Formation of environmentally persistent free radicals on molecular sieves: The role of Lewis acid sites.

Environmental Persistent Free Radicals in highly polluted soils and the association with polycyclic aromatic compounds

Distribution, influence factors, and biotoxicity of environmentally persistent free radical in soil at a typical coking plant

Environmentally persistent free radicals (EPFRs) have been recognized as one of the important emerging contaminants with biological toxicity, environmental persistence, and global mobility. Previous studies have identified the catalytic role of surface metal oxides in EPFRs formation and illustrated the metal-dependence of EPFRs by studying on various metal oxide nanoparticles and single crystals. However, there is still lack of an understanding on the formation of EPFRs from the point of view of metal sites. Various factors (e.g., crystalline phases and surface species) of metal oxides are regarded to contribute to the generation of EPFRs, which present profound difficulties for scientists to tease apart the impact of metal type. Herein, a laboratory investigation, in terms of the acidity and oxidation strength of metal cations, was conducted by selecting metal-variable isostructural metal-organic frameworks as material platforms. Specifically, we evaluated EPFRs generation on MIL-100(M) (M = Al, Cr, Fe) from chlorine-substituted phenol vapor and catechol under thermal conditions. It is found that high Lewis acidity of metal sites is crucial for capturing the above two phenolic precursors, activating the O-H bond and promoting EPFRs formation. Radical species with half-life as long as 70 days were generated on MIL-100 rich in 5-fold coordinated Al3+ sites. The unpaired electron spin density donation was further confirmed by using 27Al solid-state nuclear magnetic resonance spectroscopy. Despite their higher oxidation power than Al3+, the exposed Cr3+ and Fe3+ sites show undetectable catalytic activity for the formation of EPFRs, because of their insufficient Lewis acidity. Our results suggest that the surface species rather than Lewis acid sites may be a major contributor to the formation of EPFRs on metal oxides like Fe2O3.

Environmentally persistent free radicals (EPFRs) are a new class of pollutants that have been identified as potential environmental contaminants due to their persistence and ability to generate reactive oxygen species (ROS) that cause oxidative stress in living organisms. This study investigates the formation and behavior of EPFRs during the photodegradation of organic pollutants, emphasizing the role of metal ions, precursor concentration, and environmental conditions. Results show that light exposure significantly enhances pollutant degradation rates, EPFR yield, and formation speed, though it simultaneously shortens EPFR lifespan due to reactive oxygen species (ROS) generation. In dark conditions, EPFR formation is slower but results in more stable radicals. Metal ions play a pivotal role, with Cu(II) exhibiting the highest EPFR generation capacity due to its strong electron-accepting properties, surpassing Zn(II) and Na(I), highlighting that metal ions with greater oxidizing potential enhance EPFR formation. The precursor, as both reaction product and reactant, plays a dual role in EPFR formation. Individual compounds like anthracene (ANT) yield stable carbon-centered radicals, while mixtures of polycyclic aromatic hydrocarbons (PAHs) produce more complex radical spectra. The study of the influencing factors and transformation mechanisms of EPFR generation in soil can provide a more comprehensive understanding of the environmental behavior of new pollutants, provide a scientific basis for sustainable development, and be of great significance for the assessment and management of environmental risks and the protection of the ecological environment.

Environmentally persistent free radicals (EPFRs) are produced during biochar pyrolysis and, depending on biochar application, can be either detrimental or beneficial. High levels of EPFRs may interfere with cellular metabolism and be toxic, because EPFR-generated reactive oxygen species (e.g., hydroxyl radicals (•OH)) attack organic molecules. However, •OH can be useful in remediating recalcitrant organic contaminants in soils. Understanding the (system-specific) safe range of EPFRs produced by biochars requires knowing both the context of their use and their overall significance in the existing suite of environmental radicals, which has rarely been addressed. Here we place EPFRs in a broader environmental context, showing that biochar can have EPFR concentrations from 108-fold lower to 109-fold higher than EPFRs from other environmental sources, depending on feedstock, production conditions, and degree of environmental aging. We also demonstrate that •OH radical concentrations from biochar EPFRs can be from 104-fold lower to 1017-fold higher than other environmental sources, depending on EPFR type and concentration, reaction time, oxidant concentration, and extent of environmental EPFR persistence. For both EPFR and •OH concentrations, major uncertainties derive from the range of biochar properties and the range of data reporting practices. Controlling feedstock lignin content and pyrolysis conditions are the most immediate options for managing EPFRs. Co-application of compost to provide organics may serve as a postpyrolysis method to quench and reduce biochar EPFRs.

