RESUMO
Manganese oxides reduce arsenic (As) toxicity by promoting aqueous-phase As(III) oxidation and immobilization in natural aquatic ecosystems. In anaerobic water-sediment systems, arsenic exists both in a free state in the liquid phase and in an adsorbed state on iron (Fe) minerals. However, the influence of different manganese oxides on the fate of As in this system remains unclear. Therefore, in this study, we constructed an anaerobic microbial As(V) reduction environment and investigated the effects of three different manganese oxides on the fate of both aqueous-phase and goethite-adsorbed As under different pH conditions. The results showed that δ-MnO2 had a superior As(III) oxidation ability in both aqueous and solid phase due not only to the higher SSA, but also to its wrinkled crystalline morphology, less favorable structure for bacterial reduction, structure conducive to ion exchange, and less interference caused by the formation of secondary Fe-minerals compared to α-MnO2 and γ-MnO2. Regarding aqueous-phase As, δ-MnO2, α-MnO2, and γ-MnO2 required an alkaline condition (pH 9) to exhibit their strongest As(III) oxidation and immobilization capability. For goethite-adsorbed As, under microbial-reducing conditions, all manganese oxides had the highest As immobilization effect in neutral pH environments and the strongest As oxidation effect in alkaline environments. This was because at pH 7, Fe(II) and Mn(II) formed hydrated complexes, which was more favorable for As adsorption. At pH 9, the negatively charged state of goethite hindered As adsorption but promoted the adsorption and oxidation of As by the manganese oxides. Our research offers new insights for optimizing As removal from water using various manganese oxides and for controlling the mobilization of As in water-sediment system under different pH conditions.
Assuntos
Arsênio , Compostos de Ferro , Compostos de Manganês , Minerais , Oxirredução , Óxidos , Óxidos/química , Compostos de Manganês/química , Concentração de Íons de Hidrogênio , Arsênio/química , Arsênio/metabolismo , Minerais/química , Compostos de Ferro/química , Arseniatos/química , Adsorção , Poluentes Químicos da Água/químicaRESUMO
Stabilization of arsenic-contaminated soils with ferrous sulfate has been reported in many studies, but there are few stabilization effects assessments simultaneously combined chemical extraction methods and in vitro methods, and further explored the corresponding alternative relationships. In this study, ferrous sulfate was added at FeAs molar ratio of 0, 5, 10 and 20 to stabilize As in 10 As spiked soils. Stabilization effects were assessed by 6 chemical extraction methods (toxicity characteristic leaching procedures (TCLP), HCl, diethylenetriamine pentaacetic acid (DTPA), CaCl2, CH3COONH4, (NH4)2SO4), and 4 in vitro methods (physiologically based extraction test (PBET), in vitro gastrointestinal method (IVG), Solubility Bioaccessibility Research Consortium (SBRC) method, and the Unified Bioaccessibility Research Group of Europe method (UBM)). The results showed that the HCl method provides the most conservative assessment results in non-calcareous soils, and in alkaline calcareous soils, (NH4)2SO4 method provides a more conservative assessment. In vitro methods provided significantly higher As concentrations than chemical extraction methods. The components of the simulated digestion solution as well as the parameters may have contributed to this result. The small intestinal phase of PBET and SBRC method produced the highest and lowest ranges of As concentrations, and in the range of 127-462 mg/kg and 68-222 mg/kg when the FeAs molar ratio was 5. So the small intestinal phase of PBET method may provide the most conservative assessment results, while the same phase of SBRC may underestimate the human health risks of As in stabilized soil by 51 %(at a FeAs molar ratio of 5). Spearman correlation analysis indicated that the small intestinal phase of PBET method correlated best with HCl method (correlation coefficient: 0.71). This study provides ideas for the assessment of stabilization efforts to ensure that stabilization meets ecological needs while also being less harmful to humans.
