Arsenic Release Research Articles

The stability of poorly crystalline arsenical ferrihydrite after long-term soil suspension incubation

2- Line ferrihydrite (Fh) is widely used as a robust amendment for rapid arsenic removal or remediation in water or soil. However, the poorly crystalline phase of Fh is unstable and leads to arsenic leaching after long-term submergence in reductive aquatic and soil environments. In this study, the synthesized As(V)-bound Fh was characterized by various spectral approaches to investigate the factors that may affect the variation in As(V)-Fh in long-term continuously submerged soil suspensions. The X-ray diffraction (XRD) results showed that hematite was the main product and that goethite was the byproduct after 360 d of incubation. Approximately 12–17% and 4–5% Fh were transformed at As/Fe mole ratios of 0.005 and 0.05, respectively. After 360 d of incubation, the hematite morphology was clearly observed by scanning electron microscopy (SEM), and the As(V)-Fh surface areas were also decreased by 17.3–27.6% and 11.9–16.6% for As/Fe mole ratios of 0.005 and 0.05, respectively. In a comparison of the two tested soils (soils sampled in Sichuan Province (SC) and Hunan Province (HN)), As(V)-Fh transformed faster in HN soil suspensions, and more hematite and goethite were formed. Furthermore, during the incubation period, As(V) was transformed to As(III), and both species were released into the suspension from the As(V)-Fh surface. It was suggested that soil pH and Fe(II) concentration were key factors controlling the As(V)-Fh transformation process, and the differences between the two soils were due to the different soil pH values and contents of available Fe. Arsenic release was mainly caused by Fh transformation and ligand competition with soil organic matter (SOM).

Simultaneous evaluation of kinetic release of labile arsenic and phosphorus in agricultural soils using cerium oxide-based DGT

The adsorption/desorption of arsenic (As) in agricultural soils is of utmost importance for the evaluation of its kinetic release and potential of entering the food chain by uptake of crops. However, the mobility of As in soils is closely related to the migration behavior of soil phosphorus (P) due to their chemical similarity. Here, the distribution and desorption kinetics of As and P in four different types of farmland soils were simultaneously estimated by cerium oxide-based diffusive gradients in thin films technique (CeO2-DGT) coupled with dynamic model of DGT induced fluxes in soils (DIFS). CeO2-DGT was deployed in the soils over 400 h to investigate the interactions between As and P for their migration behaviors. The accumulated masses of As in the DGT devices showed reverse orders with those of P among the four soils, indicating their competitive adsorption on soil solids. The distribution coefficients (Kdl) for the labile As and P derived from the DIFS model were mutually exclusive. Clay in the soil reduced the pool size of the labile As by increasing the irreversible adsorption of As on soil particles. The adsorption rate constants of As were much smaller than P but their desorption rate constants were comparable. Among the four soils, the soil with the highest soil labile As/P molar ratio measured by DGT showed the largest potential of As phytotoxicity. Both As and P could reach the equilibrium of resupply within 0.7– 18 min under DGT depletion, and significant negative correlation was observed between the desorption rate (kb) of As and clay content in the soils.

The release of arsenic from biologically formed arsenic-containing FeS under aerobic environment: Implications for the stability and species variation of nano-sized iron sulfide in remediation