ABSTRACTEmission of polycyclic aromatic hydrocarbons (PAHs) is accompanied with the discharge of carbonaceous particles during the coke production. To degrade the adsorbed PAHs, hydrogen peroxide (H2O2) was applied as an oxidising agent, which might be activated by the inherent environmentally persistent free radicals (EPFRs) on coke particles. The transformation of phenanthrene (PHE), selected as model molecule, was achieved in H2O2/coke particle system without the addition of additional activating agent. This process consumed the particle-bounded EPFRs, inducing the decreasing of spin density from 1.92 × 1018 to 4.4 × 1017 spins g−1 in 30 min of reaction time. Electron paramagnetic resonance (EPR) technique coupled with spin-trapping agent 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO) was used to probe the potential formation of reactive oxygen species. A higher capture [] concentration was observed with larger decreases in EPFRs concentration, indicating that EPFRs were the main contributor to the formation of . The obtained results suggested that the activation of H2O2 by EPFRs on coke particles resulted in the generation of hydroxyl radical (), which then back-reacted with adsorbed PHE. The finding of this study shed light on a new remediation technology for toxic carbonaceous byproducts discharged during the coke production.

Seasonal variations and intercorrelations of polycyclic aromatic hydrocarbons, heavy metals and environmentally persistent free radicals in PM2.5 in Ulaanbaatar, Mongolia.

Mechanisms for light-driven evolution of environmentally persistent free radicals and photolytic degradation of PAHs on Fe(III)-montmorillonite surface.

A secondary process may be an important source of environmentally persistent free radicals (EPFRs) in atmospheric particulates; yet, this process remains to be elucidated. This study demonstrated that secondary EPFRs could be generated by visible-light illumination of atmospheric particulate matter (PM), and their lifetimes were only 30 min to 1 day, which were much shorter than the lifetimes of the original EPFRs in PM. The yields of secondary EPFRs produced by PM could reach 15-60% of those of the original EPFRs. The extractable organic matter contributed to the formation of secondary EPFRs (∼55%), and a humic-like substance was the main precursor of the secondary EPFRs and was also the most productive precursor compared to the other aerosol components. The results of simulation experiments showed that the secondary EPFRs generated by the extractable and nonextractable PM components were similar to those produced by phenolic compounds and polycyclic aromatic hydrocarbons, respectively. We have found that oxygen molecules play an important role in the photochemical generation and decay of EPFRs. The reactive oxygen capture experiments showed that the original EPFRs may contribute to singlet oxygen generation, while the secondary EPFRs generated by photoexcitation may not produce singlet oxygen or hydroxyl radicals.

Formation and biotoxicity of environmentally persistent free radicals in steelworks soil under thermal treatment

Environmentally persistent free radicals (EPFR) are emerging contaminants of health concern. Their levels in the environment are not well known because few studies have optimized EPFR extraction. Therefore, here we studied the extraction and decay of EPFR that are formed on the surfaces of Cu(II)-montmorillonite clay contaminated by polycyclic aromatic hydrocarbons (PAH) including benzo[a]pyrene and anthracene. EPFR were analyzed by electron paramagnetic resonance. Results show that acetone or dichloromethane/acetone effectively extract benzo[a]pyrene-EPFR. By contrast, CCl4, acetonitrile or methanol do not extract benzo[a]pyrene-EPFR, but extract residual benzo[a]pyrene at 62.2% for CCl4, 77.8% for acetonitrile and 59.1% for methanol. EPFR concentration decreases with ultrasonic intensity and time, from 60 s at 16 kHz to 1200 s at 40 kHz. The decay of PAH–EPFR in acetone displays two steps, a fast decay from 0 to about 5 h, then a slower decay from 5 to 50 h. The 1/e lifetime during the slow decay period was about 168 h for benzo[a]pyrene-EPFR and 180 h for anthracene-EPFR.

