The review focuses on metal and metal oxide nanoparticles, including silver, titanium dioxide, zinc oxide, cerium dioxide, iron-based materials and nanoscale zero-valent iron. Their environmental behavior is governed by a combination of particle properties and subsurface conditions. Size, shape, surface coating, crystal structure, density and electrical charge all influence mobility. So do pH, ionic strength, dissolved oxygen, natural organic matter, clay minerals, competing particles and groundwater velocity. Because nanoparticles have enormous surface areas relative to their mass, even small changes in their surroundings can alter their behavior. A particle that remains stable in clean laboratory water may rapidly aggregate, dissolve or bind to soil minerals in a natural aquifer.

One of the central scientific frameworks used to explain this behavior is the Derjaguin–Landau–Verwey–Overbeek, or DLVO, theory. DLVO theory describes the balance between attractive van der Waals forces and repulsive electrostatic forces acting between nanoparticles and mineral surfaces. When repulsion dominates, particles may remain suspended and travel with flowing water. When attractive forces become stronger, nanoparticles can attach to sand, clay, iron oxides or organic coatings. However, the review emphasizes that classical DLVO theory is not sufficient on its own. Hydration forces, steric interactions, surface roughness, chemical heterogeneity and specific ion binding can all create non-DLVO effects. These forces may either promote retention or unexpectedly enhance transport, making simple predictions unreliable.

Movement through porous media is also controlled by physical processes. Advection carries nanoparticles with the average flow of groundwater, while hydrodynamic dispersion spreads them through variations in water velocity and flow paths. Brownian diffusion causes very small particles to move randomly, allowing them to reach surfaces that might otherwise be missed. Interception occurs when flowing particles pass close enough to grains to make contact, while gravitational sedimentation becomes more important as particles aggregate and grow heavier. Straining can trap particles when their effective size approaches the dimensions of pore throats. A particle may therefore travel rapidly through a coarse sandy layer but become immobilized in finer soil, compacted sediment or a region containing narrow pore spaces.

The ratio between nanoparticle size and grain size is particularly important. When particles are much smaller than the grains forming a porous medium, they may pass through larger pores, although surface chemistry still determines whether they attach. As the size ratio increases, straining and physical trapping become more likely. Rough mineral surfaces can either capture particles in microscopic valleys or, under some conditions, reduce contact with reactive sites and promote passage. Iron oxides and clays are especially influential because they possess chemically active surfaces and may carry charges opposite to those of nanoparticles. Such mineral coatings can act as powerful filters, but they can also become saturated, change charge with pH, or be covered by organic matter, altering their filtering capacity over time.

The review highlights a phenomenon that could transform how scientists think about nanoparticle pollution: colloid-facilitated transport. Natural colloids, including clay particles, iron oxides, humic substances, biochar fragments and other nanoscale materials, can act as mobile carriers. Instead of attaching directly to stationary sand grains, metal nanoparticles may bind to these suspended particles and travel with them. This process can extend the distance nanoparticles move through soil and groundwater. In mixed suspensions, particles can also undergo hetero-aggregation, joining together with materials of a different composition. For example, iron-based nanoparticles may interact with other engineered particles or natural mineral colloids, changing their size, density, charge and reactivity.

Competition between particles creates another counterintuitive effect. When natural colloids or one type of nanoparticle occupy available attachment sites on grain surfaces, they may block those sites and prevent other particles from being retained. This process, known as competitive blocking, can increase the mobility of nanoparticles that would otherwise be filtered out. Co-transport can therefore produce results that are not predictable from single-particle experiments. One material may improve the movement of another by modifying grain surfaces, changing aggregation behavior or creating mobile carriers. In some cases, the presence of colloids increases the release of previously retained nanoparticles, especially when groundwater chemistry shifts or flow conditions intensify.

Chemical transformation is equally important because a nanoparticle’s identity does not remain fixed after release. Oxidation can convert metallic particles into oxide layers or dissolved ions. Reduction may transform metal oxides into lower-valence compounds. Sulfur-rich environments can convert silver nanoparticles into silver sulfide, often a less soluble form with different mobility and toxicity. Organic matter may coat particle surfaces, stabilize suspensions or promote aggregation, depending on its composition and concentration. Changes in pH and redox conditions can alter dissolution rates, surface charge and mineral structure. In floodplains, wetlands, paddy soils and aquifers affected by fluctuating oxygen levels, nanoparticles may repeatedly change between more mobile and more strongly retained forms.

