pollutants, leading to synergistic or antagonistic effects on cytotoxicity [150]. These interactions may enhance oxidative stress, alter signaling pathways, and modify cellular responses. It’s extremely important to understand the potential interactions and combined effects of ENMs with cellular entities for assessing the nanotoxicity risks and their potential management. The genotoxicity of ENMs in environmental contexts is profoundly influenced by their interactions with agricultural and industrial chemicals, other ENMs, and natural compounds, creating a complex interplay that can either mitigate or exacerbate toxicity [37]. Real-world exposure scenarios often involve multiple stressors, necessitating a deeper understanding of ENM behaviors in such environments. For example, the insecticide acetamiprid has been shown to alter the genotoxic effects of fullerenol ENMs in human lung cells (IMR-90), demonstrating how agrochemicals can modify ENM-induced DNA damage [151]. Similarly, the insecticide ATCBRA affects the toxicity of cardamom–silver nanoparticle (Ag ENM) composites in V. faba roots [152]. These examples illustrate how certain environmental pollutants can modulate the toxicity of ENMs, offering potential strategies for risk mitigation.

Interactions between ENMs themselves further complicate their toxicological profiles. For example, titanium dioxide (TiO₂) nanoparticles have been found to reduce cadmium-induced genotoxicity in human sperm cells by forming a protective “sandwich-like” structure that limits cadmium reactivity [153]. Similarly, TiO₂-3%CeO₂ nanocomposites exhibit no developmental toxicity in zebrafish embryos, unlike their individual components, indicating that composite ENMs may neutralize the adverse effects of their constituents [154]. However, not all ENM interactions are protective. For instance, combined exposure to aluminum oxide (Al₂O₃) and zinc oxide (ZnO) nanoparticles has been shown to induce more pronounced toxicity compared to individual exposures, with increased oxidative stress, DNA damage, and disruptions in mitochondrial function and antioxidant defenses [155]. These findings suggest that the nonadditive nature of ENM interactions, driven by factors such as surface chemistry, aggregation behavior, and ROS generation, plays a critical role in determining their overall toxicity. Understanding these interactions is essential for predicting the risks associated with ENM mixtures in environmental and biological systems.

Natural compounds, particularly antioxidants, have emerged as promising agents for mitigating ENM-induced genotoxicity [156]. For instance, anthocyanin and α-tocopherol have been effective in reducing TiO₂ ENM-induced DNA damage in sperm cells, with anthocyanin exhibiting superior DNA-stabilizing properties [157]. Similarly, Hedayati et al. [158] demonstrated that vitamin E could counteract the toxic effects of silver nanoparticles (Ag ENMs) in zebrafish (Danio rerio). In their study, Ag ENMs caused immunological dysfunction, cellular damage, and oxidative stress, as indicated by reduced lysozyme and ACH50 activity, elevated lactate dehydrogenase (LDH) and cortisol levels, and decreased catalase (CAT) and superoxide dismutase (SOD) activities [158]. Higher doses of vitamin E effectively reversed these effects, restoring normal physiological functions. Additionally, a combination of lipophilic vitamin E and hydrophilic vitamin C has proven effective in alleviating zinc oxide (ZnO ENM)-induced toxicity in Nile tilapia (Oreochromis niloticus) [159]. In a study by Abdelhalim et al., rats exposed to gold nanoparticles (Au ENMs) exhibited hepatotoxicity and elevated oxidative stress markers, including alkaline phosphatase (ALP), alanine aminotransferase (ALT), gamma-glutamyl transferase (GGT), total protein, malondialdehyde (MDA), and reduced glutathione (GSH). Treatment with L-arginine significantly reduced these oxidative stress parameters, highlighting its protective role against Au ENM-induced damage [160]. Thus, natural compounds, whether used individually or in combination, hold significant potential for mitigating the adverse effects of ENMs.

Environmental conditions further modulate ENM toxicity, often in unpredictable ways [161, 162]. Copper oxide (CuO) nanoparticles, for instance, exhibit enhanced genotoxicity under acidic conditions, particularly in the presence of glyphosate, due to increased dissolution and ROS generation [163]. Similarly, TiO₂ ENMs show enhanced toxicity in zebrafish embryos under ultraviolet (UV) light, with uncoated TiO₂ ENMs inducing oxidative stress and developmental toxicity, while polymer-coated variants increase lipid peroxidation and glutathione levels [164]. These observations underscore the importance of considering environmental factors in nanotoxicity assessments, as they can dramatically alter the biological effects of ENMs. Further, plastics degrade into micro-and nanoplastics (MNPs) and accumulate in soil and environment. Terrestrial environments accumulate 4–23 times more MNPs than marine ecosystems, with agroecosystems acting as major sinks receiving 1.15–2.41 million tons of MNPs annually. SEM analysis have detected significant levels of MNPs in many edible crops [121, 265]. Reports suggest that the interactions take place between ENMs and MNPs in the soil, and MNPs may act as carriers for toxic chemicals, facilitating their transport into hosts. However, there is limited research explicitly addressing their impact on nanotoxicity, hence specific effects of this interaction on nanotoxicity warrant future research [121, 265].

As evident, the genotoxicity of ENMs is influenced by a multitude of factors, including interactions with environmental chemicals, other ENMs, natural compounds, and environmental conditions. These interactions create a complex and dynamic system that challenges traditional approaches to toxicity assessment. Moving forward, a holistic understanding of these factors will be essential for developing accurate risk assessment frameworks and ensuring the safe use of nanomaterials in environmental and industrial applications.

