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.

Cerium anomalies in riverbanks: Highlight into the role of ferric deposits.

In wetlands, stream riverbanks represent a large redox reactive front. At their surface, ferric deposits promote their capacity to trap nutrients and metals. Given that rare earth elements (REE) are now considered as emerging pollutants, it seems that the riverbank interface is a strategic area between wetlands and streams in terms of controlling the environmental dissemination of REE. Therefore, the evolutions of the REE distribution and cerium (Ce) anomaly (Ce/Ce*, i.e. depleted or enriched Ce concentration compared to the other REE) were studied at various locations on a riverbank. The positive Ce anomaly is related to a high Fe content, a low organic carbon/iron ratio ((OC)/Fe) and newly formed Fe oxyhydroxides independently of their interactions with organic matter. Micro-X ray fluorescence (µ-XRF) mapping confirms Ce accumulation with ferric deposits. The Ce speciation exhibits a mix of Ce(III) and Ce(IV) in the ferric deposits, almost 20% of Ce occurred as Ce(IV) due to oxidation by newly formed Fe oxyhydroxides, while the subsurface horizons only display Ce(III). These results provide evidence that the Ce anomaly variation observed in stream water between low and high flow periods is partly due to the erosion of ferric deposits exhibiting a positive Ce anomaly. Therefore, the Ce anomaly can be considered as a fingerprint of the release of Fe colloids in the rivers and streams connected to the wetland.

Tracking the magnetic carriers of heavy metals in contaminated soils based on X-ray microprobe techniques and wavelet transformation.

Technogenic magnetic particles (TMPs) from industrial activities are major contamination sources of soils and dusts because they usually carry large amounts of heavy metals. The understanding of the association between TMPs and heavy metals in contaminated soils helps to trace the polluting sources and probing into the mechanism of magnetic phases enriched with heavy metals. In this study, we tracked the magnetic carries of heavy metals from different emission sources in steel industrial regions by using the synchrotron-based probe techniques and multiscale analytical methods. The µ-XRF mapping showed that TMPs contained various heavy metals, depending on their sources. The Fe K-edge µ-XANES revealed that the ferroalloy, pyrrhotite and TMPs in steel slag and coal ash were major magnetic phases in contaminated soils. Their relative content varied differently at the microscale. The multiscale analysis revealed that the heavy metals associated with magnetic phases exhibited pronounced scale dependence, depending on the size, type, and assemblage of different magnetic phases. Multiscale source apportionment revealed that the contamination sources varied differently at multiple scales. Heatmap analysis revealed that at 8-µm scale, Co, Cr, Cu and Mn were mainly derived from ferroalloy, while Ti, Zn and As from both ferroalloy and TMPs from coal ash.

Speciation and location of arsenic and antimony in rice samples around antimony mining area.

Arsenic (As) and antimony (Sb) are considered as priority environmental pollutants and their accumulation in crop plants particularly in rice has posed a great health risk. This study endeavored to investigate As and Sb contents in paired soil-rice samples obtained from Xikuangshan, the world largest active Sb mining region, situated in China, and to investigate As speciation and location in rice grains. The soil and rice samples were analyzed by coupling the wet chemistry, laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), synchrotron-based micro X-ray fluorescence mapping (µ-XRF) and micro X-ray absorption near-edge structure (µ-XANES) spectroscopy. The results of field survey indicated that the paddy soil in the region was co-polluted by Sb (5.91-322.35 mg kg-1) and As (0.01-57.21 mg kg-1). Despite the higher Sb concentration in the soil, rice accumulated more As than Sb indicating the higher phytoavailability of As. Dimethylarsinic acid (DMA) was the predominant species (>60% on average) in the rice grains while the percentage of inorganic As species was 19%-63%. The µ-XRF mapping of the grain section revealed that the most of As was distributed and concentrated in rice husk, bran and embryo. Sb was distributed similarly to As but was not in the endosperm of rice grain based on LA-ICP-MS. The present results deepened our understanding of the As/Sb co-pollution and their association with the agricultural-product safety in the vicinity of Sb mining area.

Electrochemical Adsorption on Pt Nanoparticles in Alkaline Solution Observed Using In Situ High Energy Resolution X-ray Absorption Spectroscopy.

