High Arsenic Research Articles

FeOOH and nZVI combined with superconducting high gradient magnetic separation for the remediation of high-arsenic metallurgical wastewater

Metallurgical wastewater with high arsenic (As) concentration presents important challenges to human health and the environment because of its high toxicity and carcinogenicity. Iron (Fe)-based adsorbents can effectively detoxify low As-containing wastewater but are less helpful for high concentration of As and for solid–liquid separation. Herein, an advanced strategy is proposed to dispose high As wastewater using nano-zerovalent iron (nZVI) and ferric oxyhydroxide (FeOOH) combined with superconducting high gradient magnetic separation (HGMS) technology. The superconducting HGMS technology promoted the removal of As by nZVI and FeOOH via a magnetic flocculation reaction, while simultaneously separating reaction products adsorbed As from wastewater. Interestingly, nZVI could be corroded to release Fe(II) ions which then generated Fenton reaction under aerobic conditions, facilitating the oxidization of As(III)/Fe(II) to As(V)/Fe(III) ions. The Fe(II) and Fe(III) hydrolyzed in the form of hydroxy hydroxide and further generated the magnetic flocculates and coprecipitate. The results showed that 99.06% of As was successfully removed from wastewater with an initial As concentration of 5358 mg/L, at a dosage of 20 g/L, a magnetic field strength of 5 T, and a flow velocity of 500 mL/min. Compared with FeOOH, nZVI showed more favorable adaptability for lead smelting wastewater. Removal of As from wastewater by using nZVI combined with superconducting HGMS technology has a great potential to achieve industrial application for metallurgical heavy metal wastewater.

Spatial variation in dissolved phosphorus and interactions with arsenic in response to changing redox conditions in floodplain aquifers of the Hetao Basin, Inner Mongolia

Increasing numbers of studies have reported groundwater with naturally high phosphorous (P) and arsenic (As) concentrations, which can potentially threaten the environment and human health. However, the cycling of P and its interactions with As in groundwater under changing redox conditions remain largely unknown. In this study, 83 groundwater samples and 14 sediment samples were collected from the Hetao Basin, Inner Mongolia, for systematic hydrogeochemical investigation and complementary geochemical evaluation. The results showed that P cycling in floodplain aquifers was tightly constrained by redox conditions. Under oxic/suboxic conditions, mineralization of organic matter and weathering of P-bearing minerals were the two dominant processes that mobilized considerable amounts of P in groundwater. When redox conditions became reducing, Fe(III)-oxide reduction dominated, resulting in enrichment of both P and As in groundwater. In Fe(III)-reducing conditions, secondary Ca/Fe(II)-minerals might serve as an important sink for P. When redox conditions became SO42−-reducing, preferential adsorption and incorporation of P over As on Fe(II)-sulfides might constrain the As immobilization pathway, resulting in immediate retardation of P and hysteretic immobilization of As. This P-immobilization pathway in natural aquifers has not been described before. This study provides novel insights into P cycling and As enrichment in groundwater systems. Understanding the roles of Fe(II)- and S(-II)-minerals in the immobilization of and interaction between P and As in response to SO42− reduction may help to inspire effective in-situ remediation of contaminated groundwater, in which P and As coexist and remain mobile for decades or longer.

Alcohol Consumption Moderated the Association Between Levels of High Blood Lead or Total Urinary Arsenic and Bone Loss.