Understanding interactions between inorganic ENMs is central to comprehending how their presence can alter toxicity in environmental and biological systems. While it is known that interactions between ENMs and chemicals like pesticides or fertilizers can modulate toxicity, the mechanisms behind these changes remain vague. This uncertainty stems from the complex, nonadditive nature of interactions at the nanoscale [165], where classical theories for colloidal forces—such as electrostatic, van der Waals, hydrophobic interactions—often fall short. For example, the combined effects of ENMs and environmental chemicals may not simply be the sum of their individual impacts; instead, they can exhibit synergistic or antagonistic or even additive behaviors that are difficult to predict. The concept of additive versus nonadditive interactions provides a valuable framework for understanding these mechanisms. Several heuristic rules have been identified to help discriminate between additive and nonadditive nanoscale systems, offering a practical way to categorize and predict ENM interactions [165]. By applying these rules, researchers can better understand how ENMs interact with chemicals and other ENMs at the nanoscale, shedding light on how these interactions influence toxicity. For instance, nonadditive effects may arise from changes in surface chemistry, aggregation behaviour, or the generation of ROS when ENMs and chemicals coexist. Advances in atomic simulations and experimental tools are now making it possible to probe these interactions in greater detail, offering insights into the electronic and structural changes that drive toxicity. This knowledge, combined with heuristic approaches, is critical for predicting and mitigating the risks of ENMs in real-world environments, where they often coexist with a multitude of chemicals and stressors.

Formation of bio-corona and eco-corona

Formation of bio-corona and eco-corona is another critical aspect for understanding nanotoxicity as it impacts the behaviour and fate of ENMs in living entities and ecosystems. Biocorona represents a dynamic layer formed by the adsorption of biomolecules such as proteins, polysaccharides, and lipids around the ENMs when it interacts with biological system, however, eco-corona is formed when ENMs interact with environmental components like plant exudates, extracellular polymeric substances, humic compounds, and soil organic matter. The structure and composition of biocorona evolves over time depending on ENMs properties (size, shape, surface charge), biological environment (different biomolecules, pH, and ionic strength) and duration of ENM exposure consequently leading to the formation of either soft or hard biocorona [166]. Initially formed soft corona represents the loosely bound outermost layer of biomolecules which dynamically interact with ENMs and/or the medium surrounding them whereas hard corona formed over time is the more stable innermost layer tightly attached to ENMs. Soft corona layer is defined by high exchange rates, enabling biomolecules to associate/dissociate rapidly while hard corona has slower exchange rates and therefore determines NM’s biological identity, which affects its interaction with cells. Recent research has shown the presence of both biocorona and eco-corona in plant systems [167]. In plants, biocorona is suggested to form after adsorbing proteins and other biomolecules while the eco-corona is formed by association of NMs with root exudates, polysaccharides, microbial metabolites in the rhizosphere, prior to their interaction with plant proteins and other biomolecules. Biocorona and/or eco-corona formation affects NMs stability, cellular uptake, intracellular distribution, functionality and potential toxicity in terms of activation of various pathways. The proteins and other biomolecules act as a ‘corona shield’ significantly modifying NM’s interactions with cells, toxicity behaviors and ultimately their environmental fate. Furthermore, the physiochemical properties of NMs, the cellular environment and variety of biomolecules add another tier of diversity to biocorona composition making it very complex [168]. Understanding the mechanism of biocorona formation and its effects on nanotoxicity are highly desirable for developing a clear understanding of the biological responses of ENMs. Moreover, this information is essential for safe designing and utility of NMs for various applications as well as to minimize their adverse effects on human health, plants, and ecosystems. [9, 169]. Although protein corona formation and impacts have been deciphered well in medical and environmental sectors, it has been poorly discerned in plants. Nevertheless, recent studies have unveiled the influence of protein corona on the uptake and translocation of ENMs wherein corona reduces the ENM bioavailability via altering their surface properties, thereby mitigating nanotoxicity. Moreover, role of biocorona in regulating vital processes and plant responses such as pathogenesis, abiotic stress tolerance, and senescence via reducing excessive ROS formation has also been established [169,170,171]. Various investigations have analyzed the implication of bio and/or eco-coronas on plant health and nanotoxicity. Table 1 summarizes the relevant studies focusing on the implications of biocorona and eco-corona in plants. A recent study by Kang et al. showed the size and surface properties dependent effect of zinc oxide ENMs on metabolic function and eco-corona formation in Vigna radiata sprouts [172] Another study revealed that formation of extracellular polymeric substances eco-corona counteracts the graphene oxide ENMs induced cytogenotoxicity in A. cepa root tip cells by reducing oxidative stress within the cells [173]. Similar findings were observed by Arya et al. where protein corona reduced the genotoxicity of vanillin capped Au ENMs in A. cepa root thus emphasizing the relevance of biocorona in modulating nanoparticle toxicity in plants [174]. It was observed that protein corona formation enhanced the salt tolerance in in the C. annuum seedlings owing to improved protein stability [175]. Although the aforementioned studies clearly showed the crucial role of corona in altering the nanotoxicity of ENMs it still needs to be extensively studied. Thus, future research should focus on developing eco-friendly ENMs and exploring strategies to control corona formation for sustainable nanotechnology applications. In this direction, The Minimum Information about Nanomaterial Biocorona (MINBE) [176], a set of guidelines that includes a flexible checklist for designing experiments and standardized reporting of results was introduced to allow proper studying and reporting of the NM biocorona thus maintaining reproducibility and comparison across different studies.

