Characterization of dissolved organic matter in rivers impacted by acid mine drainage: Components and complexation with metals.

Dissolved organic matter (DOM), a ubiquitous and active ingredient, is extensively involved in the transformation and migration of environmental pollutants in aquatic ecosystems. However, its chemical composition in acid mine drainage (AMD)-impacted rivers remains poorly characterized, hindering our understanding of its role in the biogeochemistry of key elements in contaminated fluvial environments. Here, we investigated the concentration of dissolved organic carbon (DOC) and spectroscopic and molecular characteristics of DOM in a headwater river contaminated with polymetallic mine-derived AMD in southern China. Terrestrial humic-like (C1) and typically groundwater-supplied aromatic protein/tyrosine-like (C2) substances which were partially from AMD, were identified as the predominant fluorescent components in the river water. Notably, tryptophan-like (C3) substances originating from tailings pond spills were only occasionally detected in the river. Although DOM biogeochemical transformations and degradation occurred in the lateral soil-water riparian interface and longitudinal in-stream transport processes, the molecular compositions identified by FT-ICR MS showed a core set of molecular formulae in the lignin/saturated compound/tannin region of the van Krevelen diagram of the water samples across the rivers. The complexation of DOM with typical metals in AMD was investigated using fluorescence quenching experiments. The results showed that the highest binding ability of Fe(III) to C2 followed by C1, with both detected in the experimental water samples. Mg(II) and Ca(II) strengthened the binding of DOM-Fe(III) when the ferric/DOM ratio was low, while Cu(II) weakened the binding of DOM-Fe(III) due to competition. Ca(II) inhibited the binding of Fe(III) to C1 but promoted the binding of the complex to C2 when both Cu(II) and Mg(II) were present. Since DOM-Fe(III) complexation was associated with the cotransport of AMD-derived metals/metalloids in diverse aqueous environments with multiple co-existing ions (typically Ca(II) input for remediation), our study on the composition of DOM and its complexation with metals can contribute to managing and remediating AMD-impacted rivers.

Vortex vein engorgement and different shapes of venous drainage systems in polypoid choroidal vasculopathy vs. age­related macular degeneration on indocyanine green angiography.

There are differences in vortex vein engorgement and appearance in polypoid choroidal vasculopathy (PCV), age-related macular degeneration (AMD), and healthy eyes. The present study aimed to use indocyanine green angiography (ICGA) to find a simple, clinically meaningful method for evaluating the filling degree of vortex veins in various eye diseases. Participant clinical characteristics were recorded. The number of vortex veins (NVV), central vortex vein diameter (CVVD), mean root area of the vortex vein (MRAVV), mean diameter of the thickest peripheral branch (MDPTB), subfoveal choroidal thickness and percentage of vortex vein anastomosis (PVVA) were obtained by marking the vortex veins on ICGA. The proportion of subretinal haemorrhage and the numbers and types of vortex veins in each quadrant were counted separately. The CVVD and MDPTB were significantly increased in the PCV compared with those in the AMD group (P<0.05). The CVVD, MRAV, and PVVA were significantly increased in the PCV compared with those in the healthy group (P<0.05). The type IV vortex vein (complete with ampulla) proportion was the lowest while the type I (vortex vein absent) proportion was the highest in the PCV group (P<0.001). NVV in the inferior-temporal region was increased in the PCV compared with that in the AMD group (P=0.034). Subretinal haemorrhage occurred in the inferior temporal choroid in 47.62% of examined eyes in PCV group, and in the superior temporal choroid in 23.81% of the PCV group, with significant differences between the quadrants (P<0.001). Vortex vein engorgement and shape differed significantly between PCV, AMD and healthy eyes. The vortex vein branches in PCV eyes were significantly dilated in the posterior pole; moreover, the peripheral choroid and the lower proportion of type IV vortex veins may be pathognomonic for PCV.

Phosphate interactions with iron-titanium oxide composites: Implications for phosphorus removal/recovery from wastewater.

