Jay N. Meegoda

Engineered nanoparticles (ENPs) are being used with increasing frequency in industrial and consumer products across applications in industry, agriculture, ecology, and biomedicine. The unique physicochemical characteristics that make nanoparticles desirable in product design also affect their fate in the environment, interactions with living systems, and mechanisms of toxicity. Traditional testing methods and toxicological paradigms based on dissolved chemicals are poorly suited to understand ENP risks, primarily due to their small size, large SA:Vs, increased reactivity, and a surface chemistry that can be tuned during synthesis. Nanoparticle toxicity is dependent on complex relationships between particle characteristics, transformations in the environment, resulting exposure scenarios, and biological effects. Here we review ENP toxicity across a property → transformation → exposure → toxicity continuum, with a focus on how particle properties affect environmental and biological transformations relevant to toxicity. Properties such as size, shape, surface chemistry, dissolution, redox activity, and aggregation propensity are reviewed with respect to effects on transport and bioavailability, cellular uptake, biodistribution, and toxicity mechanisms. Transformations including aggregation, oxidation, dissolution/sulfidation, aging and eco-corona formation are discussed with regard to impacts on exposure and risk. Finally, major mechanisms of toxicity including oxidative stress, ion toxicity, membrane damage, inflammation, and genotoxicity are discussed with regard to nano–bio interactions. Analytical challenges associated with studying ENPs, shortcomings of the current risk assessment methods, and emerging Safe-by-Design approaches are also reviewed. Furthermore, connections between the fields of engineered nanoparticle toxicology and microplastics/nanoplastics are discussed, with particular focus on overlapping physicochemical properties, transformations, exposures, and biological mechanisms.

Per- and polyfluoroalkyl substances (PFASs) are pollutants that have demonstrated a high level of environmental persistence and are very difficult to remediate. Sonochemical processes have shown considerable potential for PFAS destruction, but the relationships between ultrasound operating conditions, cavitation behavior, and reactor performance remain insufficiently understood. Ultrasonic cavitation is a key mechanism in sonochemical processes, yet the coupled effects of ultrasound frequency, cavitation activity, energy efficiency, and bubble characteristics remain insufficiently understood. This study systematically investigated these interactions in an intermediate scale sonochemical reactor operated at 680, 850, and 950 kHz under different power densities. Cavitation was quantified using potassium iodide (KI) dosimetry, while energy transfer and efficiency were evaluated by calorimetric analysis. Bubble size, bubble concentration and zeta potential were measured to characterize cavitation-generated nanobubbles and added argon nanobubbles, and their interfacial properties. The results showed that ultrasound frequency strongly influenced cavitation behavior and energy utilization. The 850 kHz system exhibited the highest cavitation activity, whereas the 950 kHz system showed the highest calorimetric efficiency. Increased power density enhanced cavitation intensity but also increased thermal losses. Higher frequencies produced smaller bubbles, while power density and solution properties had weaker effects on bubble size and surface charge. Zeta potential measurements revealed consistently negative surface charges, with markedly greater negative values in the presence of perfluorooctanoic acid (PFOA) and argon nanobubbles, consistent with possible interfacial association of PFAS rather than direct confirmation of adsorption. Nanobubble concentration and size were also highly dependent on ultrasound and solution properties, with ultrasound promoting nanobubble generation and PFAS contributing to their stability and growth. Overall, the findings demonstrate that cavitation activity, energy efficiency, and bubble interfacial properties are strongly interdependent and primarily governed by ultrasonic frequency. This work provides new insights into sonochemical reactor characterization and optimization and identifies operating conditions that may be beneficial for future PFAS degradation studies and other advanced oxidation processes.

