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Persulfate advanced oxidation technology is widely utilized for remediating organic-contaminated groundwater. Post-remediation by persulfate oxidation, the aromaticity of dissolved organic matter (DOM) in groundwater is significantly reduced. Nevertheless, the evolution trends of aromaticity and related structural changes in DOM remained unclear. Here, we selected eight types of DOM to analyze the variation in aromaticity, molecular weight, and fluorescence characteristics during oxidation by persulfate using optical spectroscopy and parallel faction analysis combined with two-dimensional correlation spectroscopy analysis (2D PARAFAC COS). The results showed diverse trends in the changes of aromaticity and maximum fluorescence intensity (Fmax) among different types of DOM as the reaction time increases. Four types of DOM (humic acid 1S104H, fulvic acid, and natural organic matters) exhibited an initially noteworthy increase in aromaticity followed by a decrease, while others demonstrated a continuous decreasing trend (14.3%-69.4%). The overall decreasing magnitude of DOM aromaticity follows the order of natural organic matters ≈ commercial humic acid > fulvic acid > extracted humic acid. The Fmax of humic acid increased, exception of commercial humic acid. The Fmax of fulvic acid initially decreased and then increased, while that of natural organic matters exhibited a decreasing trend (86.4%). The fulvic acid-like substance is the main controlling factor for the aromaticity and molecular weight of DOM during persulfate oxidation process. The oxidation sequence of fluorophores in DOM is as follows: fulvic-like substance, microbial-derived humic-like substance, humic-like substance, and aquatic humic-like substance. The fulvic-like and microbial-derived humic-like substances at longer excitation wavelengths were more sensitive to the response of persulfate oxidation than that of shorter excitation wavelengths. This result reveals the structure evolution of DOM during persulfate oxidation process and provides further support for predicting its environmental behavior.
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Many gastrointestinal simulation methods have been used to predict bioavailability, but the suitability of different methods for the same metal(loid)s varies widely, which inevitably affects the accuracy of human health risk assessment. Arsenic is a common and important contaminant in many contaminated land situations. It can be readily absorbed and has teratogenic and mutagenic toxicity. Therefore, in this study, four the most commonly used in vitro simulation methods (the Physiologically Based Extraction Test (PBET), In Vitro Gastrointestinal Method (IVG), Soluble Bioavailability Research Consortium (SBRC), the Unified BARGE Method (UBM)) were tested against an in vivo animal live model, to evaluate their effectiveness for the prediction of soil As bioavailability in 10 industrially contaminated soils. The soil As relative bioavailability (RBA) varied between 15% and 68% in the different soils. As bioaccessibility differed between the 4 gastro-intestinal simulation methods. Gastric phase of UBM (UBMG) predicted As relative bioavailability the best of the 4 assays (R2 = 0.81). This study provides theoretical and technical support to refine human health risk assessment of As in soils from urban industrial legacy contaminated sites.
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Arsênio , Poluentes do Solo , Animais , Humanos , Arsênio/análise , Solo , Disponibilidade Biológica , Poluentes do Solo/análise , Poluição AmbientalRESUMO
Iron in biochar composite loaded with Fe (Fex@biochar) is crucial for persulfate activation. However, the iron dosages-driven mechanism linked to the speciation, electrochemical property, and persulfate activation with Fex@biochar remains ambiguous. We synthesized and characterized a series of Fex@biochar and evaluated its catalytic performance in 2,4-dinitrotoluene removal experiments. With increasing FeCl3 dosage, iron speciation in Fex@biochar changed from γ-Fe2O3 to Fe3O4, and the variation in functional groups was as follows: Fe-O, aliphatic C-O-H, O-H, aliphatic C-H, aromatic CC or CO, and C-N. The electron accepting capacity of Fex@biochar increased as the FeCl3 dosage increased from 10 to 100 mM but decreased at 300 and 500 mM FeCl3. 2,4-dinitrotoluene removal first increased and subsequently decreased, reaching 100% in the persulfate/Fe100@biochar system. The Fe100@biochar also showed good stability and reusability for PS activation, verified by five test cycles. The mechanism analysis indicated that the iron dosage altered the Fe (⠢) content and electron accepting capacity of Fex@biochar during pyrolysis, further controlling persulfate activation and 2,4-dinitrotoluene removal. These results support the preparation of eco-friendly Fex@biochar catalysts.