Surface atomic arrangement of nanoparticles

Besides the physicochemical properties (size, shape, chemical composition, charge etc.) of engineered ENMs in influencing the biomolecular interactions and cytotoxicity, reports have shown that the surface atomic arrangement of ENMs is also a crucial factor in determining their binding affinity, cellular uptake, protein interactions, nanotoxicity and biological activity. [177, 178]. A recent study showed that atomic scale rearrangements in monolayer molybdenum disulfide (MoS₂), nanosheets regulate their interaction with biological systems, affecting toxicity at multiple levels, from molecular binding to metabolic disruptions [179]. It also showed that surface atomic arrangements of MoS₂ nanosheets through different coordination positions (octahedral or 1 T-phase and triangular prism or 2H-phase) leads to modification of affinity sites, interfacial protein structure, metabolic pathways and development of zebrafish embryos. Recent experiments have shown that MoS₂ nanosheets with triangular prism (1H-MoS₂) coordination bind phosphate groups before interacting with proteins thus not alter the proteins significantly and exhibiting lesser binding affinity with biological interfaces. On the contrary, octahedral (2H-MoS₂) coordination nanosheets interacts with proteins first, thereby leading to significant alterations in protein structures (from β-sheets to turns, bends, and random coils) and exhibiting higher binding affinity with biological membranes. Furthermore, 2H-MoS₂ enters the embryos through caveolae-mediated endocytosis making it more bioavailable, induces higher ROS production than 1 T-MoS₂ causing oxidative stress, mitochondrial dysfunction, lipid peroxidation and higher developmental toxicity (pericardial edema, yolk sac edema, and mortality) in zebrafish embryos [179]. To conclude, these studies confirmed that sub-atomic scale rearrangements in nanomaterials alters their interaction with biological interfaces and nanotoxicity, ranging from molecular binding to metabolic disruptions. These insights emphasize the necessity to engineer safer nanomaterials by cautiously regulating their atomic structures in order to minimize their adverse effects on health and environment.

Geno- and cytotoxicity of engineered nanomaterials in plants

The literature is abreast with reports of nanotoxicity (see Table 1) including both geno- and cytotoxic effects across various organisms, with notable reviews highlighting these findings [180,181,182]. In plants, studies emphasize the importance of understanding genotoxicity responses and developing strategies for mitigating the genotoxic effects of pollutants and other plant stressors. In agriculture, nano fertilizers and nano pesticides have shown genotoxic and cytotoxic effects, influenced by ENM concentration, exposure time, and size [181, 182]. Figure 6 illustrates the mechanism of ENMs-induced geno-and cytotoxicity in plants, followed by a detailed discussion of reported genotoxic and cytotoxic effects of various ENMs (see Table 2) (Fig. 7).

Table 1 Implications of biocorona and eco-corona in regulating phytotoxicity in plants

Fig. 6

Mechanism of nanomaterials induced genotoxicity and cytotoxicity in plants

Table 2 Genotoxic effects of metal-based nanomaterials in plants in various plant species

Geno- and cytotoxicity of silver nanomaterials in plants

Silver nanoparticles (Ag ENMs) have been shown to induce oxidative stress and DNA damage in various plants [183] including wheat (Triticum aestivum) and soybean (G. max) [184], B. napus [185], A. thaliana [186] and A. cepa [187]. The resulting accumulation of ROS leads to cell injury and caspases’ activation leading to apoptosis. Studies have highlighted the use of environmentally friendly Ag ENMs, synthesized from microbes like Trichoderma viride and Shewanella oneidensis as well as certain vegetative plant parts. However, Ag ENMs bio-synthesized from Lactobacillus paracasei were found to inhibit the growth of root hairs in wheat, negatively affect apical meristem tissue, alter metabolic pathways, and increase ROS levels [188].

Additionally, Ag ENMs have been reported to inhibit cell division at higher concentrations while promoting accelerated root growth in A. thaliana [189]. In V. faba, exposure to Ag ENMs resulted in increased chromosomal aberrations, micronucleus induction (MN), along with a decrease in mitotic index, suggesting potential interference of silver nanoparticles in the cell cycle. Ag ENMs induced oxidative stress leading to lipid peroxidation and DNA damage has been demonstrated in many plant species [190]. Similarly, biosynthesized Ag ENMs using endophytic bacteria exhibited antimicrobial activities but also affected plant growth and physiology [191]. These findings underscore the importance of Ag ENMs as antimicrobial agents but also posing risks to plant health depending on their concentration, synthesis method and duration of exposure.

Geno- and cytotoxicity of gold nanomaterials in plants

ENMs of gold (Au ENMs), have been widely used in a variety of applications, including biomedical imaging and site-specific drug delivery, due to their unique optical, chemical, and physical characteristics [192]. However, their potential genotoxic effects on plants have been documented in various studies [193] including N. xanthi [194], A. cepa [187] and O. sativa [195]. In barley, root growth reduction was observed post-exposure to Au ENMs [196]. Administration of Au ENMs and Ag ENMs as a colloidal solution caused DNA damage response ( DDR) in N. tabacum seedlings, with considerable damage at higher Ag ENM concentrations (30 mg·kg − 1) and no effect at higher Au ENM concentrations [197]. Further, Au ENMs have been shown to induce oxidative stress in plants. They have been shown to penetrate cells and accumulate in various organelles resulting in DNA damage and genetic mutations [85, 198, 199].