Understanding the interactions between phosphate (P) and mineral adsorbents is critical for removing and recovering P from wastewater, especially in the presence of both cationic and organic components. To this end, we investigated the surface interactions of P with an iron-titanium coprecipitated oxide composite in the presence of Ca (0.5-3.0 mM) and acetate (1-5 mM), and quantified the molecular complexes and tested the possible removal and recovery of P from real wastewater. A quantitative analysis of P K-edge X-ray absorption near edge structure (XANES) confirmed the inner-sphere surface complexation of P with both Fe and Ti, whose contribution to P adsorption relies on their surface charge determined by pH conditions. The effects of Ca and acetate on P removal were highly pH-dependent. At pH 7, Ca (0.5-3.0 mM) in solution significantly increased P removal by 13-30% by precipitating the surface-adsorbed P, forming hydroxyapatite (14-26%). The presence of acetate had no obvious influence on P removal capacity and molecular mechanisms at pH 7. At pH 4, the removal amount of P was not obviously affected by the presence of Ca and acetate. However, acetate and high Ca concentration jointly facilitated the formation of amorphous FePO4 precipitate, complicating the interactions of P with Fe-Ti composite. In comparison with ferrihydrite, the Fe-Ti composite significantly decreased the formation of amorphous FePO4 probably by decreasing Fe dissolution due to the coprecipitated Ti component, facilitating further P recovery. An understanding of these microscopic mechanisms can lead to the successful use and simple regeneration of the adsorbent to recover P from real wastewater.

Trace Metal(loid) Migration from Road Dust to Local Vegetables and Tree Tissues and the Bioaccessibility-Based Health Risk: Impacts of Vehicle Operation-Associated Emissions.

Traffic activities release large amounts of trace metal(loid)s in urban environments. However, the impact of vehicle operation-associated emissions on trace metal(loid) enrichment in road dust and the potential migration of these trace metal(loid)s to the surrounding environment remain unclear. We evaluated the contamination, sequential fraction, and bioaccessibility of trace metal(loid)s in urban environments by assessing their presence in road dust, garden vegetables, and tree tissues, including bark and aerial roots, at a traffic-training venue impacted by vehicle operation emissions and, finally, calculated the bioaccessibility-based health risk. The results indicated a significant accumulation of trace metal(loid)s in road dust, with the highest lead (Pb), cadmium (Cd), and antimony (Sb) concentrations in the garage entrance area due to higher vehicle volumes, frequent vehicle starts and stops, and lower speeds. Aerial roots exposed to hill start conditions exhibited the highest Pb, Zn, and Sb levels, potentially caused by high road dust resuspension, confirming that this tree tissue is an appropriate bioindicator. Sequential extraction revealed high percentages of carbonate-, Fe/Mn oxide-, and organic/sulphide-associated fractions of Pb, copper (Cu), and zinc (Zn) in road dust, while most Cd, Cr, Ni, and Sb occurred as residual fractions. According to the potential mobilizable fractions in sequential extraction, the in vitro gastrointestinal method could be more suitable than the physiologically based extraction test to evaluate the bioaccessibility-related risk of traffic-impacted road dust. The bioaccessibility-based health risk assessment of the road dust or soil confirmed no concern about noncarcinogenic risk, while the major risk originated from Pb although leaded gasoline was prohibited before the venue establishment. Furthermore, the cancer risks (CRs) analysis showed the probable occurrence of carcinogenic health effects from Cd and Ni to adults and from Cd, Cr, and Ni to children. Furthermore, the Cd and Pb concentrations in the edible leaves of cabbage and radish growing in gardens were higher than the recommended maximum value. This study focused on the health risks of road dust directly impacted by vehicle emissions and provides accurate predictions of trace metal(loid) contamination sources in the urban environment.

Geochemical Contamination, Speciation, and Bioaccessibility of Trace Metals in Road Dust of a Megacity (Guangzhou) in Southern China: Implications for Human Health.

Road dust has been severely contaminated by trace metals and has become a major health risk to urban residents. However, there is a lack of information on bioaccessible trace metals in road dust, which is necessary for an accurate health risk assessment. In this study, we collected road dust samples from industrial areas, traffic intersections, and agricultural fields from a megacity (Guangzhou), China, and conducted a geochemical enrichment, speciation, and bioaccessibility-based health risk assessment of trace metals. In comparison with local soil background values, the results revealed a significant accumulation of trace metals, including Zn, Cd, Cu, and Pb in the road dust, which is considered moderate to heavy pollution. Sequential extraction indicated that most trace metals in the road dust were primarily composed of a Fe/Mn oxide-bound fraction, carbonate-bound fraction, and residual fraction, while the dominant fraction was the organic matter-bound fraction of Cu, and the residual fractions of As, Cr, and Ni. The in vitro gastrointestinal (IVG) method revealed that high percentages of Zn, Cd, Cu, and As were bioaccessible, suggesting the possible dissolution of trace metals from adsorbed and carbonate-associated fractions in road dust exposed to the biological fluid matrix. The IVG bioaccessibility-based concentration largely decreased the noncarcinogenic health risk to a negligible level. Nevertheless, the entire population is still exposed to the cumulative probability of a carcinogenic risk, which is primarily contributed to by As, Cd, Cr, and Pb. Future identification of the exact sources of these toxic metals would be helpful for the appropriate management of urban road dust contamination.