Biologically formed nano-FeS is a potential and low-cost adsorbent and soil remediation agent. Remediation of arsenic from contaminated groundwater and soil by biological FeS is promising, however, the fate and transport of arsenic associated with nano-FeS in the natural environment are poorly understood. To investigate the fate of adsorbed arsenic on nano-FeS under aerobic conditions, static and dynamic experiments were carried out at different pH values and different oxidants. Batch and column sets showed that arsenic(V)-loaded FeS could release arsenic into solutions at pH 3.0 and 9.0. Especially noteworthy is the release of arsenic sustained at pH 9.0. Introducing Fe3+ and H2O2 at pH 3.0 showed that Fe3+ and a high concentration of H2O2 could reduce the release of arsenic, which might be ascribed to the oxidants promoting secondary Fe mineral phases to form on the arsenic(V)-FeS solid surface. X-ray diffraction patterns indicated that elemental S(0) and arsenic(V)-bearing Fe(II)/Fe(III) minerals formed as the main products. The generated secondary parasymplesite and FeAsO4 were mainly responsible for dissolved arsenic retention. The performance of hydraulic conductivity followed the sequence pH 7.0 > 50 mg/L Fe3+ > 1 mg/L Fe3+ > pH 9.0 > pH 3.0. In addition, H2O2 always kept good hydraulic conductivity. XPS analysis demonstrated that arsenic(III) and arsenic(V) were the main arsenic speciation on the surfaces of the solids, implying that lower valence arsenic was oxidized to arsenic(III/V) during the oxidation processes. The present study facilitates a better understanding of the stability of arsenic-loaded FeS in aerobic environment.

Red mud-metakaolin based cementitious material for remediation of arsenic pollution: Stabilization mechanism and leaching behavior of arsenic in lollingite

The proper treatment of lollingite is of great significance due to its rapid oxidation leading to release of arsenic into the environment. Herein, a green multi-solid waste geopolymer, consisting of red mud, metakaolin, blast furnace slag, and flue gas desulfurization gypsum, was developed. The obtained red mud-metakaolin-based (RMM) geopolymer demonstrated good arsenic retention capability. The results showed that the replacement of SO42− in ettringite with AsO42− via ion exchange, formation of Ca-As and Fe-As precipitates, and physical encapsulation with aluminosilicate gel were the main mechanisms that prevented the release of arsenic. Further dissolution of ettringite in RMM was alleviated by adding a suitable amount of Ca(OH)2 and controlling the pH of the leachate. TCLP results verified that RMM materials possessed an outstanding ability to stabilize arsenic, with a leaching rate below the permitted value of 5 mg/L for safe disposal. The low leachability of the RMM geopolymers (<0.50 mg/L) is potentially related to the pH buffering capacity of the hydration products at a pH range of 2–5. RMM geopolymers showed a high compressive strength (>15 MPa) and low arsenic leaching concentration (<2.66 mg/L) after 28 days of curing. These results demonstrate the potential of RMM geopolymers to be utilized as an environmentally friendly backfilling cementitious material for sustainable remediation of arsenic pollution.

Comparison of the effects of competitive adsorption and reductive dissolution on migration of arsenic in lake sediment

ABSTRACT Arsenic-contaminated sediment of Lake Yangzonghai (Yunnan province, China) and its overlying water was used to investigate the effects of phosphate ion (PO4 3−) and microbial activity on the migration of arsenic in the sediment. The results showed that the competitive adsorption of PO4 3− was the primary factor for the release of arsenic from the sediment to the overlying water, while microbial activity played a minor role in promoting the reductive dissolution of iron/arsenic (hydro) oxides. The reductive dissolution of ferrous ion (Fe2+) occurred in the initial stage, and partly contributed to the increase of arsenic concentration in the overlying water. The increase of PO4 3− concentration in the overlying water enhanced the mobility and biological toxicity of the arsenic in the sediment. After PO4 3− in the overlying water was depleted, arsenic in the overlying water could be adsorbed and precipitated again by iron salts, resulting in the decrease of arsenic concentration in the overlying water. The study implies that among those arsenic-contaminated lakes, eutrophication will aggravate the risks of secondary pollution of arsenic.

Sea-level-rise-induced flooding drives arsenic release from coastal sediments

Sea-level rise (SLR) has a vital influence on coastal hydrogeological systems, biogeochemical processes, and the fate of coastal contaminants. However, the effects of SLR-induced perturbations on the mobilization of coastal pollutants are not fully understood. In this study, the impact of SLR-induced flooding on the concentration and speciation of arsenic and selected hazardous chemicals is investigated using exceedingly contaminated sediments (5–6% As) collected from an urban coastal site in Wilmington, DE, USA. The release of contaminants from sediments was monitored before, during, and after flooding with different intensities (bottom shear stresses) through laboratory-based erosion chamber experiments. Significantly increased release of As (up to 150%) and NO3 (up to 50%) from sediments at shear stress levels typically measured in estuaries were found. The release of toxic chemicals from contaminated coastal sediments is thus not restricted to extreme flooding events but can occur throughout the year. The results also suggest that the dissolved concentrations of pollutants continue to be considerably high even after the flooding. SLR-induced flooding can hence increase the release of contaminants not only during erosion events but over longer timescales. The release mechanism proposed here contributes to improving the risk assessment of coastal water pollution as climate change and SLR continue to occur.

