Influence of microplastics and environmentally persistent free radicals on the ability of biochar components to promote degradation of antibiotics by activated peroxymonosulfate

Microplastics (MPs) in sludge can affect the ability of biochar-activated peroxymonosulfate (PMS) to degrade antibiotics. In this work, biochar was prepared by mixing sludge and polystyrene (PS) through hydrothermal carbonization (HTC) and high-temperature pyrolysis processes. The resulting biochar was used to activate PMS to degrade ofloxacin (OFX), levofloxacin (LEV), and pefloxacin (PFX). The addition of PS significantly enhanced the ability of biochar/PMS to degrade antibiotics and the levels of environmentally persistent free radicals (EPFRs, 4.59 × 1020 spin/g) due to the decomposition of PS. The addition of PS resulted in a slight decrease in the specific surface area of biochar (2-3 m2/g on average), but a significant increase in the concentration of EPFRs increased the removal efficiency. The activation of PMS by biochar is dominated by free radicals, accounting for about 70%, in which SO4•- and •OH contribute the most and O2•- the least. However, 1O2 contributes 15-20% to the degradation of antibiotics in non-free radical processes. Overall, the process of biochar/PMS degradation of antibiotics is mainly dominated by free radicals, and the effect of non-free radicals is not obvious. Both hydrochar and pyrocarbon samples showed good hydrophilicity, and this property should improve the ability of active sites on biochar to degrade antibiotics. In the HTC process, PS can decompose during hydrochar preparation, with a maximum reduction value of 40.09%. The three-dimension excitation emission matrix fluorescence spectroscopy (3D-EEM) and total organic carbon (TOC) results show that the protein content in sludge plays a major role in reducing PS, with little effect of polysaccharide and SiO2. There are six to seven degradation intermediates of quinolone antibiotics, which are eventually degraded into CO2, H2O, and inorganic substances. The regeneration experiment showed good reusability of hydrochar and pyrocarbon, further demonstrating the suitability of biochar for the degradation of antibiotics.

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

Thermal treatment are commonly used to address organic contaminated soils. In particular, the pyrolysis of organic substances can result in the creation of environmentally persistent free radicals (EPFRs). We investigated a steelworks site in Chongqing (China) to observe changes in EPFRs before and after thermal treatment. Our findings revealed that the EPFRs were carbon-centered radicals with a g-factor < 2.0030 and a spin density ranging from n.d.-5.23 × 1015 spins/mg. The formation of EPFRs was driving by polycyclic aromatic hydrocarbons (PAHs), Mn, Cu, and total organic carbon (TOC). Following the thermal treatment, the spin densities of EPFRs increased by a factor of 0.25 to 1.81, with maximum levels reached at 300 °C. High molecular weight PAHs exhibited high heat capacity, enabling the generation of more EPFRs. The thermal decay of EPFRs occurred in two stages, with the shortest 1/e lifetime lasting up to 16.8 h. Raising the temperature or prolonging time can significantly reduce EPFRs levels. Thermal treatment increased the generation of EPFRs, hydroxyl radicals (•OH) and superoxide radical (•O2-), leading to a decrease in bacterial luminescence. Specifically, •OH contributed to approximately 73% of the B. brilliantus inhibition. Our results highlight that the thermal treatment significantly enhance EPFRs concentrations, and the treated soil remained ecologically risky. The knowledge of the formation of EPFRs and their biotoxicity is shedding new light on the thermal treatment risk management.

Molecular characterization of diverse quinone analogs for discrimination of aerosol-bound persistent pyrolytic and photolytic radicals

Aerosol-bound organic radicals, including environmentally persistent free radicals (EPFRs), are key components that affect climate, air quality, and human health. While putative structures have been proposed, the molecular characteristics of EPFRs remain unknown. Here, we report a surrogate method to characterize EPFRs in real ambient samples using mass spectrometry. The method identifies chemically relevant oxygenated polycyclic aromatic hydrocarbons (OxPAH) that interconvert with oxygen-centered EPFR (OC-EPFR). We found OxPAH compounds most relevant to OC-EPFRs are structurally rich and diverse quinones, whose diversity is strongly associated with OC-EPFR levels. Both atmospheric oxidation and combustion contributed to OC-EPFR formation. Redundancy analysis and photochemical aging model show pyrolytic sources generated more oxidized OC-EPFRs than photolytic sources. Our study reveals the detailed molecular characteristics of OC-EPFRs and shows that oxidation states can be used to identify the origins of OC-EPFRs, offering a way to track the development and evolution of aerosol particles in the environment.

Environmentally persistent free radicals on photoaged microplastics from disposable plastic cups induce the oxidative stress-associated toxicity

Microplastics (MPs) are ubiquitous environmental contaminants that exerting multiple toxicological effects. Most studies have focused primarily on the models of unaged MPs and lack environmental relevance. The generation and toxicity of environmentally persistent free radicals (EPFRs) on photoaging MPs from disposable plastic cups (DPC-MPs) have not been well studied. Here, the formation of EPFRs on photoaged DPC-MPs and their toxic effects in nematodes were investigated. UV irradiation generated EPFRs, which influenced the characterization of DPC-MPs. Exposure to photoaged DPC-MPs at environmentally relevant concentrations （100-1000 μg/L） reduced the locomotion behavior, body length, and brood size. The Reactive oxygen species (ROS) production, lipofuscin accumulation, malondialdehyde (MDA), and 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels were increased along with the downregulation of the expression levels of associated genes, such as clk-1, clt-1, and gst-4，in nematodes. Moreover, the toxicity and oxidative stress response of nematodes were significantly inhibited due to N-acetyl-l-cysteine (NAC). Pearson's correlation analysis revealed that the oxidative stress was significantly associated with adverse physiological effects. Therefore, EPFRs on photoaged DPC-MPs cause toxicity in nematodes, and oxidative stress is important for regulating toxicity. This study offers novel insights into the potential risks of DPC-MPs under UV irradiation, highlighting the need to consider the role of EPFRs in toxicity assessments of DPC-MPs.

Inhalation of particulate matter containing environmentally persistent free radicals induces endothelial dysfunction mediated via AhR activation at the air-blood interface

Particulate matter (PM) containing environmentally persistent free radicals (EPFR) is formed by the incomplete combustion of organic wastes, resulting in the chemisorption of pollutants to the surface of PM containing redox-active transition metals. In prior studies in mice, EPFR inhalation impaired endothelium-dependent vasodilation. These findings were associated with aryl hydrocarbon receptor (AhR) activation in the alveolar type-II (AT-II) cells that form the air-blood interface in the lung. We thus hypothesized that AhR activation in AT-II cells promotes the systemic release of mediators that promote endothelium dysfunction peripheral to the lung. To test our hypothesis, we knocked down AhR in AT-II cells of male and female mice and exposed them to 280 µg/m3 EPFR lo (2.7e + 16 radicals/g) or EPFR (5.5e + 17 radicals/g) compared with filtered air for 4 h/day for 1 day or 5 days. AT-II-AhR activation-induced EPFR-mediated endothelial dysfunction, reducing endothelium-dependent vasorelaxation by 59%, and eNOS expression by 50%. It also increased endothelin-1 mRNA levels in the lungs and peptide levels in the plasma in a paracrine fashion, along with soluble vascular cell adhesion molecule-1 and iNOS mRNA expression, possibly via NF-kB activation. Finally, AhR-dependent increases in antioxidant response signaling, coupled to increased levels of 3-nitrotyrosine in the lungs of EPFR-exposed littermate control but not AT-II AhR KO mice suggested that ATII-specific AhR activation promotes oxidative and nitrative stress. Thus, AhR activation at the air-blood interface mediates endothelial dysfunction observed peripheral to the lung, potentially via release of systemic mediators.