Key Technology of the Medical Image Wise Mining Method Based on the Meanshift Algorithm.

Mean-shift originally refers to the mean vector of the offset. The algorithm idea is to assume that the data sets of different clusters conform to different probability density distributions, and the area with high sample density corresponds to the center of the cluster. With the wide application of hospital information system, especially the popularity of the meanshift algorithm in the outpatient system, it has greatly improved the efficiency of medical staff. Medical imaging refers to the technology and process of obtaining internal tissue images of the human body or a certain part of the human body in a noninvasive manner for medical treatment or medical research. It contains the following two relatively independent research directions: medical imaging system and medical image processing. In this paper, we expect to improve the mining ability of medical image information with the help of the meanshift algorithm based on the key technology of the medical image intelligent mining algorithm. This paper proposes a method to enhance image feature extraction and data mining and how to apply relevant analysis rules for mining. Applying this integrated algorithm to extract simplified rules is more beneficial to people's understanding than the raw data and helps doctors quickly understand the patient's condition.

Partitioning and (im)mobilization of arsenic associated with iron in arsenic-bearing deep subsoil profiles from Hong Kong.

Understanding the arsenic (As) enrichment mechanisms in the subsurface environment relies on a systematic investigation of As valence species and their partitioning with the Fe (oxyhydr)oxide phases in the subsoil profile. The present study explored the distribution, speciation, partitioning, and (im)mobilization of As associated with Fe in four subsoil cores (∼30 m depth) from Hong Kong using sequential chemical extraction and X-ray absorption near edge spectroscopy. The subsoil profiles exhibited relatively high concentrations of As at 26.1-982 mg/kg (median of 112 mg/kg), and the As was dominated by As(V) (85-96%) and primarily associated with the residual fraction (50.7-94.7%). A small amount of As (0.002-13.2 mg/kg) was easily mobilized from the four subsoil profiles, and a concentration of water-soluble As higher than 100 µg/L was observed for only some subsoil layers. The molar ratios of As:Fe in the oxalate-extractable Fe fraction ranged from 1.2 to 76.5 mmol/mol (median of 11.1 mmol/mol), revealing the participation of poorly crystalline Fe (oxyhydr)oxides in immobilizing most of the high geogenic As. The primary phases of ferric (oxyhydr)oxides were characterized as ferrihydrite (16-53%), lepidocrocite (0-32%), and goethite (0-62%), and these phases contributed to the sufficient ability of the subsoil to sequester 45.3-100% (median of 98.8%) of the exogenous As(V) (1.0 mg/L) in adsorption experiments. In contrast to As(V), exogenous As(III) showed a lower removal percentage (3.9-79.1%, median of 45.1%). The study revealed that the chemical speciation of As and Fe in the subsoil profiles is useful for predicting the immobilization of high geogenic As in the region, which is also helpful for the safe utilization of As-containing soil during land development worldwide.

Roxarsone transformation and its impacts on soil enzyme activity in paddy soils: A new insight into water flooding effects.

The aromatic arsenical roxarsone (ROX) has been used as feed additive for decades worldwide. The past or present application of animal manure containing ROX in paddy fields results in arsenic (As) accumulation in rice grain. However, the degradation and transformation mechanisms of ROX in paddy soil which determine As bioavailability and uptake by rice are still unclear. The current study investigated the variation of As speciation and soil enzyme activities in ROX-treated soils under flooded and non-flooded conditions for six months. Our results showed that 70.2% of ROX persisted in non-flooded paddy soils after 180 d while ROX degraded completely within 7 d in flooded soils. The rapid degradation of ROX under flooded conditions owed to the enhanced biotic transformation that was caused by the low Eh and the predominant presence of Clostridium spp. and Bacillus spp. ROX was not only transformed to As(III) and As(V) in non-flooded soils but also to 3-amino-4-hydroxyphenylarsonic acid and methyl arsenicals in flooded soils. The degradation products significantly inhibited soil enzyme activities for 7-30 d, but the inhibition effects disappeared after 90 d due to the sorption of transformed As products to amorphous Fe oxides. This study provides new insights into the flooding effect on ROX fate in paddy fields, which is important for the management of animal waste and risk control on polluted sites.