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Poluentes Químicos da Água , Poluentes Químicos da Água/química , Ferro/química , Carvão Vegetal/químicaRESUMO
Risk assessment has been recognized as an important tool for evaluating heavy metal pollution and providing risk-based information for decision makers. In order to accurately assess the risk of heavy metals in contaminated soil to human health, it is necessary to conduct bioavailability studies on heavy metals in soil. Bioavailability of heavy metals in soils and the implications for risk assessment and land management/remediation has evolved over the decades and now has considerable practical and economic implications internationally. This article aims to explore its evolution by undertaking a bibliometric analysis of the research fields which have addressed heavy metal bioavailability in soils, with a focus on the risk assessment of contaminated land and human exposure to soil-borne metals. Bibliometric analysis techniques are applied to monitor and assess the changing research literature on the bioavailability of heavy metals in contaminated soils. Over 5000 articles were found for the period 1979-2020. The purpose was not to perform an exhaustive literature review, but to draw out trends and patterns in the literature, and to make observations on past and current priorities. Key words were extracted from the analysis and the roles of different countries in driving the research literature identified. Three phases in literature/subject development were identified. Between 1979 and 2000 (initial phase, 213 articles), studies used extraction procedures and solubility studies to investigate the roles of soil properties on metal form/speciation and focused on bioavailability to (crop) plants in agricultural soils. Between 2001 and 2010 (slow development phase, 1105 articles), attention switched to metals introduced in soil amendments and wastes, metal impacts on soil microbial processes, and incorporating bioavailability in risk assessment. More rigorous techniques were being used, such as the diffusive gradients in thin films technique, to better understand kinetic and metal speciation in soils and the quantitative relationship to bioavailability. By 2011-2020 (rapid development phase, 3137 articles), research was being conducted in many countries (site specific, often industrially contaminated and urban sites), with a focus shift to health risk assessment, remediation, and bioavailability to various ecological receptors (e.g., humans and animals), with the development of many methods of bioavailability (e.g., simulated gastrointestinal tract enzymolysis methods). Some priorities for research on soil heavy metal bioavailability are identified.
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Metais Pesados , Poluentes do Solo , Humanos , Disponibilidade Biológica , Poluentes do Solo/análise , Metais Pesados/análise , Medição de Risco , SoloRESUMO
Arsenic is a metalloid with carcinogenic properties and has been classified as a Category I carcinogen by the International Agency for Research on Cancer (IARC). Freeze-thaw processes affect the migration and transformation of soil heavy metals, as well as adsorption/desorption and redox reactions. However, there is limited research directly addressing the impact of freeze-thaw processes on the bioavailability of soil heavy metals. In this study, we focused on As and selected As-contaminated soil samples from three types of legacy sites in heavy industrial areas. Under controlled freeze-thaw experimental conditions, we utilized both in vivo and in vitro bioavailability measurement methods to investigate whether and how freeze-thaw processes affect the bioavailability of soil As. The results of this study showed that freeze-thaw processes reduced soil pH (P < 0.05), CEC, SOM, and particle size, with decreases of 0.33, 1.2 cmol/kg, 5.2 g/kg, and 54 µm, respectively. It also increased weight specific surface area (BET) (P < 0.05), with an increase of 300 m2/kg. Freeze-thaw processes increased the proportions of exchangeable (P < 0.05), carbonate-bound, and iron-manganese oxide-bound As (P < 0.05), but reduced the proportions of organic-bound and residual As (P < 0.05). Freeze-thaw processes significantly increased the relative bioavailability and bioaccessibility of As, with increases of 32 ± 9.6% and 13 ± 0.23%, respectively. Soil pH, SOM, BET and electronic conductivity (EC) were identified as factors which could contribute to the increased bioavailability of As due to freeze-thaw processes. These results provide new insights and evidence for refining the assessment of human health risks associated with heavy metal contamination in polluted soils.
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Arsênio , Metais Pesados , Poluentes do Solo , Humanos , Solo/química , Disponibilidade Biológica , Metais Pesados/análise , Ferro/análise , Poluentes do Solo/análiseRESUMO
Persulfate/Fe2+-based advanced oxidation processes are widely used to treat water contaminated with 2,4-dinitrotoluene (DNT). However, the oxidation of DNT by persulfate/Fe2+ in the presence of the chloride ion (Clâ») has not been addressed, and the transformation pathways and toxicities of the intermediate products remain unclear. In this study, the effect of different Clâ» concentrations on the oxidation of DNT was investigated by persulfate/Fe2+. After the addition of 1.0 mM Clâ» and 6 h of oxidation, the removal efficiency of DNT increased by 68.5%. Scavenging experiments and an electron spin resonance analysis suggested that Clâ» caused hydroxyl radicals to increase in content in the persulfate/Fe2+ system, thus promoting the removal of DNT. Eight intermediate products of DNT were accurately detected using high-resolution mass spectrometry, and the transformation pathways of DNT were proposed, including hydroxylation/oxidation, elimination of the nitro group, and chlorination process. The acute and chronic toxicities of the intermediate products decreased during the oxidation process, but chlorinated by-products posed a higher toxicological risk. This result is vital for the practical application and environmental safety evaluation of persulfate/Fe2+-based advanced oxidation.
