Environmentally Persistent Free Radicals Research Articles

Comparative 6+studies of environmentally persistent free radicals on nano-sized coal dusts

Coal dust is the major hazardous pollutant in the coal mining environment. Recently environmentally persistent free radicals (EPFRs) were identified as one of the key characteristics which could impart toxicity to the particulates released into the environment. The present study used Electron Paramagnetic Resonance (EPR) spectroscopy to analyze the characteristics of EPFRs present in different types of nano-size coal dust. Further, it analyzed the stability of the free radicals in the respirable nano-size coal dust and compared their characteristics in terms of EPR parameters (spin counts and g-values). It was found that free radicals in coal are remarkably stable (can remain intact for several months). Also, Most of the EPFRs in the coal dust particles are either oxygenated carbon centered or a mixture of carbon and oxygen-centered free radicals. EPFRs concentration in the coal dust was found to be proportional to the carbon content of coal. The characteristic g-values were found to be inversely related to the carbon content of coal dust. The spin concentrations in the lignite coal dust were between 3.819 and 7.089 μmol/g, whereas the g-values ranged from 2.00352 to 2.00363. The spin concentrations in the bituminous coal dust were between 11.614 and 25.562 μmol/g, whereas the g-values ranged from 2.00295 to 2.00319. The characteristics of EPFRs present in coal dust identified by this study are similar to the EPFRs, which were found in other environmental pollutants such as combustion-generated particulates, PM2.5, indoor dust, wildfires, biochar, haze etc., in some of the previous studies. Considering the toxicity analysis of environmental particulates containing EPFRs similar to those identified in the present study, it can be confidently hypothesized that the EPFRs in the coal dust might play a major role in modulating the coal dust toxicity. Hence, it is recommended that future studies should analyze the role of EPFR-loaded coal dust in mediating the inhalation toxicity of coal dust.

Enhanced Formation of 6PPD-Q during the Aging of Tire Wear Particles in Anaerobic Flooded Soils: The Role of Iron Reduction and Environmentally Persistent Free Radicals.

Rapid urbanization drives increased emission of tire wear particles (TWPs) and the contamination of a transformation product derived from tire antioxidant, termed as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q), with adverse implications for terrestrial ecosystems and human health. However, whether and how 6PPD-Q could be formed during the aging of TWPs in soils remains poorly understood. Here, we examine the accumulation and formation mechanisms of 6PPD-Q during the aging of TWPs in soils. Our results showed that biodegradation predominated the fate of 6PPD-Q in soils, whereas anaerobic flooded conditions were conducive to the 6PPD-Q formation and thus resulted in a ∼3.8-fold higher accumulation of 6PPD-Q in flooded soils than wet soils after aging of 60 days. The 6PPD-Q formation in flooded soils was enhanced by Fe reduction-coupled 6PPD oxidation in the first 30 days, while the transformation of TWP-harbored environmentally persistent free radicals (EPFRs) to superoxide radicals (O2•-) under anaerobic flooded conditions further dominated the formation of 6PPD-Q in the next 30 days. This study provides significant insight into understanding the aging behavior of TWPs and highlights an urgent need to assess the ecological risk of 6PPD-Q in soils.

Formation of environmentally persistent free radicals on microplastics under UV irradiations

Microplastics (MPs) are widely distributed in the environment due to breakdown of widespread plastic wastes through physicochemical and biological processes. Environmentally persistent free radicals (EPFRs) might be generated as intermediates when MPs are further fragmented and decomposed under ultraviolet (UV) radiation. Formation of EPFRs is highly depended upon the radiation energy level. This study was designed to establish the correlation between EPFRs concentrations and UV energy. Polystyrene (PS) and polyethylene (PE) were employed to investigate the generation of EPFRs under the irradiation of three ultraviolet light sources (long-wave UVA, medium-wave UVB and short-wave UVC). Electron paramagnetic resonance (EPR) spectroscopy revealed that free radical signals were detected on PS irradiated by UVC and UVB and PE irradiated by UVC, which may be due to the difference in the MPs structure and UV energy. The g-factor and ΔHp-p of EPR suggested that three different types of EPFRs may be formed on PS while two types of EPFR may be formed on PE. Meanwhile, EPFRs were detected within shorter time under UVC radiation than UVB and UVA, indicating that UVC radiation could lead to faster generation of free radicals. Results of Fourier transform infrared spectroscopy (FTIR) and two-dimensional correlation spectroscopy revealed that tertiary alkyl radicals, peroxy radicals and tertiary alkoxy radicals were dominant in PS whereas alkoxy radicals and keto radicals for PE. The study provides insight to the mechanisms for EPFRs formation on ubiquitously found microplastic particles. Our finding is of great significance as EPFRs may not only play important roles in decomposition of MPs and abiotic reactions of MPs-bound pollutants, but also affect physicochemical properties of MPs and MPs toxicity to aquatic organisms, hence possessing broad impacts on MPs fate and transport in aquatic environmental systems.