Root microbiome assembly of As-hyperaccumulator Pteris vittata and its efficacy in arsenic requisition.

The assemblage of root-associated microorganisms plays important roles in improving their capability to adapt to environmental stress. Metal(loid) hyperaccumulators exhibit disparate adaptive capability compared to that of non-hyperaccumulators when faced with elevated contents of metal(loid)s. However, knowledge of the assemblage of root microbes of hyperaccumulators and their ecological roles in plant growth is still scarce. The present study used Pteris vittata as a model plant to study the microbial assemblage and its beneficial role in plant growth. We demonstrated that the assemblage of microbes from the associated bulk soil to the root compartment was based on their lifestyles. We used metagenomic analysis and identified that the assembled microbes were primarily involved in root-microbe interactions in P. vittata root. Notably, we identified that the assembled root microbiome played an important role in As requisition, which promoted the fitness and growth of P. vittata. This study provides new insights into the root microbiome and potential valuable knowledge to understand how the root microbiome contributes to the fitness of its host.

Mechanistic insight into the interactions of EDDS with copper in the rhizosphere of polluted soils.

The biodegradable S,S-ethylenediaminedisuccinic acid (EDDS) is a promising chelant for chelant-assisted phytoextraction of trace metals in polluted soil. The interactions between EDDS and trace metals/major elements in the soil affect the metal bioavailability and their subsequent phytoextraction efficiency. This study aimed to investigate the macroscopic and molecular-level interactions of EDDS with Cu in the rhizosphere and non-rhizosphere of a Cu-polluted agricultural soil. A multi-interlayer rhizobox planted with ryegrass was used to simulate the transport of EDDS and Cu from the non-rhizosphere to rhizosphere soils. The results showed that EDDS (5 mM kg-1) significantly dissociated Cu (285-690 fold), Fe (by 3.47-60.2 fold), and Al (2.43-5.31 fold) from the soil in comparison with a control group. A combination of micro-X-ray fluorescence, X-ray absorption near-edge structure spectroscopy, and sequential extraction analysis revealed that EDDS primarily chelated the adsorbed fraction of Cu by facilitating the dissolution of goethite. Moreover, as facilitated by ryegrass transpiration, CuEDDS was moved from the non-rhizosphere to rhizosphere and accumulated in ryegrass. In situ processes of Cu extraction and transport by EDDS in the rhizosphere were further elucidated with chemical speciation analysis and geochemical modeling methods.

Health risk-oriented source apportionment of PM2.5-associated trace metals.

In health-oriented air pollution control, it is vital to rank the contributions of different emission sources to the health risks posed by hazardous components in airborne fine particulate matters (PM2.5), such as trace metals. Towards this end, we investigated the PM2.5-associated metals in two densely populated regions of China, the Yangtze River Delta (YRD) and Pearl River Delta (PRD) regions, across land-use gradients. Using the positive matrix factorization (PMF) model, we performed an integrated source apportionment to quantify the contributions of the major source categories underlying metal-induced health risks with information on the bioaccessibility (using simulated lung fluid) and speciation (using synchrotron-based techniques) of metals. The results showed that the particulate trace metal profiles reflected the land-use gradient within each region, with the highest concentrations of anthropogenically enriched metals at the industrial sites in the study regions. The resulting carcinogenic risk that these elements posed was higher in the YRD than in the PRD. Chromium was the dominant contributor to the total excessive cancer risks posed by metals while manganese accounted for a large proportion of non-carcinogenic risks. An elevated contribution from industrial emissions was found in the YRD, while traffic emissions and non-traffic combustion (the burning of coal/waste/biomass) were the common dominant sources of cancer and non-cancer risks posed by metals in both regions. Moreover, the risk-oriented source apportionment of metals did not mirror the mass concentration-based one, suggesting the insufficiency of the latter to inform emission mitigation in favor of public health. While providing region-specific insights into the quantitative contribution of major source categories to the health risks of PM2.5-associated trace metals, our study highlighted the need to consider the health protection goal-based source apportionment and emission mitigation in supplement to the current mass concentration-based framework.