Metal exposure and lifestyle are important risk factors for osteoporosis. Our study aimed to investigate the association between red blood cell lead and cadmium, total urinary arsenic, and plasma selenium levels and bone mineral density (BMD). In addition, we explored whether alcohol and coffee consumption modified the association between BMD and metals and metalloids. In total, 437 participants who underwent adult or senile physical examinations were recruited. Bone loss was defined as a calcaneus BMD T-score of <-1. Blood cadmium and lead and plasma selenium levels were measured using inductively coupled plasma mass spectrometry. Levels of urinary arsenic species were determined using high-performance liquid chromatography–hydride generator–atomic absorption spectrometry. The total urinary arsenic level was defined as the sum of the levels of urinary arsenic species. The BMD T-scores decreased significantly with increasing blood lead levels. The BMD T-scores also showed a downward trend with increasing total urinary arsenic levels. The odds ratio (OR) and 95% confidence interval (CI) for bone loss in patients with blood lead levels >57.58 versus 35.74 μg/dL were 1.98 and 1.17–3.34. In addition, the greater the lead or arsenic exposure and alcohol intake was the higher the OR for bone loss with multivariate ORs of 2.57 (95% CI 1.45–4.56) and 2.96 (95% CI 1.67–5.22), respectively. To the best of our knowledge, this study is the first to demonstrate that high total urinary arsenic or blood lead levels and frequent or occasional alcohol consumption had a significant multiplicative interaction for increasing the OR for bone loss.

Column bio-oxidation of low-grade refractory gold ore containing high-arsenic and high-sulfur: Insight on change in microbial community structure and sulfide surface corrosion

Currently, there is a lack of research on column bio-oxidation for low-grade refractory gold ore with high arsenic and sulfur content. Therefore, it is essential and significative to investigate column bio-oxidation for this type of gold ore. The column bio-oxidation process of refractory gold ore was characterized by a variety of analytical methods, including X-ray diffraction, 16S rRNA gene analysis, scanning electron microscope coupled with energy-dispersive X-ray spectroscopy and 3D confocal laser scanning microscopy. The evolution of the microbial community structure was analyzed. Simultaneously, the process of passive film formation and the behavior of the dynamic corrosion on the sulfide surfaces were described in detail. The results showed that the cyanidation of gold yielded 81 ± 2% after column bio-oxidation. The oxidation extent for As, Fe and S were 57 ± 1%, 38 ± 1% and 44 ± 1%, respectively. The community structure of attached and planktonic microorganisms was different and changed with the oxidation time. Importantly, the Sulfur film was observed on the arsenopyrite surface under scanning electron microscope, yet it was not found on the pyrite surface. This finding revealed that the inhibitory effect generated by the passive film of arsenopyrite was significantly higher than that of pyrite. Furthermore, the average corrosion pit volume per unit area of pyrite and arsenopyrite were 161 ± 6 μm3/μm2 and 65 ± 3 μm3/μm2. This indicated that arsenopyrite was more easily oxidized during the column bio-oxidation.

Arsenic hyperaccumulator Pteris vittata shows reduced biomass in soils with high arsenic and low nutrient availability, leading to increased arsenic leaching from soil

Plant-soil interactions affect arsenic and nutrient availability in arsenic-contaminated soils, with implications for arsenic uptake and tolerance in plants, and leaching from soil. In 22-week column experiments, we grew the arsenic hyperaccumulating fern Pteris vittata in a coarse- and a medium-textured soil to determine the effects of phosphorus fertilization and mycorrhizal fungi inoculation on P. vittata arsenic uptake and arsenic leaching. We investigated soil arsenic speciation using synchrotron-based spectromicroscopy. Greater soil arsenic availability and lower nutrient content in the coarse-textured soil were associated with greater fern arsenic uptake, lower biomass (apparently a metabolic cost of tolerance), and arsenic leaching from soil, due to lower transpiration. P. vittata hyperaccumulated arsenic from coarse- but not medium-textured soil. Mass of plant-accumulated arsenic was 1.2 to 2.4 times greater, but aboveground biomass was 74% smaller, in ferns growing in coarse-textured soil. In the presence of ferns, mean arsenic loss by leaching was 195% greater from coarse- compared to the medium-textured soil, and lower across both soils compared to the absence of ferns. In the medium-textured soil arsenic concentrations in leachate were higher in the presence of ferns. Fern arsenic uptake was always greater than loss by leaching. Most arsenic (>66%) accumulated in P. vittata appeared of rhizosphere origin. In the medium-textured soil with more clay and higher nutrient content, successful iron scavenging increased arsenic release from soil for leaching, but transpiration curtailed leaching.