The generation of environmentally persistent free radicals on photoaged microbeads from cosmetics enhances the toxicity via oxidative stress

Microbeads used in personal care products have been one of the important sources of microplastics (MPs), and little has been reported on their environmental behaviors and health risks. The characteristics of environmentally persistent free radicals (EPFRs) and the toxicity assessment of MPs (environmentally relevant concentrations) from cosmetics during photoaging remains largely unknown. In this study, the formation of EPFRs on polyethylene (PE) microbeads from facial scrubs under light irradiation and their toxicity were investigated using C. elegans as a model organism. The results suggested that light irradiation induced the generation of EPFRs, which accelerates the aging process and alters the physicochemical properties of PE microbeads. Acute exposure to PE (1 mg/L) at photoaged times of 45–60 d significantly decreased the physiological indicators (e.g., head thrashes, body bends, and brood size). The oxidative stress response and stress-related gene expression were also enhanced in nematodes. The addition of N-acetyl-l-cysteine induced significant inhibition of toxicity and oxidative stress in nematodes exposed to 45–60 d of photoaged PE. The Pearson correlation results showed that the concentration of EPFRs was significantly correlated with physiological indicators, oxidative stress, and related-genes expression in nematodes. The data confirmed that the generation of EPFRs combined with heavy metals and organics contributed to toxicity induced by photoaged PE, and oxidative stress might be involved in regulating adverse effects in C. elegans. The study provides new insight into the potential risks of microbeads released into the environment during photoaging. The findings also highlight the necessity for considering the role of EPFRs formation in evaluating the impacts of microbeads.

Biochar Extracts Can Modulate the Toxicity of Persistent Free Radicals in the Nematode Caenorhabditis elegans

As an effective soil amendment, biochars require a comprehensive ecological evaluation before they can be widely used in agriculture because endogenous contaminants, such as environmentally persistent free radicals (EPFRs), certainly pose an ecological risk to soil invertebrates. In this study, Caenorhabditis elegans (C. elegans) was used as a model organism to investigate the neurotoxicity of two rice straw biochars pyrolyzed at 500 and 700 °C. After 24 h exposure to unwashed biochar, washed biochar, and leaching fluids (supernatants), the neurobehavioral parameters of C. elegans were determined in a liquid toxicity test. The results showed that the washed 700 °C biochar particles significantly impaired locomotion and prolonged the defecation interval at a biochar concentration of 4 g·well−1, while the unwashed biochar and supernatants caused no apparent impairment. Supporting this, electron paramagnetic resonance (EPR) results showed that the intensity of EPFRs in unwashed 700 °C biochar was stronger than that of the corresponding washed particles. This indicates that, in the liquid test, the EPR signal alone is not indicative of particle toxicity. The accessibility and activity of the EPFRs should be considered. Dissolved organic matter (DOM) was observed in the leaching fluids. The neurotoxic activity of the washed biochar was alleviated after the re-addition of leaching fluids to the washed biochar, suggesting that the dissolved organic materials modulate the reactivity of the EPFRs in the liquid phase. This study suggests that the leaching process may increase the risk of biochar when used in the field environment.

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.

