Assessment of the ecological risk and mobility of arsenic and heavy metals in soils and mine tailings from the Carmina mine site (Asturias, NW Spain).

An evaluation of the pollution, distribution, and mobility of arsenic and heavy metals in spoil heaps and soils surrounding the abandoned Carmina lead-zinc mine (Asturias, northern Spain) was carried out. Fractionation of arsenic was performed by an arsenic-specific sequential extraction method; while, heavy metal fractionations was carried out using the protocol of the Bureau Community of Reference (BCR) (now renamed Standards, Measurements and Testing Programme). Arsenic appeared predominantly associated with amorphous iron oxyhydroxides. Among the heavy metals, lead and zinc showed high availability since significant amounts were extracted in the nonresidual fractions; whereas, chromium, copper and nickel showed very low availability, indicating their lithogenic origins. The results showed that the extractability of heavy metals in soils is influenced mainly by the presence of iron and manganese oxides as well as by pH and Eh. Multiple pollution indices, including the enrichment factor (EF), geoaccumulation index (Igeo), ecological risk index (Er) and potential ecological risk index (PERI), were used to assess the degree of soil pollution in the mine area. All results showed that lead was the key factor causing the pollution and ecological risk in the studied area, and copper, zinc and arsenic also had significant contributions. Notably, the sites at higher risk coincided with those with high availability of arsenic and heavy metals. This study provides an integrative approach that serves as a powerful tool to evaluate the metal pollution status and potential threats to the local environment of abandoned mining areas, and the results are useful for making management decisions in these areas.

Bioaccumulation of Non-Essential Trace Elements Detected in Women's Follicular Fluid, Urine, and Plasma Is Associated with Poor Reproductive Outcomes following Single Euploid Embryo Transfer: A Pilot Study.

This study aims to determine the association of non-essential trace elements present in follicular fluid, plasma, and urine with reproductive outcomes of women undergoing intracytoplasmic sperm injection (ICSI), preimplantation genetic testing for aneuploidies (PGT-A) and single frozen euploid embryo transfer (SET/FET). This single-center, prospective cohort study included sixty women undergoing ICSI with PGT-A and SET/FET between 2018 and 2019. Urine, plasma and follicular fluid samples were collected on the vaginal oocyte retrieval day to simultaneously quantify ten non-essential trace elements (i.e., Ba, Sr, Rb, Sn, Ti, Pb, Cd, Hg, Sb, and As). We found several associations between the levels of these non-essential trace elements and clinical IVF parameters. Specifically, the increased levels of barium in follicular fluid were negatively associated with ovarian function, pre-implantation development and embryo euploidy, while elevated strontium concentrations in this biofluid were negatively associated with impaired blastulation and embryo euploidy. Elevated plasma strontium levels were negatively associated with ovarian function, fertilization and blastulation. Enhanced presence of other trace elements in plasma (i.e., rubidium and arsenic) were associated with a diminished ovarian function and limited the number of recovered oocytes, mature oocytes and zygotes, respectively. Fully adjusted models suggested significantly lower odds of achieving a live birth when increased concentrations of barium and tin were found in urine.

Comparison of Thermal and Laser-Reduced Graphene Oxide Production for Energy Storage Applications.

A way to obtain graphene-based materials on a large-scale level is by means of chemical methods for the oxidation of graphite to obtain graphene oxide (GO), in combination with thermal, laser, chemical and electrochemical reduction methods to produce reduced graphene oxide (rGO). Among these methods, thermal and laser-based reduction processes are attractive, due to their fast and low-cost characteristics. In this study, first a modified Hummer's method was applied to obtain graphite oxide (GrO)/graphene oxide. Subsequently, an electrical furnace, a fusion instrument, a tubular reactor, a heating plate, and a microwave oven were used for the thermal reduction, and UV and CO2 lasers were used for the photothermal and/or photochemical reduction. The chemical and structural characterizations of the fabricated rGO samples were performed by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), scanning electron microscope (SEM) and Raman spectroscopy measurements. The analysis and comparison of the results revealed that the strongest feature of the thermal reduction methods is the production of high specific surface area, fundamental for volumetric energy applications such as hydrogen storage, whereas in the case of the laser reduction methods, a highly localized reduction is achieved, ideal for microsupercapacitors in flexible electronics.