Geno- and cytotoxicity of titanium oxide nanomaterials in plants

Titanium oxide ENMs (TiO₂ ENMs) are widely used in a variety of consumer products such as sunscreens and cosmetics. However, concerns about their potential genotoxic effects on plants have been raised [200, 201]. In Lens culinaris, exposure of TiO₂ ENMs to plants caused DNA damage, elevated stress enzymes levels, and CAs. Similar genotoxic effects have been reported in other studies [202, 203]. On the contrary, several studies have documented the use of TiO₂ ENMs in mitigating the toxicity of arsenic [204], cadmium [205, 206], chromium [203]. TiO₂ ENMs have also been found useful in managing salinity stress, reducing lead bioaccumulation and increasing photosynthetic efficiency [207].

Geno- and cytotoxicity of copper and copper oxide nanomaterials in plants

Copper (Cu) and copper oxide (CuO) ENMs have diverse applications, including use in water purification, electronic devices, and antimicrobial coating. Studies have highlighted the role of CuO ENMs in altering pathways involved in pollen germination and their potential across generations in A. thaliana [208]. Jia et al. [209] reported a reduced actin filament growth rate in root tip cells, supporting the involvement of CuO ENMs in modifying F-actin dynamics. Additionally, copper transfer from root to shoot decreased following the application of 5–40 mg/L of CuO ENMs in plants. Genotoxic and cytotoxic effects of CuO ENMs have also been observed in many other plant species including Cucumis sativus [210], Coriandrum sativum [211], B. rapa ssp. rapa [212] and Pisum sativum [213].

Geno- and cytotoxicity of iron oxide nanomaterials in plants

Iron oxide ENMs (Fe₂O₃ ENMs) are widely used in applications such as magnetic resonance imaging and drug delivery, majorly primarily due to their useful properties like super-paramagnetism and high surface area-to-volume ratios. The genotoxic effects of Fe₂O₃ ENMs are often concentration dependent and have been observed in many plant species [214]. Research indicates that Fe₂O₃ ENMs are harmful even at doses lower than those of ionic iron supplementation. Additionally, FeO ENMs have been conspicuously shown to help S. melongena and B. oleracea var. italica plants cope with drought and cadmium toxicity stress by activating multiple genetic processes [215, 216].

Geno- and cytotoxicity of cerium oxide nanomaterials in plants

The toxic effects of CeO₂ ENMs (CENMs) have been reported by Allium and Comet tests [217] in soybean and butterhead lettuce. The presence of Ce (III) produced in the roots has been perceived as a result of biotransformation of the applied CeO₂ ENMs. Similarly, it has been found that exposing barley (H. vulgare) seedlings to CeO₂ ENMs elevated oxidative stress. In cilantro plants, CENMs affected the nutritional content of the plants, altering root growth, catalase and peroxidase activity at 125 mg/kg, while higher concentration (500 mg/kg) increased CENM accumulation and modifying carbohydrate metabolism affecting nutritional parameters [218] CENMs have been observed to exhibit both oxidant and anti-oxidant properties based on their surface chemistry. In a study on an aquatic microorganism model [219], the CENM toxicity was linked to the percentage of surface Ce³⁺ sites, with higher (40–58%) Ce³⁺ content causing toxicity, while lower concentration (26–36%) being non- toxic. It was further demonstrated that phosphate treatment blocked Ce³⁺ sites and led to reduction in CENM toxicity, while iron-induced colloidal destabilization elevated the toxicity. These findings underscore the surface Ce³⁺ content as a determinant of CENM bioactivity, aiding safer nanoparticle design.

Geno- and cytotoxicity of zinc oxide nanomaterials in plants

ENMs made of zinc oxide (ZnO ENMs) are widely used in applications such as sunscreens, food packaging, and biomedical and textile industries. However, their potential genotoxic effects on plants have not been thoroughly investigated. Recent studies have shown that ZnO ENMs can induce toxic effects on plants by triggering biochemical changes [220]. In a study by Khan et al. [221] ZnO ENMs at varying concentrations (50, 100, 200, and 300 mg/L) were tested in A. thaliana. Further, a study conducted by Kolackova [222], reported that ZnSe quantum dots suppressed Agrobacterium tumefaciens growth by 60% at 250 µM, though plants showed no substantial harmful effect at the same dose. Du et al. [223] observed that ZnO ENMs demonstrate considerable toxicity at higher doses, yet their effects are less severe compared to chemical fertilizers like ZnSO₄. In H. vulgare, ZnO ENMs at concentrations of 0.4–0.8 g/L induced cytotoxicity by inhibiting mitosis, inducing Cas, and causing DNA fragmentation. They also reduced photosynthetic efficiency and antioxidant efficiency and altered miRNA expression (miR156a, miR159a, miR159c) in a dose-dependent manner [224]. Further, ZnO ENMs disrupted metabolic pathways linked to oxidative stress, energy generation and DNA integrity, and their combined exposure with other environmental substances amplified ecological risks in plants [225].

Environmental risk assessment (ERA) and mitigation of nanotoxicity

For understanding the impact of ENMs on ecosystems and ensuring their safe application, it is important to assess the environmental risks of nanotoxicity. Studies have shown that ENMs can enter the environmental systems during production, use and disposal, and interact with biota and other environmental co-contaminants potentially triggering elevated toxic responses in the target species as depicted in Fig. 7 [30, 34, 36, 225,226,227,228]. Their small size, large surface area, high reactivity, ability to penetrate tissues and generate ROS contribute to toxicological outputs in natural ecosystems. The toxicity of ENMs is further influenced by their bioaccumulation potential and environmental persistence [33]. Further, upon their release into the terrestrial and aquatic ecosystems, ENMs might undergo transformations such as dissociation, dissolution and aggregation, that can lead to bioaccumulation and biomagnification and affect the food chains [34, 36]. The widely used metallic nanomaterials (MNMs) have demonstrated bioaccumulation in aquatic ecosystems due to their interactions with environmental factors [29, 34, 228], with trophic transfers across the food chains posing potential risks to higher organisms, including humans. Studies indicate that MENMs disrupt microbial processes such as nitrogen fixation, ammonification, and phosphate solubilization, which are essential for plant growth and ecosystem stability [229].