Distribution of environmentally persistent free radicals in size-segregated PMs emitted from residential biomass fuel combustion

Environmentally persistent free radicals (EPFRs) are considered as an emerging pollutant due to their potential environmental risks, but the distribution characteristics of particulate matters (PMs)-EPFRs from residential combustion source are poorly understood. In this study, biomass (corn straw, rice straw, pine and jujube wood) combustion was studied in lab-controlled experiments. More than 80% of PM-EPFRs were distributed in PMs with aerodynamic diameter (dae) ≤ 2.1 µm, and their concentration in fine PMs was about 10 times that in coarse PM (2.1 µm ≤ dae ≤ 10 µm). The detected EPFRs were carbon-centered free radicals adjacent to oxygen atoms or a mixture of oxygen- and carbon-centered radicals. The concentrations of EPFRs in coarse and fine PMs were positively correlated with char-EC, but the EPFRs in fine PMs exhibited a negative correlation with soot-EC (p < 0.05). The increase of PM-EPFRs signals with the increased dilution ratio during pine wood combustion was more significant than that from rice straw, which may be resulted from the interactions between the condensable volatiles and the transition metals. Our study provides useful information for better understanding the formation of combustion-derived PM-EPFRs, and will be instructive for its purposeful emissions control.

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 0.56-1.0µm particles during heating season, while it shifted to 5.6-10µm 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.

Characteristics and Risk Assessment of Environmentally Persistent Free Radicals (EPFRs) of PM2.5 in Lahore, Pakistan.

Environmentally persistent free radicals (EPFRs) are an emerging pollutant and source of oxidative stress. Samples of PM2.5 were collected at the urban sites of Lahore in both winter and summertime of 2019. The chemical composition of PM2.5, EPRF concentration, OH radical generation, and risk assessment of EPFRs in PM2.5 were evaluated. The average concentration of PM2.5 in wintertime and summertime in Lahore is 15 and 4.6 times higher than the national environmental quality standards (NEQS) of Pakistan and WHO. The dominant components of PM2.5 are carbonaceous species. The concentration of EPFRs and reactive oxygen species (ROS), such as OH radicals, is higher in the winter than in the summertime. The secondary inorganic ions do not contribute to the generation of OH radicals, although the contribution of SO42+, NO3-, and NH4+ to the mass concentration of PM2.5 is greater in summertime. The atmospheric EPFRs are used to evaluate the exposure risk. The EPFRs in PM2.5 and cigarette smoke have shown similar toxicity to humans. In winter and summer, the residents of Lahore inhaled the amount of EPFRs equivalent to 4.0 and 0.6 cigarettes per person per day, respectively. Compared to Joaquin County, USA, the residents of Lahore are 1.8 to 14.5 times more exposed to EPFRs in summer and wintertime. The correlation analysis of atmospheric EPFRs (spin/m3) and carbonaceous species of PM2.5 indicates that coal combustion, biomass burning, and vehicle emissions are the possible sources of EPFRs in the winter and summertime. In both winter and summertime, metallic and carbonaceous species correlated well with OH radical generation, suggesting that vehicular emissions, coal combustion, and industrial emissions contributed to the OH radical generation. The study's findings provide valuable information and data for evaluating the potential health effects of EPFRs in South Asia and implementing effective air pollution control strategies.

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) (OPDTT). 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.

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.

Environmentally persistent free radicals enhance SARS-CoV-2 replication in respiratory epithelium.

Epidemiological evidence links lower air quality with increased incidence and severity of COVID-19; however, mechanistic data have yet to be published. We hypothesized air pollution-induced oxidative stress in the nasal epithelium increased viral replication and inflammation. Nasal epithelial cells (NECs), collected from healthy adults, were grown into a fully differentiated epithelium. NECs were infected with the ancestral strain of SARS-CoV-2. An oxidant combustion by-product found in air pollution, the environmentally persistent free radical (EPFR) DCB230, was used to mimic pollution exposure four hours prior to infection. Some wells were pretreated with antioxidant, astaxanthin, for 24 hours prior to EPFR-DCB230 exposure and/or SARS-CoV-2 infection. Outcomes included viral replication, epithelial integrity, surface receptor expression (ACE2, TMPRSS2), cytokine mRNA expression (TNF-α, IFN-β), intracellular signaling pathways, and oxidative defense enzymes. SARS-CoV-2 infection induced a mild phenotype in NECs, with some cell death, upregulation of the antiviral cytokine IFN-β, but had little effect on intracellular pathways or oxidative defense enzymes. Prior exposure to EPFR-DCB230 increased SARS-CoV-2 replication, upregulated TMPRSS2 expression, increased secretion of the proinflammatory cytokine TNF-α, inhibited expression of the mucus producing MUC5AC gene, upregulated expression of p21 (apoptosis pathway), PINK1 (mitophagy pathway), and reduced levels of antioxidant enzymes. Pretreatment with astaxanthin reduced SARS-CoV-2 replication, downregulated ACE2 expression, and prevented most, but not all EPFR-DCB230 effects. Our data suggest that oxidant damage to the respiratory epithelium may underly the link between poor air quality and increased COVID-19. The apparent protection by antioxidants warrants further research.