Effects of excess sludge composting process, environmentally persistent free radicals, and microplastics on antibiotics degradation efficiency of aging biochar

Simulation of microbial aging biochar in compost is an important index for evaluating the biochar degradation efficiency of antibiotics. In this study, biochar was prepared by adding microplastics (MPs) to sludge, and the degradation effect of biochar/(peroxymonosulfate, PMS) on antibiotics was evaluated during the compost aging process of biochar. After the compost aging of biochars, the antibiotic degradation efficiency of HPBC500, HPBC500 + polystyrene (PS), HPBC900/PMS, and HPBC900 + PS/PMS decreased by 6.47, 15.2, 10.16, and 10.33 %, respectively. Environmentally persistent free radicals (EPFRs) and defect structure were the main contributors to the activation of PMS. EPFRs produced through PS pyrolysis of biochar exhibited strong reactivity but poor stability during the degradation of antibiotics. Biochar enhanced the growth of microorganisms in compost but reduced its specific surface area. The antibiotic degradation efficiency of the biochar was positively correlated with the concentration of EPFRs. This study elucidated the durability of different biochar toward antibiotic degradation.

Investigating environmentally persistent free radicals (EPFRs) emissions of 3D printing process

In recent years, the emission of particles and gaseous pollutants from 3D printing has attracted much attention due to potential health risks. This study investigated the generation of environmentally persistent free radicals (EPFRs, organic free radicals stabilized on or inside particles) in total particulate matter (TPM) released during the 3D printing process. Commercially available 3D printer filaments, made of acrylonitrile-butadiene-styrene (ABS) in two different colors and metal content, ABS-blue (19.66 μg/g Cu) and ABS-black (3.69 μg/g Fe), were used for printing. We hypothesized that the metal content/composition of the filaments contributes not only to the type and number of EPFRs in TPM emissions, but also impacts the overall yield of TPM emissions. TPM emissions during printing with ABS-blue (11.28 μg/g of printed material) were higher than with ABS-black (7.29 μg/g). Electron paramagnetic resonance (EPR) spectroscopy, employed to measure EPFRs in TPM emissions of both filaments, revealed higher EPFR concentrations in ABS-blue TPM (6.23 × 1017 spins/g) than in ABS-black TPM (9.72 × 1016 spins/g). The presence of copper in the ABS-blue contributed to the formation of mostly oxygen-centered EPFR species with a g-factor of ~2.0041 and a lifetime of 98 days. The ABS-black EPFR signal had a lower g-factor of ~2.0011, reflecting the formation of superoxide radicals during the printing process, which were shown to have an "estimated tentative" lifetime of 26 days. Both radical species (EPFRs and superoxides) translate to a potential health risk through inhalation of emitted particles.

A short review on environmental distribution and toxicity of the environmentally persistent free radicals

Environmentally Persistent Free Radicals (EPFRs) are usually generated by the electron transfer of a certain radical precursor on the surface of a carrier. They are characterized with high activity, wide migration range, and relatively long half-life period. In this review, we summarized the literature on EPFRs published since 2010, including their environmental occurrence and potential cytotoxicity and biotoxicity. The EPFRs in the atmosphere are the most abundant in the environment, mainly generated from the combustion of raw materials or biochar, and the C-center types (quinones, semiquinones radicals, etc.) may exist for a relatively long time. These EPFRs can transform into other substances (such as reactive oxygen species, ROS) under the influence of environmental factors, and partly enter soil and water by wet and dry deposition of particulate matter, which may promote the generation of EPFRs in those media. The wide distribution of EPFRs in the environment may lead to their exposure to biota including humans, resulting in cytotoxicity and biotoxicity. The EPFRs can influence the normal redox process of the biota, and generate a large number of free radicals like ROS. Exposure to EPFRs may change the expression of gene and activity of metabolic enzymes, and damage the cells, as well as some organs such as the lung, trachea, and heart. However, due to the difficulty in sample extraction, identification, and quantification of the specific EPFR individuals, the toxicity and exposure evaluation of biota are still limited which merits study in the future.

Environmentally persistent free radicals: Methods for combustion generation, whole-body inhalation and assessing cardiopulmonary consequences

Particulate matter (PM) containing environmentally persistent free radicals (EPFRs) results from the incomplete combustion of organic wastes which chemisorb to transition metals. This process generates a particle-pollutant complex that continuously redox cycles to produce reactive oxygen species. EPFRs are well characterized, but their cardiopulmonary effects remain unknown. This publication provides a detailed approach to evaluating these effects and demonstrates the impact that EPFRs have on the lungs and vasculature. Combustion-derived EPFRs were generated (EPFR lo: 2.1e-16 radical/g, EPFR hi: 5.5e-17 radical/g), characterized, and verified as representative of those found in urban areas. Dry particle aerosolization and whole-body inhalation were established for rodent exposures. To verify that these particles and exposures recapitulate findings relevant to known PM-induced cardiopulmonary effects, male C57BL6 mice were exposed to filtered air, ∼280 μg/m3 EPFR lo or EPFR hi for 4 h/d for 5 consecutive days. Compared to filtered air, pulmonary resistance was increased in mice exposed to EPFR hi. Mice exposed to EPFR hi also exhibited increased plasma endothelin-1 (44.6 vs 30.6 pg/mL) and reduced nitric oxide (137 nM vs 236 nM), suggesting vascular dysfunction. Assessment of vascular response demonstrated an impairment in endothelium-dependent vasorelaxation, with maximum relaxation decreased from 80% to 62% in filtered air vs EPFR hi exposed mice. Gene expression analysis highlighted fold changes in aryl hydrocarbon receptor (AhR) and antioxidant response genes including increases in lung Cyp1a1 (8.7 fold), Cyp1b1 (9 fold), Aldh3a1 (1.7 fold) and Nqo1 (2.4 fold) and Gclc (1.3 fold), and in aortic Cyp1a1 (5.3 fold) in mice exposed to EPFR hi vs filtered air. We then determined that lung AT2 cells were the predominate locus for AhR activation. Together, these data suggest the lung and vasculature as particular targets for the health impacts of EPFRs and demonstrate the importance of additional studies investigating the cardiopulmonary effects of EPFRs.

Contamination profiles and potential health risks of environmentally persistent free radicals in PM2.5 over typical central Chinese megacity

As one of the most important transportation hubs and industrial bases in China, Zhengzhou has suffered from serious PM2.5 pollution for a long time. However, the investigation of contamination status and possible exposure risks of environmentally persistent free radicals (EPFRs) in PM2.5 from Zhengzhou is rare. In this work, a comprehensive study of pollution levels, seasonal variations, sources, and potential health risks of PM2.5-bound EPFRs in Zhengzhou was conducted for the first time. The atmospheric concentrations of EPFRs in PM2.5 from Zhengzhou ranged from 1.732 × 1012 spin m-3 to 7.182 × 1014 spin m-3 between 2019 and 2020. Relatively serious contamination was noticed in winter and spring. Primary fossil fuel combustion and Fe-mediated secondary formation were apportioned as possible sources of PM2.5-bound EPFRs in Zhengzhou. Moreover, to avert the bias of the toxicity assessment induced by utilization of incompletely extracted EPFRs from sample filter, simulatively generated EPFRs were applied to toxicological evaluations (cell viability and reactive oxygen species assays). Corresponding experimental dosages were based on the estimated adults' annual exposure amounts of EPFRs in real PM2.5 samples. The results elucidated that EPFRs might cause growth inhibition and oxidative stress of human lung cells, suggesting the possible exposure-induced health concerns for local people in Zhengzhou. This study provides practical information of real contamination status of PM2.5-bound EPFRs in Zhengzhou, which is favorable to local air pollution control and reduction of exposure risks on public health in central China.