These transformations directly affect environmental risk. A particle that is immobilized in soil may later be remobilized when the pH changes, ionic strength decreases, organic coatings are degraded or water flow becomes stronger. Conversely, dissolution can reduce the number of particles while releasing metal ions that may be more biologically available. Aggregation can make particles easier to settle but may also create larger reactive surfaces or facilitate transport through preferential flow channels. The review notes that nanoparticle behavior cannot be judged solely by measuring total metal concentration. Researchers must distinguish between individual nanoparticles, aggregates, dissolved ions and nanoparticle–colloid complexes. Their chemical form, size distribution and surface state may be more important than their overall abundance.

To investigate these processes, scientists use a combination of laboratory experiments and field-scale observations. Packed-column experiments allow researchers to control grain size, flow rate, pH, electrolyte concentration and nanoparticle coatings while tracking breakthrough curves and retention profiles. Lysimeters provide a more realistic bridge between laboratory columns and natural soils by allowing rainfall, vegetation, microbial activity and long-term aging to influence transport. Quartz crystal microbalance with dissipation monitors the attachment of nanoparticles to model mineral surfaces and can reveal whether deposited layers are rigid, soft or viscoelastic. Parallel-plate systems simplify flow and surface interactions, while atomic force microscopy maps nanoscale roughness and measures forces between particles and collectors.

Advanced chemical analysis is becoming essential because conventional measurements often cannot reveal what is actually moving. Single-particle inductively coupled plasma mass spectrometry can count individual metal-containing nanoparticles, estimate their sizes and distinguish them from dissolved metal. Asymmetrical flow field-flow fractionation coupled with ICP-MS separates particles according to hydrodynamic size while simultaneously identifying their elemental composition. Diffusive gradients in thin films can measure labile and potentially bioavailable metal species within soils and sediments. Microscopy combined with spectrometry can show where nanoparticles accumulate and what chemical phases form around them. Together, these methods provide a more detailed picture of nanoparticle fate than bulk concentration measurements alone.

Researchers also use mathematical models to predict transport, retention, dissolution, aggregation and co-transport. Advection–dispersion equations describe the movement of particles through flowing water, while colloid filtration theory estimates the probability that particles will collide with and attach to porous-media grains. More advanced models include attachment and detachment, blocking, straining, ripening, aggregation and chemical transformation. Reactive transport models attempt to connect groundwater flow with redox reactions, dissolution and changes in particle surface chemistry. Yet the review warns that model predictions remain limited because most models simplify natural soils and aquifers. Real subsurface environments contain irregular pores, layered structures, preferential flow paths, fluctuating water saturation, biological coatings and chemically diverse mineral surfaces.

The consequences extend beyond nanoparticle transport itself. Mobile metal nanoparticles may carry adsorbed contaminants, alter the movement of heavy metals and organic pollutants, or influence the distribution of nutrients and microorganisms. Conversely, nanoparticles may acquire new coatings and chemical properties as they move, changing their ecological effects. Particles reaching plant roots can interact with soil minerals, microbial communities and root exudates before entering plants or remaining in the rhizosphere. In groundwater, their persistence and mobility may determine whether drinking-water resources are exposed. The same properties that make nanoparticles useful for pollution cleanup—high reactivity, small size and engineered surface chemistry—can also allow them to travel beyond their intended treatment zones.

The review’s central message is that there is no universal rule stating whether a metal nanoparticle will move or remain trapped. Retention is generally favored by fine-grained porous media, rough collector surfaces and opposite surface charges, while stable colloidal conditions, natural carriers and competitive blocking can promote transport. Particle aging can make these relationships change with time. The authors call for experiments that combine realistic soils, longer observation periods, fluctuating chemical conditions and multiple nanoparticles rather than relying exclusively on simplified laboratory systems. They also emphasize the need to link nanoscale measurements with field-scale hydrology. As metal nanoparticles continue to enter the environment, understanding their underground journey will be essential for assessing risks, designing safer technologies and preventing invisible contamination from moving through the world’s most important groundwater pathways.

Subject of Research: Transport, transformation, retention, co-transport and modeling of metal nanoparticles in subsurface porous media, soils, sediments and groundwater.

Article Title: Metal nanoparticles transport in the subsurface: a review

Article References: Wan, Q., Zhang, M., Zhao, M. et al. “Metal nanoparticles transport in the subsurface: a review.” Environmental Chemistry Letters 24, 201–227 (2026).

Image Credits: AI Generated

DOI: https://doi.org/10.1007/s10311-025-01879-8

Keywords: Stability; colloid-facilitated transport; aggregation; competitive blocking; transformation; modeling

Graphene and graphene oxide are renowned for their remarkable strength, electrical conductivity, and versatility, making them prime candidates for a plethora of applications, ranging from electronics to water purification. However, their environmental fate when released into ecosystems is a crucial concern. Given their nanoscale dimensions, understanding how these materials interact with their surroundings, particularly in saturated porous media, is vital for mitigating any adverse environmental effects. The present study delves into these interactions, providing insights that could guide future research and policy.