Culture-dependent study of arsenic-reducing bacteria in deep aquatic sediments of Bengal Delta.

Biogeochemical release of soil-bound arsenic (As) governs mobilization of the toxic metalloid into the groundwater. The present study has examined AsV-reduction ability of bacteria from anoxic aquatic sediments that might contribute to arsenic mobilization in the Bengal Delta. Arsenic-reducing bacteria from deep layers of pond sediment were enriched and isolated in anaerobic environments and AsV reduction was assessed in culture medium. The pond sediment enrichments harboured AsV-reducing bacteria belonging to the phyla Firmicutes and Proteobacteria with dominance of Paraclostridium benzoelyticum and P. bifermentans. Among total 17 isolates, the respiratory reductase genes were not detected by the most common primers and only 3 strains had arsenic reductase ArsC gene suggesting involvement of resistance and some unknown mechanisms in AsV reduction. Presence of high levels of organic matter, As, and As-reducing bacteria might make deep aquatic sediments a hot spot of As mobilization and aquifer contamination.

The Effect of Manure Application on Arsenic Mobilization and Methylation in Different Paddy Soils.

Organic matter plays an important rolein controlling arsenic(As) release and transformation in soil, however, little is known about the effect of manure application on As behavior in soils with different As contents. In this study, waterlogged incubations using various As-contaminated paddy soils with manure amendment were conducted to investigate how manure application influence As mobilization and methylation in different paddy soils. The results indicated that manure application increased As release in paddy soils with high As (> 30mgkg-1) contents. Moreover, our findings also showed that manure application increased the relative abundance of arsM-harboring Euryacheota and Planctomycetes at the phylum level and arsM-harbouring Methanocellaceae, Anaerolinea and Bellinea at genus level, thereby promoting As methylation. These results provide important insights for the significant variation in As mobilization and methylation in paddy soils amended with manure. Moreover, our results suggest that serious consideration should be given to the manure application in As-contaminated paddy soil.

Characteristics of the immobilization process of arsenic depending on the size fraction released from excavated rock/sediment after the addition of immobilization materials

Chemical immobilization is an effective technique to suppress the release of arsenic from naturally arsenic-containing excavated rock/sediment. For designing the chemical immobilization technique, it is important to understand that the immobilization of arsenic depends on the sizes of ionic arsenic and arsenic retained on the colloids and suspended particles that are released from the excavated rock/sediment. Tests on the size fractionation of the arsenic released and the subsequent immobilization were conducted. The total amount of the size fraction of arsenic released from six excavated rock/sediment ranged from 0.16 to 0.75 mg kg−1. The distributions of size fraction of arsenic released were categorized into three types: the dominant fraction was suspended particle fraction (SP–F) and ionic fraction (I–F), and a compatible amount of SP-F and I–F was included. Steel slag, calcium oxide, and ferrihydrite, which can effectively and stably immobilize ionic arsenic with different mechanisms, decreased the total amounts of the size fraction of arsenic released at 28%–84%, 59%–83%, and 57%–84%, respectively. Ferrihydrite and calcium oxide greatly reduced the I–F and the small and large colloid fractions. The steel slag was effective in reducing the SP-F at >86 %. In most arsenic fractions, the immobilized arsenic was not re-released at <7 %. This study provides the first experimental evidence of the variation in the released arsenic size depending on the excavated rock/sediment. In addition, the size fraction of the arsenic that could be immobilized depended on the immobilizing material. Thus, it is suggested that the combined application of immobilization materials would present a useful approach for immobilizing various released arsenic phases and preventing immobilized arsenic from re-release.