Particle-size distributions of environmentally persistent free radicals and oxidative potential of soils from a former gasworks site

The formation of toxic by-products, such as environmentally persistent free radicals (EPFRs), is one of the causes for concern by polycyclic aromatic hydrocarbons (PAHs) in soils. However, the distribution of EPFRs in different soil fractions and their relative contribution to the oxidation potential (OP) have not been investigated. In the present paper, contaminated samples were obtained from the former gasworks sites and were fractionated into different size particles, which were analyzed for EPFRs, reactive oxygen species (ROS), and OP-assayed by dithiothreitol (DTT) (OP^DTT). The results showed the highest concentration of EPFRs in the soil particle size with diameters <0.15 mm due to co-existence of PAHs and transition metals. ROS generation is in accordance with the size-specific distribution of EPFRs. Using the DTT assays, the redox activity of various size soil particles was examined, and found it was approximately 4- to 8-folds higher than that of un-contaminated samples and strongly associated with EPFRs, ROS, and PAHs. The obtained results advanced our knowledge on the EPFRs distribution in soil fractions at former MGP sites and emphasized the significance of PAH-EPFRs as a class of compounds to be considered in risk assessment of contaminated sites.

Effect of aged biochar after microbial fermentation on antibiotics removal: Key roles of microplastics and environmentally persistent free radicals

For the first time, biochar was prepared by changing the polystyrene (PS) content in sludge, and the efficiency of antibiotics removal by biochar was evaluated after fermentation aging. Fermentation aging affects the efficiency of antibiotics removal by reducing the specific surface area and active sites of biochar. The antibiotics removal efficiency of different types of biochar after aging decreased by 5.95%-13.59%. Owing to the biotoxicity of biochar, the relative abundance of most communities decreased during fermentation, whereas Anaerolineae still increased (14.29% to 33.05% or 33.02%). However, controlled experiments confirmed that biochar was much less toxic to Scenedesmus obliquus than to antibiotics, with concentrations of 11.09 × 10⁵ cells/mL and 0.188 × 10⁵ cells/mL, respectively. With the positive effect of environmentally persistent free radicals (EPFRs) considered, increasing the PS content in sludge facilitated the removal of antibiotics by biochar. This study assesses the stability of biochar in removing antibiotics after long-term microbial aging.

Removal mechanism of tetracycline-Cr(Ⅵ) combined pollutants by different S-doped sludge biochars: Role of environmentally persistent free radicals

In this work, by using sodium thiosulfate as the S source, S-doped biochars were prepared to remove tetracycline/hexavalent chromium (TC-Cr (Ⅵ)) combined pollutants in aqueous solutions. The concentration of environmentally persistent free radicals (EPFRs) was used to directly determine the degradation of TC and the reduction of Cr (Ⅵ). The concentration of EPFRs in S-doped hydrothermal + pyrocarbon (S-HPBC) (3.64 × 10¹⁹ spins/g) was greater than that of S-doped hydrochar (S-HBC) (5.64 × 10¹⁸ spins/g) and S-doped pyrocarbon (S-PBC) (6.53 × 10¹⁸ spins/g). The increase in EPFRs concentration after S doping was positively correlated with the number of defect structures. In the TC-Cr (Ⅵ) system, the reduction efficiency of Cr (Ⅵ) decreased due to competition for electrons, while the TC degradation efficiency remained high. This was likely because Cr (Ⅵ) reduction promoted the degradation of TC. In addition, de-complexation was the primary factor for the removal of TC-Cr (Ⅵ), and some ROS were consumed during this process. The thiophene groups (-C-S-C-) that formed after S-doping of biochar were the main functional groups involved in the catalytic degradation of TC. In the radical pathway, SO₄^•- and •OH provided the greatest contribution to the degradation of TC, while ¹O₂ contributed the most to TC degradation via a non-radical pathway. The regeneration experiment confirmed that S-doped biochar could be reused and maintained a high pollutant removal efficiency. S-HPBC is a promising modified biochar material for removing mixed pollutants.

Size-resolved environmentally persistent free radicals in cold region atmosphere: Implications for inhalation exposure risk

Environmental persistent free radicals (EPFRs) have attracted more attentions recently due to their potential adverse effects to human. EPFRs in full-size range particles were comprehensively investigated in this study. The average EPFRs concentration during heating season was 3.01 × 10¹⁴ spins/m³, which was much higher than that in non-heating season (4.30 × 10¹³ spins/m³). The highest concentration of EPFRs presented in 0.56-1.0 µm particles during heating season, while it shifted to 5.6-10 µm particles during non-heating season. Besides, the contributions of EPFRs on PM_>10 to the total concentration of EPFRs cannot be neglected, especially in the non-heating season. The International Commission on Radiological Protection model and the specific factors of the Chinese population were applied to evaluate the inhalation exposure risk of EPFRs. The results indicated that the exposure levels of EPFRs to the upper respiratory tract were much higher. The daily exposure dose of EPFRs suggested the inhalation exposure risk of 3-4 years old was higher than other age groups. In summary, these finding provided new insights for the full range particle size distribution and the inhalation exposure risk of EPFRs, which improved our understanding on the environmental fate and the health risk of EPFRs in atmosphere.

The overlooked toxicity of environmentally persistent free radicals (EPFRs) induced by anthracene transformation to earthworms (Eisenia fetida)

Environmentally persistent free radicals (EPFRs) as intermediate products exist widely in the PAHs-contaminated soils, but toxicity assessment associated with EPFRs for terrestrial invertebrates remains unclear. Using the model organism Eisenia fetida, we compared the adverse effects among anthracene (ANT), anthraquinone (ANQ), and EPFRs induced by ANT transformation on clay surfaces. Our results showed that EPFRs-exposed earthworms experienced histopathological damage, which was more severe than ANT and ANQ-exposed earthworms. The source of EPFRs damage was associated with the obvious dysbiosis of reactive oxygen species in earthworms. Specifically, EPFRs trigged more severe antioxidant responses and oxidative damages (e.g., membrane lipid and DNA injury) in comparison with ANT and ANQ exposure, as evidenced by the values of integrated biomarker response (IBR) following the order of EPFRs (14.5) > ANT (12.8) > ANQ (10.9). Moreover, high-throughput sequencing found that EPFRs induced dramatic changes in the composition and structure of earthworm gut microbiota, which may involve immune and metabolism dysfunction, in turn aggravated EPFRs toxicity. Overall, the obtained information highlights the more severe injury of EPFRs to terrestrial organisms, deserving more attentions for the assessment of potential risks associated with radical intermediates in PAHs-contaminated soils.

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

Environmentally persistent free radicals (EPFRs) are emerging pollutants in contaminated soils and have attracted significant attention. Chinese coke production making a great contribution to the globe is increasingly identified as the non-ignorable source of EPFRs. However, the distribution level, influence factors, and biotoxicity of EPFRs at coking sites remain poorly understood. Herein, a typical coking plant in Tangshan, China, featuring two functional regions (the reconstructed project (RP) and elimination engineering (EE)) was used to study the existence of EPFRs. The spin density of the EPFRs in coking soils was 3.20 × 10²⁰-3.11 × 10²¹ spins/g with g-factor values of 2.0020-2.0036. The EPFRs presented higher concentrations and g-factor values in RP region than in EE region, and a mixture of carbon-centered radicals and carbon-centered radicals with adjacent oxygen atoms as well as carbon-centered radical was ascertained in the former and the latter, respectively. Correlation analysis and FT-ICR-MS results indicated that polycyclic aromatic hydrocarbons (PAH) together with other unsaturated hydrocarbons and condensed aromatic contaminants, might contribute to the EPFRs formation in the soils of RP region, whereas PAHs were the main source of EPFRs in EE region. Soil components were determined to investigate the influence factors in EPFRs formation. Cu and Fe₂O₃ were recognized as the markedly positive influence factors, while TOC had a negative impact on EPFR formation. Visible light irradiation can induce the transformation and generation of EPFRs. As representative contaminants, both toluene and 2-chlorophenol can create EPFRs in coking soil under visible light irradiation. The potential biotoxicity tests of Photobacterium phosphoreum T3 spp. showed that EPFRs from the soils diminished bacterial luminescence. Such effect was proven to be induced by the OH based on the quenching experiment. Understanding the influence factors of EPFRs formation and their biotoxicity in coking soils is critical for developing risk assessments and prevention strategies.