GIS-based spatio-temporal and geostatistical analysis of groundwater parameters of Lahore region Pakistan and their source characterization

Assessment of groundwater quality is critical, especially in the areas where it is continuously deteriorating due to unplanned industrial growth. This study utilizes GIS-based spatio-temporal and geostatistical tools to characterize the groundwater quality parameters of Lahore region. For this purpose, a large data set of the groundwater quality parameters (for a period of 2005–2016) was obtained from the deep unconfined aquifers. GIS-based water quality index (WQI) and entropy water quality index (EWQI) models were prepared using 15 water quality parameters pH (power of hydrogen), TDS (Total dissolve solids), EC (Electrical conductivity), TH (Total hardness), Ca2+ (Calcium), Mg2+ (Magnesium), Na+ (Sodium), K+ (Potassium), Cl− (Chloride), As (Arsenic), F (Fluoride), Fe (Iron), HCO3– (Bicarbonate), NO3− (Nitrate), and SO42− (Sulfate). The data analysis exhibits that 12% of the groundwater samples fell within the category of poor quality that helped to identify the permanent epicenters of deteriorating water quality index in the study area. As per the entropy theory, Fe, NO3−, K, F, SO42− and As, are the major physicochemical parameters that influence groundwater quality. The spatio-temporal analysis of the large data set revealed an extreme behavior in pH values along the Hudiara drain, and overall high arsenic concentration levels in most of the study area. The geochemical analysis shows that the groundwater chemistry is strongly influence by subsurface soil water interaction. The research highlights the significance of using GIS-based spatio-temporal and geostatistical tools to analyze the large data sets of physicochemical parameters at regional level for the detailed source characterization studies.

Modification of DNMTs Gene Expressions by GST O1 and GST O2 Polymorphism in Chronic Arsenic Exposed People With and Without Malignancy from West Bengal, India

Chronic Arsenic exposure causes skin manifestations and even cancer. However, the response varies widely among persons despite receiving similar cumulative exposure through their food or drinking water or both. These differentiations in manifestations may be due to polymorphic distribution of arsenic metabolizing genes among exposed people. Polymorphism of GSTO1, GSTO2 and their frequency distribution may modify skin manifestations and development of arsenic-induced cancer in exposed persons through food chain. Polymorphic variations of GSTO1 and GSTO2 have been studied on 112 subject including control. They were recruited from one of major arsenic affected district, Nadia of West Bengal, India, having high arsenic content in their food. Exposed subjects were categorized into three groups, i.e., with arsenical skin lesions and without arsenical skin lesions and arsenic-induced cancer. Control subjects were 33 in number. Concentration of arsenic in their urine, hair, drinking water, food, extent of clinical manifestations, GST O1and O2status was determined. DNMT1, 3A, and 3B were studied for their expression profile and analyzed with GSTO1 and O2 polymorphisms. Genetic polymorphism of GSTO1 gene polymorphism is significantly associated with arsenic-induced skin scores in skin lesion positive cases and arsenic-induced cancer cases and also significant increase is seen in DNMT expression and MDA level in exposed cases with homozygous wild type variants. Total urinary arsenic decreases significantly in wild type GSTO1 genotype, although, GSTO2 polymorphism showed no statistically significant differences in skin manifestations, and DNMTs expression. Frequency of GSTO1 and O2 polymorphic variety showed prevalence of wild type homozygous in arsenic-induced cancer cases. GSTO1 polymorphism shows significant association with DNMT expression profile in arsenic exposed people.

Groundwater Arsenic-Attributable Cardiovascular Disease (CVD) Mortality Risks in India