Improvement of water quality in the Pearl River Estuary, China: a long-term (2008-2017) case study of temporal-spatial variation, source identification and ecological risk of heavy metals in surface water of Guangzhou.

A series of environmental protective policies have been taken recently in the Pearl River Estuary (PRE) to alleviate water pollution; however, their influence on the reduction of heavy metals in estuarine water has not been known. This study selected Guangzhou as a representative city in the PRE and collected estuarine water monthly from 2008 to 2017 to track the variation of As, Hg, Pb, Cd, Cu, Zn, and Se. During the last decade, the high time-resolved record showed that the concentration of Hg, Pb, Cd, Cu, and Zn in estuarine water reduced by 39.5%, 91.0%, 86.2%, 74.6%, and 97.3%, respectively. However, the concentration of As kept in a stable range (1.89-2.69 µg L-1) and Se (0.17-0.65 µg L-1) increased slightly. The principal component analysis (PCA) and absolute principal component scores-multiple linear regression (APCS-MLR) results suggested that the upstream industrial effluents were major sources for Hg (45.5-92.7%), Pb (47.3-100%), Cd (42.0-90.6%), Cu (85.5-100%), and Zn (100%) and the geogenic source was major origin for As (84.6-98.3%) and Se (0-67.5%). The risk quotient of Hg, Pb, Cd, Cu, and Zn to aquatic organisms largely decreased from 0.03, 0.59, 0.03, 2.06, and 0.26 in 2008 to 0.02, 0.05, 0.006, 0.52, and 0.007 in 2017, respectively. The effective control of heavy metal pollution in the study area can be primarily due to the relocation of hundreds of polluting factories during the last decade.

Transformation of Fe-P Complexes in Bioreactors and P Recovery from Sludge: Investigation by XANES Spectroscopy.

The transformation of Fe-P complexes in bioreactors can be important for phosphorus (P) recovery from sludge. In this research, X-ray absorption near-edge structure analysis was conducted to quantify the transformation of Fe and P species in the sludge of different aging periods and in the subsequent acidogenic cofermentation for P recovery. P was readily removed from wastewater by Fe-facilitated coprecipitation and adsorption and could be extracted and recovered from sludge via acidogenic cofermentation and microbial iron reduction with food waste. The fresh Fe-based sludge mainly contained fresh ferrihydrite and amorphous FePO4 with sufficient accessible surface area, which was favorable for Fe-P mobilization and dissolution via microbial reaction. Ferric iron dosed into wastewater underwent rapid hydrolysis, clustering, aggregation, and slow crystallization to form hydrous iron oxides (HFO) with various complicated structures. With the aging of sludge in bioreactors, the HFO densified into phases with much reduced surface area and reactivity (e.g., goethite), which greatly increased the difficulty of P release and recovery. Thus, aging of P-containing sludge should be minimized in wastewater treatment systems for the purpose of P recovery.

Spatial distribution and molecular speciation of copper in indigenous plants from contaminated mine sites: Implication for phytostabilization.

Contaminated mining sites require ecological restoration work, of which phytoremediation using appropriate plant species is an attractive option. Our present study is focused on one typical contaminated mine site with indigenous plant cover. The X-ray absorption near edge structure (XANES) analysis indicated that Cu (the major contaminant) was primarily associated with goethite (adsorbed fraction), with a small amount of Cu oxalate-like species (organic fraction) in mine affected soil. With growth of plant species like Miscanthus floridulus and Stenoloma chusanum, the Cu-oxalate like organic species in rhizosphere soil significantly increased, with corresponding decrease in Cu-goethite. In the root cross-section of Miscanthus floridulus, synchrotron-based micro-X-ray fluorescence (µ-XRF) microscopy and micro-XANES results indicated that most Cu was sequestered around the root surface/epidermis, primarily forming Cu alginate-like species as a Cu-tolerance mechanism. From the root epidermis to the cortex and vascular bundle, more Cu(I)-glutathione was observed, suggesting reductive detoxification ability of Cu(II) to Cu(I) during the transport of Cu in the root. The observation of Cu-histidine in root internal cell layers showed another Cu detoxification pathway based on coordinating amino ligands. Miscanthus floridulus showed ability to accumulate phosphorous and nitrogen nutrients in rhizosphere and may be an option for in situ phytostabilization of metals in contaminated mining area.