Assuntos
Arsênio , Compostos Ferrosos , Poluentes do Solo , Humanos , Arsênio/análise , Poluentes do Solo/análise , Poluição Ambiental/análise , Solo , Disponibilidade BiológicaRESUMO
INFOGEST is a standardized in vitro digestion method suitable for foods, but rarely used to study the bioaccessibility of heavy metals in food. This study aimed to explore the differences between INFOGEST and the extensively used Physiologically Based Extraction Test (PBET) and Unified Bioaccessibility Research Group of Europe Method (UBM) methods for determining the bioaccessibility of As and Cd in rice. Intestinal As (79.3 ± 8.5 %, 75.8 ± 12.7 %, and 72.3 ± 12.2 % for INFOGEST, PBET, and UBM, respectively) and Cd (47.0 ± 6.4 %, 40.7 ± 13.8 %, and 38.1 ± 15.7 % for INFOGEST, PBET, and UBM, respectively) bioaccessibilities in the rice samples determined by the three methods were generally similar (p > 0.1, except for As bioaccessibility between INFOGEST and UBM). Furthermore, PBET was significantly correlated with INFOGEST for As bioaccessibility (R2 = 0.416) and with UBM for Cd bioaccessibility (R2 = 0.879). Additionally, PBET indicated that the bioaccessibilities of As and Cd in the polished rice were 17.0 % and 19.8 % higher, respectively, than that in the unpolished rice. This study highlights the influence of in vitro methods and rice matrices on heavy metal bioaccessibility values, necessitating a more accurate assessment of health risks associated with rice consumption.
Assuntos
Arsênio , Metais Pesados , Oryza , Cádmio , Disponibilidade BiológicaRESUMO
The annual microplastic (MP) release into soils is 4-23 times higher than that into oceans, significantly impacting soil quality. However, the mechanisms underlying how MPs impact soil properties remain largely unknown. Soil-MP interactions are complex because of soil heterogeneity and varying MP properties. This lack of understanding was exacerbated by the diverse experimental conditions and soil types used in this study. Predicting changes in soil properties in the presence of MPs is challenging, laborious, and time-consuming. To address these issues, machine learning was applied to fit datasets from peer-reviewed publications to predict and interpret how MPs influence soil properties, including pH, dissolved organic carbon (DOC), total P, NO3--N, NH4+-N, and acid phosphatase enzyme activity (acid P). Among the developed models, the gradient boost regression (GBR) model showed the highest R2 (0.86-0.99) compared to the decision tree and random forest models. The GBR model interpretation showed that MP properties contributed more than 50% to altering the acid P and NO3--N concentrations in soils, whereas they had a negligible impact on total P and 10-20% impact on soil pH, DOC, and NH4+-N. Specifically, the size of MPs was the dominant factor influencing acid P (89.3%), pH (71.6%), and DOC (44.5%) in soils. NO3--N was mainly affected by the MP type (52.0%). The NH4+-N was mainly affected by the MP dose (46.8%). The quantitative insights into the impact of MPs on soil properties of this study could aid in understanding the roles of MPs in soil systems.
Assuntos
Poluentes do Solo , Solo , Microplásticos , Plásticos , Poluentes do Solo/análiseRESUMO
Dietary calcium (Ca) intake can alleviate fluoride (F) induced fluorosis to maintain bone health. However, it is unclear whether calcium supplements can reduce the oral bioavailability of F present in contaminated soils. Here we evaluated the effects of Ca supplements on F bioavailability in three soils using an in vitro method (Physiologically Based Extraction Test) and an in vivo mouse model. Seven Ca salts, commonly used in calcium supplements, significantly reduced the F bioaccessibility in the gastric and small intestinal phases. Particularly for Ca phosphate at 150 mg Ca supplementation, F bioaccessibility in the small intestinal phase was reduced from 35.1-38.8% to 0.7-1.9% where soluble F concentrations were less than 1 mg/L. Overall, the eight Ca tablets tested in this study showed greater efficiency at decreasing F solubility. The in vitro bioaccessibility after Ca supplementation was consistent with the relative bioavailability of F. As supported by X-ray photoelectron spectroscopy, a possible mechanism is that freed F can be bound by Ca to form insoluble CaF2 and exchanged with OH groups from Al/Fe hydroxide to strongly adsorb F. These findings provide evidence of Ca supplementation in reducing health risks associated soil F exposure.