Per- and polyfluoroalkyl substances (PFASs) are persistent environmental contaminants whose mobility in soil and groundwater is strongly controlled by adsorption and desorption processes. In saturated clay-rich soils, these processes are complex because PFASs interact with hydrated mineral surfaces, organic matter, metal oxides, exchangeable cations, and pore-water constituents. This review synthesizes the current literature on PFAS adsorption and desorption in saturated soils, with an emphasis on clay mineralogy, mineral–water interfaces, pore-water chemistry, and electrochemical double layer (EDL) effects. PFAS retention is influenced by molecular properties such as chain length, functional head group, and charge state, as well as soil properties such as organic carbon content, clay mineral type, surface charge, cation exchange capacity, and Fe/Al oxide content. Longer-chain PFASs and sulfonate-based compounds generally show stronger retention, while shorter-chain PFASs tend to remain more mobile. This review focuses particularly on how an EDL affects PFAS behavior in saturated clay systems. Unlike dry clay surfaces, saturated clay surfaces are covered by structured water, exchangeable ions, and diffuse counterion layers. These hydrated interfacial conditions influence how closely anionic PFASs can approach negatively charged clay surfaces, how dissolved cations reduce electrostatic repulsion or promote cation-mediated binding, and how effectively short-range interactions such as hydrophobic association, van der Waals forces, hydrogen bonding, and surface association contribute to adsorption. Desorption is also emphasized because adsorption does not necessarily represent permanent immobilization. Changes in pH, ionic strength, cation composition, dissolved organic matter, or competing solutes can weaken retention and promote PFAS release. Overall, PFAS mobility in saturated clay-rich soils should be interpreted as a coupled interfacial process rather than simple partitioning to soil solids. Future work should better connect molecular-scale mechanisms, EDL behavior, adsorption–desorption experiments, and saturated transport studies to improve predictions of PFAS retention and long-term groundwater release.

Pervasive microplastics (MPs) and per- and polyfluoroalkyl substances (PFAS) frequently co-occur across aquatic and terrestrial environments due to shared sources, transport pathways, and persistence, yet their interaction-driven effects on environmental fate, bioavailability, and toxicity remain incompletely resolved. This review critically synthesizes current knowledge on the environmental co-occurrence of MPs and PFAS, the physicochemical mechanisms governing their interactions, and the resulting ecological and toxicological consequences across aquatic, terrestrial, and biological systems. Emphasis is placed on sorption and desorption processes; environmental modifiers such as pH, salinity, dissolved organic matter (DOM), and aging; and biological responses under combined exposure scenarios. Across laboratory and field studies, MPs–PFAS co-exposure is frequently associated with altered PFAS partitioning and enhanced organismal uptake, with reported bioaccumulation increases of up to ~2.5-fold relative to PFAS-only exposures. These changes are often accompanied by amplified oxidative stress, immune dysregulation, metabolic disturbance, and reproductive impairment, particularly in aquatic invertebrates and early life stages of fish. Evidence further indicates that the magnitude and direction of combined effects depend on polymer type, particle size, surface aging, and biological context, underscoring the highly system-specific nature of MPs–PFAS interactions. By integrating findings from environmental monitoring, laboratory toxicology, and mechanistic and modeling studies, this review identifies key knowledge gaps related to nanoplastics detection, environmentally realistic exposure conditions, sorption reversibility, and mixture toxicity assessment. Collectively, these insights highlight limitations in current single-contaminant risk frameworks and underscore the importance of incorporating MPs-mediated PFAS transport and bioavailability into exposure assessment and regulatory evaluation.

Per- and polyfluoroalkyl substances (PFAS) are emerging contaminants that persist in soil environments, necessitating reliable models to predict their fate and transport. This study evaluates the performance of three theoretical models in estimating the maximum adsorption capacity (Qmax) of perfluorooctanoic acid (PFOA) on kaolinite and montmorillonite clay minerals. The models assessed include a van der Waals interaction-based approach, a monolayer adsorption capacity model, and a surface site density model emphasizing reactive hydroxyl groups at mineral edges. Benzene, nitrogen, and glyphosate molecules were used as reference compounds for model validation. Results indicated that the van der Waals model significantly underestimated Qmax (0.0007 mg·g⁻¹ for kaolinite), while the monolayer capacity model produced substantial overestimations (17.51 mg·g⁻¹) compared to the experimental range (0.10–10.0 mg·g⁻¹). The surface site density model provided the most accurate predictions (3.39 mg·g⁻¹ for kaolinite), although it slightly underestimated values for montmorillonite (0.20 mg·g⁻¹) by excluding interlayer adsorption. These discrepancies demonstrate that simplified models cannot adequately capture the complex adsorption behavior of PFAS. Accurate prediction requires site-specific approaches incorporating electrostatic forces, hydrogen bonding, and steric effects. As PFAS accumulation in soil directly contributes to groundwater contamination, improving adsorption models is essential for accurate risk assessment and the development of effective remediation strategies.