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Cloretos , Poluentes Químicos da Água , Oxirredução , Dinitrobenzenos/toxicidade , Halogênios , Poluentes Químicos da Água/toxicidade , Poluentes Químicos da Água/química , Sulfatos/químicaRESUMO
In-situ thermal desorption (ISTD) has attracted increasing attention owing to the efficient removal of organic contaminants from contaminated sites. However, it is poorly understood that whether and to what extent contamination degradation occurs upon oxygenation of reduced Fe-bearing clay minerals (RFC) in the subsurface during ISTD. In this study, we evaluated the mechanism of contaminant degradation upon oxygenation of reduced clay minerals during the ISTD. Reduced nontronite (rNAu-2) and montmorillonite (rSWy-3) were selected as RFC models. Results showed that thermal treatment during ISTD could significantly enhance phenol degradation, which increased from 25.8 % at 10 °C to 74.4 % at 70 °C in rNAu-2 and from 17.7 % at 10 °C to 49.8 % at 70 °C in rSWy-3. Correspondingly, the cumulative â¢OH at steady-state ([â¢OH]ss) increased by 3.7 and 1.5 times, respectively. The acceleration of Fe(II) oxidation with increasing temperature could be mainly responsible for [â¢OH]ss generation, which degrades phenol. Moreover, thermal treatment improved the fast oxidation of trioctahedral entities Fe(II)Fe(II)Fe(II) (TOF) and the slow oxidation of dioctahedral entities Fe(II)Fe(II) (DTF1), AlFe(II) (DAF1), and Fe(II)Fe(III) (DTF2). Our study suggests that the overlooked degradation progress of phenol by oxygenation of RFC during ISTD, and it could be favorable for contaminant degradation during remediation.
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Radical Hidroxila , Fenol , Argila , Compostos Férricos , Fenóis , MineraisRESUMO
As global warming intensifies, there will be increased uncertainty as to the environmental behavior and risks from heavy metals in industrial/legacy contaminated sites in permafrost regions. Bioavailability has been increasingly used for human health risk assessment of heavy metals in contaminated soils. Soil heavy metal bioavailability depends on soil physicochemical properties, and freeze-thaw affects soil physical, chemical and biological processes. However it is not clear whether freeze-thaw has an effect on the bioavailability of soil heavy metals. In this study, soils contaminated with Pb and As were collected from 10 industrial sites in northeast China. Extractability and bioavailability of soil Pb and As were determined by the Tessier sequential extraction method and four in vitro gastron-intestinal simulation methods under control and freeze-thaw treatments. The aims were: to compare the results of extraction and bioavailability from laboratory experiments which artificially simulate freeze-thaw conditions against control soils; to explore the correlation between bioavailability of Pb/As and soil properties. Freeze-thaw significantly decreased soil pH, and increased the soil weight surface area. Freeze-thaw decreased the percentage in the residual fraction, and increased the percentage of Pb and As in the exchangeable fraction, carbonate-bound fraction, Fe-Mn oxides-bound fraction and organic-bound fraction, relative to control soils. Freeze-thaw significantly increased Pb and As bioavailability compared to the controls. Pb and As released in the gastric phase of the four methods was significantly higher than that in the intestinal phase. Further analysis of correlations between Pb and As bioavailability and soil properties indicated that total concentrations of Al, Fe and Mn, particle size, and weight surface area significantly correlated to Pb and As bioavailability. Overall, this study demonstrated that freeze-thaw did influence the bioavailability of soil heavy metals. It suggests the freeze-thaw action should be comprehensively considered in the human risk assessment of soil pollutants in permafrost regions.