Effect of polystyrene microplastics on the degradation of sulfamethazine: The role of persistent free radicals

Microplastic (MPs) pollution is increasingly becoming a global environmental problem. MPs entering the environment are subjected to various aging processes, among which photoaging is the most important process leading to MPs oxidation. Persistent free radicals (EPFRs) are formed on the surface of MPs during photoaging, but it is not clear whether EPFRs on the surface of MPs can produce reactive oxygen species (ROS) and thus degrade organic pollutants. In this study, with polystyrene (PS) as the representative plastic and sulfamethazine (SMT) degradation as the target pollutant, the effect and mechanism of light-induced PS on SMT degradation were investigated by experiment and theoretical calculation. It was found that PS can stimulate the production of ROS under sunlight, which can significantly improve the degradation rate of SMT. Through quenching experiment and free radical trapping experiment, it was found that the mechanism of PS promoting the degradation of SMT was mainly due to the production of hydroxyl radical (·OH) in the system, and ·OH was the main ROS species affecting the oxidative degradation of SMT. The characterization results show that the high reactive oxygen generation ability of PS under solar irradiation was due to the abundant photoactive oxidation functional groups on its surface. In addition, the key reaction sites of SMT were predicted by density functional theory (DFT) calculation. The results of different calculations consistently showed that the sulfonamide group of SMT, the pyrimidine heterocycle and the amino group of aniline are the reaction sites of ·OH priority attack. The main intermediates were determined by UHPLC-HRMS/MS. Combined with theoretical calculation, it was proposed that the oxidative degradation pathway of SMT mainly includes SN bond cleavage, SMILES rearrangement and SO₂ group removal. This study clarified the effect of PS on the degradation of organic pollutants under light, and provided theoretical guidance for the degradation mechanism.

Effect of pyrolysis temperature on the activated permonosulfate degradation of antibiotics in nitrogen and sulfur-doping biochar: Key role of environmentally persistent free radicals

Because of the increasingly widespread contamination of antibiotics, the preparation of biochar by heteroatom doping to further improve the catalytic degradation efficiency of antibiotics has become a major focus of research. In this study, N-doped (NBC), S-doped (SBC), and NS-doped (NSBC) moso bamboo biochar were obtained at preparation temperatures of 300-700 °C. The concentration of environmentally persistent free radicals (EPFRs) in all biochars peaked when the preparation temperature was 500 °C: 2.45 × 10¹⁹ spins·g^-1 (BC), 9.23 × 10¹⁹ spins·g^-1 (NBC), 6.10 × 10¹⁹ spins·g^-1 (SBC), and 4.36 × 10¹⁹ spins·g^-1 (NSBC). After heteroatom doping, EPFR species were more abundant, and the distribution of three types of EPFRs (oxygen-centered (g > 2.0040), carbon-centered (g < 2.0030), and carbon-centered radicals with oxygen atom free radicals (2.0030 < g < 2.0040) varied with the preparation temperature. In the process of antibiotic degradation, both NBC and SBC increased the degradation rate of antibiotics, whereas NSBC reduced the degradation rate. Compared with the degradation rate of antibiotics of biochar (79.86%), the degradation rate of antibiotics by NBC, SBC, and NSBC via PMS activation was 92.23%, 88.86%, and 70.97% on average in 30 min, respectively. The greatest contributors to the catalytic degradation were SO₄^•-, followed by ¹O₂, •OH, and O₂^•-. EPFRs and ¹O₂ might be the main contributors to the free radical and non-free radical pathways. The enhancement of EPFRs following the N doping or S doping of biochar is the key factor underlying PMS activation. Therefore, changes in the structure of biochar can better activate PMS to produce reactive oxygen species-degrading antibiotics. The mineralization rate of antibiotics by BC, NBC, SBC, and NSBC was 42.12%, 47.06%, 44.99%, and 39.01%, respectively. This means that a small portion of the antibiotics was completely decomposed into CO₂, H₂O, and inorganic substances after degradation. Cyclic experiments showed that heteroatom-doped biochar had higher reusability, and the degradation rate decreased less than 15%.

Spatial distribution, pollution characterization, and risk assessment of environmentally persistent free radicals in urban road dust from central China

Environmentally persistent free radicals (EPFRs) have aroused widespread concern due to their potential adverse health effects. Research on EPFRs in road dust is still very limited. In this study, 86 road dust samples were collected using vacuum sampling in a rapidly developing city in central China. The pollution characterization and health risk of EPFRs in the urban road dust were then systematically analyzed. The results showed the average concentrations of EPFRs in urban road dust and fraction of particle with aerodynamic diameters lower than 10 μm (PM₁₀) were 2.24 × 10¹⁷ to 3.72 × 10¹⁹ spins·g^-1 and 6.02 × 10¹⁷ to 1.41 × 10²⁰ spins g^-1, respectively. The concentrations of EPFRs in dust from expressways, arterial roads, and secondary trunk roads were significantly higher than those found in the remaining road types. The g-factors of 2.0032-2.0039 indicated that the EPFRs have consisted of oxygen-centered and carbon-centered radicals or carbon-centered radicals with nearby oxygen or halogen atoms. Moreover, three decay patterns of EPFRs were observed: a fast decay followed by a slow decay, a single slow decay, and the slowest decay. In addition, a comparative evaluation was made for probabilistic risk assessments of exposure to the EPFRs in road dust and the PM₁₀ fraction. Compared with road dust, the probability of the number of equivalent cigarettes to exceed the 100 and 200 cigarettes for inhaling EPFRs in the PM₁₀ fraction increased by 27.0% and 25.0%, respectively. The simulation results showed the PM₁₀ fraction were primarily deposited in the upper respiratory tract regions (57.1%) and pulmonary regions (28.8%). The findings of this study suggest a potential risk of EPFRs in inhalable particles and provide a new insight for further exploration of the EPFRs in fine particles of road dust.

Photoformation of environmentally persistent free radicals on particulate organic matter in aqueous solution: Role of anthracene and formation mechanism

Environmentally persistent free radicals (EPFRs) generated under irradiation have been widely detected in soil particles, atmospheric particles and microplastic particles, but the formation of EPFRs in water is not well understood. This study investigated the formation of EPFRs on particulate organic matter (POM) in water contaminated by anthracene (Ant) under irradiation. The photoformation and decay progress of EPFRs was represented with the help of electron paramagnetic resonance (EPR) technique on both actual POM and Fe(III)-montmorillonite simulated samples. EPR signals at the range of 10¹⁶ to 10¹⁷ spin/g were detected and the half-life time of EPFRs stored in water was at around 16.62 h and 60.80 h, much shorter than those in the air. The g factors were all larger than 2.0040, which indicated the generation of oxygen centered EPFRs. The primary intermediates were identified by gas chromatography-mass spectrometer (GC-MS) and a possible EPFR formation pathway during Ant degradation was proposed. The interaction between Ant and POM, and the hydroxylation and carbonylation of the intermediates made contributions to the generation of EPFRs. Meanwhile, the indirect photodegradation of bisphenol A (BPA) has been demonstrated by analyzing the reactive oxygen species (ROS) and photogenerated electrons in the solution with POM containing EPFRs. It is found that hydroxyl radicals (•OH) and singlet oxygen (¹O₂) were induced and might promote the photodegration. Overall, our present study provided useful information to understand the photoformation of EPFRs on POM and their fate in aqueous environments.