Fig. 7

Pathways through which NPs from various sources enter agriculture, the food chain, humans, and animals, ultimately causing harmful effects to human health and the environment

The environmental risks of ENMs can be measured by field or laboratory tests using in vivo and in vitro methods [230] and modern computational toxicological analyses [231, 232]. Kumar et al. [7] depicted the bioaccumulation of metallic engineered nanomaterials (MENMs) in soil affecting microbial biodiversity and soil health. Studies involving nano-TiO₂ demonstrated its potential entry into the food chain via dietary routes affecting both primary producers and consumers [233]. It accumulated in algal cells and was subsequently transferred to consumers with BMF values exceeding 1, indicating trophic transfer. Nano-TiO₂ decreased algal cell density and significantly affected rotifer production. It was indicated that concentration of ENMs and duration of exposure played key roles, underscoring its environmental threat to aquatic ecosystems.

Lately, advancements in artificial intelligence and machine learning have enhanced in silico assessment of nanotoxicity, offering efficient alternatives to traditional analyses. Many computational models have been developed to predict ENM behavior, toxicity and environmental fate reducing tedious experimentation. A recent meta-analysis by Zheng and Novack [231] studied bioaccumulation data of eight non-dissolvable ENMs and their environmental impact across three trophic levels, using bioconcentration factor (BCF), the bioaccumulation factor (BAF) and the biomagnification factor (BMF) as the key endpoints. The BCF and BAF values showed that ENMs accumulated more in primary consumers. Further, although biomagnification with a BMF of 17.4 was observed in the zooplankton, no significant trophic transfer to fish was observed. Notably carbon-based ENMs bioaccumulated more than other tested ENMs except TiO₂. The study emphasizes the need for comprehensive risk assessments that account for trophic level variations in bioaccumulations with standardized testing procedures and advance kinetic modeling [228, 232, 234]. Likewise, Tang et al. [232] highlighted the efficiency of computational nanotoxicology models including material flow analysis models, multimedia environmental models, physiologically based toxico-kinetics models, quantitative nanostructure–activity relationships, and meta-analysis for assessing the environmental risks associated with ENMs and highlighted the challenges in accurately predicting their fate, exposure and toxicity. It was emphasized that the standardized datasets, improved model validation and multi-scale predictive modeling approaches are essential to improve risk assessment [232].

Given these concerns, it is crucial to establish a structured risk assessment framework that incorporates data on the life cycle, environmental toxicity, and interactions of nanomaterials with ecosystems. Combining experimental data, field studies, computational modeling, and AI-driven risk assessment tools will enhance the efficiency of ERA. Additionally, developing comprehensive databases on bioaccumulation and integrating them with ERA frameworks can guide informed regulatory decisions. Future research should focus on understanding the complex interactions between environmental variables with nanotoxicity while exploring mitigation strategies to minimize their impact on ecosystems [225, 228].

Strategies to mitigate the toxicity of nanomaterials

Approaches for mitigating nanotoxicity refer to strategies used to minimize or prevent the harmful effects of ENMs on human health and the environment. Since nanotoxicity is largely influenced by the physicochemical properties of the ENMs, and generally results in ROS generation, the key toxicity mitigation strategies include the use of antioxidants and surface modifications. Recent omics-based based approaches, including epi-genetical modifications, have also been useful in nanotoxicity management. The nanotoxicity mitigation strategies have been discussed under the following headings and summarized as Table 3.

Table 3 Strategies for mitigating genotoxicity caused by nanomaterials in plants

Manipulation of surface chemistry and properties

Surface coatings play a significant role in modulating the behaviour of ENMs and offering advantages such as reducing toxicity and improved performance in various applications. These coatings act as protective layers, potentially limiting the release of toxic ions or reactive species from ENM cores, while enhancing biocompatibility, and improving stability and dispersibility [235]. The effectiveness of a surface coating in reducing toxicity is contingent on numerous factors, including the choice of coating material, ENM type, target organism, and toxicity mechanisms. Coated ENMs may form a ‘biocorona,’ integrating with cellular proteins and biomolecules, and/or an ‘eco-corona’ with the rhizosphere components. Both of which can influence ENM's interactions with cells and tissues, potentially affecting toxicity [167, 174]. Further, ENM designs can be modified to change their surface chemistry and reactivity on the basis of toxicity mechanisms and the target organism. The strategies to reduce ENM binding affinity to cell surfaces include modifying designs with negatively charged ligands, altering morphologies or applying coatings such as silica, trisodium citrate, polyvinyl pyrrolidone (PVP), zwitterionic polymers, and poly (N-isopropyl acrylamide) (PNIPAM), and polyvinyl alcohol (PVA), polyethylene glycol (PEG) or biomolecules like proteins [236]. While, silica coatings, and PEG encapsulation can reduce disintegration of ENMs and biocorona formation, PEG’s immunogenic properties, imply finding safer alternatives with comparable camouflaging potential.