[Mobilization of Heavy Metals in a Soil-Plant System and Risk Assessment in the Dabaoshan Mine Area, Guangdong Province, China].

This study analyzed heavy metal concentrations in mining/agricultural soil and plant samples from the Dabaoshan mining-impacted region, Guangdong Province, and evaluated the corresponding health risks. The results showed that most of the soil samples exhibited a pH<5, which, in some cases, facilitated the release of Cu, Pb, and Al from soil and hence affected the availability for plant uptake. Farmland in Shaxi town was found to be seriously polluted by Cd, whereas the mining area was seriously polluted by Cd, Pb, Cu, and As, which present potential ecological risks. Farmland in Xinjiang town was seriously polluted by Cu, As, and Cd, and also present ecological risks for this area. The concentrations of heavy metals (especially Al and Fe) in the eight plant species assessed were mostly higher than that in plants grown in non-contaminated soil. Only 10% of the bioconcentration factors and 18% of the translocation factors were higher than 1 in the aerial parts of plants, indicating that most heavy metals were concentrated in plant roots. Heavy metal concentrations in shoots of Miscanthus and Blechnum orientale were not high, and their accumulation from soil to plant was poor. These plants are excluder species and can be used for in situ phyto-stabilization and management. Weeds like Soliva anthemifolia species in contaminated agricultural field showed a strong enrichment ability for Cd. Rice mainly accumulated As and Cd in the roots and belongs to root compartment plants.

A review of arsenic interfacial geochemistry in groundwater and the role of organic matter.

Recent discoveries on arsenic (As) biogeochemistry in aquifer-sediment system have strongly improved our understanding of As enrichment mechanisms in groundwater. We summarize here the research results since 2015 focusing on the As interfacial geochemistry including As speciation, transformation, and mobilization. We discuss the chemical extraction and speciation of As in environmental matrices, followed by As redox change and (im)mobilization in typical minerals and aquifer system. Then, the microbial-assisted reductive dissolution of Fe (hydr)oxides and As transformation and liberation are summarized from the aspects of bacterial isolates, microbial community and gene analysis by comparing As rich groundwater cases worldwide. Finally, the potential effect of organic matter on As interfacial geochemistry are addressed in the aspects of chemical interactions and microbial respiring activities for Fe and As reductive release.

Deciphering source contributions of trace metal contamination in urban soil, road dust, and foliar dust of Guangzhou, southern China.

Trace metal contamination prevails in various compartments of the urban environment. Understanding the roles of various anthropogenic sources in urban trace metal contamination is critical for pollution control and city development. In this study, the source contribution from various contamination sources to trace metal contamination (e.g., Cu, Pb, Zn, Co, Cr and Ni) in different environmental compartments in a typical megacity, Guangzhou, southern China, was investigated using the receptor model (Absolute Principal Component Scores-Multiple Linear Regression, APCS-MLR) coupled with the Kriging technique. Lead isotopic data and APCS-MLR analysis identified industrial and traffic emissions as the major sources of trace metals in surface soil, road dust, and foliar dust in Guangzhou. Lead isotopic compositions of road dust and foliar dust exhibited similar ranges, implying their similar sources and potential metal exchange between them. Re-suspended soil contributed to 0-38% and 25-58% of the trace metals in the road dust and foliar dust, respectively, indicating the transport of the different terrestrial dust. Spatial distribution patterns implied that Cu in the road dust was a good indicator of traffic contamination, particularly with traffic volume and vehicle speed. Lead and Zn in foliar dust indicated mainly industrial contamination, which decreased from the emission source (e.g., a power plant and steel factory) to the surrounding environment. The spatial influence of industry and traffic on the contamination status of road dust/foliar dust was successfully separated from that of other anthropogenic sources. This study demonstrated that anthropogenic inputs of trace metals in various environmental compartments (e.g., urban soil, road dust, and foliar dust) can be evaluated using a combined APCS-MLR receptor model and geostatistical analysis at a megacity scale. The coupled use of APCS-MLR analysis, geostatistics, and Pb isotopes successfully deciphered the spatial influence of the contamination sources in the urban environment matrix, providing some important information for further land remediation and health risk assessment.

Distribution and speciation of copper in rice (Oryza sativa L.) from mining-impacted paddy soil: Implications for copper uptake mechanisms.