Cardiovascular diseases (CVDs) have been recognized as the most serious non-carcinogenic detrimental health outcome arising from chronic exposure to arsenic. Drinking arsenic contaminated groundwaters is a critical and common exposure pathway for arsenic, notably in India and other countries in the circum-Himalayan region. Notwithstanding this, there has hitherto been a dearth of data on the likely impacts of this exposure on CVD in India. In this study, CVD mortality risks arising from drinking groundwater with high arsenic (&gt;10 μg/L) in India and its constituent states, territories, and districts were quantified using the population-attributable fraction (PAF) approach. Using a novel pseudo-contouring approach, we estimate that between 58 and 64 million people are exposed to arsenic exceeding 10 μg/L in groundwater-derived drinking water in India. On an all-India basis, we estimate that 0.3–0.6% of CVD mortality is attributable to exposure to high arsenic groundwaters, corresponding to annual avoidable premature CVD-related deaths attributable to chronic exposure to groundwater arsenic in India of between around 6500 and 13,000. Based on the reported reduction in life of 12 to 28 years per death due to heart disease, we calculate value of statistical life (VSL) based annual costs to India of arsenic-attributable CVD mortality of between USD 750 million and USD 3400 million.

Unraveling iron speciation on Fe-biochar with distinct arsenic removal mechanisms and depth distributions of As and Fe

Tailored manipulation of iron speciation has become a critical challenge for the further development of Fe-biochar as an economical and eco-friendly amendment for arsenic (As) immobilization. Herein, a series of Fe-biochars with manipulated iron speciations were fabricated by controlling the carbon structures and pyrolysis conditions. Results revealed that abundant labile-/amorphous-C induced more reductive-Fe(0) formation (10.9 mg g−1) in the Fe-biochar. The high Fe(0) content resulted in the effective As immobilization (4.34 mg g−1 As(V) and 7.72 mg g−1 As(III)) as evidenced by Pearson correlation coefficient (PCC) analysis. The hierarchical depth distributions of As and Fe on the Fe-biochar caused by the redox reaction and concomitant sorption of As proved the decisive role of Fe(0). An iron-oxide shell (~10–20 nm) with a high arsenic accumulation was revealed on the surface, while deeper within the particles, Fe(0) was found to be associated with elemental As (As(0), up to 19.4%). By contrast, pyrolysis with the stable-/graphitic-C generated more amorphous-Fe (61.9 mg g−1) on the Fe-biochar, which accounted for the high As removal (10.1 mg g−1 As(V) and 7.70 mg g−1 As(III)) despite the limited Fe(0) content. In comparison to the reductive Fe(0), distinct depth distribution was observed that the As/Fe ratio was marginally changed within 200 nm depth of the amorphous-Fe biochar after As decontamination. Co-precipitation of As with Fe released from amorphous-Fe contributed to this depth distribution, as evidenced by the high correlation between released-Fe and As immobilization capacity (PCC as 0.84–0.95). This study unveiled a crucial role of iron speciation on distinct mechanisms for As removal, guiding the application-oriented design of multifunctional Fe-biochar for broad environmental remediation.

Wild Zebrafish Sentinels: Biological Monitoring of Site Differences Using Behavior and Morphology.

Environmental change poses a devastating risk to human and environmental health. Rapid assessment of water conditions is necessary for monitoring, evaluating, and addressing this global health danger. Sentinels or biological monitors can be deployed in the field using minimal resources to detect water quality changes in real time, quickly and cheaply. Zebrafish (Danio rerio) are ideal sentinels for detecting environmental changes due to their biomedical tool kit, widespread geographic distribution, and well-characterized phenotypic responses to environmental disturbances. Here, we demonstrate the utility of zebrafish sentinels by characterizing phenotypic differences in wild zebrafish between two field sites in India. Site 1 was a rural environment with flowing water, low-hypoxic conditions, minimal human-made debris, and high iron and lead concentrations. Site 2 was an urban environment with still water, hypoxic conditions, plastic pollution, and high arsenic, iron, and chromium concentrations. We found that zebrafish from Site 2 were smaller, more cohesive, and less active than Site 1 fish. We also found sexually dimorphic body shapes within the Site 2, but not the Site 1, population. Advancing zebrafish sentinel research and development will enable rapid detection, evaluation, and response to emerging global health threats.

