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.

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.

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.

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.

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.

Speciation, mobilization, and bioaccessibility of arsenic in geogenic soil profile from Hong Kong.

The behaviour of arsenic (As) from geogenic soil exposed to aerobic conditions is critical to predict the impact of As on the environment, which processes remain unresolved. The current study examined the depth profile of As in geologically derived subsoil cores from Hong Kong and investigated the mobilization, plant availability, and bioaccessibility of As in As-contaminated soil at different depths (0-45.8 m). Results indicated significant heterogeneity, with high levels of As in three layers of soil reaching up to 505 mg/kg at a depth of 5 m, 404 mg/kg at a depth of 15 m, and 1510 mg/kg at a depth of 27-32 m. Arsenic in porewater samples was <11.5 µg/L in the study site. X-ray absorption spectroscopy (XAS) indicated that main As species in soil was arsenate (As(V)), as adsorbed fraction to Fe oxides (41-69% on goethite and 0-8% on ferrihydrite) or the mineral form scorodite (30-57%). Sequential extraction procedure demonstrated that 0.5 ± 0.4% of As was exchangeable. Aerobic incubation experiments exhibited that a very small amount (0.14-0.48 mg/kg) of As was desorbed from the soil because of the stable As(V) complex structure on abundant Fe oxides (mainly goethite), where indigenous microbes partly (59 ± 18%) contributed to the release of As comparing with the sterilized control. Furthermore, no As toxicity in the soil was observed with the growth of ryegrass. The bioaccessibility of As was <27% in the surface soil using simplified bioaccessibility extraction test. Our systematic evaluation indicated that As in the geogenic soil profile from Hong Kong is relatively stable exposing to aerobic environment. Nevertheless, children and workers should avoid incidental contact with excavated soil, because high concentration of As was present in the digestive solution (<0.1-268 µg/L).

Role of chelant on Cu distribution and speciation in Lolium multiflorum by synchrotron techniques.

Chelants are known to enhance metal translocation in plants; however, the underlying mechanisms are still not fully understood. This study aimed to elucidate the distribution and speciation of Cu in ryegrass (Lolium multiflorum) in both absence and presence of the biodegradable chelant [S,S']-ethylenediamine disuccinic acid (EDDS). The results showed that EDDS increased the Cu translocation factor from root to shoot by 6-9 folds under CuEDDS in comparison with free Cu (50-250µM). Synchrotron-based microscopic X-ray fluorescence (µ-XRF) mapping revealed that EDDS alleviated Cu deposition in the root meristem of root apex and the junction of lateral root zone, and facilitated Cu transport to root stele for subsequent translocation upwards. X-ray absorption near edge structure (XANES) analysis found that free Cu was sequestered in plants as a mixture of Cu-organic ligands. In the EDDS treatment, Cu was primarily present as CuEDDS (49-67%) in plants with partial chemical transformation to Cu-histidine (21-36%) and Cu(I)-glutathione (0-24%). These results suggest that EDDS improves internal Cu mobility through forming CuEDDS, thus decreasing the root sequestration of Cu, and ultimately facilitating Cu transport to plant shoots.

Speciation and leaching of trace metal contaminants from e-waste contaminated soils.

Primitive electrical and electronic waste (e-waste) recycling activities have caused serious environmental problems. However, little is known about the speciation and leaching behaviors of metal contaminants at e-waste contaminated sites. This study investigated trace metal speciation/mobilization from e-waste polluted soil through column leaching experiments involving irrigation with rainwater for almost 2.5 years. Over the experimental period, Cu and Zn levels in the porewater were 0.14±0.08mg/L, and 0.16±0.08mg/L, respectively, increasing to 0.33±0.16mg/L, and 0.69±0.28mg/L with plant growth. The amounts of Cu, Zn, and Pb released in surface soil (0-2cm) contributed 43.8%, 22.5%, and 13.8%, respectively, to the original levels. The released Cu and Zn were primarily caused by the mobilization of the carbonate species of metals, including Cu(OH)2, CuCO3, and Zn5(CO3)2(OH)6, and amorphous Fe/Mn oxides associated fractions characterized by sequential extraction coupling with X-ray absorption spectroscopy. During the experiments, trace metals were not detected in the effluent, and the re-sequestration of trace metals was mainly attributed to the adsorption on the abundant Fe/Mn oxides in the sub-layer soil. This study quantitatively elucidated the molecular speciation of Cu and Zn in e-waste contaminated soil during the column leaching process.