Pollution characteristics of environmental persistent free radicals (EPFRs) and their contribution to oxidation potential in road dust in a large city in northwest China.

Environmental persistent free radicals (EPFRs) are new environmental health risk substances in the atmosphere, and their oxidative toxicity (OT) has not been strongly confirmed. In this study, the fugitive characteristics of EPFRs in road dust in a metropolitan city located in northwest China, and their potential oxidative toxicity were investigated. The results showed that the road dust contains Carbon-centered EPFRs with the mean mass concentration of (6.6±5.0) ×1017 spins/g. EPFRs in road dust are degradable and have a half-life of 4.5 years. The water insoluble (WIS) components contribute 71% to the oxidative toxicity of road dust and show a rapid toxicity generation process, while the oxidative toxicity generation rate of water-soluble dust is more stable. Based on the positive matrix factorization (PMF) model, the contribution of EPFRs-dominated factors to Total-OT and WIS-OT is 17.3% and 33.3%, respectively. The PMF model results indicated that different types of EPFRs contributed differently to the oxidative toxicity of road dust and Carbon-centered EPFRs are more likely to participate in reactive oxygen species generation. Our results highlight that the EPFRs are an important contributor to the oxidative toxicity of atmospheric particulate matter, and their oxidative toxicity is dependent on the types of free radicals. It also provides an important insight into the influence of other potentially toxic substances on the oxidative toxicity of atmospheric PM.

Insights into the formation of environmentally persistent free radicals during photocatalytic degradation processes of ceftriaxone sodium by ZnO/ZnIn2S4

At present, the researches on photocatalysis were mainly focused on the design, improvement and development of catalysts, and less attention was paid to the existing characteristics of environmentally persistent free radicals (EPFRs) during the process of photocatalytic oxidation. In this study, A flower-like Z-type heterojunction ZnO/ZnIn2S4 (ZnO/ZIS) and typical antibiotic ceftriaxone sodium (CS) were taken as study objects, concentrating on the generation characteristics of EPFRs during the degradation of CS by ZnO/ZIS, and clarifying the degradation mechanism of CS in which EPFRs participated. The results showed that the degradation efficiency of 10 mg/L CS by 0.40 g/L ZnO/ZIS reached 85.3% in 150 min under the irradiation of 500 W xenon lamp. It was clear that ·O2− and h+ play major roles in CS degradation by ZnO/ZIS under visible light, and ·OH plays an auxiliary role. Furthermore, the formation mechanism of EPFRs during photocatalytic degradation processes of CS by ZnO/ZIS were first investigated thoroughly via experimental analysis and density functional theory (DFT) calculations. The concentration level of EPFRs centered on oxygen atoms is 1011 spin/mm3, which were generated in the process of degradation of CS by ZnO/ZIS under visible light. The production of EPFRs chiefly includes two procedures: chemical adsorption and transfer of electrons. The adsorption energy of precursor P8 on ZnIn2S4 side is −1.91 eV, the electrons transferred from precursor P8 and P11 to ZnO/ZnIn2S4 heterojunction. Surprisingly, EPFRs have little negative effects on the degradation process of CS by ZnO/ZIS. The study was not only a key field in the development of photocatalysis technology, but also a new way to study the removal mechanism of antibiotics.

Ecotoxicological characterization of engineered biochars produced from different feedstock and temperatures