Red mud regulates arsenic fate at acidic pH via regulating arsenopyrite bio-oxidation and S, Fe, Al, Si speciation transformation

Red mud (RM) as waste of industrial aluminum production is piling up in huge ponds. RM could be a cost-effective adsorbent for heavy metals, but adsorption is vulnerable to pH changes, metal ions speciation and the occurrence of iron bearing minerals. In this study, the precipitation and elemental speciation transformation relevant to arsenic fate in responding to the addition of RM during arsenopyrite bio-oxidation by Sulfobacillus thermosulfidooxidans was investigated. The results show that the addition of RM significantly changed the arsenic precipitation and the solution chemistry and thus affected the arsenopyrite bio-oxidation and arsenic fate. An addition of a small amount (≤ 4 g/L) of RM substantially promoted arsenopyrite bio-oxidation with formation of SiO2 @ (As, Fe, Al, Si) spherical nanoparticles that can enhance the stability of the immobilized arsenic. The SiO2-based spherical nanoparticles precipitate was mainly composed of jarosites, amorphous ferric arsenate and crystalline scorodite, and its formation were controlled by Fe3+ concentration and solution pH. An addition of increased amount of RM (≥ 6 g/L) resulted in a significant increase of the solution pH and a decrease in the Fe2+ bio-oxidation activity, and spherical nanoparticles were not formed. Consequently, the dissolution of arsenopyrite was inhibited and the release of arsenic was blocked. This study suggests the applicability of RM in mitigation of arsenic pollution from bio-oxidation of As-bearing sulfide minerals.

Effects of anode/cathode electroactive microorganisms on arsenic removal with organic/inorganic carbon supplied

This study reports the effects of an external voltage (0 V, 0.4 V and 0.9 V) on soil arsenic (As) release and sequestration when amended with organic carbon (NaAc) and inorganic carbon (NaHCO3), respectively, in a soil bioelectrochemistry system (BES). The results demonstrated that although an external voltage had no effect on the As removal capacity in an oligotrophic environment fueled with NaHCO3, 93.6% of As(III) in the supernatant was removed at 0.9 V with an NaAc amendment. Interestingly, the content of As detected on the electrodes was higher than that removed from the supernatant, implying a continuous release of soil As under external voltages and rapid adsorption onto the electrodes, especially the cathode. In addition, the species of As on the cathode were similar to those in the supernatant (the As(III)/As(V) ratio was approximately 3:1), indicating that the removal capacity was independent of preoxidation. From the viewpoint of electroactive microorganisms (EABs), the relative abundances of the arrA gene and Geobacter genus were specifically enriched at the anode, thus signifying stimulation of the reduction and release of soil As in the anode region. By comparison, Bacillus was particularly abundant at the cathode, which could contribute to the oxidation and sequestration of As in the cathode region. Additionally, specific extracellular polymeric substances (EPSs) secreted by EABs could combine with As, which was followed by electrostatic attraction to the cathode under the effect of an electric field. Furthermore, the formation of secondary minerals and coprecipitation in the presence of iron (Fe) may have also contributed to As removal from solution. The insights from this study will enable us to further understand the biogeochemical cycle of soil As and to explore the feasibility of in situ As bioremediation techniques, combining the aspects of microbial and physicochemical processes in soil bioelectrochemical systems.

The chemical-microbial release and transformation of arsenic induced by citric acid in paddy soil

Citric acid (CA) is the major exudate of rice roots, yet the effects of CA on arsenic (As) transformation and microbial community in flooded paddy soil have not been clearly elucidated. In this study, microcosms were established by amending CA to As contaminated paddy soils, mimicking the rhizosphere environment. Results showed that 0.5% CA addition significantly enhanced As mobilization after one-hour incubation, increased total As in porewater by about 20-fold. CA addition induced arsenate release into porewater, and subsequently formed ternary complex of As, iron and organic matters, inhibiting further As transformation (including arsenate reduction and arsenite methylation). Furthermore, the results of linear discriminant analysis (LDA) effect size (LEfSe) and network analysis revealed that CA addition significantly enriched bacteria associated with arsenic and iron reductions, such as Clostridium (up to 35-fold) and Desulfitobacterium (up to 4-fold). Our results suggest that CA exhibits robust ability to mobilize As through both chemical and microbial processes, increasing the risk of As accumulation by rice. This study sheds light on our understanding of As mobilization and transformation in rhizosphere soil, potentially providing effective strategies to restrict As accumulation in food crops by screening or cultivating varieties with low CA exuding.