Preparation of graphene thin films for radioactive samples.

A new method for the preparation of conductive thin films is presented. The metallization of VYNS films guarantees the electrical conductivity but it results in the breaking of a high proportion of them. Graphene, a two-dimensional nanostructure of monolayer or few layers graphite has attracted a great deal of attention because of its excellent properties such as a good chemical stability, mechanical resistance and extraordinary electronic transport properties. In this work, the possibilities of graphene have been explored as a way to produce electrical conductive thin films without an extra metallization process. The procedure starts with preparing homogenous suspensions of reduced graphene oxide (rGO) in conventional VYNS solutions. Ultra-sonication is used to ensure a good dispersibility of rGO. Graphene oxide (GO) is prepared via oxidation of graphite and subsequent exfoliation by sonication. Different chemically rGO were obtained by reaction with hydrazine sulfate, sodium borohydride, ascorbic acid and hydroiodic acid as reducing agents. The preparation of the thin graphene films is done in a similar way as the conventional VYNS foil preparation procedure. Drops of the solution are deposited onto water. The graphene films have been used to prepare sources containing some electron capture radionuclides ((109)Cd, (55)Fe, (139)Ce) with an activity in the order of 3kBq. The samples have been measured to test the attainable low energy electron efficiency and the energy resolution of Auger and conversion electrons by 4π (electron capture)-γ coincidence measurements. The 4π (electron capture)-γ coincidence setup includes a pressurized proportional counter and a NaI(Tl) detector. Tests with different pressures up to 1000kPa were carried out. All these tests show similar values in both parameters (efficiency and resolution) as those obtained by using the conventional metallized films without the drawback of the high percentage of broken films.

Arsenic partitioning among particle-size fractions of mine wastes and stream sediments from cinnabar mining districts.

Tailings from abandoned mercury mines represent an important pollution source by metals and metalloids. Mercury mining in Asturias (north-western Spain) has been carried out since Roman times until the 1970s. Specific and non-specific arsenic minerals are present in the paragenesis of the Hg ore deposit. As a result of intensive mining operations, waste materials contain high concentrations of As, which can be geochemically dispersed throughout surrounding areas. Arsenic accumulation, mobility and availability in soils and sediments are strongly affected by the association of As with solid phases and granular size composition. The objective of this study was to examine phase associations of As in the fine grain size subsamples of mine wastes (La Soterraña mine site) and stream sediments heavily affected by acid mine drainage (Los Rueldos mine site). An arsenic-selective sequential procedure, which categorizes As content into seven phase associations, was applied. In spite of a higher As accumulation in the finest particle-size subsamples, As fractionation did not seem to depend on grain size since similar distribution profiles were obtained for the studied granulometric fractions. The presence of As was relatively low in the most mobile forms in both sites. As was predominantly linked to short-range ordered Fe oxyhydroxides, coprecipitated with Fe and partially with Al oxyhydroxides and associated with structural material in mine waste samples. As incorporated into short-range ordered Fe oxyhydroxides was the predominant fraction at sediment samples, representing more than 80% of total As.

Total mercury, organic mercury and mercury fractionation in soil profiles from the Almadén mercury mine area.