Long term mining activities can cause significant metal pollution in the environment, thereby showing potential risk to the paddy field. Elucidating the interfacial processes of trace metals from contaminated paddy soil to rice within the rhizosphere can provide important information on metal biogeochemistry and food safety. The current study aims to explore the spatial distribution and molecular speciation of Cu from rhizosphere to rice plant in a mining-impacted paddy soil, and reveal the possible uptake mechanisms. X-ray absorption near edge structure (XANES) analysis indicated that Cu was primarily associated with iron oxide and sulfide in soil with a minor proportion of organic complexed species. In the rice samples, Cu showed much higher concentrations in the roots than the shoots, as most Cu was sequestered in the root surface and epidermis (primarily in the form of C/N ligands bound Cu species), rather than root xylem, as identified by micro X-ray fluorescence (µ-XRF) imaging coupling with µ-XANES. By contrast, in the root xylem, thiol-S bound Cu(I) complex was observed, representing the reduced product of Cu(II) by thiol-S ligands in rice root. The absorbed Cu was probably transported from the root to the aerial part as C/N ligand bound Cu complex such as Cu-histidine like species, which was observed in the root xylem. The large retention capacity and reduction of Cu(II) in rice root alleviated Cu toxicity to rice, which was beneficial for food safety (e.g., lower concentration of Cu in rice grains). These findings showed for the first time that the uptake mechanisms by rice from field contaminated sites, which shed light on Cu detoxification process and potential remediation strategies.

Phosphorus Removal and Recovery from Wastewater using Fe-Dosing Bioreactor and Cofermentation: Investigation by X-ray Absorption Near-Edge Structure Spectroscopy.

A new phosphorus (P) removal and recovery process that integrates an FeCl3-dosing, membrane bioreactor (MBR), and side-stream cofermentation was developed for wastewater treatment. The Fe and P species and their transformation mechanisms via aerobic and anaerobic conditions were investigated with X-ray absorption near edge structure (XANES) spectroscopy. In the new treatment system, 98.4% of the total P in domestic wastewater was removed and retained in activated sludge in the MBR. During the subsequent acidogenic cofermentation with food waste, P in the MBR sludge was released and eventually recovered as vivianite, achieving an overall P recovery efficiency of 61.9% from wastewater. The main pathways for P removal and recovery with iron dosing and acidogenic fermentation were determined by XANES analysis. The results showed that Fe-enhanced P removal with the MBR was mainly achieved by precipitation as ferric phosphate (24.2%) and adsorption onto hydrous iron oxides (60.3%). During anaerobic fermentation, transition from Fe(III)-P to Fe(II)-P complex occurred in the sludge, leading to Fe(II) dissolution and P release. The pH decrease and microbial Fe reduction were crucial conditions for effective P extraction from the MBR sludge. The efficiency of P recovery increased with an increase in the fermentation time and organic load and a decrease of pH in the solution.

Effects of low-alkalinity binders on stabilization/solidification of geogenic As-containing soils: Spectroscopic investigation and leaching tests.

The low-alkalinity stabilization/solidification (S/S) treatment of the soil containing high concentrations of geogenic As by physical encapsulation is considered as a proper management before land development; however, the choice of an effective binder and the leaching potential of As remain uncertain. In this study, the influence of S/S binders (cement blended with fuel ash (FA), furnace bottom ash (FBA), or ground granulated blast furnace slag (GGBS)) on the speciation and leaching characteristics of geogenic As was studied. The results of X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS) showed the reduced amount of calcium silicate hydrate phase and the decrease in oxidation state of As(V)-O on the surface of Fe(III) oxides/hydroxides in the low-alkalinity S/S treated soils. This might be due to the binder incorporation and change in pH conditions, which slightly affected the As-Fe interaction and increased the non-specifically sorbed species of As. Therefore, the S/S treatment increased the leachability and bioaccessibility of geogenic As to varying degree but decreased the phyto-extractable As. The S/S treatment by cement incorporating 25% of class C fly ash (O4C1) could achieve comparable or better performance, while reducing the risk assessment code (RAC) to a greater extent compared to that of using cement only. This study illustrates the effectiveness and limitations of low-alkalinity binders (e.g., O4C1) for geogenic As immobilization and encapsulation, which provides a new insight for determining the appropriate S/S binder in soil remediation.