Recently, Hanif et al. [237] showed that doping Indole-3-acetic acid onto CuO ENMs produced CuO-IAA ENMs (30.4 nm), which effectively mitigated toxicity in L. sativa. This coating reduced non-enzymatic antioxidants and enhanced plant biomass by promoting a cumulative antioxidative response. Arya et al. [174] found that green synthesized, protein-coated valine-capped gold ENMs at > 100 µg/mL caused negligible genotoxic effects in A. cepa meristematic root cells compared to their non-protein coated valine-capped gold ENMs. ENMs are known to release toxic ions upon dissolution which can be mitigated by modifying ENM morphology, using less toxic materials, or incorporating chelator and capping materials. Interestingly, while surface coatings are generally considered protective, some studies suggest that the choice of coating material and design may not always reduce toxicity. For instance, El Badawy et al. [238] reported that Ag ENMs toxicity toward Bacillus species was surface charge-dependent. Studies also highlight that the impact of surface coatings on ENM toxicity can be complex and context-dependent. For instance, Ag ENM-PVP induced only mild toxicity on tobacco seedling growth, whereas Ag ENM-CTAB exhibited severe negative effects on growth, photosynthesis, and alterations in chloroplast ultrastructure and photosynthetic pigments, surpassing the effects of AgNO₃ itself [239].

The introduction of cysteine generally reduced the negative effects caused by AgENM-PVP, indicating that its toxicity may be linked to the release of Ag⁺ ions. Conversely, cysteine did not improve germination and growth parameters following AgENM-CTAB exposure, indicating that Ag ENM-CTAB might be associated with the surface coating itself, rather than the release of ion. Tan et al. [240] studied the effects of unmodified, hydrophobic (aluminium oxide and dimethicone coated), and hydrophilic (aluminium oxide and glycerol coated) variants of TiO₂ ENMs on Ocimum basilicum growth. Results revealed significant reductions in seed germination and shoot biomass, alongwith disturbances in essential element balance, impaired root elongation, and alterations in starch, and reducing sugars. In another study, Lolium multiflorum seedlings exposed to 40 mg/L of GA-coated Ag ENMs (gum arabic-coated Ag ENMs), exhibited the absence of root hairs, vacuolated and collapsed cortical cells, as well as fractured epidermis and root cap, effects not seen in Ag ENM exposure alone at same concentrations [241]. These findings underscore the complex interactions between ENM core properties, surface coatings, and resulting toxicity, emphasizing that while coatings are generally seen as protective measures, the specific material and design can lead to varying effects.

Manipulating ion release kinetics of metallic nanomaterials

Characterizing ion release kinetics of ENMs is important for understanding their transport, uptake, and biological interactions. Zhang et al. [242] found that the release of silver ions from Ag ENMs depended on their size and concentration. Similarly, Hahn et al. [243] showed that ENMs loading density, chemistry, and texture played equally important roles in the in vitro release of metal ions from their corresponding ENMs. Similar findings were reported for gold, zinc oxide, and titanium oxide ENMs as well [136]. A mathematical and experimental method utilizing a shrinking core model was employed to understand the release of copper ions from copper-modified membranes [244]. Thin film composite reverse osmosis membranes (TFC-RO) were used to study the dissolution and ionization of copper ions from Cu and CuO ENMs and Cu-oligomer complexes. Mathematical modeling indicated that copper toxicity in the membrane was associated with two key factors namely, the dissolution capacity of the ENMs and the level of ROS production [244].

Antioxidants

ENMs exert toxicity through multiple interconnected mechanisms. For example, the accumulation of ROS has been shown to be linked to oxidative stress [245]. Naturally occurring antioxidants in living organisms are often insufficient to mitigate nanotoxicity due to their limited dissolution and rapid degradation. Therefore, the addition of enzymatic and non-enzymatic antioxidants like SOD, CAT, POX, MDHAR, DHAR, and APX, ascorbic acid, phenolic compounds, alpha-tocopherols, and alkaloids has been employed to alleviate ROS generation. These antioxidants are often covalently linked, encased in crosslinked nanogels to enhance their stability and effectiveness [246]. Eugenol is commonly used in the synthesis and stabilization of various ENMs [229]. In Amaranthus tricolor, ascorbic acid was found to reduce phytotoxicity caused by multi-walled carbon nanotubes by scavenging ROS, reducing apoptosis, improving growth, and minimizing leaf necrosis [247]. Additionally, synthesizing Cu ENMs using ascorbic acid has been shown to improve their stability [248].

Hormone-mediated nanotoxicity mitigation

Plant hormones have also been found to reduce ENM-induced toxicity. In tomato seedlings, supplementation with 24-epibrassinolide along with ZnO ENMs reduced oxidative stress, decreased accumulation of Zn in root and shoot, and increased enzymatic antioxidants like superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase. In Cajanus cajan, seed priming with methyl jasmonates activated the antioxidant machinery and increased the production of proline, glutathione, and ascorbic acid, thereby mitigating oxidative stress [249]. Similarly, in T. aestivum, the application of gibberellic acid along with TiO₂ (up to 400 mg/kg) increased plant height, spike length, chlorophyll content, antioxidant enzyme activity ( SOD, POD, CAT, APX), while reducing H₂O₂ and MDA content [250].