Soil profiles located in the mining district of Almadén were investigated for total Hg, organic Hg fraction and Hg distribution by selective sequential extraction. A four-step sequential extraction method (labile Hg species, humic and fulvic complexes, elemental Hg and bound to crystalline oxides and Hg sulfide and refractory species) was performed. Total Hg concentrations ranged from 13 to 64 mg per kg dry mass. A clear relationship between the depth and Hg content was found since Hg concentration decreases downwards, which is indicative of anthropogenic contamination via deposition processes from nearby mine waste. Significant organic Hg concentrations were found in all the tested soil profiles ranging from 79 to 287 µg kg(-1) (dry weight). It seems that organic Hg was strongly influenced by elemental Hg (r = 0.79) and to a lesser extent by the organic carbon content (r = 0.57). The fractionation revealed that Hg exists mainly as cinnabar in the studied soils, which is one of the least available and mobile Hg species, and as elemental Hg as well. The most mobile Hg fractions only accounted for 3.2 to 7.7% of the total Hg content, with the main contribution being the humic and fulvic complexes fraction. The elemental Hg fraction increased with depth indicating a migration to deeper soil layers. In contrast, the surface layers showed an enrichment in the fraction bound to sulfide, which means that Hg is mostly deposited as cinnabar particles from non-processed ore in this area.

Assessment of a sequential extraction method to evaluate mercury mobility and geochemistry in solid environmental samples.

The development of a sequential extraction method for mercury in solid environmental samples is presented. The scheme recognizes and quantifies four major phase associations of mercury: "Labile mercury species", "Hg bound to humic and fulvic complexes", "elemental Hg and bound to crystalline oxides" and "Hg sulfide and refractory species". Model solids were used in this study to evaluate different extracting solutions and to determine optimum extraction conditions. Sequential and single-step extractions were conducted to evaluate the interaction among the successive steps. Different variables such as extractant concentration, time, temperature and number of extractions were optimized for each stage when necessary. The selectivity of the selected extractions was assured through experiments with natural and synthetic matrices of some specific Hg-bearing phases. The suitability of the proposed method was evaluated by using four certified reference materials from different Hg sources, physicochemical properties and total Hg content (from 0.3µgg(-1) to 33µgg(-1)). Recovery of total Hg by the sum of fractions in reference materials showed that the accuracy of the method ranges from 85 percent to 105 percent.

Arsenic pollution and fractionation in sediments and mine waste samples from different mine sites.

A characterization of arsenic pollution and its associations with solid mineral phases in sediments and spoil heap samples from four different abandoned mines in Spain is performed. Three of them were mercury mines located in the same mining district, in the province of Asturias, and the other one, devoted to arsenic mining, is in the province of León. A sequential extraction procedure, especially developed for arsenic, was applied for the study of arsenic partitioning. Very high total arsenic concentrations ranging 300-67,000 mg·kg(-1) were found. Arsenic fractionation in each mine is broadly in accordance with the mineralogy of the area and the extent of the mine workings. In almost all the studied samples, arsenic appeared predominantly associated with iron oxyhydroxides, especially in the amorphous form. Sediments from cinnabar roasted piles showed a higher arsenic mobility as a consequence of an intense ore treatment, posing an evident risk of arsenic spread to the surroundings. Samples belonging to waste piles where the mining activity was less intense presented a higher proportion of arsenic associated with structural minerals. Nevertheless, it represents a long-term source of arsenic to the environment.

Comparison of three sequential extraction procedures for fractionation of arsenic from highly polluted mining sediments.

Three sequential extraction procedures were evaluated for the study of fractionation of arsenic in environmental solid samples. The procedures considered were as follows: i) the standardized and widely recognised BCR procedure, conceived for the study of the partitioning of heavy metals; ii) the procedure developed by Manful, who adapted a phosphorus scheme for arsenic fractionation; and iii) a novel sequential extraction scheme especially devised for arsenic. The efficiency and suitability of these methods and the corresponding extraction steps for partitioning arsenic obtained from the most important solid forms were tested by application of the methods to real sediment samples heavily polluted by mining activity. Results showed the BCR scheme was inappropriate for arsenic fractionation. The procedure could, nevertheless, be a first approach for the assessment of arsenic partitioning, because its first extraction step can be regarded as adequate for the estimation of the most easily mobilizable arsenic. Although the Manful scheme results in a more differentiated arsenic pattern, some drawbacks arise from the lack of selectivity of some of the reagents used, for example overlapping of specific target phases, overestimation of adsorbed arsenate because of inadequate coprecipitation processes, and the inability to discriminate among amorphous and crystalline oxyhydroxides which are mainly responsible for arsenic retention. The novel procedure achieves the most suitable arsenic fractionation, because the main phases retaining arsenic are selectively targeted according to mobilization potential. In addition, the simplicity of its extraction steps would enable automation in a continuous flow scheme.