Ultrasound is an acoustic technology that uses the properties and concepts of sound waves to transmit and receive information through a medium in the gas, liquid, or solid phase. It has been used for several decades as either destructive or nondestructive technology. In this manuscript, an attempt is made to describe piezoelectric transducers, which are one of the most used types of transducers across different industries. Multiple new industrial applications that involve this technology are now available. This manuscript provides an overview of the following aspects of ultrasonic technology: (i) components or transducer types; (ii) wave propagation and associated phenomena; (iii) types of measuring techniques; and (iv) various mechanisms. The main purpose of this manuscript is to provide the reader with information about low-intensity (mostly nondestructive applications or focused destructive applications) or high-intensity (i.e., power, energy, or amplitude and destructive applications) piezoelectric ultrasound applications. This is further divided into multiple applications, based on low (large-scale applications) and high (small-scale applications) frequencies, under either high or low ultrasound intensities. Finally, this manuscript addresses the use of piezoelectric ultrasound in areas such as civil and environmental industries; by discussing all of these in one document, providing a valuable resource for the reader. Though an attempt was made to include multiple ranges of values of intensities and frequencies of piezoelectric transducers that are used for various applications, a full spectrum was not included for the sake of concision.

This study evaluates the effectiveness of ultrasound technology for degrading per- and polyfluoroalkyl substances (PFAS) in three complex environmental matrices: groundwater (GW), still bottom (SB), and aqueous film-forming foam (AFFF). A 10-L ultrasonic reactor, equipped with multi-frequency piezoelectric elements (850 kHz and 950 kHz), was used to treat PFAS-contaminated samples for 6 to 12 h. Degradation efficiency was measured using liquid chromatography-mass spectrometry (LC–MS/MS), fluoride ion-selective electrode (F-ISE), suppressed conductivity ion chromatography (IC), nuclear magnetic resonance (NMR) spectroscopy, total organically bound fluorine (TOF) analysis, and inductively coupled plasma mass spectrometry (ICP-MS). LC–MS/MS confirmed PFAS degradation, while F-ISE quantified fluoride release, indicating defluorination. IC analysis measured changes in anion concentrations, particularly sulfate and chloride, to assess transformation pathways. NMR and TOF provided structural insights into PFAS breakdown, and ICP-MS tracked variations in metal concentrations, highlighting potential interactions with degradation byproducts. In SB samples, fluoride concentration increased from 0 to 8.71 mg/L after 12 h, indicating successful defluorination of PFAS compounds. For GW samples, fluoride levels rose moderately from 0.54 to 1.78 mg/L, demonstrating that sonolysis can degrade PFAS in lower-concentration matrices. However, AFFF samples, dominated by perfluorooctanesulfonic acid (PFOS), showed only a slight increase in fluoride concentration (0.75 to 1.37 mg/L), indicating resistance to sonolytic degradation due to strong carbon–fluorine bonds. Anion and metal analysis revealed matrix-specific interactions influencing sonolysis outcomes, with energy distribution analysis highlighting the competitive role of chemical oxygen demand (COD) in scavenging reactive radicals. This research demonstrates ultrasound as a promising technology for PFAS degradation in complex matrices. However, the test results for AFFF suggest that with high surfactant concentrations, modifications may be necessary for complete mineralization of PFAS compounds.

PFASs, or per- and polyfluoroalkyl substances, comprise a diverse group of synthetic chemicals known for their widespread use, persistence, and potential environmental and health risks. The sonolytic treatment of PFASs is one of the technologies with the ability to complete destruction without harmful byproducts. This study aims to provide a theoretical explanation for the sonolytic treatment of PFAS. Combining insights from molecular dynamics simulations with experimental data, the influence of chain length and functional headgroups on the PFAS destruction mechanism was investigated. The findings revealed that the impact on functional head groups and chain length on PFAS degradation via sonolysis treatment is complex and multifaceted. The preliminary degradation step is attributed to be headgroup cleavage, while differences in degradation rates between perfluorocarboxylic acids (PFCAs) and perfluorosulfonic acids (PFSAs) are primarily influenced by adsorption at the air–water interface of micro/nanobubbles created by ultrasound and dictated by compound hydrophobicity characteristics. Moreover, longer-chain PFAS compounds tend to degrade faster than shorter-chain counterparts due to their enhanced hydrophobic characteristics, facilitating adsorption and subsequent mineralization. The sonolytic environment significantly influences PFAS degradation, with aqueous sonolysis proving the most effective compared to dry pyrolysis or thermal combustion, highlighting the importance of considering environmental factors in remediation strategies. These insights provide valuable guidance for designing effective PFAS remediation strategies, emphasizing the need to consider molecular structure and environmental conditions. Further research and technological innovation are essential for developing sustainable approaches to mitigate PFAS pollution’s adverse impacts on human health and the environment.