Arsenic fate in upper Indus river basin (UIRB) aquifers: Controls of hydrochemical processes, provenances and water-aquifer matrix interaction

Major river basins of the Himalayas contain a significant amount of arsenic (As) in the geological matrix, which tends to contaminate the groundwater at a local and regional scale. Although As enrichment in Quaternary deposits has been linked to primary provenances (Himalayan orogeny), limited studies have reported As enrichment in bedrock aquifers. In the present study, the hard rock and groundwater samples were collected across the upper Indus river basin (UIRB), Ladakh to assess the hydrogeochemical processes and environments responsible for As mobilization and release. The higher As concentrations were found in Khardung volcanics followed by Ophiolitic melange, Dras volcanics, Nindam sandstone, and Nindam Shale. The variability in As concentration among different rock samples is largely governed by the presence of felsic minerals and the type of magmatic setting. The groundwater is less mineralized, with moderate electrical conductivity (EC), and weakly acidic to alkaline in nature. The results indicated that mineral weathering, dissolution, and active cation exchange reactions have a strong influence on the major ion chemistry of the groundwater. Redox-sensitive processes are influencing the As mobilization and release under reducing environmental conditions. As in groundwater poses a serious threat to human health hence awareness is urgent towards achieving sustainable As mitigation globally. The study provided a significant dataset to better understand the processes and environmental conditions responsible for hydrogeochemical evolution, sources of solutes, and As mobilization and release in groundwater which will help in sustainable water resource management policies and ecosystem restoration across the Himalayas.

Kinetics and mechanisms of arsenic and sulfur release from crystalline orpiment

Arsenic trisulfide (As2S3), in both amorphous and crystalline form, is a significant arsenic-containing compound naturally occurring in mine waste rock or generated as metallurgical waste. It is typically unstable in the enviroment, especially under alkaline and oxidizing conditions, which is a significant barrier to fixation of arsenic present in metallurgical waste streams in the form of arsenic trisulfide. Our previous study has shown the effect of different factors on the kinetics and mechanisms of arsenic and sulfur release from amorphous As2S3. To assess the effect of crystallinity on the stability of arsenic trisulfide, a series of laboratory leaching tests were performed with crystalline orpiment under fully controlled conditions. The experimental results showed that the release of arsenic and sulfur increased with pH, dissolved oxygen concentration, and temperature, but the release rates were much slower than those of amorphous arsenic trisulfude. The speciation analyses indicated that arsenic was present in the leachates as arsenite, which was subsequently oxidized to arsenate to different extents; thiosulfate was the main soluble sulfur species, which was converted to sulfate via oxidation and disproportionation pathways. The kinetic modeling suggested that the arsenic release process is a mixed-control reaction, in which the surface chemical reaction and the diffusion of dissolved oxygen through a product layer control the arsenic release rate. The solid surface characterization supported the presence of an arsenic-deficient phase enriched in elemental sulfur on the solid surfaces. The product layer acted as a barrier to the diffusion of reagents, as evidenced by the leaching being sensitive to the removal of elemental sulfur.