Arsenic contamination and speciation in surrounding waters of three old cinnabar mines.

The impact of arsenic pollution in waters from the surroundings of three abandoned Hg mines in Northern Spain, as well as reaching the Caudal River, was evaluated. For assessing the factors controlling arsenic release, an extensive study based on the physicochemical characterization and multivariate statistical analysis of waters upstream and downstream each mine site was performed. Waters downstream of the La Soterraña mine present the highest arsenic concentrations, up to 38.8 mg L(-1), coming mainly from the solubilisation of calcium, magnesium and strontium arsenates at a pH close to neutral. Although arsenic concentrations downstream of La Peña are markedly lower, these values remain too high, indicating that the encapsulation carried out in this spoil heap is insufficient. In addition, the high water flow in this point involves an extremely high input of arsenic to the surroundings (0.3 g s(-1)). Waters close to tailings from Los Rueldos suffer from acid mine drainage, provoking an important solubilisation of arsenic and heavy metals, a situation which is rapidly softened with distance. The study of arsenic speciation reveals the omnipresence of As(v) in waters from the three mines, whereas in La Peña low amounts of As(iii) were also detected. Different preservation methods for As speciation were compared, such as the addition of HCl, EDTA and the storage of samples without any additive, and no alteration of samples in any case up to nine months after the collection was observed. A study of seasonal variations of As and the main parameters affecting its concentration and speciation was completed throughout a year, showing no remarkable dependency with rainfall for any studied variable.

A methodological approach to evaluate arsenic speciation and bioaccumulation in different plant species from two highly polluted mining areas.

Arsenic accumulation and speciation in different plant species growing in two polluted sites were examined, in addition to arsenic transfer from soils to plants. The studied areas were two abandoned mercury mines in Northern Spain, La Soterraña and Los Rueldos. Plants accumulated extremely high amounts of arsenic in their tissues. Accumulation rates depend on both the grade of pollution of the site and on the plant species itself. Total arsenic concentrations varied depending on the part of the plant, with roots accumulating the most arsenic in all the studied plants (up to 1400 mg · kg(-1)). A suitable extraction method for arsenic speciation in the studied samples was developed and optimized using 0.3M orthophosphoric acid as the extracting agent in a graphite block digestion system at 90 °C for 1h. Extraction efficiencies were above 80% and speciation was not altered, since recoveries of the spiked arsenic species (As(III), As(V), DMA (dimethylarsonic acid) and MMA (monomethylarsonic acid)) were between 94 and 102%. Speciation studies were performed on the parts of each plant species by means of HPLC-ICP-MS with the results indicating no significant differences in the speciation between parts of the plants. As(V) was always the predominant species, although a non-negligible amount of As(III) was found for all samples. Little amounts of MMA and DMA occurred in certain samples. Arsenic uptake by plants depends on the plant available arsenic fraction in soils, here considered as the sum of water-soluble and phosphate-extractable fractions. Although soils from La Soterraña were less polluted, arsenic bioavailability was much higher than in Los Rueldos. Soil-to-plant transfer factors, based on total and available arsenic in soils, were evaluated for the studied plants. Dryopteris filix-mas and Calluna vulgaris (L.) Hull, from La Soterraña and Los Rueldos respectively, were the plants with the highest abilities to extract arsenic from their corresponding soils.

