Isabel Rucandio

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.

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 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.

A simplified method for determination of organic mercury in soils

Monitoring levels of organic mercury species at very low concentrations in the environment is of concern due to their high toxicity. However, conventional methods for organic mercury determination are usually expensive and time consuming because they involve many preparation steps and require instrumentation which is not available in most laboratories. In order to make it easier the organic mercury determination this paper presents a simple, fast and reliable extraction method for isolating and quantifying the organic mercury fraction in soil samples. The proposed method is based on one single digestion stage using a CuBr2 solution in HCl to release the organic mercury compounds from the solid matrix and their simultaneous and selective extraction into dichloromethane. After the separation of the organic phase, reextraction into aqueous media using N-acetyl-L-cysteine solution allows the determination of the extracted organic mercury by electrothermal atomic absorption spectrometry with the direct mercury analyzer DMA-80. Experimental and instrumental variables were optimized by the analysis of synthetic samples of methylmercury dispersed in pulverized silica. The method was validated by the analysis of the certified CRM 580 reference material. The detection limit of the procedure is 9.6 ng of organic mercury per gram of dry soil. The applicability of the proposed method to real samples was demonstrated through recovery studies of methylmercury in spiked soils. In addition, the influence of the TOC (Total Organic Carbon) content in soils was studied. The recoveries obtained under optimal experimental conditions ranged from 90% to 105% for all tested samples, indicating the suitability of the proposed method for determination of the organic mercury fraction in soils.

Determination of rare earth and concomitant elements in magnesium alloys by inductively coupled plasma optical emission spectrometry

An Inductively Coupled Plasma Optical Emission Spectrometry method for simultaneous determination of Al, Ca, Cu, Fe, In, Mn, Ni, Si, Sr, Y, Zn, Zr and rare earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) in magnesium alloys, including the new rare earth elements-alloyed magnesium, has been developed. Robust conditions have been established as nebulizer argon flow rate of 0.5mLmin(-1) and RF incident power of 1500W, in which matrix effects were significantly reduced around 10%. Three acid digestion procedures were performed at 110°C in closed PFA vessels heated in an oven, in closed TFM vessels heated in a microwave furnace, and in open polypropylene tubes with reflux caps heated in a graphite block. The three digestion procedures are suitable to put into solution the magnesium alloys samples. From the most sensitive lines, one analytical line with lack or low spectral interferences has been selected for each element. Mg, Rh and Sc have been studied as internal standards. Among them, Rh was selected as the best one by using Rh I 343.488nm and Rh II 249.078nm lines as a function of the analytical lines. The trueness and precision have been established by using the Certified Reference Material BCS 316, as well as by means of recovery studies. Quantification limits were between 0.1 and 9mgkg(-1) for Lu and Pr, respectively, in a 2gL(-1) magnesium matrix solution. The method developed has been applied to the commercial alloys AM60, AZ80, ZK30, AJ62, WE54 and AE44.

Assessment of a sequential extraction procedure for arsenic partitioning and application to samples from different pollution sources

In this paper, a seven-step sequential extraction procedure (SEP) is proposed to evaluate As fractionation in environmental solid samples of concern. The protocol covers the most relevant As-bearing phases in soils and sediments, stressing the importance of the most mobilizable fractions, in accordance with their potential environmental hazards. The considered fractions are (1) readily soluble As, (2) strongly adsorbed As onto mineral surfaces, (3) As associated with Al oxyhydroxides, (4) As bound to organic matter, (5) As incorporated into amorphous Fe oxyhydroxides, (6) As associated with poorly crystalline Fe (hydr)oxides and (7) As coprecipitated with refractory minerals. Although this protocol is suitable for all kinds of environmental solid samples, it was especially designed for those that are highly polluted. Hence, optimization of some operational parameters in every extraction step such as the extraction time and solid-to-solution ratio was carried out by using highly polluted solids as control samples. The selectivity of the selected agents for every extraction step was assured through experiments with natural and synthetic matrices of As-bearing minerals and As-spiked materials. The validation of the proposed method was accomplished with five certified materials of soils and sediments covering a diverse range of As contents. The results of its application to As-contaminated samples from different geological origins and within a wide range of As contents revealed As fractionation to be largely in accordance with the pollution source of samples and with their geochemical composition, which confirmed this methodology to be suitable for fractionation assessment of As in environmental solid samples of different nature. In addition, one of the strengths of this method is that the simplicity of its steps would easily allow for its automation.

Mercury Soil Pollution in Spain: A Review

Spain has been the main mercury producer worldwide, with mines or mining districts scattered across its geography. In particular, two main areas show generally higher contents of this element in the soils, namely, Asturias (or the Cantabrian Zone in geological terms) and the Almaden area in the Southern Central Iberian Zone. In this review six different aspects are considered: (1) distribution of total concentrations, (2) mercury mobility and availability, (3) soil to plant transfer, (4) mercury transfer to animal biota, (5) soil to atmosphere transfer and (6) possibility of remediation for sites polluted by mercury. The conclusions drawn from the available results highlight significant differences in contents, mobility and transfer processes depending on the different types of mercury pollution and different climatic conditions. A general background level for Spanish soils can be established at 20 μg kg−1, but very different ranges can be found in different areas according to the volumetric importance of each source and depending on other local factors. Mercury mining appears to be the most important source of soil pollution, and studies on the possible mobility and transfer to other environmental compartments demonstrate the highest levels at which mercury affects the population living in the proximity of such sources.

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.