Use of organic molecules

Some organic molecules such as chalcones are found to mitigate genotoxicity and reproductive toxicity induced by ZnO ENMs. For instance, Sharma et al. [251] reported that chalcone derivatives effectively reduced ZNO ENMs induced oxidative stress and DNA damage by enhancing antioxidant enzyme activity and stabilizing cellular redox balance [252]. Humic acid substances in B. napus reduce the toxicity of CuO and ZnO ENMs by elevating protein levels, antioxidant enzyme activity, and chlorophyll content [253]. Similarly, Ali et al. [254] demonstrated that humic acid improved germination, root length and biomass accumulation in T. aestivum under ZnO and CuO ENM stress largely due to improved nutrient uptake and enhanced antioxidant defense mechanism. The study further emphasized the role of humic acid in maintaining cellular homeostasis and reducing metal ion bioavailability in plants.

In S. lycopersicum, humic acid alleviates nanoplastic toxicity by promoting seed germination, growth, and chlorophyll content [255]. Wang et al. [256] showed that the phytotoxic effects of Cu²⁺ in O. sativa were reduced when treated with TiO₂ and CeO₂ ENMs (100 mg/L), and humic acid coating further increased root length by improving nutrient absorption and minimizing oxidative stress. Moreover, treatment with Zn ENMs at various concentrations improved chlorophyll and carotenoid content, increased plant height, and enhanced enzymatic activity in Philadendron plants, accompanied by noticeable anatomical changes [257]. Zhang et al. [258] further reported that humic acid modified Zn ENMs improved water retention, enhanced nutrient delivery, and boosted photosynthetic efficiency, contributing to improved plant growth under environmental stress conditions.

Omics technologies in nanotoxicity studies

The application of high-throughput systems biology approaches, referred to as ‘omics technologies’ has revolutionized the field of plant nanotoxicology, facilitating the unraveling of the complex mechanisms regulating the interactions of ENMs with plants. Considering the dynamic nature of biological processes and networks, coupled with environmental interactions, nanotoxicological outputs often get complex and may escape detection by conventional toxicological approaches. In this context, omics technologies including genomics, transcriptomics, proteomics and metabolomics offer robust platforms to assess nanotoxicity at multiple molecular endpoints. All these approaches provide comprehensive insights into the mechanisms of action, biomarker discovery, DNA damage, alteration at molecular level, in gene expression profiles and novel protein/metabolic targets in plants [259,260,261,262]. Recently, omics technologies have been extensively employed for nanotoxicity assessment to understand how plants regulate the biochemical and physiological machinery following ENMs exposure [260, 263,264,265]

Various studies pertaining to epigenetic changes like histone tail modification, DNA methylation and hypomethylation caused by SiO₂, ZnO, TiO₂, and Ag ENMs exposure are documented well Study by Sotoodehnia-Korani et al. [266] revealed that exposure to low doses of selenium ENMs (nSe ENMs) enhanced the growth and biochemical activity like soluble phenol content, and nitrate reductase activity in Capsicum annuum however, high doses of nSe ENMs induces nanotoxicity and leads to abnormal development, DNA hyper-methylation and enhanced proline content suggesting epigenetic and metabolomic alterations. Further, upregulation of significant transcription factors such as bZIP1 and WRKY1 along with inhibition in the differentiation of xylem tissues indicated nSe-induced nanotoxicity in higher doses [266]. Meanwhile, numerous multiomics (transcriptomics, proteomic and metabolomic) studies have identified key genes, metabolic pathways and protein expression, respectively that modifies plant adaptive molecular mechanism to tolerate metal or metallloid stress. [267]. Perhaps, combined physiological, transcriptomic and metabolomic approaches have shown that exposure to ZnO ENMs and TiO₂ ENMs in tomato plants led to upregulation of the genes associated with nutrient uptake, carbon/nitrogen metabolism, and secondary metabolism. The study showed that foliar application of these ENMs promoted the photosynthetic activity and growth via boosting the chlorophyll, sugar as well as amino acids content [268]. Another study revealed that simultaneous treatment with Cd and TiO₂ ENMs in Oryza sativa, induced alterations in the gene expression and metabolic pathways associated with oxidative stress, energy metabolism and amino acid synthesis thereby indicating combined nanotoxicity effects [269]. Corresponding transcriptomic study in Morus alba showed that exposure to TiO₂ ENMs modifies the expression of genes associated with energy synthesis, transport, protein metabolism, and stress response. Further, metabolomic analysis revealed differential modulation of 42 metabolites related to primary (citric acid and tricarboxylic acid cycle) and secondary metabolite biosynthesis indicating deleterious impacts [270]. Recent proteomic analyses have revealed that ENMs have the potential to substantially alter the expression of proteins associated with stress responses, photosynthesis, and metabolic processes. A study by Mustafa et al. [271] showed that treatment of G. max (soybean) seedlings with ZnO ENMs led to variations in the folding of protein, hormone metabolism, and redox processes. Further, an increase in heat shock protein 70 (HSP70), ascorbate peroxidase, and peroxiredoxin levels was also observed after treatment with ZnO ENMs. Similarly, another study revealed that treatment with Mentha arvensis biosynthesized Zn ENMs led to alterations in genes and proteins associated with transport, stress response, glycolysis, photosynthesis, ribosome structural constituents, and oxidative stress response in B. napus varieties thus indicating that ENMs regulate the transcriptome and proteome to promote the growth and development [272]. Proteome analysis of N. tabacum seedlings exposed to Ag ENMs revealed alteration of proteins associated with defense and oxidative stress responses in roots, and energy metabolism, photosynthesis, and electron transport in leaves thereby indicating the crucial role of combined omics approaches in assessing the nanotoxicological risks in plants [273, 274].