Environmentally persistent free radicals (EPFRs) are occasionally detected in Superfund sites but the formation of EPFRs induced by polycyclic aromatic hydrocarbons (PAHs) is not well understood. In the present work, the formation of EPFRs on anthracene-contaminated clay minerals was quantitatively monitored via electron paramagnetic resonance (EPR) spectroscopy, and surface/interface-related environmental influential factors were systematically explored. The obtained results suggest that EPFRs are more readily formed on anthracene-contaminated Fe(III)-montmorillonite than in other tested systems. Depending on the reaction condition, more than one type of organic radicals including anthracene-based radical cations with g-factors of 2.0028-2.0030 and oxygenic carbon-centered radicals featured by g-factors of 2.0032-2.0038 were identified. The formed EPFRs are stabilized by their interaction with interlayer surfaces, and such surface-bound EPFRs exhibit slow decay with 1/e-lifetime of 38.46 days. Transformation pathway and possible mechanism are proposed on the basis of experimental results and quantum mechanical simulations. Overall, the formation of EPFRs involves single-electron-transfer from anthracene to Fe(III) initially, followed by H2O addition on formed aromatic radical cation. Because of their potential exposure in soil and atmosphere, such clay surface-associated EPFRs might induce more serious toxicity than PAHs and exerts significant impacts on human health.

Environmentally persistent free radicals (EPFRs) and polycyclic aromatic hydrocarbons (PAHs) are persistent pollutants in atmospheric particulate matter that are detrimental to human health. This study collected atmospheric particulate matter during and after the spring festival travel season in Tainan, Taiwan, from various locations and analyzed the carbon composition and PAH isomeric ratios to identify the sources. In this study, EPFR concentrations were measured using electron paramagnetic resonance spectroscopy, with the highest concentration found to be 3.04 × 10(12) spins/m3. EPFRs contained predominantly oxygen-centered radicals in PM2.5, which are mainly existed in PM1. The results show that EPFR concentrations on PM, measured per unit volume (spins/m3) or mass (spins/g), were highest during the spring festival travel season. The daily inhalation exposure to the sum of EPFRs and PAHs in PM2.5 was estimated to be equivalent to inhaling 0.11-0.15 cigarette tar EPFRs per day. This report is the first to document EPFRs in environmental atmospheric particulate matters in Taiwan, which has significantly contributed to local air pollution control and reduced exposure risks to public health in Tainan.

Carbon-centered environmentally persistent free radicals induce stronger toxicity than oxygen-centered ones in earthworms (Eisenia fetida)

This research focuses on the environmental fate of particle associated pollutants such as Polybrominated Diphenyl Ethers (PBDEs), Polyaromatic Hydrocarbons (PAHs), and Environmentally Persistent Free Radicals (EPFRs) with a special emphasis on their transformation due to interaction with a matrix or co-pollutants. It encompasses two approaches to the stated problems: analysis of samples collected in the environment and laboratory simulation of the molecular transformations. The PBDE studies relied on the ambient air Particulate Matter (PM) samples collected from Bangkok, Thailand. Results showed the presence of various PBDE homologs from tri- to hepta-PBDEs on both PM2.5and Total Suspended Particle (TSP) samples. Sample comparison based on distance from reclamation site indicated elevated levels of PBDEs in close proximity to the e-waste site. Interestingly, a shift in the congener pattern was observed with lower brominated PBDEs being more prevalent on nearby e-waste sites samples. Overall, a clear trend can be observed indicating a debromination of PBDEs during the reclamation process and later during air transport. The results show PBDEs were translocated from treated materials to ambient air PM, and thermal treatment methods produced congener transformation as well as increased emissions of toxic PBDEs. This dissertation presents the impacts EPFR-laden particles have on the transformation of PAHs into oxy-/hydroxy-PAHs based on the laboratory simulation of the model molecule 1-Methylnaphthalene (1-MN). We found that for PM surrogates suspended in aqueous media, the presence of EPFRs resulted in the oxidation of 1-MN and formation of the several oxygenated PAHs products. EPFRs have been shown to produce .OH in the redox cycle when transferred to aqueous media. Produced .OH can reach other PM constituents, changing PM chemistry and potential exposure characteristics. Differences were observed in oxidation product yields, depending on whether EPFRs and PAHs were cohabiting or present on separate PM. This effect is attributed to the .OH concentration gradient as a factor in the oxidation process, further strengthening the hypothesis of EPFRs’ role in the PAH oxidation process. We propose that EPFRs on PM increase the risk associated with PAHs exposure, increase PAHs transformation to an aqueous medium, thus increasing their bioavailability.