The osteogenic niche-targeted arsenic nanoparticles prevent colonization of disseminated breast tumor cells in the bone

Up to 70% of patients with late-stage breast cancer have bone metastasis. Current treatment regimens for breast cancer bone metastasis are palliative with no therapeutic cure. Disseminated tumor cells (DTCs) colonize inside the osteogenic niches in the early stage of bone metastasis. Drug delivery into osteogenic niches to inhibit DTC colonization can prevent bone metastasis from entering its late stage and therefore cure bone metastasis. Here, we constructed a 50% DSS6 peptide conjugated nanoparticle to target the osteogenic niche. The osteogenic niche was always located at the endosteum with immature hydroxyapatite. Arsenic-manganese nanocrystals (around 14 nm) were loaded in osteogenic niche-targeted PEG-PLGA nanoparticles with an acidic environment-triggered arsenic release. Arsenic formulations greatly reduced 4T1 cell adhesion to mesenchymal stem cells (MSCs)/preosteoblasts (pre-OBs) and osteogenic differentiation of osteoblastic cells. Arsenic formulations also prevented tumor cell colonization and dormancy via altering the direct interaction between 4T1 cells and MSCs/pre-OBs. The chemotactic migration of 4T1 cells toward osteogenic cells was blocked by arsenic in mimic 3D osteogenic niche. Systemic administration of osteogenic niche-targeted arsenic nanoparticles significantly extended the survival of mice with 4T1 syngeneic bone metastasis. Our findings provide an effective approach for osteogenic niche-specific drug delivery and suggest that bone metastasis can be effectively inhibited by blockage of tumor cell colonization in the bone microenvironment.

Liposome-Coated Arsenic-Manganese Complex for Magnetic Resonance Imaging-Guided Synergistic Therapy Against Carcinoma.

PurposeA liposome-coated arsenic–manganese complex, denoted as LP@MnAsx was constructed for the targeted delivery of arsenic trioxide (ATO) against carcinoma.MethodsArsenite, the prodrug of ATO, was encapsulated within a liposome via electrostatic interaction with the manganese ions. The as-prepared material was characterized with dynamic light scattering and transmission electron microscopy. The entrapment efficiency and drug loading of arsenic in the carrier were measured using inductively coupled plasma spectrometry. The in vitro release of arsenic was evaluated by using the dialysis bag method. Furthermore, the Fenton-like activity and in vitro cytodynamics research of LP@MnAsx were monitored in this work. And the cellular uptake study was used to investigate the in vitro entry mechanism. Furthermore, the cytotoxicity, cell apoptosis and cell cycle study were performed to evaluate the tumor-killing efficiency. Also, the pharmacokinetic and antitumor studies were investigated in HepG2 tumor-bearing nude mice.ResultsThe as-prepared LP@MnAsx possessed a spherical morphology, uniformly distributed hydrodynamic diameter, and excellent drug-loading efficiency. LP@MnAsx displayed robust stability and sustained-release profile under physiological environments. LP@MnAsx could degrade with high sensitivity to the pH variation in the tumor microenvironment. As such, this could lead to a burst release profile of Mn2+ and arsenite to achieve a synergistic therapy of chemodynamic therapy and chemotherapy. When compared to the carrier-free arsenate, in vitro experiments revealed that LP@MnAsx exhibited enhanced cellular uptake and tumor-killing efficiency. LP@MnAsx also demonstrated significantly enhanced tumor-specific in vivo distribution of arsenic, prolonged systemic circulation lifetime, and increased accumulation at the tumor site.ConclusionBased on the experimental results, LP@MnAsx is an ideal arsenic-based nanodelivery system, whereby it can improve the non-specific distribution of NaAsO2 in vivo. Thus, this work can expand the research and application of arsenic trioxide against solid tumors.

Influence of Ferric Ions on the Electrochemical Dissolution Behaviors of Arsenopyrite in Sulfuric Acid of pH 1

ABSTRACT This study investigated the electrochemical oxidation behaviors of arsenopyrite in sulfuric acid (pH 1) containing various concentrations of ferric ions by cyclic voltammetry, Tafel polarization curves and electrochemical impedance spectra (EIS) measurements. Results indicated that the addition of ferric ions did not affect the electrochemical dissolution mechanism of arsenopyrite. With the increase of the ferric concentration, the corrosion potential of arsenopyrite shifted positively, and the corrosion current density increased. EIS tests showed that arsenopyrite oxidation consisted of two charge transfer processes, i.e., the release of iron and arsenic from arsenopyrite lattice and the oxidation of elemental sulfur formed on the arsenopyrite surface. The overall oxidation of arsenopyrite was controlled by the oxidation of elemental sulfur. The presence of ferric ions decreased the electron transfer resistances of both processes, contributing to the accelerated dissolution of arsenopyrite. Cyclic voltammetry and Tafel plots implied that the enhanced cathodic reaction was the dominant reason for the improved dissolution of arsenopyrite in the presence of ferric ions.