Surface water monitoring in the mercury mining district of Asturias (Spain).

Systematic monitoring of surface waters in the area of abandoned mine sites constitutes an essential step in the characterisation of pollution from historic mine sites. The analytical data collected throughout a hydrologic period can be used for hydrological modelling and also to select appropriate preventive and/or corrective measures in order to avoid pollution of watercourses. Caudal River drains the main abandoned Hg mine sites (located in Mieres and Pola de Lena districts) in Central Asturias (NW Spain). This paper describes a systematic monitoring of physical and chemical parameters in eighteen selected sampling points within the Caudal River catchment. At each sampling station, water flow, pH, specific conductance, dissolved oxygen, salinity, temperature, redox potential and turbidity were controlled "in situ" and major and trace elements were analysed in the laboratory. In the Hg-mineralised areas, As is present in the form of As-rich pyrite, realgar and occasionally arsenopyrite. Mine drainage and leachates from spoil heaps exhibit in some cases acidic conditions and high As contents, and they are incorporated to Caudal River tributaries. Multivariate statistical analysis aids to the interpretation of the spatial and temporary variations found in the sampled areas, as part of a methodology applicable to different environmental and geological studies.

Physicochemical characterization and mercury speciation of particle-size soil fractions from an abandoned mining area in Mieres, Asturias (Spain).

Soils from old cinnabar mining areas usually exhibit high Hg contents, whose mobility depends on soil parameters and environmental conditions. This paper presents the study of the Hg speciation in soil samples from an abandoned Hg mine and metallurgical plant in Mieres (Asturias, Spain), in relation to their mineralogical and chemical composition and their particle-size distribution. A characterization of samples was made by X-Ray Diffraction Spectrometry, Scanning Electron Microscopy and Atomic Absorption and Emission Spectroscopy analyses. A sequential extraction method was applied to establish Hg mobility in the samples and their grain-size subsamples. The highest Hg mobility was found in well-developed soils, as a consequence of the adsorption processes by iron and manganese oxides, whereas in those more contaminated soils, a higher proportion of Hg was leached in the non-mobile fraction. A higher Hg mobility was found in the finest grain-size subsamples, probably due to the accumulation of clay minerals and oxides in these ranges.

Distribution and mobility of mercury in soils from an old mining area in Mieres, Asturias (Spain).

Mercury content in soils near abandoned mine wastes in the mercury mining area of Mieres (Asturias, Spain) is highly elevated as a result of the long period of mining and abundant Hg production. In this work, an evaluation of Hg concentration, distribution, and mobility in three soil samples from the immediate vicinity of a chimney used for vapour evacuation during pyrometallurgical treatment of the ore was carried out. For that purpose, total Hg contents were determined for the original samples and their grain-size subsamples. The study of mercury mobility in the original samples and in the different particle-size subsamples was made by the application of a sequential extraction method. Results showed that Hg concentration in soils decreases directly with the distance from the chimney and the dispersion of Hg is not influenced by the topographic height of the site tested. The sample collected in the base of the chimney exhibited appreciable amounts of mobile Hg. In general, a higher Hg concentration was found for the finest particle-size subsamples. Hg mobility was found to be higher for quite developed soils. The sample collected downstream from the chimney showed a significant Hg mobile content as a result of a more intensive weathering. An increase of Hg mobility at decreasing particle size was found in all three analysed samples.

Study of the suitability of HNO3 and HCl as extracting agents of mercury species in soils from cinnabar mines.