The oxygen reduction reaction (ORR) on Pt/C in alkaline solution was studied by in situ high energy resolution X-ray absorption spectroscopy. To discuss the X-ray absorption near-edge structure (XANES), this paper introduced the rate of change of the Δµ (RCD), which is an analysis method that is sensitive to surface adsorption. The surface adsorptions as hydrogen (below 0.34 V), superoxide anion (from 0.34 V to 0.74 V), hydroxyl species (from 0.44 V to 0.74 V), atomic oxygen (above 0.74 V), and α-PtO2 (above 0.94 V) were distinguished. It is clarified that the catalytic activity in an alkaline solution is enhanced by the stability of atomic oxygen and the low stability of superoxide anion/peroxide adsorption on the platinum surface.

Distributions of cadmium, zinc, and polyphenols in Gamblea innovans.

Gamblea innovans is a Cd- and Zn-accumulating deciduous tree widely distributed in the secondary forests of Japan. We aimed to understand the characteristics of Cd and Zn accumulation in G. innovans in order to effectively utilize the species for phytoremediation. To accomplish that, we studied the relationship between secondary metabolite concentrations and the accumulation and distributions of Cd and Zn in G. innovans leaves and basal stems using micro-X ray fluorescence (µ-XRF). Our results showed a negative correlation between Zn leaf concentrations and polyphenol/2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity. This finding might be related to stress or the manifestation of a mechanism for tolerance to Cd and Zn accumulation. In addition, we observed that Cd accumulated primarily in the apoplastic region of surface tissues such as bark and the epidermis of leaves, whereas Zn accumulated in both apoplastic and symplastic regions. Thus, it might be possible that G. innovans can distinguish between Cd and Zn and control their translocation.

Chromium Speciation in the Size-Fractions of a Soil Polluted by Weathered Chromate Ore Process Residue Using Synchrotron X-ray Analysis.

The chromate ore process residues (COPR) polluted soil was physically separated into coarse sand (2.000-0.425 mm), fine sand (0.425-0.053 mm) and silt to clay (< 0.053 mm) fractions. The Cr speciation was characterized by synchrotron based micro X-ray fluorescence (µ-XRF) and micro X-ray absorption near-edge spectra (µ-XANES). The results indicated that Cr was bearing both in COPR parent minerals and hydrated products and was dominated by Cr(III) in three size-fractions. The synchrotron results indicated that Cr(III) was dominated by chromite, organic matter bound Cr(III) and particle adsorbed Cr3+ in the selected hotspots from the coarse sand, fine sand and silt to clay sized fraction, respectively. While Cr(VI) occurred in the form of CrO42- in the selected hotspots from three size fractions. The difference of Cr(III) species in the size-fractions suggested that higher edaphic effects occurred in the fine size-fractions than in the coarse size-fraction for the weathered COPR.

Bioaccumulation of CeO2 Nanoparticles by Earthworms in Biochar-Amended Soil: A Synchrotron Microspectroscopy Study.

The interactions of nanoparticles (NPs) with biochar and soil components may substantially influence NP availability and toxicity to biota. In the present study, earthworms ( Eisenia fetida) were exposed for 28 days to a residential or agricultural soil amended with 0-2000 mg of CeO2 NP/kg and with biochar (produced by the pyrolysis of pecan shells at 350 and 600 °C) at various application rates [0-5% (w/w)]. After 28 days, earthworms were depurated and analyzed for Ce content, moisture content, and lipid peroxidation. The results showed minimal toxicity to the worms; however, biochar (350 or 600 °C) was the dominant factor, accounting for 94 and 84% of the variance for the moisture content and lipid peroxidation, respectively, in the exposed earthworms. For both soils with 1000 mg of CeO2/kg at 600 °C, biochar significantly decreased the accumulation of Ce in the worm tissues. Amendment with 350 °C biochar had mixed responses on Ce uptake. Analysis by micro X-ray fluorescence (µ-XRF) and micro X-ray absorption near edge structure (µ-XANES) was used to evaluate Ce localization, speciation, and persistence in CeO2- and biochar-exposed earthworms after depuration for 12, 48, and 72 h. Earthworms from the 500 mg of CeO2/kg and 0% biochar treatments eliminated most Ce after a 48 h depuration period. However, in the same treatment and with 5% BC-600 (biochar pyrolysis temperature of 600 °C), ingested biochar fragments (∼50 µm) with Ce adsorbed to the surfaces were retained in the gut after 72 h. Additionally, Ce remained in earthworms from the 2000 mg of CeO2/kg and 5% biochar treatments after depuration for 48 h. Analysis by µ-XANES showed that, within the earthworm tissues, Ce remained predominantly as Ce4+O2, with only few regions (2-3 µm2) where it was found in the reduced form (Ce3+). The present findings highlight that soil and biochar properties have a significant influence in the internalization of CeO2 NPs in earthworms; such interactions need to be considered when estimating NP fate and effects in the environment.