Biochar (BC) engineering, which has recently gained a lot of interest, allows designing the functional materials. BC modification improves the properties of pristine biochar, especially in terms of adsorption parameters. An interesting type of modification is the introduction of metals into the BC's structure. There is a knowledge gap regarding the effects of modified BC (e.g., BC-Mg, BC-Zn) on organisms. The aim of this study was the ecotoxicological evaluation of BC-Mg and BC-Zn composites, received under diverse conditions from willow or sewage sludge at 500 or 700 °C. The ecotoxicological tests with bacteria Vibrio fischeri (V. fischeri) and invertebrates Folsomia candida (F. candida) were applied to determine the toxicity of BC. The content of toxic substances (e.g., polycyclic aromatic hydrocarbons (PAHs), heavy metals (HMs), environmentally persistent free radicals (EPFRs)) in BC were also determined and compared with ecotoxicological parameters. The ecotoxicity of studied BCs depends on many variables: feedstock type, pyrolysis temperature and the modification type. The Zn and Mg modification reduced (from 28 to 63 %) the total Ʃ16 PAHs content in willow-derived BCs while in SL-derived BCs the total Ʃ16 PAHs content was even 1.5–3 times higher compared to pristine BCs. The Zn modified willow-derived BCs affected positively on F. candida reproduction but showed inhibition of luminescence V. fischeri. BC-Mg exhibited harmful effect to F. candida. The ecotoxicological assessment carried out sheds light on the potential toxicity of BC-Zn and BC-Mg composites, which are widely used in the removal of heavy metals, pharmaceuticals, dyes from waters and soils.

The overlooked formation of environmentally persistent free radicals on particulate matter collected from biomass burning under light irradiation

BackgroundThe illumination process may be an important contributor to environmentally persistent free radicals (EPFRs) in atmospheric particles, but the ability of light to generate EPFRs in combustion products remains unclear. ObjectiveThis paper studies the characteristics and formation mechanism of EPFRs in combustion particles after photoexcitation. MethodThe secondary photochemical processes and the generation and decay capability of EPFRs in size-resolved (<10 µm) biomass combustion particles were analysed by electron paramagnetic resonance (EPR) spectroscopy. ResultOur results indicated that secondary EPFRs can be generated after illumination and the produced EPFRs have a lifetime of approximately 1 day. The content of secondary EPFRs after light exposure increased by 20 %–30 % compared to that of the original EPFRs. Through the analysis of components of different polarities, it was found that non-extractable substances were the main contributors to secondary EPFRs (75 %), followed by extractable organics. This study showed that metal species and quinones are important precursors for the formation of secondary EPFRs from non-extractable and extractable PM components, respectively. We found that O2 molecules are an important factor for the formation of secondary EPFRs from organic substances without oxygen functional groups. ConclusionsThis study presents information about the effects of light and O2 on the generation of EPFRs, and the unstable nature of secondary EPFRs has important implications for assessing the health risks of atmospheric particles.

Toxic effects and primary source of the aged micro-sized artificial turf fragments and rubber particles: Comparative studies on laboratory photoaging and actual field sampling

Numerous micro-sized artificial turf fragments (MATF) and rubber particles (MRP) are generated and accumulated during the use of the artificial playing field. However, attention has rarely been paid to the potential toxic effects of MATF and MRP on sportsmen. In this study, the active components and chemical composition of aged MATF and MRP derived from laboratory photoaging and actual field sampling were detected, and their effects on cytotoxicity were examined correspondingly. Laboratory photoaging significantly increased environmental persistent free radicals (EPFRs), reactive oxygen species (ROS) abundances and oxidative potential (OP) levels on MATF and MRP, but they have limited cytotoxicity. Unfortunately, in the actual field, aged MATF and MRP with higher heavy metals and polycyclic aromatic hydrocarbons (PAHs) contents exhibited markedly higher cytotoxicity with the survival rate of cells of 78 % and 26 % (p < 0.05), although they had lower EPFRs and ROS yields. Correlation analysis revealed that the cell viability was closely linked to heavy metals of MATF (p < 0.05), and to organic hydroperoxide (OHP), PAHs and heavy metals of MRP (p < 0.05). By systematically considering the above results, heavy metals and PAHs enriched on MATF and MRP from the surrounding environment played the important role in the cytotoxicity, which was different from conventional perspectives. Our findings demonstrate that MATF and MRP associated with an artificial turf field contain potent mixtures of pollutants and can, therefore, be relevant yet underestimated factors contributing to the health risks.