The aim of this study was to compare the influence and feasibility of two common extracting agents (50% v/v HCl and 50% v/v HNO3) on the leaching of Hg from soils. The solubility of a number of Hg species in each acid solution was evaluated under selected conditions. Most species were quantitatively dissolved in both acids with the exception of HgS. The application of both acid solutions to a soil sample from the Almaden mining area provided different recoveries of Hg: about 5% in 50% v/v HNO3 and 50% in 50% v/v HCl. The following experiments were designed and developed in order to evaluate the matrix influence on HgS solubility and leaching: (1) study of the solubility of HgS in the presence of different potential interfering compounds such as FeCl3, KCl, KI, Fe2O3, CuSO4, FeSO4, MnO2 and NaNO3; (2) study of the recovery of HgS spiked in soil samples; (3) study of the extraction process in soil samples spiked with the critical interfering compounds. Results showed the existence of a greater matrix influence with the HCl solution, since much higher Hg recoveries were obtained with this reagent. In addition, the presence of nitrates and Mn oxides drastically promotes the solubility of HgS in an HCl solution. On the other hand, halide compounds drastically enhanced the extractability of Hg in the HNO3 and they must be considered as potential interfering compounds when this acid solution is used as extracting agent. In summary, neither acid is totally free of matrix effects from common soil constituents; conclusions about mercury mobility resulting from the general application of these extraction procedures must therefore be made with caution.

Application of ICP-OES to the determination of CuIn(1-x)Ga(x)Se2 thin films used as absorber materials in solar cell devices.

CuIn(1-x)Ga(x)Se2 [CIGS; x=Ga/(In+Ga)] thin films are among of the best candidates as absorber materials for solar cell applications. The material quality and main properties of the polycrystalline absorber layer are critically influenced by deviations in the stoichiometry, particularly in the Cu/(In+Ga) atomic ratio. In this work a simple, sensitive and accurate method has been developed for the quantitative determination of these thin films by inductively coupled plasma optical emission spectrometry (ICP-OES). The proposed method involves an acid digestion of the samples to achieve the complete solubilization of CIGS, followed by the analytical determination by ICP-OES. A digestion procedure with 50% HNO3 alone or in the presence of 10% HCl was performed to dissolve those thin films deposited on glass or Mo-coated glass substrates, respectively. Two analytical lines were selected for each element (Cu 324.754 and 327.396 nm, Ga 294.364 and 417.206 nm, In 303.936 and 325.609 nm, Se 196.090 and 203.985 nm, and Mo 202.030 and 379.825 nm) and a study of spectral interferences was performed which showed them to be suitable, since they offered a high sensitivity and no significant inter-element interferences were detected. Detection limits for all elements at the selected lines were found to be appropriate for this kind of application, and the relative standard deviations were lower than 1.5% for all elements with the exception of Se (about 5%). The Cu/(In+Ga) atomic ratios obtained from the application of this method to CIGS thin films were consistent with the study of the structural and morphological properties by X-ray diffraction (XRD) and scanning electron microscopy (SEM).

Study of extraction conditions for the quantitative determination of Hg bound to sulfide in soils from Almaden (Spain).

Almaden mine (Spain) is the largest source of cinnabar (HgS) in the world. The purpose of this study is to evaluate, compare and optimize the analytical conditions for the quantitative determination of Hg bound to sulfide in soil samples from mining area of Almaden. A sequential extraction procedure was performed in two stages. The first one was based on a nitric acid leaching. An optimization of certain extraction conditions in this stage was carried out. In order to assess the suitability of the nitric acid leaching, an additional study of possible interfering compounds that might promote the solubility of HgS in nitric acid was developed. The quantitative determination of Hg bound to sulfide was considered in a second stage. A comparative study was carried out among three different procedures: i) extraction with a saturated Na(2)S solution from the residue remaining in the first stage, ii) microwave assisted dissolution of the remaining Hg in this residue with aqua regia, and iii) quantification by difference between total Hg content and Hg extracted in the first stage. The recoveries of Hg bound to sulfide were found to be comparable for the three proposed procedures. Soil samples coming from Almaden mining area were analysed by this method. The distribution of Hg chemical forms was found to be similar for the two parcels tested, and the recoveries of bound to sulfide Hg ranged from 83% to 96% of total Hg content.