The aforementioned studies underscore the utility of integrative omics approaches in revealing the complex networking between ENMs and plants and provides valuable insights into the nanotoxicological risk assessment. However, to make the heterogenous and enormous multi-omics data more comparable and comprehensive, bioinformatic tools should be combined along with omics analysis. In future, emerging high throughput muti-omics technologies integrated with bioinformatics and systems biology approach may help in identifying ENM induced stress adaptive responses in plants, predictive nanotoxicity modelling and development of safer ENMs. The strategy will help in strengthening the understanding of plant stress biology in order to develop stress-resilient crop varieties able to tolerate wide range of stresses including metal(loid) toxicity. Thus, future investigations should aim for standardizing the methodology to enhance reproducibility of data set as well as to develop robust computational tools for effective risk assessment in nanotoxicology.

Conclusion

Nanotechnology offers promising opportunities to achieve circularity, however, knowledge gaps pertaining to nanotoxicity and its mitigation remain major challenges. Despite significant advancements in nanotoxicity research over recent decades, understanding the cyto-and genotoxic effects of ENMs remains incomplete. While recent studies have explored various aspects of ENM toxicity including synthesis, physicochemical characterization, cellular uptake, and interactions, key areas still require further elucidation. These include understanding the mechanism of DNA damage, identifying gene mutations induced by ENMs, molecular targets, synergistic effects of factors such as composition, size, structure, surface properties and cell types. Additionally, data on ENM presence in waste streams, and long-term ENM toxicity studies are essential for a comprehensive and transparent risk–benefit analysis of nanotechnology to resolve the nano-paradox. Further, environmental risk assessment is crucial for evaluating nanotoxicity risks, ensuring the safe integration of ENMs into ecosystems. As nanotechnology advances, robust ERA frameworks become essential to predict, manage, and mitigate nanotoxicity risks effectively. Integrating AI-driven predictive and computational nanotoxicological models [232] with comprehensive bioaccumulation databases with ERA frameworks can significantly contribute to the accuracy and efficiency of nanotoxicity assessments. Strengthening these facets will enable informed regulatory decisions and ensure safe and sustainable application of nanomaterials.

At present, ENMs are tested on a case-to-case basis, underscoring the need for standardized testing procedures, and uniform policy framework regulations for comprehensive risk–benefit assessment across organisms. However, challenges persist in developing nano-specific guidelines, as the validation process by organization for economic cooperation and development (OECD) can be slow. Efforts such as NANORIGO and PATROLS, which provide online standard operating procedures (SOPs), aim to facilitate knowledge exchange, yet their practical adoption in laboratories remains uncertain. To ensure the safe deployment of nanotechnology, field validation of ENM applications in commercial settings and long-term experiments in plants are essential. These studies should analyze dynamic factors like soil, climate and other physical parameters to comprehensively demonstrate both benefits and safety of ENMs, thereby enhancing public confidence in nanotechnology Striking a balance between innovation and safety through collaborative efforts will pave the way to resolve the nano-paradox, ensuring nanotechnology’ contribution to circular economy practices, sustainable development and achievement of SDGs, particularly SDGs 9, 12, and 13.

Future perspectives

To minimize nanotoxicity risks, and ensure responsible development, key strategic perspectives including implementing safety by design principles throughout the lifecycle of ENMs is essential. Currently, nanotoxicological assessments rely largely on cost-effective in vitro systems, which overlook the effects of biological interactions at the systems level. To address this limitation, it is imperative to complement in vitro studies with in vivo experiments to better understand ENMs-induced systemic effects. Additionally, combining in silico toxicological analysis that offer faster, cost-effective and ethical alternatives for nanotoxicity assessment with in vitro and in vivo study models can enhance risk prediction and regulatory policy decisions. Standardizing testing procedures and developing nano-specific regulatory frameworks will promote consistent risk–benefit assessment in alignment with circular economy, bioeconomy, resource efficiency and sustainable development goals.

Further, research should prioritize (a) identifying potential hazards and sensitive biomarkers, (b) improving risk assessment methods, (c) engineering NMs with reduced toxicity and enhanced surface properties emphasizing bioeconomy and sustainability and (d) establishing proper nano-waste disposal methods to prevent environmental contamination and promote circular economy principles. Global toxicity databases, such as EFSA’s ‘OpenFoodTox’ can aid in disseminating verified information globally, promoting uniform regulatory decisions and improved risk management. Long-term experimental studies analyzing ENM interactions with soil, climate and ecosystems are necessary to validate their safety for human consumption and environmental sustainability.

Interdisciplinary collaborations and knowledge exchange among researchers, industry, regulatory agencies and policy makers are crucial to developing robust safety protocols and regulatory frameworks aligned with sustainable development goals and circular economy principles. Additionally, ongoing monitoring and surveillance programs are essential to track the environmental fate of nanoparticles and assess their long-term impacts on ecosystems and human health. Integration of emerging technologies such as AI and advance analytics, can expedite data analysis and risk assessment, accelerating innovations while ensuring safety and sustainability. Cross-sector collaborations are essential, with companies innovating in circular design and policymakers enhancing material reuse and resource productivity through supportive policies and financing. Further, public engagement initiatives and transparent communication will be important in fostering trust and informed decision making regarding nano-material adoption. Capacity building programs will be essential to empower researchers and regulatory agencies, particularly in developing countries, with the necessary expertise to manage nanotechnology risks effectively. By embracing a multidisciplinary, collaborative and data-driven approach, nanotechnology can contribute significantly to sustainable development while minimizing environmental risk and ensuring public safety. Safer nano-enabled solutions can address global challenges including food security, environmental restoration and resource efficiency. Prioritizing sustainability will enable agriculture to unlock the transformative benefits of nanotechnology while safeguarding the environment and human health for future generations.