Aging Process of Microplastics in the Aquatic Environments: Aging Pathway, Characteristic Change, Compound Effect, and Environmentally Persistent Free Radicals Formation

Plastic wastes are becoming one of the most serious environmental pollutants because of their high antidegradation properties and the damage they cause to human health. More seriously, plastics can become smaller in size and form microplastics (MPs), attributing to the oxidation, weathering, and fragmentation processes. The influx of MPs into water bodies seriously affects the quality of the aquatic environment. Therefore, it is necessary to summarize the aging process of MPs. In this review, we first provided an overview of the definition and source of MPs. Then we analyzed the potential aging pathways of MPs in the current aquatic environment and elaborated on the changes in the physicochemical properties of MPs during the aging process (e.g., particle size, crystallinity, thermodynamic properties, and surface functional groups). In addition, the possible synergistic contamination of MPs with other pollutants in the environment is illustrated. Finally, the mechanisms of generation and toxicity of environmental persistent free radicals (EPFRs) that may be generated during the photoaging of MPs were described, and the feasibility of using photoaged MPs as photosensitizers to catalyze photoreactive degradation of organic pollutants is proposed. Overall, this review provides a comprehensive and objective evaluation of the behavior of MPs in the aquatic environment.

Impact of biochar, fertilizers and cultivation type on environmentally persistent free radicals in agricultural soil.

Environmentally persistent free radicals (EPFRs) have been considered as emerging contaminants due to their detrimental effects on human health. The adverse health impacts are attributed to oxidative stress induced by EPFRs through the formation of reactive oxygen species (ROS). In soils, it may also increase the degradation process of polymeric organic matter and/or undesired organic pollutants through hydroxyl radical activity. The biochar pyrolysis process entails the thermal decomposition of organic compounds in the biomass, with the carbonization conditions and feedstock type facilitating the formation of EPFRs. When biochar is used to amend soil, these radicals may promote the formation of ROS, and thus influence the transformation of organic and inorganic contaminants in soil and impact the rhizosphere. Agricultural soils are being amended with biochar to mainly increase carbon content and facilitate the plant growing conditions. Therefore, agricultural soils may become a source of EPFRs. However, the fate and transformations of EPFRs in soils after biochar amendment are not well understood or studied. This paper presents the first (to our knowledge) studies of EPFRs behaviour in agricultural soil with different input of biochar, cultivation types and residence time period. Different cultivation types, addition of fertilisers and variation in biochar input, on the one hand, and presence of metals in soil, biochar and fertilizers, on the other hand, provide different conditions for EPFRs formation, accumulation and fate in agricultural soils. Two significant factors have been found to determine the fate of EPFRs in soil: transition metal content (particularly those in reaction available form) and cultivation level of soil. Cultivation significantly decreased presence of EPFRs, both carbon-centered and oxygen-centered, in relatively short periods of time, while metal presence (and particularly through fertilizer supplementation) increases the half-life of radicals and transforms organic matter to more oxygen-centered EPFRs. The amount of biochar addition plays a secondary role as the EPFRs content in the soils is in a longer term primarily controlled by the other two factors.

Formation and regulation of environmentally persistent free radicals in biochar and removal of diethyl-phthalate in water

Biochar contains environmentally persistent free radicals (EPFRs), a class of pollutants whose regulation and influencing factors need to be studied. In this study, electron paramagnetic resonance (EPR) signals were observed for biochar samples obtained by the pyrolysis of wheat straw, corn straw, peanut shell, and cotton stalk. The effects of pyrolysis temperature, residence time, and alkali/alkaline earth metals (AAEMs) on EPFRs in biochar were investigated. The adsorption effect of diethyl phthalate (DEP) on biochar obtained from the pyrolysis of wheat straw impregnated with K, Na, Ca, and Mg was also studied. The concentration of EPFRs increased first and then decreased upon increasing the pyrolysis temperature within the rage of 300–700 ℃, conforming to a Gaussian fit. Residence time experiments showed that the concentration of EPFRs was the highest at a residence time of 10 min. The effect of AAEMs on the EPFRs concentration followed the order Mg > K > Ca > Na due to the catalysis of a secondary reaction. Because of hole-filling and electrostatic attraction, biochar obtained by pyrolysis of wheat straw impregnated with MgCl2 (WSMg) had the highest DEP removal rate of 95.969%. DEP removal efficiency of the five adsorbents followed the order WSMg > WSCa (88.701%) > WS (68.867%) > WSNa (53.852%) > WSK (50.845%). Hydroxyl radicals (•OH) signals were detected in these five adsorption systems, showing that EPFRs could activated H2O2 to produce •OH. However, the five •OH signals had similar intensities, indicating that AAEMs had not significantly effects on the process of activation of H2O2 to produce •OH by EPFRs. The results of this study are of great significance for understanding the formation and regulation of EPFRs and the utilization of biochar.