Formation of arsenic−copper-containing particles and their sulfation decomposition mechanism in copper smelting flue gas

The heat recovery steam generator (HRSG) of copper smelting generates a large number of arsenic−copper- containing particles, and the in-situ separation of arsenic and copper is of importance for cutting off environmental risk and realizing resource recovery. The formation of arsenic−copper-containing particles was simulated, the method of in-situ decomposition of arsenic−copper-containing particles by pyrite was proposed, and the decomposition mechanism was confirmed. It was found that particles with high arsenic content were formed in the simulated HRSG, and copper arsenate was liable for the high arsenic content. Pyrite promoted the sulfation of copper, leading to the in-situ decomposition of copper arsenate. In this process, gaseous arsenic was released, and thus the separation of arsenic and copper was realized.

Living to the High Extreme: Unraveling the Composition, Structure, and Functional Insights of Bacterial Communities Thriving in the Arsenic-Rich Salar de Huasco Altiplanic Ecosystem.

ABSTRACTMicrobial communities inhabiting extreme environments such as Salar de Huasco (SH) in northern Chile are adapted to thrive while exposed to several abiotic pressures and the presence of toxic elements such as arsenic (As). Hence, we aimed to uncover the role of As in shaping bacterial composition, structure, and functional potential in five different sites in this altiplanic wetland using a shotgun metagenomic approach. The sites exhibit wide gradients of As (9 to 321 mg/kg), and our results showed highly diverse communities and a clear dominance exerted by the Proteobacteria and Bacteroidetes phyla. Functional potential analyses show broadly convergent patterns, contrasting with their great taxonomic variability. As-related metabolism, as well as other functional categories such as those related to the CH4 and S cycles, differs among the five communities. Particularly, we found that the distribution and abundance of As-related genes increase as the As concentration rises. Approximately 75% of the detected genes for As metabolism belong to expulsion mechanisms; arsJ and arsP pumps are related to sites with higher As concentrations and are present almost exclusively in Proteobacteria. Furthermore, taxonomic diversity and functional potential are reflected in the 12 reconstructed high-quality metagenome assembled genomes (MAGs) belonging to the Bacteroidetes (5), Proteobacteria (5), Cyanobacteria (1), and Gemmatimonadetes (1) phyla. We conclude that SH microbial communities are diverse and possess a broad genetic repertoire to thrive under extreme conditions, including increasing concentrations of highly toxic As. Finally, this environment represents a reservoir of unknown and undescribed microorganisms, with great metabolic versatility, which needs further study.IMPORTANCE As microbial communities inhabiting extreme environments are fundamental for maintaining ecosystems, many studies concerning composition, functionality, and interactions have been carried out. However, much is still unknown. Here, we sampled microbial communities in the Salar de Huasco, an extreme environment subjected to several abiotic stresses (high UV radiation, salinity and arsenic; low pressure and temperatures). We found that although microbes are taxonomically diverse, functional potential seems to have an important degree of convergence, suggesting high levels of adaptation. Particularly, arsenic metabolism showed differences associated with increasing concentrations of the metalloid throughout the area, and it effectively exerts a significant pressure over these organisms. Thus, the significance of this research is that we describe highly specialized communities thriving in little-explored environments subjected to several pressures, considered analogous of early Earth and other planets, that have the potential for unraveling technologies to face the repercussions of climate change in many areas of interest.

High nuclear expression of HIF1α, synergizing with inactivation of LIMD1 and VHL, portray worst prognosis among the bladder cancer patients: association with arsenic prevalence.