Assuntos
Cálcio da Dieta , Suplementos Nutricionais , Fluoretos , Poluentes do Solo , Animais , Camundongos , Disponibilidade Biológica , Cálcio , Solo/química , Poluentes do Solo/análise , Fluorose Dentária/prevenção & controleRESUMO
The oxidation and immobilization of arsenic (As) by manganese oxides have been shown to reduce As toxicity and bioavailability under abiotic conditions. In this study, we investigate the impact of manganese oxide (δ-MnO2) on the fate of different Fe-minerals-adsorbed As in the presence of As(V)-reducing bacteria Bacillus sp. JQ. Results showed that in the absence of δ-MnO2, As release in goethite was much higher than in ferrihydrite and hematite during microbial reduction. Adding 3.1 mM Mn reduced As release by 0.3%, 46.3%, and 6.7% in the ferrihydrite, goethite, and hematite groups, respectively. However, aqueous As was dominated by As(III) in the end, because the oxidation effect of δ-MnO2 was limited and short-lived. Additionally, the fraction of solid-phase As(V) increased by 9.8% in ferrihydrite, 39.4% in goethite, and 7.4% in hematite in the high-Mn treatments, indicating that δ-MnO2 had the most significant oxidation and immobilization effect on goethite-adsorbed As. This was achieved because goethite particles were evenly distributed on δ-MnO2 surface, which supported As(III) oxidation by δ-MnO2; while ferrihydrite strongly aggregated, which hindered the oxidation of As(III). Our study shows that As-oxidation and immobilization by manganese oxides cannot easily be assessed without considering the mineral composition and microbial conditions of soils.
Assuntos
Arsênio , Ferro , Óxidos , Compostos de Manganês , Arsênio/metabolismo , Manganês , Compostos Férricos , Minerais , OxirreduçãoRESUMO
Arsenic (As) exposure in humans is primarily caused through food and drinking water. Iron (Fe) is one of the most common element of the human and can influence the toxicity and bioavailability of As. However, information on the interaction between As and Fe when present together is limited. In this study, the interaction effects of Fe(III) (0, 3, and 10 mg/L) and As (As(III) at 0, 0.05, 0.1 mg/L, and As(V) at 0, 0.1, and 2 mg/L, respectively) on their absorption and bioavailability in Caco-2 cells were analyzed. As(III) absorption significantly decreased with the addition of Fe, while Fe absorption significantly increased. Compared with 0.1 mg/L As(III) addition alone, 3 and 10 mg/L Fe(III) addition significantly reduced the As(III) absorption by 8.6 and 11 µg/L, respectively. The absorption of As and Fe(III) and the bioavailability of Fe(III) significantly increased with the addition of As(III/V). Compared with 10 mg/L Fe(III) alone, the absorption of As(III) was significantly increased by 1 and 1.3 mg/L with 0.05 and 0.1 mg/L As(III) addition, respectively. Furthermore, the absorption and bioavailability of Fe(III) were significantly increased by 1.2 mg/L and 8% and 1.2 mg/L and 8.2%, respectively, after adding 0.1 and 2 mg/L As(V).
Assuntos
Arsênio , Ferro , Humanos , Arsênio/toxicidade , Células CACO-2 , Disponibilidade BiológicaRESUMO
Trivalent metals-modified-biochar (BC) has been widely used for the removal of fluorine (F) in water, but little is known about its effects on the stability and mobility of F-contaminated soil. Two types of modified-BC materials (BC-loaded iron-lanthanide (BC/Fe-La) and BC-loaded aluminum-lanthanide (BC/Al-La)) were synthesized and used for the remediation of F-contaminated soil. The forms of BC/LaxFe3x(OH)y in BC/Fe-La and BC/LaxAl3x(OH)y in BC/Al-La were identified by spectroscopy, X-ray dispersion, thermogravimetric, and pore diameter/volume analyses. Following application (4-12%, w/w) to F-contaminated soil for 30 d, water soluble fluoride (WSF) decreased significantly. The modified-BC with a 1:1:1 molar ratio (BC: Al3+ or Fe3+: La3+) were more effective than those at 1:0.5:0.5. The BC/Al-La were the most effective to stabilize F. In particular, the highest decrease in WSF (by 91.75%) was obtained with the application of 12% BC/Al-La-2, while 8% BC/Al-La-2% and 12% BC/Al-La-1 reduced the WSF by 87.58% and 90.17%, respectively; all values obtained were lower than the national standard of China (< 1.5 mg/L). In addition, the sequential extraction results showed that modified-BC promoted the transformation of the other chemical speciation to the Fe/Mn-F.