Impacts of External Organic Carbon on Arsenic Release in Aquifer of Jianghan Plain, Central China

This study investigated the effects of organic carbon, e.g., glucose, humic acid, and fulvic acid, on the As enrichment of groundwater from an As-bearing aquifer under the Jianghan Plain, China. Sediments were obtained by drilling samples and cultured in the laboratory by adding exotic organic matter. On the basis of high-throughput sequencing, it can be found that the addition of organic matter causes the change of microbial community diversity in the sediments. We found the co-occurrence of organic carbon and indigenous microfloral assemblage (family Clostridiaceae) promoted the transfer of As to a liquid phase by dissolving and destroying Fe oxides. Through XPS, XRD, and EXAFS analyses of sediments in different periods, we can conclude that, in this process, As was converted into labile and unstable intermediates (As2S3, As2S5, or AsS) through the degradation of organic carbon. These novel results provide valuable information for the remediation and risk control of As-contaminated sites.

Fate of arsenic in living systems: Implications for sustainable and safe food chains

Arsenic, a group 1 carcinogen for humans, is abundant as compared to other trace elements in the environment and is present mainly in the Earth’s crust and soil. The arsenic distributions in different geographical regions are dependent on their geological histories. Anthropogenic activities also contribute significantly to arsenic release into the environment. Arsenic presents several complications to humans, animals, and plants. The physiology of plants and their growth and development are affected by arsenic. Arsenic is known to cause cancer and several types of organ toxicity, such as cardiotoxicity, nephrotoxicity, and hepatotoxicity. In the environment, arsenic exists in variable forms both as inorganic and organic species. From arsenic containing compartments, plants can absorb and accumulate arsenic. Crops grown on these contaminated soils pose several-fold higher toxicity to humans compared with drinking water if arsenic enters the food chain. Information regarding arsenic transfer at different trophic levels in food chains has not been summarized until now. The present review focuses on the food chain perspective of arsenic, which affects all components of the food chain during its course. The circumstances that facilitate arsenic accumulation in flora and fauna, as components of the food chain, are outlined in this review.

Effect of construction and demolition waste on the long-term geo-environmental behaviour of cemented paste backfill

The construction and demolition waste (CDW) could be used as backfill material to fill the voids created during the ore production in underground mining. However, there is a need to clarify the impact of CDW on groundwater pollution when it is used as backfill material in cemented paste backfill (CPB) of sulphide-rich tailings (S-rT). This study presents the influence of CDW on the long-term geo-environmental behaviour of CPB samples (CPBs) when used as replacement (10 wt.%) to S-rT. For this reason, the dynamic-tank leaching test was conducted on CPBs and pH, conductivity (Ec), sulphate (SO42−) and heavy metals (HMs) analyses were executed for leachates over 30–360 days of leaching period. The effects of mineralogy and microstructure on the geo-environmental behaviour of CPBs were also analysed via X-ray fluorescence (XRD) and mercury intrusion porosimeter (MIP). The utilisation of CDW in CPB mixtures was found to reduce the SO42− release (up to 13.89%), neutralise the acid generated and lower the Ec (up to 22.16%). Furthermore, the HMs releases (except As, Cu and Zn) were prevented (Ni and Cr) or reduced up to 92%, which is compatible with the improved CPB microstructure. Only the release of arsenic (As) exceeded the limit value for groundwater in CPB of CDW leachate. These findings suggest that not only the cost, strength and stability but also the impact on groundwater pollution should be considered when disposing of CDW as CPB material in underground voids.