Spectroscopic characterization of the complexes between Fe/Mn and natural organic matters by electron paramagnetic resonance and synchrotron-based techniques.

The surface interaction between heavy metals and natural organic matters (NOM) substantially affects their migration and conversion in natural environments. In this study, the chemical speciation and element mapping of Fe and Mn in reduced NOM were investigated. The results show that quinone and semiquinone moieties dominated the redox properties in NOM, and the EPR signal intensity exhibited pH dependence with an increase of EPR signal intensity at a higher pH value. The EPR results indicate that the complexes displayed the characteristics of superparamagnetic oxides/oxyhydroxides after Fe/Mn complexed with NOM. µ-XRF results suggest that the scatterplots of Fe and Mn distributions at pH 11 had the most positive linearly-related plot points, indicating strong correlations for Mn-Fe binary metallic ions. µ-XANES results further interpret the presence of higher Mn oxidation state at pH 11, while Fe kept trivalent in all samples. These results reveal that the surface interactions are closely related to the redox state of NOM and are beneficial for better understanding the speciation, immobilization, transport, and toxicity of metal ions in natural waters.

Species- and tissue-specific bioaccumulation of arsenicals in various aquatic organisms from a highly industrialized area in the Pohang City, Korea.

Contamination of water and sediment with arsenic (As) in a highly industrialized area of Pohang City, Korea was investigated, with emphasis on in situ bioaccumulation of arsenicals by various aquatic organisms. Species- and tissue-specific concentrations of arsenicals were determined by use of HPLC-ICP/MS and µ-X-ray absorption near-edge structure (µ-XANES). Concentrations of arsenic in aquatic organisms were strongly associated with corresponding water concentrations, which indicates point sources associated with land use and activities. Arsenobetaine was the most dominant form of arsenic found in fishes, bivalves, crabs, and shrimps, while As(III) was predominant in freshwater snails. The µ-XANES analysis provided additional information about the unidentified arsenicals such as As-thiol. Arsenicals were mainly localized in intestine of mullet and marsh clam. Distribution and bioaccumulation of arsenic were strongly correlated with salinity, which indicates that natural processes controlling biogeochemistry of arsenic would be important in estuarine lotic system.

Aging effect on Zn retention on a calcareous soil: column experiments and synchrotron X-ray micro-spectroscopic investigation.

In this study, a combination of column experiments and micro-analytical techniques exploiting synchrotron generated X-rays was used to assess the effect of aging time on Zn retention and mobility in the specific case of calcareous soils (high pH value, ≈ 8). The samples were subjected to aging for 2, 6, 17, and 63 days. Freshly added Zn mainly existed as an exchangeable form, and this metal fraction decreased over time due to Zn redistribution to stronger binding sites. Thus, after aging for 63 days, 45% of Zn is remobilized from exchangeable sites to stronger binding sites. µ-XRF maps were used to find correlations among elements in the sample, and µ-XANES spectra were recorded to precise Zn speciation. These analyses evidenced an increasing partitioning of Zn from organic matter to iron oxy(hydr)oxides over time. The occurrence of hydrozincite is evidenced in all samples.

Heavy metal distribution in an urban wetland impacted by combined sewer overflow.

The heavy metal content and distribution in an urban wetland affected by combined sewer overflow (CSO) discharge during dry conditions was evaluated. Metals identified in the CSO discharge were also measured upstream and downstream of the CSO. Metals were detected in the acid-extractable fraction of the wetland sediments and the roots of Phragmites australis plants. Sediment from the banks of a pool created by the CSO, and from a clay bed upstream were found to be moderately contaminated with Cu, Pb and Zn. Micro X-ray fluorescence (µ-XRF) of Phragmites roots from the CSO banks showed a correlation in the spatial distribution of Fe and Mn, attributed to the formation of mineral plaques on the root surface. Micro X-ray absorption near edge spectroscopy (µ-XANES) revealed that Cu and Zn were complexed with the organic ligands phytate and cysteine. The findings indicated that continuous discharge from the CSO is a source of heavy metals to the wetland. Metals bound to sediments are susceptible to remobilization and subsequent transport, whereas those associated with Phragmites roots may be more effectively sequestered. These observations provide insight into the behavior of heavy metals in urban areas where CSOs discharge into wetlands.