Our study was aimed to understand the importance of LIMD1-VHL-HIF1α pathway in development of bladder carcinoma (BlCa) in association with arsenic prevalence. At first, the mRNA expression pattern of the genes of this pathway (LIMD1, VHL and HIF1α) was checked in GEO datasets and in our samples. Next, genetic and epigenetic profiling of LIMD1 and VHL was done in our sample pool, validated in T24 BlCa cell line. The results were next correlated with various clinico-pathological parameters. Differential under-expression of LIMD1 and VHL genes was found in muscle-invasive BlCa (MIBC) in comparison to non-muscle-invasive BlCa (NMIBC). However, HIF1α protein, but mRNA, was found to be overexpressed among the MIBC samples; depicting the probability of HIF1α protein stabilization. Analysis of genetic and epigenetic profiles of LIMD1 and VHL exposed a frequent promoter methylation of LIMD1 gene in MIBC samples. Further, in-depth look into the results unveiled that the high nuclear expression of HIF1α was significantly correlated with genetic alterations of LIMD1, alone or in combination with VHL. Moreover, treating the T24 cells with a de-methylating agent (5-aza-2'-deoxycytidine) re-expressed the methylated LIMD1 and VHL genes, which in turn, reduced the HIF1α protein level significantly. Additionally, patients with high arsenic content (> 112ng/g, AsH) seemed to have recurrent promoter methylation in LIMD1, as well as co-methylation/alteration of LIMD1 and VHL gene. Lastly, high nuclear expression of HIF1α in association with co-alteration of VHL and LIMD1 showed the worst overall survival (OS) among the patients. To conclude, MIBC samples portrayed higher alterations in VHL and LIMD1, thereby, stabilizing HIF1α protein and lowering the OS of patients.

Separation and stabilization of arsenic in copper smelting wastewater by zinc slag

Copper smelting wastewater shows strong acidity, has a high arsenic concentration and has many types of heavy metals, which not only restricts the sustainable development of copper smelting enterprises but also poses a danger to the ecological environment. Here, we propose a new process for treating copper smelting wastewater with zinc slag. We studied both the solid-liquid chemical reaction process as well as the mechanism by which zinc slag removes arsenic in copper smelting wastewater in a water bath at 85 °C under atmospheric pressure. Specifically, 5 g of zinc slag reacted with copper smelting wastewater with an initial arsenic concentration of 6000 mg/L for 4 h resulted in an arsenic removal rate of 99.65%, and the leaching concentration of arsenic in the toxicity characteristic leaching procedure experiment was only 0.52 mg/L. Zinc slag is dissolved in Copper smelting wastewater to release iron ions and silicate. The solid-liquid reaction of the two is accompanied by coprecipitation of iron arsenate and the in-situ covering of silica gel, resulting in a core-shell precipitate with iron arsenate as the core and silica gel as the shell. The colloidal chemistry of silica gel and cations and its chemical stability can effectively prevent the dissolution of arsenic ions and significantly improve the stability of iron arsenate. Zinc slag, a dual functional material for removing arsenic and fixing arsenic, shows extraordinary potential for the removal and fixation of arsenic in copper smelting wastewater. This approach could further improve wastewater treatment in the non-ferrous smelting industry.

4DEMON: Integrating 40 Years of Data on PCB and Metal Contamination in Marine Sediments of the Belgian Part of the North Sea

The assessment of historical data is important to understand long-term changes in the marine environment. Whereas time series analyses based on monitoring data typically span one or two decades, this work aimed to integrate 40 years of monitoring and research data on polychlorinated biphenyls (PCBs) and metals in the Belgian Part of the North Sea (BPNS). Multiple challenges were encountered: sampling locations changed over time, different analytical methods were applied, different grain size fractions were analyzed, appropriate co-factors were not always analyzed, and measurement uncertainties were not always indicated. These issues hampered the use of readily available, highly standardized trend modeling approaches like those proposed by regional sea conventions such as OSPAR, named after the Oslo and Paris conventions.Therefore, we applied alternative approaches, allowing us to include most older historical data that have been obtained during the nineteen seventies and eighties. Our approach included reproducible and quality controlled procedures from data collection up to data assessment. It included spatial clustering, data normalization and parametric linear mixed effect modeling. A Ward hierarchical clustering was applied on recently obtained contaminant data, as the basis for a spatial division of the BPNS into five distinct areas with different contamination profiles. To minimize the risk of normalization errors for the metal data analyses, four normalization approaches were applied and mutually compared: granulometric and nickel (Ni) normalization, next to two hybrid normalization methods combining aluminum (Al) and iron (Fe) normalization. The long-term models revealed decreasing trends for most metals, except zinc (Zn) for which three out of four models showed increasing concentrations in all five zones of the BPNS. Offshore sediments contained the lowest normalized mercury (Hg) and cadmium (Cd) concentrations but high arsenic (As) concentrations. Trend analysis revealed a strong decrease in PCB concentrations in the nineteen eighties and nineties, followed by a slight increase over the last decade. The extended timeframe for contaminant assessment, as applied in this study, is of added value for scientists and policy makers, as the approach allows to detect trends and effects of anthropogenic activities within the marine environment within a broad perspective.