Photoaged polystyrene microplastics serve as photosensitizers that enhance cimetidine photolysis in an aqueous environment

Microplastics (MPs) have received much attention in recent years because of their continuous photoaging process in aquatic environments. However, little research has been conducted on the photochemistry of aged microplastics and the associated effects on coexisting pharmaceuticals. This study investigated the photodegradation of cimetidine via aged polystyrene microplastics (PS-MPs) with different aging times (0-7 d) under simulated sunlight irradiation (700 W/m²). PS-MPs with 5 d of aging time resulted in much faster cimetidine degradation (>99%) after 2 h of irradiation than pristine PS-MPs (<8%). The enhanced photodegradation of cimetidine by aged PS-MPs was related to the increase in chromophoric oxygenated groups (CO, C-O) followed by redshifted absorbance through the photoaging process, which induced the formation of the environmentally persistent free radicals (EPFRs) OH, ¹O₂ and ³PS*. However, only ¹O₂ and ³PS* contributed to enhanced cimetidine photodegradation, with ¹O₂ playing a more important role in our case. This work also demonstrated that other compounds that are susceptible to indirect photolysis, such as codeine and morphine, are likewise significantly degraded under irradiation in the presence of aged PS-MPs. Although previous studies have reported how MPs can increase the persistence of contaminants, this study demonstrates that MPs can serve as photosensitizers and alter the fate of coexisting pharmaceuticals in aquatic environments.

A critical review of environmentally persistent free radical (EPFR) solvent extraction methodology and retrieval efficiency

Long-lived environmentally persistent free radical (EPFR) exposures have been shown in toxicology studies to lead to respiratory and cardiovascular effects, which were thought to be due to the persistence of EPFR and their ability to produce reactive oxygen species. To characterize EPFR exposure and resulting health impacts, it is necessary to identify and systematize analysis protocols. Both direct measurement and solvent extraction methods have been applied to analyze environmental samples containing EPFR. The use of different protocols and solvents in EPFR analyses makes it difficult to compare results among studies. In this work, we reviewed EPFR studies that involved solvent extraction and carefully reported the details of the extraction methodology and retrieval recovery. EPFR recovery depends on the structure of the radical species and the solvent. For the limited number of studies available for review, the polar solvents had superior recovery in more studies. Radicals appeared to be more oxygen-centered following extraction for fly ash and particulate matter (PM) samples. Different solvent extraction methods to retrieve EPFR may produce molecular products during the extraction, thus potentially changing the sample toxicity. The number of studies reporting detailed methodologies is limited, and data in these studies were not consistently reported. Thus, inference about the solvent and protocol that leads to the highest EPFR extraction efficiency for certain types of radicals is not currently possible. Based on our review, we proposed reporting criteria to be included for future EPFR studies.

Mechanism of persulfate activation by biochar for the catalytic degradation of antibiotics: Synergistic effects of environmentally persistent free radicals and the defective structure of biochar

The abuse of antibiotics threatens the water environment and human health. Green treatment method is needed to degrade antibiotics such as biochar. Few studies have examined the environmentally persistent free radicals (EPFRs) and defective structure of biochar during the biochar-mediated catalytic degradation of antibiotics. In this study, biochar prepared from poplar and pine sawdust was used to activate peroxymonosulfate (PMS) to generate instant radicals (SO₄^•- and •OH) and degrade tetracycline (TC), chlortetracycline (CTC) and doxycycline (DOX). The preparation temperatures ranged from 300 °C to 900 °C. EPFRs were the main activator of PMS at 300-500 °C, and the defective structure of biochar was the main activator at 800-900 °C. The concentrations of EPFRs ranged from 1.75 × 10¹⁸ spins/g to 6.44 × 10¹⁸ spins/g. According to the electron paramagnetic resonance (EPR) parameter (g-factor), the main types of EPFRs were carbon-centered radicals (g₁ < 2.0030) or carbon-centered radicals with oxygen atoms (2.0030 < g₂ < 2.0040). Optimization of the degradation experiment revealed that the removal rate of antibiotics peaked when the preparation temperature was 500 °C and 900 °C. In the biochar/PMS system, the antibiotics removal rate of 90% was achieved in 40 min with an average apparent rate constant (k_obs) of 0.0588 min^-1. Analysis of the mechanism revealed that the free radical pathway (EPFRs and defective structure) can effectively activate PMS to generate SO₄^•- and •OH. However, control experiments suggested that the non-free radical pathway (singlet oxygen) had little effect on antibiotic degradation. After five cycles, the removal rate of antibiotics by biochar was still greater than 70%, indicating that biochar retains a high degradation ability. These results indicate that optimizing the preparation conditions can effectively expand the application range of the biochar/PMS system and improve the degradation of antibiotic wastewater.

Phytosampling-a supplementary tool for particulate matter (PM) speciation characterization

Ambient air particulate matter (PM) and PM-associated environmentally persistent free radicals (EPFRs) have been documented to contribute to pollution-related health effects. Studies of ambient air PM potentially bear artifacts stemming from the collection methods. We have investigated the applicability of PM phytosampling (PHS) as a supplementary tool to a classic PM sampler in respect of achieving better PM chemical composition assessment (primarily organic fraction). Phytosampling is a static PM collection method relying on the particle entrapment by the plant's leaf through electrostatic forces and surface trichomes. We have investigated the differences in the EPFR and polycyclic aromatic hydrocarbon (PAH) speciation and concentration on ambient air PM for PHS and high-volume PM sampler (HVS). The advantages of PHS are easy particle recovery from the matrix, collection under natural environmental conditions, and the ability to apply a dense collection network to accurately represent spatial pollutant distribution. The experimental results show that the PHS can provide valuable speciation information, sometimes different from that observed for HVS. For PM collected by PHS, we detected the larger contribution of oxygen-centered EPFRs, different decay behavior, and more consistent PAH distribution between different PM sizes compared to the PM from HVS. These results indicate that the isolation of samples from the ambient during HVS sampling and exposure to high-volume airflow may alter the chemical composition of the samples, while the PHS method could provide details on the original speciation and concentration and be more representative of the PM surface. However, PHS cannot evaluate an absolute air concentration of PM, so it serves as an excellent supplementary tool to work in conjunction with the standard PM collection method.

Formation of environmentally persistent free radicals from thermochemical reactions of catechol

In many anthropogenic activities, catechol as a widespread organic chemical could be released and also environmentally persistent free radicals (EPFRs) can be unintentionally formed. However, the underlying links between EPFRs and the role of catechol as an important precursor are not well understood. In this study, EPFR formation from catechol during heating was monitored online by electron paramagnetic resonance spectroscopy. It was found that catechol can produce significant amounts of EPFRs via thermochemical reactions. The EPFR species formed from catechol on metal oxides were oxygen-centered phenoxy and semiquinone radicals. Their half-lives were evaluated to be in the range of 113-909 h. The promotional effects of CaO and CuO on EPFR formation from catechol were stronger than that of Fe₂O₃. The promotional abilities and underlying mechanisms of various metal oxides in EPFR formation were clarified by X-ray photoelectron spectroscopy. Significant EPFR formation was observed during the cooling stage of a heating reaction system when CaO was used as the reaction medium. The obtained knowledge on the formation of EPFRs from catechol and the key factors involved will enable better control of the formation of EPFRs from anthropogenic activities.

Assessment of personal exposure to environmentally persistent free radicals in airborne particulate matter

Environmentally persistent free radicals (EPFRs) are a type of emerging contaminants. The EPFR species in airborne particulate matter are similar to carcinogenic tar paramagnetic species in cigarettes that can cause DNA damage. However, understanding on daily EPFR exposure levels and risks are lacking currently. We used personal aerosol exposure monitors worn by volunteers to assess EPFR exposure in a spatio-temporal, non-static manner. Daily individual exposure to EPFRs for urban residents in Beijing, China ranged from 1.11 × 10¹⁷ to 7.42 × 10¹⁷ spins/m³ during the heating period (winter) and from 4.79 × 10¹⁴ to 7.76 × 10¹⁶ spins/m³ during the non-heating period (summer). Carbon-centered radicals were dominant in winter, while oxygen-centered radicals were dominant in summer because of higher atmospheric oxidizing capacity contributing to oxidation reactions. Coal combustion in winter is a key influencing factor in EPFR exposure levels. An intuitional assessment was used to evaluate the inhalation risks of EPFRs by converting their concentrations in inhaled particulate matter to equivalents in cigarettes smoked. The assessment concluded that one urban resident may, on average, inhale the equivalent of 46 cigarettes per day in EPFRs. The health risks of these free radicals, especially during winter, should be researched in depth.