Surfactants, which are surface-active agents, play a pivotal role in modifying the properties of aqueous solutions. They can significantly enhance the transport efficiency of nanoparticles through porous materials by altering surface tension and facilitating interactions between the particles and the surrounding medium. This research emphasizes the importance of surfactant presence, examining their influence on the migration patterns of graphene and graphene oxide particles. By characterizing these interactions, the study presents a nuanced understanding of how surfactants can either hinder or promote nanoparticle transport.

The experimental approach utilized in this study is methodologically rigorous, employing a variety of techniques to address the complexities inherent in nanoparticle transport. Researchers conducted a series of controlled experiments, meticulously measuring the retention and movement of graphene and graphene oxide in various surfactant solutions. The study’s design ensures that findings are robust and applicable to real-world scenarios, providing critical data for assessing the environmental transport of these nanoparticles.

One key finding is that specific surfactants can significantly enhance the mobility of graphene and graphene oxide. The presence of these surfactants leads to a reduction in particle aggregation, thereby promoting a more uniform distribution within the porous matrix. As a result, the study suggests that leveraging surfactants may be an effective strategy for improving the remediation of pollution, as it enables more efficient transport of nanomaterials to targeted areas. This insight opens up new avenues for research and practical applications in environmental management.

In contrast to the promoting effects, the study also identifies scenarios where surfactants can hinder the movement of graphene particles. The complex interplay between surfactant types, concentrations, and the characteristics of the porous media itself introduces variability in transport outcomes. This nuanced understanding emphasizes that while surfactants can be advantageous in specific contexts, they may also present challenges that require careful consideration in practical applications.

To further support their findings, the researchers employed advanced analytical techniques, including spectroscopic methods and imaging technologies. These tools provided high-resolution insights into the behavior of graphene and graphene oxide at the nanoscale, revealing how surfactants interact with both the particles and the porous media. Such detailed characterization is essential for advancing our understanding of nanomaterial transport dynamics and refining remediation strategies.

The implications of this research extend beyond environmental science; they resonate with a broad spectrum of industries where graphene and graphene oxide are already making an impact. For instance, in the field of water treatment, optimizing the transport and delivery of these nanomaterials could lead to more efficient purification processes, enhancing the quality of drinking water and reducing pollution levels. Additionally, in the realm of electronics, understanding transport mechanics could improve the design of graphene-based devices, driving innovations that leverage these materials’ unique properties.

Furthermore, the study underscores the need for interdisciplinary collaboration in addressing environmental challenges associated with nanotechnology. The integration of expertise from chemistry, environmental science, and engineering is crucial for developing holistic solutions that account for both the benefits and risks posed by nanomaterials. As researchers continue to explore the implications of this work, it could pave the way for more sustainable practices and policies geared toward managing the environmental impact of nanoscale materials.

The findings presented by Wang and Brusseau not only advance scientific knowledge but also raise pertinent questions regarding regulatory frameworks surrounding the deployment of nanomaterials. As industries increasingly embrace these technologies, policymakers must remain vigilant in monitoring potential environmental risks. Clear guidelines based on empirical research can help mitigate unintended consequences, ensuring that the advantages of nanotechnology are fully realized without compromising ecological integrity.

In conclusion, the exploration of surfactant-influenced transport of graphene and graphene oxide within saturated porous media represents a vital step forward in both scientific inquiry and practical applications. As our understanding deepens, it becomes increasingly apparent that we stand at a crossroads where innovation meets responsibility. The trajectory of nanotechnology depends on a careful balance of harnessing its immense potential while safeguarding the environment in which we operate. As Wang and Brusseau’s research indicates, the integration of surfactants into these dynamics can provide a path toward achieving that balance.

The ongoing investigations into nanomaterial behavior are essential for developing effective strategies to address environmental pollutants and enhance industrial applications. As the field continues to advance, the insights gained from this research could shape not only future studies but also practical approaches to managing the complexities associated with nanomaterials in various settings. Engaging stakeholders, from scientists to policymakers, will be key to navigating the challenges and opportunities that lie ahead in the age of nanotechnology.

Subject of Research: Transport mechanisms of graphene and graphene oxide in saturated porous media influenced by surfactants.

Article Title: Surfactant-influenced transport of graphene and graphene oxide in saturated porous media.

Article References:

Wang, Y., Brusseau, M.L. Surfactant-influenced transport of graphene and graphene oxide in saturated porous media.
Environ Sci Pollut Res (2026). https://doi.org/10.1007/s11356-025-37367-3

Image Credits: AI Generated

DOI: https://doi.org/10.1007/s11356-025-37367-3

Keywords: Graphene, Graphene Oxide, Surfactants, Porous Media, Nanotechnology, Environmental Science, Transport Mechanisms, Nanoscale Materials.