Deposition of Arsenic from Nitric Acid Leaching Solutions of Gold–Arsenic Sulphide Concentrates

At present, the processing of refractory gold–arsenic sulphide concentrates is becoming more relevant due to the depletion of rich crude ore reserves. In the process of the nitric acid leaching of arsenic sulphide minerals, solutions are formed containing 20–30 g/L of arsenic (III). Since market demand for arsenic compounds is limited, such solutions are traditionally converted into poorly soluble compounds. This paper describes the investigation of precipitating arsenic sulphide from nitric acid leaching solutions of refractory sulphide raw materials of nonferrous metals containing iron (III) ions using sodium hydrosulphide with a molar ratio of NaHS/As = 2.4–2.6, which is typical for pure model solutions without oxidants. The work studied the effect of temperature, the pH of the solution and the consumption of NaHS and seed crystal on this process. The highest degree of precipitation of arsenic (III) sulphide (95–99%) from nitric acid leaching solutions containing iron (III) ions without seed occurs with a pH from 1.8 to 2.0 and a NaHS/As molar ratio of 2.8. The introduction of seed crystal significantly improves the precipitation of arsenic (III) sulphide. An increase in seed crystal consumption from 0 to 34 g/L in solution promotes an increase in the degree of transition of arsenic to sediment from 36.2 to 98.1% at pH = 1. According to SEM/EDS and XRF sediment data, from the results of experiments on the effect of As2S3 seed crystal consumption, acidity and molar ratio of NaHS/As on the precipitation of arsenic (III) sulphide and the Fetotal/Fe2+ ratio in the final solution, it can be concluded that the addition of a seed accelerates the crystallisation of arsenic (III) sulphide by increasing the number of crystallisation centres; as a result, the deposition rate of As2S3 becomes higher. Since the oxidation rate of sulphide ions to elemental sulphur by iron (III) ions does not change significantly, the molar ratio of NaHS/As can be reduced to 2.25 to obtain a precipitate having a lower amount of elemental sulphur and a high arsenic content similar to that precipitated from pure model solutions.

Insight into the Influence of Mineralogical Properties of Pristine Pyrite on Its Bioleaching with Thermophiles

ABSTRACT To expound the relationship between bioleaching behaviors and mineralogical properties of pristine pyrite samples, chemical compositions, semiconductive properties, surface morphologies, and chemical species of synsedimentary pyrite (SSP) and mesothermal pyrite (MTP) were compared, accompanying with bioleaching behaviors analysis by three thermophiles. Mineralogical characterizations showed that both pyrites belonged to p-type semiconductors with an S/Fe ratio higher than 2, and the arsenic content in MTP was as high as 0.6%. The fractured surface of SSP had more kinks and steps, and higher concentrations of S2- and oxides, as compared with that of MTP. Bioleaching results indicated that SSP was leached faster than MTP. The more kinked and stepped structures and the larger contents of S2- and oxides on pyrite surfaces were the dominant reasons for the faster bioleaching kinetics of SSP. The high arsenic content in MTP limiting the cell growth was another cause for its slower leaching.

Separation of arsenic from lead smelter ash by acid leaching combined with pressure oxidation

Smelter ash contains appreciable valuable metals and a large amount of arsenic due to its volatilization. The safe treatment of smelter ash with high arsenic is of great importance both for environmental protection and resource comprehensive utilization. In the present study, an acid leaching process combined with pressure oxidation was used to separate arsenic from lead smelter ash. In the acid leaching process, the effects of acid concentration, partial oxygen pressure, temperature, liquid-to-solid ratio, leaching time, and agitating speed were investigated, and the optimized leaching conditions were established: 100 g/L of H2SO4 concentration, 2.5 h of leaching time, 170 °C of temperature, 10 mL/g of liquid-to-solid ratio, 500r/min of agitating speed and 2.5 MPa of partial oxygen pressure. Under these conditions, the extractions of As, Cd, In, Zn, and Sb were 98.19%, 98.98%, 91.72%, 95.32%, and 24.23% respectively. The kinetic study reveals that the arsenic leaching process is in accordance with the diffusion-controlled type in the Avrami model, and the apparent activation energy is 2.38 kJ/mol.