Regulation of biochar mediated catalytic degradation of quinolone antibiotics: Important role of environmentally persistent free radicals

Antibiotic pollution threatens aquatic ecosystems and water supplies, so analysis of ecofriendly remediation approaches like biochars with catalytic degradation abilities is a top priority. In this work, quinolone antibiotics were degraded by activating oxidants to generate transient radicals using the environmentally persistent free radicals (EPFRs) carried by biochar. The physical and chemical characterization confirmed that biochar is suitable for the removal of organic pollutants. By regulating biochar preparation parameters, it was found that EPFR generation peaked at 500 °C. As the temperature increased from 300 °C to 500 °C, the EPFRs changed from oxygen-centered radicals (g > 2.0040) to carbon-centered radicals (g < 2.0030). The catalytic degradation efficiencies of the EPFR activated oxidants from large to small were: peroxydisulfate (PDS), peroxymonosulfate (PMS), H₂O₂ and flowing O₂. The combined actions of SO₄^•- and •OH effectively degraded antibiotics. The results showed that biochar activating persulfate is a promising technique for the degradation of antibiotics.

Enhanced cytotoxicity of photoaged phenol-formaldehyde resins microplastics: Combined effects of environmentally persistent free radicals, reactive oxygen species, and conjugated carbonyls

Phenol-formaldehyde resin microplastic (PF-MP) is one of the major inhalable microplastics in environments released from the manufacture, processing and usage of PF materials. The associated toxicities of PF-MP might be affected by photoaging. In this study, the dynamic evolutions of the oxidative potential (OP) and redox-active species, including environmentally persistent free radicals (EPFRs), reactive oxygen species (ROS), peroxides and conjugated carbonyls, as well as the associated cytotoxicity of PF-MP were systematically investigated as a result of the simulated sunlight irradiation. As the photoaging time extended, the OP of PF-MP increased. The contents of the produced conjugated carbonyls, ROS and PF-bound EPFRs due to light irradiation increased as well, and displayed significant correlations with the OP (Spearman r > 0.6, p < 0.05). The photoaged PF-MP distinctly increased the cellular ROS and reduced the cell viability of human lung epithelial adenocarcinoma cells (A549). The cytotoxicity of PF-MP showed a similar trend with the OP level in PF-MP, suggesting that the produced active species induced the in vitro toxicities. The results not only highlight the adverse health effects of photoaged PF-MP, but also provide new perspectives for the environmental risks of airborne MPs.

Biochar-mediated Fenton-like reaction for the degradation of sulfamethazine: Role of environmentally persistent free radicals

Swine manure biochar (SBC) pyrolyzed at 300 °C, 600 °C and 900 °C were utilized to degrade sulfamethazine (SMT) in heterogeneous Fenton-like systems which achieved excellent degradation efficiency (over 85% in 30 min). Experiments results demonstrated that SBC possessed the poor SMT adsorption capacity but high catalytic performance. Electron Paramagnetic Resonance (EPR) and X-ray photoelectron spectroscopy (XPS) analysis revealed that there were oxygen-centered environmentally persistent free radicals (EPFRs) and carbon-centered EPFRs with an adjacent oxygen atom in SBC. The oxygen-centered EPFRs played a major role in the catalytic process which tended to convert to carbon-centered EPFRs after the reaction. Besides, the electron transfer pathways were the most likely catalytic mechanism of SBC and the contribution of OH was dominant through Electron capture experiments and Linear sweep voltammetry (LSV) measurements. The acidic or alkaline condition can promote the catalytic ability of SBC. The presence of dissolved salts (NaCl) inhibited the catalytic process but the inhibition was slightly weakened at high concentration of NaCl, which showed the high tolerance of Cl^- in Fenton/Fenton-like systems. Moreover, real wastewater application suggested that SBC600/H₂O₂ system possessed excellent catalytic efficiency and good adaptability. This research provides a novel swine manure reuse process with high practicability and presents a more explicit perspective about the reaction mechanisms of EPFRs in biochar.

Mechanism of Cr(VI) reduction by humin: Role of environmentally persistent free radicals and reactive oxygen species

Humic substances, especially humin (HM) in its solid phase, is considered to be the main electron donor during the reduction of Cr(VI) in the environment. This work explores the reaction mechanism between Cr(VI) and the functional groups contained in HM, environmentally persistent free radicals (EPFRs), and reactive oxygen species (ROS). We examine the changes in the functional groups, EPFRs, and ROS on HM during the reaction, and inhibit the production of ROS to verify their effect. Our results demonstrate that the carboxyl and phenolic hydroxyl groups contained in HM are consumed during the reaction. The phenolic hydroxyl group can directly react with Cr(VI) as an electron donor, and can also transfer electrons to molecular oxygen to generate superoxide radicals to reduce Cr(VI). EPFRs also exhibit the same reaction pathway. The molecular oxygen in the solution gains electrons to generate O₂^·-, which further reacts with Cr(VI) to reduce it to Cr(III). The production and effect of active oxygen are verified by removing oxygen from the solution. In this study, the contribution of active oxygen to the reduction of Cr(VI) is approximately 30%. This study provides theoretical support for revealing the effects of humic substances on the conversion of Cr(VI).

Implication for adsorption and degradation of dyes by humic acid: Light driven of environmentally persistent free radicals to activate reactive oxygen species

Humic acid (HA) was applied as the biosorbent for the adsorption and degradation of dyes in the presence of environmentally persistent free radicals (EPFRs). Scanning Electron Microscope (SEM) analysis showed that the microstructure of the HA surface and the thermal stability was analyzed by thermogravimetric analysis (TGA). Following irradiation, semiquinone EPFRs (g-factor > 2.0045) were generated on the HA surface. Both O₂ and the addition of H₂O₂ were able to promote the generation of hydroxyl and superoxide radicals for the degradation of dye in aqueous solution. Furthermore, adsorption was observed to remove large amounts of the dyes, while the instantaneous free radical degradation process reduced the dyes to the lower concentration. In addition, a linear relationship was observed between the consumption of EPFRs and dye degradation rates. In ternary systems, HA conformed to Langmuir (476.19-1250.12 mg/L) and pseudo-second-order kinetic models. This work offers new insights into HA-EPFRs and their potential applications.

Risk evaluation of environmentally persistent free radicals in airborne particulate matter and influence of atmospheric factors

Environmentally persistent free radicals (EPFRs) was considered unrecognized composition of air pollutants and might help explain the long-standing medical mystery of why non-smokers develop tobacco-related diseases like lung cancer. EPFRs in airborne fine particulate matter (PM_2.5) can induce oxidative and DNA damage when inhaled. We assessed the inhalation risk of EPFRs in PM_2.5 and factors influencing this risk in Beijing as a large city with frequent haze events. The average concentration of EPFRs in PM_2.5 was 6.00 × 10¹⁷ spins/m³ in spring, autumn, and winter; lower concentrations were recorded in the summer. To estimate the daily inhalation risk of EPFRs in PM_2.5, we used the equivalent EPFRs in cigarette tar. The average daily inhalation exposure of EPFRs in PM_2.5 was estimated to be the equivalent of 33.1 cigarette tar EPFRs per day (range: 0.53-226.9) during both haze and non-haze days. The major factors influencing EPFR concentrations in the atmosphere were precipitation and humidity, which reduced airborne concentrations. Levels of PM_2.5 and carbon monoxide were positively correlated with EPFR concentrations. The health risks of inhaling airborne EPFRs could be significant and should be recognized and quantified.