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Metais Pesados , Poluentes do Solo , Humanos , Chumbo/análise , Disponibilidade Biológica , Poluição Ambiental/análise , Metais Pesados/análise , Solo/química , Poluentes do Solo/análiseRESUMO
BACKGROUND: Olfactory decline is an indicator of early-stage Alzheimer's disease (AD). Although the anterior piriform cortex (aPC) is an important brain area involved in processing olfactory input, little is known about how its neuronal activity is affected in early-stage AD. OBJECTIVE: To elucidate whether odor-induced electrophysiological responses are altered in the aPC of 3-5-month-old APP/PS1 mice. METHODS: Using head-fixed multi-channel recording techniques in APP/PS1 AD mouse model to uncover potential aberrance of the aPC neuronal firing and local field potential (LFP) in response to vanillin. RESULTS: We show that the firing rate of aPC neurons evoked by vanillin is significantly reduced in conscious APP/PS1 mice. LFP analysis demonstrates reduced low- and high-gamma (γlow,γhigh) oscillations during both the baseline and odor stimulation periods in APP/PS1 mice. Moreover, according to spike-field coherence (SFC) analysis, APP/PS1 mice show decreased coherence between odor-evoked spikes and γlow rhythms, while the coherence with γhigh rhythms and the ΔSFC of the oscillations is unaffected. Furthermore, APP/PS1 mice show reduced phase-locking strength in the baseline period, such that there is no difference between baseline and odor-stimulation conditions. This contrasts markedly with wild type mice, where phase-locking strength decreases on stimulation. CONCLUSION: The abnormalities in both the neuronal and oscillatory activities of the aPC may serve as electrophysiological indicators of underlying olfactory decline in early AD.
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Doença de Alzheimer , Córtex Piriforme , Animais , Camundongos , Odorantes , Camundongos Transgênicos , Doença de Alzheimer/genética , Modelos Animais de Doenças , Precursor de Proteína beta-Amiloide/genética , Precursor de Proteína beta-Amiloide/metabolismo , Presenilina-1/genética , Presenilina-1/metabolismoRESUMO
Understanding the influence of soil microstructure on light non-aqueous phase liquids (LNAPLs) behavior is critical for predicting the formation of residual LNAPLs under spill condition. However, the roles of soil particle and pore on LNAPLs migration and residue remains unclear. Here, the experiment simulated an LNAPLs (diesel) spill that was performed in fourteen types of soils, and the key factors affecting diesel behavior are revealed. There were significant differences between fourteen types of soils, with regard to the soil particle, soil pore, and diesel migration and residue. After 72 h of leakage, the migration distance of diesel ranged from 3.42 cm to 8.82 cm in the soils. Except for sandy soil, diesel was mainly distributed in the 0−3 cm soil layer, and the residual amounts were 7.85−26.66 g/kg. It was further confirmed from microstructure that the consistency of soil particle and volume of soil macropores (0.05−7.5 µm) are important for diesel residue in the 0−1 cm soil layer and migration distance. The large soil particles corresponding to 90% of volume fraction and volume of soil mesopores (<0.05 µm) are key factors affecting diesel residue in the 1−3 cm soil layer. The result helps to further comprehend the formation mechanism of residual LNAPLs in the soil.
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Weathered petroleum-contaminated soil (WPCS) with a high proportion of heavy hydrocarbons is difficult to remediate. Our previous research demonstrated that Fe2O3-assisted pyrolysis was a cost-effective technology for the remediation of WPCS. However, the pyrolysis behaviors, products, and mechanisms of the WPCS with Fe2O3 are still unclear. In this study, a combination of Thermogravimetric-Fourier transform infrared spectroscopy (TG-FTIR) and pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) techniques were used to explore these pyrolysis characteristics. The thermal desorption/degradation of light and heavy hydrocarbons in the WPCS mainly occurred at 200-400 °C and 400-550 °C, respectively. The activation energy of thermal reaction of heavy hydrocarbons was decreased in the presence of Fe2O3 during the WPCS pyrolysis processes. In the process, the released inorganic gaseous products were mainly H2O and CO2, while the released organic gaseous compounds were primarily cycloalkanes, alkanes, acids/esters, alcohols, and aldehydes. Compared with the WPCS pyrolysis without Fe2O3, the yields of gaseous products released during the WPCS pyrolysis with Fe2O3 were reduced significantly, and some gaseous products were even not detected. This phenomenon was contributed by the following two reasons: 1) heavy hydrocarbons in the WPCS were more easily transformed into coke in the presence of Fe2O3 during pyrolysis; 2) some released gaseous products were reacted with Fe2O3 and fixed on the soil particles. Therefore, the WPCS pyrolysis with Fe2O3 can effectively reduce the burden of tail gas treatment. Criado method analysis results suggested that the reaction mechanism of heavy hydrocarbons during the WPCS pyrolysis with Fe2O3 was rendered as the synergic effects of diffusion, order-based, and random nucleation and growth reactions.