Assuntos
Elementos da Série dos Lantanídeos , Poluentes do Solo , Alumínio , Carvão Vegetal , Fluoretos , Flúor , Ferro/análise , Solo , Poluentes do Solo/análiseRESUMO
Incidental oral ingestion is considered to be an important exposure route for humans to soil contaminants, such as fluoride (F). For 25 soil samples containing 4000 mg F/kg from aluminium smelting site in southwestern China, this study investigated F bioaccessibility in the human gastrointestinal tract in vitro. Fluoride bioaccessibility (2.4-48.8%) in the gastric phase was primarily caused by the dissolution of F-Ca and F-Al compounds (assigned to residual phase), identified by X-ray photoelectron spectroscopy and sequential extraction. Following modification to the small intestinal phase, the variation in F bioaccessibility (2.5-38.8%) should be the result of concurrent processes, including the formation of F complexes and competitive adsorption, and inversely the precipitation of fluorite and surface adsorption of formed F-Al complexes. The colon incubation with human gut microbiota yielded a 1.3-fold increase in F bioaccessibility (3.9-45.7%), probably due to the dissolution of F bound to Fe (hydr)oxides. Bioaccessibility adjustment can reduce hazard quotient of fluoride, and non-carcinogenic risk for children should be noted that soil F intake contributed 21.7% on average, up to 76.6% of oral reference dose. This will result in better understanding of human health risk assessment associated with F exposures.
Assuntos
Alumínio , Poluentes do Solo , Alumínio/metabolismo , Alumínio/toxicidade , Disponibilidade Biológica , Criança , Fluoretos/toxicidade , Trato Gastrointestinal/metabolismo , Humanos , Medição de Risco , Solo , Poluentes do Solo/metabolismoRESUMO
In this work, a novel cobalt-doped magnetic carbon (CDMC) was prepared to boost hydrogen (H2) and methane (CH4) generation. A one-pot approach was employed to produce H2 and CH4 with an incompletely heat-treated mixed culture. A moderate amount of CDMC promoted biogas evolution, while excess CDMC eroded both H2 and CH4 productivity. The CDMC (600 mg L-1) group achieved the highest biogas yields of 176 mL H2 per g glucose and 358 mL CH4 per g glucose, which were higher than those (102 mL H2 per g glucose and 288 mL CH4 per g glucose) found in the control group without CDMC. The mechanisms of H2 and CH4 production via the one-pot approach with CDMC were speculated to be as follows: CDMC provided beneficial sites and two elements (Co and Fe) for culture growth and boosted electron transfer, facilitating glucose degradation and conversion. Supplementation of carbon matrix composites and trace elements in biogas production has been shown to be an efficient strategy.
RESUMO
Carbon-based materials such as graphite, graphene, biochar, activated carbon, carbon cloth and nano-tube, and maghemite and magnetite carbons are capable for adsorbing chemicals onto their surfaces. Currently, this review is to highlight the relevance of carbons in enhancing hydrogen or methane production. Some key roles of carbons in improving cell growth, enrichment and activity, and accelerating their co-metabolisms were elaborated with regard to their effects on syntrophic communities, interspecies electron transfer, buffering capacity, biogas upgrading, and fertilizer nutrient retention and land application. Carbons can serve as a habitation for microbial immobilization, and a provision for bioelectrical connections among cells, and provide some essential elements for anaerobes. Besides, an outlook on the possible options towards the large scale and improvement solutions has been provided. Further studies in this area could be encouraged to intend and operate continuous mode by designing carbon-amended bioreactor with stability and reliability.
Assuntos
Anaerobiose , Reatores Biológicos , Carbono , Metano , Reprodutibilidade dos TestesRESUMO
Effects of biochar (BC) and ferrous iron (Fe2+) additions on hydrogen (H2) production from glucose were investigated using batch experiment. The glucose with both BC and Fe2+ additions were incubated at 37°C for H2 production. As compared with the control group (without BC and Fe2+ additions), the synergic effects of BC and Fe2+ make the lag phase time decease from 4.25 to 2.12h, and H2 yield increase from 158.0 to 234.4ml/g glucose. Moreover, suitable concentrations of BC and Fe2+ serve to enhance volatile fatty acid generation during H2 evolution. These results indicate that H2 production is improved by BC and Fe2+ regulations, where synergic mechanisms are described as follows: BC acts as support carriers of anaerobes and system pH buffers, which promotes the biofilm formation and maintains suitable pH environment; Appropriate Fe2+ concentration can improve hydrogenase activity in H2 production.