Short-term exposure to ZnO/MCB persistent free radical particles causes mouse lung lesions via inflammatory reactions and apoptosis pathways

Environmentally persistent free radicals (EPFRs) are easily generated in the combustion processes of municipal solid waste (MSW) and can cause adverse effects on human health. This study focuses on understanding the toxicity of EPFR particles (ZnO/MCB containing EPFRs) to human bronchial epithelial cell lines BEAS-2B and 16HBE, murine macrophages Raw264.7, and the lung of BALB/c mice after a short exposure (7 days). Exposure of BEAS-2B, 16HBE, and Raw264.7 cells to ZnO/MCB particles significantly increased the reactive oxygen species (ROS) production and perturbed levels of intracellular redox conditions (decreased the intracellular GSH level and the activity of cytosolic SOD, and stimulated oxidative stress related proteins such as HO-1 and Nrf2). EPFR particles decreased the mitochondrial membrane potential (MMP) and induced cell apoptosis, including the activation of Caspase-3, Bax, and Bcl-2 apoptotic signalling pathways. A signature inflammatory condition was observed in both cell models and the mouse model for lung lesions. Our data suggest that EPFRs in particles have greater toxicity to lung cells and tissues that are potential health hazards to human lung.

Evolution and stabilization of environmental persistent free radicals during the decomposition of lignin by laccase

Soil microbial enzymes may induce lignin decomposition, accompanied by generation of free radicals. The evolution of environmentally persistent free radicals (EPFRs) and reactive oxygen species (ROS) during laccase-catalyzed lignin decomposition remains unclear. Characterization by electron paramagnetic resonance spectroscopy revealed gradually increased concentration of EPFRs, with maximum levels within 6 h that remained constant, accompanied by the increase in g-factor from 2.0037 to 2.0041. The results suggested the generation of oxygen-centered radicals on lignin. The EPFRs produced on solid samples slowly decreased by 17.2% over 17 d. ROS were also detected to have a similar trend as that of the evolution of EPFRs. Scanning electron microscopy, attenuated total reflectance-Fourier transform infrared spectroscopy, gel permeation chromatography and nuclear magnetic resonance analyses suggested the demethylation and oxidation of lignin. We clarify the biogeochemical transformation of lignin and potential contributions to the generation of EPFRs and ROS in soil.

Role of coke-bounded environmentally persistent free radicals in phenanthrene degradation by hydrogen peroxide

Emission 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 [[Formula: see text]] concentration was observed with larger decreases in EPFRs concentration, indicating that EPFRs were the main contributor to the formation of [Formula: see text]. The obtained results suggested that the activation of H₂O₂ by EPFRs on coke particles resulted in the generation of hydroxyl radical ([Formula: see text]), 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.

Long-term phototransformation of microplastics under simulated sunlight irradiation in aquatic environments: Roles of reactive oxygen species

Microplastics may experience photoaging and breakdown into nanoplastics in aquatic environment as a result of long-term light irradiation. However, the underlying mechanisms responsible for the photodegradation of microplastics are largely overlooked. In this study, the photodegradation of microplastics, utilizing polystyrene microplastic (PS-MP) as a model, was investigated under irradiation with simulated solar light for as long as 150 d. A large amount of reactive oxygen species (ROS), including O₂^•-, ¹O₂, H₂O₂ and •OH, were detected in the PS-MP suspension due to light irradiation, which displayed significant relationships with the generated environmentally persistent free radicals (EPFRs). Distinct photoaging of PS-MP was observed with increased surface roughness and decreased particle size. However, these photoaging effects were significantly inhibited by ROS quenchers, suggesting that the generation ROS played a vital role in the PS-MP phototransformation. In addition, ROS induced formation of more oxidative functional groups on the PS-MP, thus enhancing the negative surface potential and the stability of PS-MP in water. This study elucidated the mechanism of formation of ROS by simulated solar light irradiated MPs and their subsequent roles in the phototransformation of MP, thus expanding current knowledge on the fate of MPs in aquatic environments.

Levels, spatial distribution, and source identification of airborne environmentally persistent free radicals from tree leaves

Environmentally persistent free radicals (EPFRs) are receiving increasing concern due to their toxicity and ubiquity in the environment. To avoid restrictions imposed when using a high-volume active sampler, this study uses tree leaves to act as passive samplers to investigate the spatial distribution characteristics and sources of airborne EPFRs. Tree leaf samples were collected from 120 sites in five areas around China (each approximately 4 km × 4 km). EPFR concentrations in particles (<2 μm) on the surface of 110 leaf samples were detected, ranging from 7.5 × 10¹⁶ to 4.5 × 10¹⁹ spins/g. For the 10 N.D. samples, they were all collected from areas inaccessible by vehicles. The g-values of EPFRs on 68% leaf samples were larger than 2.004, suggesting the electron localized on the oxygen atom, and they were consistent with the road dust sample (g-value: 2.0042). Significant positive correlation was found between concentrations of elemental carbon (tracer of vehicle emissions) and EPFRs. Spatial distribution mapping showed that EPFR levels in various land uses differed noticeably. Although previous work has linked atmospheric EPFRs to waste incineration, the evidence in this study suggests that vehicle emissions, especially from heavy-duty vehicles, are the main sources. While waste incinerators with low emissions or effective dust-control devices might not be an important EPFR contributor. According to our estimation, over 90% of the EPFRs deposited on tree leaves might be attributed to automotive exhaust emissions, as a synergistic effect of primary exhausts and degradation of aromatic compounds in road dust. With adding the trapping agent into the particle samples (<2 μm), signals of hydroxyl radicals were observed. This indicates that EPFRs collected from this phytosampling method can lead to the release of reactive oxygen species (ROS) once they are inhaled by human beings. Thus, this study helps highlight EPFR "hotspots" for potential health risk identification.

Occurrence, formation, environmental fate and risks of environmentally persistent free radicals in biochars

Biochars are used globally in agricultural crop production and environmental remediation. However, environmentally persistent free radicals (EPFRs), which are stable emerging pollutants, are generated as a characteristic feature during biomass pyrolysis. EPFRs can induce the formation of reactive oxygen species, which poses huge agro-environmental and human health risks. Their half-lives and persistence in both biochar residues and in the atmosphere may lead to potentially adverse risks in the environment. This review highlights the comprehensive research into these bioreactive radicals, as well as the bottlenecks of biochar production leading up to the formation and persistence of EPFRs. Additionally, a way forward has been proposed, based on two main recommendations. A global joint initiative to create an all-encompassing regulations policy document that will improve both the technological and the quality control aspects of biochars to reduce EPFR generation at the production level. Furthermore, environmental impact and risk assessment studies should be conducted in the extensive applications of biochars in order to protect the environmental and human health. The highlighted key research directions proposed herein will shape the production, research, and adoption aspects of biochars, which will mitigate the considerable concerns raised on EPFRs.

Interaction of benzo[a]pyrene with Cu(II)-montmorillonite: Generation and toxicity of environmentally persistent free radicals and reactive oxygen species

This paper presents the interaction of benzo[a]pyrene (B[a]P) with Cu(II)-montmorillonite to investigate the formation, evolution and potential toxicity of environmentally persistent free radicals (EPFRs) under dark and visible light irradiation conditions. Degradation of B[a]P and the generated transformative products on clay mineral are monitored by gas chromatography-mass spectrometry (GC-MS) technique. Hydroxyl-B[a]P and B[a]P-diones are observed during the transformation of B[a]P under dark condition. B[a]P-3,6-dione and B[a]P-6,12-dione are the main products under visible light irradiation. B[a]P transformation is accompanied by the formation of EPFRs, which are quantified by electron paramagnetic resonance (EPR) spectroscopy. With increasing reaction time, the concentrations of the produced EPFRs are initially increased and then gradually decrease to an undetectable level. The deconvolution results of EPR spectra reveal formation of three types of organic radicals (carbon-centered radicals, oxygen-centered radicals, and carbon-centered radicals with a conjugated oxygen), which also co-exist. Correspondingly, visible-light irradiation promotes the formation and the decay of these EPFRs. The produced B[a]P-type EPFRs induce the generation of reactive oxygen species (ROS), such as superoxide (O₂^-) and hydroxide radicals (OH), which may cause oxidative stress to cells and tissues of organisms. The toxicity of degradation products is evaluated by the livability of human gastric epithelial GES-1cells. The toxicity is initially increased and then decreases with the elapsed reaction time, which correlates with the evolution of EPFRs concentrations. The present work provides direct evidence that the formation of EPFRs in interaction of PAHs with metal-contaminated clays may result in negative effects to human health.

