On the Behavior of Perfluorinated Persistent Organic Pollutants (POPs) at Environmentally Relevant Aqueous Interfaces: An Interplay of Hydrophobicity and Hydrogen Bonding

Rate, Efficiency, and Mechanisms of Electrochemical Perfluorooctanoic Acid Degradation with Boron-Doped Diamond and Plasma Electrodes

The removal of per- or polyfluorinated alkyl substances (PFAS) has received increasing attention because of their extreme stability, our increasing awareness of their toxicity at even low levels, and scientific challenges for traditional treatment methods such as separation by activated carbon or destruction by advanced oxidation processes. Here, we performed a direct and systematic comparison of two electrified approaches that have recently shown promise for effective degradation of PFAS: plasma and conventional electrochemical degradation. We tailored a reactor configuration where one of the electrodes could be a plasma or a boron-doped diamond (BDD) electrode and operated both electrodes galvanostatically by continuous direct current. We show that while both methods achieved near-complete degradation of PFAS, the plasma was only effective as the cathode, whereas the BDD was only effective as the anode. Compared to the BDD, plasma required more than an order of magnitude higher voltage but lower current to achieve similar degradation efficiency with more rapid degradation kinetics. All these factors considered, it was noted that plasma or BDD degradation resulted in similar energy efficiencies. The BDD electrode exhibited zero-order kinetics, and thus, PFAS degradation using the conventional electrochemical method was kinetically controlled. On the contrary, analysis using a film model indicated that the plasma degradation kinetics of PFAS using plasma were mass-transfer-controlled because of the fast reaction kinetics. With the help of a simple quantitative model that incorporates mass transport, interfacial reaction, and surface accumulation, we propose that the degradation reaction kinetically follows an Eley-Rideal-type mechanism for the plasma electrode, and an intrinsic rate constant of 2.89 × 10⁸ m⁴ mol^-1 s^-1 was obtained accordingly. The investigation shows that to realize the true kinetic potential of plasma degradation for water treatment, mass transfer to the interface must be enhanced.

Obesogens in Foods

Obesogens, as environmental endocrine-disrupting chemicals, are supposed to have had an impact on the prevalence of rising obesity around the world over the last forty years. These chemicals are probably able to contribute not only to the development of obesity and metabolic disturbances in individuals, but also in their progeny, having the capability to epigenetically reprogram genetically inherited set-up points for body weight and body composition control during critical periods of development, such as fetal, early life, and puberty. In individuals, they may act on myriads of neuro-endocrine–immune metabolic regulatory pathways, leading to pathophysiological consequences in adipogenesis, lipogenesis, lipolysis, immunity, the influencing of central appetite and energy expenditure regulations, changes in gut microbiota–intestine functioning, and many other processes. Evidence-based medical data have recently brought much more convincing data about associations of particular chemicals and the probability of the raised risk of developing obesity. Foods are the main source of obesogens. Some obesogens occur naturally in food, but most are environmental chemicals, entering food as a foreign substance, whether in the form of contaminants or additives, and they are used in a large amount in highly processed food. This review article contributes to a better overview of obesogens, their occurrence in foods, and their impact on the human organism.

Headgroup-Specific Interaction of Biological Lipid Monolayer/Water Interface with Perfluorinated Persistent Organic Pollutant (f-POP): As Observed with Interface-Selective Vibrational Spectroscopy

Perfluoro compounds are widely used in various manufacturing processes, which leads to their bioaccumulation and subsequent adverse effects on human health. Using interface-selective vibrational spectroscopy (heterodyne-detected vibrational sum frequency generation (HD-VSFG)), we have elucidated the molecular mechanism of the perturbation of lipid monolayers on the water surface using a prototype perfluorinated persistent organic pollutant, perfluoroheptanoic acid (PFHA). PFHA disrupts the well-ordered all-trans conformation of a cationic lipid (1,2-dipalmitoyl-3-trimethylammonium propane (DPTAP)) monolayer and reduces the interfacial electric field at the lipid/water interface. In contrast, the hydrophobic packing of an anionic lipid (1,2-dipalmitoyl-sn-glycero-3-phospoglycerol (DPPG)) monolayer remains largely unaffected in the presence of PFHA, though the interfacial electric field is reduced. For a zwitterionic lipid (1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC))/water interface, both alkyl chain ordering and interfacial electric field are fairly perturbed by PFHA. Lipid headgroup-specific interaction of PFHA and the repulsive interaction of oleophobic fluoroalkyl chain with the lipid alkyl chains govern these distinct perturbations of the lipid monolayers on the water surface.

Influence of Water Concentrations of Perfluoroalkyl Acids (PFAAs) on Their Size-Resolved Enrichment in Nascent Sea Spray Aerosols

Perfluoroalkyl acids (PFAAs) are persistent organic substances that have been widely detected in the global oceans. Previous laboratory experiments have demonstrated effective enrichment of PFAAs in nascent sea spray aerosols (SSA), suggesting that SSA are an important source of PFAAs to the atmosphere. In the present study, the effects of the water concentration of PFAAs on their size-resolved enrichment in SSA were examined using a sea spray simulation chamber. Aerosolization of the target compounds in almost all sizes of SSA revealed a strong linear relationship with their water concentrations (p < 0.05, r² > 0.9). The enrichment factors (EF) of the target compounds showed no correlation with their concentrations in the chamber water, despite the concentrations varying by a factor of 500 (∼0.3 to ∼150 ng L^-1). The particle surface-area-to-volume ratio appeared to be a key predictor of the enrichment of perfluoroalkyl carboxylic acids (PFCAs) with ≥7 perfluorinated carbons and perfluoroalkanesulfonic acids (PFSAs) with ≥6 perfluorinated carbons in supermicron particles (p < 0.05, r² > 0.8), but not in submicron particles. The different enrichment behaviors of PFAAs in submicron and supermicron particles might be a result of the different production mechanisms of film droplets and jet droplets. The results suggest that the variability in seawater concentrations of PFAAs has little influence on EFs and that modeling studies designed to quantify the source of PFAAs via SSA emissions do not need to consider this factor.

Adsorption of Iodine Species (I3-, I-, and IO3-) at the Nuclear Paint Monolayer-Water Interface and Its Relevance to a Nuclear Accident Scenario

Following a nuclear accident, radioactive iodine causes great concern to public health and safety. Organic iodide, because of its ability to escape reactor containment building and high environmental mobility, constitutes a predominant fraction of airborne radioiodine at places far away from the accident site. As the iodine released from a reactor core is inorganic iodine, it is vital to understand the mechanism of organic iodide formation inside reactor containment. In this context, we investigated the surface prevalence and adsorption of various inorganic iodines, I^-, I₃^-, and IO₃^-, at a nuclear paint (used in nuclear installations) monolayer-water interface, mimicking the painted inner walls of an accident-affected containment building that are exposed to the iodine-containing condensed water layer. Vibrational sum frequency generation (VSFG) measurements in the OH and CH stretch regions reveal that the paint-water interface changes its charge characteristics with the pH of the water that affects the degree of interaction with the iodine species. At the acidic condition (bulk pH < 7), the paint becomes positively charged and strongly adsorbs the negatively charged iodine species dissolved in the aqueous phase, whereas at the alkaline condition (bulk pH > 9.5), the paint becomes net neutral and weakly interacts with the iodine species. These interactions change the conformation of the paint such that its hydrophobic alkyl groups orient increasingly away from the aqueous phase. The order of adsorption increases as IO₃^- < I^- < I₃^- for the different iodine species studied.