English

Experiments were conducted with arsenic-hyperaccumulator, Pteris vittata, and non-hyperaccumulator, Pteris ensiformis, subjected to various arsenic toxicity levels (0 to 1500 mg As kg-1) in peat-moss or soil for up to 14 weeks, to evaluate phenotypic responses and total lipid with fatty acid profiles, and P. vittata influence on rhizosphere enzyme activities. P. ensiformis exhibited significant phenotypic toxicity response compared to P. vittata. P. vittata sequestered significantly (p&lt;0.5) higher arsenic (5,160.6 mg As kg-1) than P. ensiformis (313.4 mg As kg-1). Cellular damage and physiological death occurred in P. ensiformis with alteration in fatty acids and lipid compositions but no significant changes in P. vittata. Both showed no detectable C16:3 but a decrease in C18:3, which was more pronounced in P. ensiformis (51.2%); hence, are reported as C18:3 plants for the first time. Acid phosphatase, &beta;-glucosidase, alrysulphatase, and N-acetyl-&beta;-D-glucosaminidase activities were inhibited by As and significantly (p&lt;0.5) negatively correlated to As concentration. Enzyme inhibition range from 6% in &beta;-glucosidase to 67% in N-acetyl-&beta;-D-glucosaminidase. These results revealed P. vittata phenotypic tolerance to As stress was mediated through metabolic-readjustment, especially its fatty acid and lipid compositions. Additionally, P. vittata rhizospheric events modulate soil enzyme activities in the As-contaminated soil. Key words: Fern, heavy metal, phenotypic response, fatty acids, acid phosphatase, &beta;-glucosidase, alrysulphatase, N-acetyl-&beta;-D-glucosaminidase, rhizosphere.

Metal accumulations in aquatic organisms and health risks in an acid mine-affected site in South China

Metal contamination from base metal sulphide mines is a major environmental challenge that poses many ecological and health risks. We examined the metal concentrations in the Dabaoshan mine in South China in water, sediments, and aquatic organisms and their specific characteristics (i.e. size, body tissue, species, and habitat) along the Hengshi and Wengjiang River courses to assess acid mine drainage remediation efforts. Metal concentrations of arsenic, cadmium, chromium, copper, lead, nickel, thallium, and zinc were examined in tissues (i.e. gills, intestines, and muscles) of 17 freshwater species of fish, shrimps, and crabs. Metals in tissues followed the trend: intestines > gills > muscles; nearly all intestine samples exceeded the safe limits of metals analysed in this study. There is a positive correlation between distance from the mine and metal concentrations related to the flow of surface water and the habitat of aquatic organisms. The concentrations of arsenic, copper, and zinc were the highest in aquatic organisms, and the distribution was influenced by physical (distance from mine, currents, and seasonality), chemical (pH and competing ions), and biological (species, habitat, and predator–prey relation) factors. Large demersal fish and benthic fauna had higher concentrations of metals. Bioaccumulation and biomagnification of metals, as well as the high metal pollution index and target hazard quotient (arsenic, cadmium, copper, lead, thallium, and zinc), occurred in bottom feeders (C. aumtus, X. argentea) and fish belonging to higher trophic levels (P. fulvidraco, O. mossambicus). Lead and cadmium indicated the highest level of biomagnification from prey to predator. Health risks exist from the dietary intake of common aquatic species such as tilapia and carp besides crustaceans due to high arsenic, cadmium, lead, and thallium levels. Further reduction of metals is necessary to improve the effects of acid mine drainage in the catchment.