Role of Fe2O3 in fly ash surrogate on PCDD/Fs formation from 2-monochlorophenol

The correlation between the content and morphology of Fe₂O₃ and the yields of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) was studied in this work. Three fly ash surrogates containing 1%, 2.5%, and 4% of Fe₂O₃ were prepared and their effects on PCDD/Fs formation were investigated and compared to our previously studied 5% iron oxide sample using 2-monochlorophenol precursor model. As the intermediate of PCDD/Fs, environmentally persistent free radical formation propensity was correlated with the PCDD/Fs formation yields for different iron oxide samples. PCDD/Fs yield increases exponentially with the increasing iron content under pyrolytic conditions. On the contrary, low iron oxide content promotes oxidation and lowers yields of PCDD/Fs. Changing iron oxide clusters' morphology (crystallinity and cluster size) affects the mechanism of PCDD/Fs formation - on larger crystallites, a bidentate chemisorption of precursor is preferred leading to lower chlorinated congeners, while smaller clusters promote formation of PCDFs through mixed monodentate-bidentate surface species, resulting in formation of congeners with 1 chlorine more. This study further confirms the propensity of iron oxide to predominantly form PCDFs. The iron content also defines PCDDs:PCDFs ratio.

Characteristics of environmentally persistent free radicals in PM2.5: Concentrations, species and sources in Xi'an, Northwestern China

Environmentally persistent free radicals (EPFRs) are a new class of environmental risk substances that can stably exist in atmospheric particles and pose a potential threat to human health. In this study, electron paramagnetic resonance (EPR) spectroscopy was used to study the concentration levels, species characteristics, and sources of EPFRs in PM_2.5 in Xi'an in 2017. The results showed that the concentrations of EPFRs in PM_2.5 in Xi'an in 2017 ranged from 9.8 × 10¹¹ to 6.9 × 10¹⁴ spins/m³. The highest concentration of EPFRs occurred in winter when the average concentration was 2.1 × 10¹⁴ spins/m³. The lowest concentration of EPFRs occurred in autumn when the average concentration was 7.0 × 10¹³ spins/m³. According to the annual average atmospheric concentration of EPFRs, the amount of EPFRs inhaled by people in Xi'an is equivalent to approximately 5 cigarettes per person per day and approximately 23 cigarettes per person per day in winter when haze occurs. The results of the study on the EPFR characteristics show that the EPFRs in PM_2.5 in Xi'an are mainly C-center organic radicals that are primarily non-decaying types, accounting for approximately 75% and 85% of total concentration of EPFRs in autumn and winter, respectively. Finally, a correlation analysis was used to explore the origins of EPFRs in PM_2.5. Significant positive correlations were found between EPFRs and SO₂, NO₂ and the thermally derived OC3 and OC4 carbonaceous components. The results suggested that coal-fired and traffic may be important sources of EPFRs in PM_2.5 in Xi'an. In addition, EPFRs are significantly positively correlated with O₃ in summer, suggesting that some EPFRs may also originate from secondary processes. This study provides important basic data and evidence for further assessments of the potential health risks of EPFRs in PM_2.5 and the development of effective air pollution control measures.

Formation of environmentally persistent free radicals during the transformation of anthracene in different soils: Roles of soil characteristics and ambient conditions

Transformation of PAHs, i.e., anthracene, and production of environmentally persistent free radicals (EPFRs) on seven types of representative soils were investigated, focusing on the influences of soil characteristics and ambient conditions on these reactions. The transformation rate of anthracene exhibits the order of red earth > yellow earth > latosol ∼ fluvo-aquic soil > brown earth > chernozem > calcic brown soil, which is positively correlated with Fe content in soils. Afterwards, batch reactions on pure representatives of soil minerals, including Fe₂O₃, Fe₃O₄, FeOOH, and MnO₂, demonstrate that anthracene is prone to mineral-promoted transformation. The presence of higher amount of organic carbon lower the transformation rate of anthracene, whereas the formed EPFRs can be stabilized for a longer time. Subsequent experiments associated with the influences of environmental conditions on mineral-promoted reactions suggest that both anthracene transformation and EPFRs generation readily occur under dry condition. Light irradiation not only promotes the formation of EPFRs, but also greatly accelerates the decay of EPFRs and the 1/e lifetime decreases from 5 to 20 d in dark to approximately 1 d. Meanwhile, the anoxic condition is favorable for the persistence of EPFRs. The obtained results suggested the potential environmental risks association with EPFRs in PAHs-contaminated soils.

Catalytic degradation of the soil fumigant 1,3-dichloropropene in aqueous biochar slurry

Biochar has been explored as a cost-effective sorbent of contaminants, such as soil fumigant. However, contaminant-loaded biochar probably becomes a source of secondary air pollution. In this study, biochars developed from cow manure and rice husk at 300°C or 700°C were used to investigate the catalytic degradation of the soil fumigant 1,3-dichloropropene (1,3-D) in aqueous biochar slurry. Results showed that the adsorption of 1,3-D on the biochars was influenced by Langmuir surface monolayer adsorption. The maximum adsorption capacity of cow manure was greater than that of rice husk at the same pyrolysis temperature. Batch experiments revealed that 1,3-D degradation was improved in aqueous biochar slurry. The most rapid 1,3-D degradation occurred on cow manure-derived biochar produced at 300°C (C-300), with t1/2=3.47days. The degradation efficiency of 1,3-D on C-300 was 95.52%. Environmentally persistent free radicals (EPFRs) in biochars were detected via electron paramagnetic resonance (EPR) techniques. Dissolved organic matter (DOM) and hydroxyl radical (·OH) in biochars were detected by using a fluorescence spectrophotometer coupled with a terephthalic acid trapping method. The improvement of 1,3-D degradation efficiency may be attributed to EPFRs and DOM in aqueous biochar slurry. Our results may pose implications in the development of effective reduction strategies for soil fumigant emission with biochar.

Environmentally persistent free radical-containing particulate matter competitively inhibits metabolism by cytochrome P450 1A2

Combustion processes generate different types of particulate matter (PM) that can have deleterious effects on the pulmonary and cardiovascular systems. Environmentally persistent free radicals (EPFRs) represent a type of particulate matter that is generated after combustion of environmental wastes in the presence of redox-active metals and aromatic hydrocarbons. Cytochromes P450 (P450/CYP) are membrane-bound enzymes that are essential for the phase I metabolism of most lipophilic xenobiotics. The EPFR formed by chemisorption of 2-monochlorophenol to silica containing 5% copper oxide (MCP230) has been shown to generally inhibit the activities of different forms of P450s without affecting those of cytochrome P450 reductase and heme oxygenase-1. The mechanism of inhibition of rat liver microsomal CYP2D2 and purified rabbit CYP2B4 by MCP230 has been shown previously to be noncompetitive with respect to substrate. In this study, MCP230 was shown to competitively inhibit metabolism of 7-benzyl-4-trifluoromethylcoumarin and 7-ethoxyresorufin by the purified, reconstituted rabbit CYP1A2. MCP230 is at least 5- and 50-fold more potent as an inhibitor of CYP1A2 than silica containing 5% copper oxide and silica, respectively. Thus, even though PM generally inhibit multiple forms of P450, PM interacts differently with the forms of P450 resulting in different mechanisms of inhibition. P450s function as oligomeric complexes within the membrane. We also determined the mechanism by which PM inhibited metabolism by the mixed CYP1A2-CYP2B4 complex and found that the mechanism was purely competitive suggesting that the CYP2B4 is dramatically inhibited when bound to CYP1A2.