Search

Proportional electroluminescence (EL) in noble gases is used in two-phase detectors for dark matter searches to record (in the gas phase) the ionization signal induced by particle scattering in the liquid phase. The "standard" EL mechanism is considered to be due to noble gas excimer emission in the vacuum ultraviolet (VUV). In addition, there are two alternative mechanisms, producing light in the visible and near infrared (NIR) ranges. The first is due to bremsstrahlung of electrons scattered on neutral atoms ("neutral bremsstrahlung", NBrS). The second, responsible for electron avalanche scintillation in the NIR at higher electric fields, is due to transitions between excited atomic states. In this work, we have for the first time demonstrated two alternative techniques of the optical readout of two-phase argon detectors, in the visible and NIR range, using a silicon photomultiplier matrix and electroluminescence due to either neutral bremsstrahlung or avalanche scintillation. The amplitude yield and position resolution were measured for these readout techniques, which allowed to assess the detection threshold for electron and nuclear recoils in two-phase argon detectors for dark matter searches. To the best of our knowledge, this is the first practical application of the NBrS effect in detection science., Comment: 26 pages, 22 figures, 3 tables

Proximal sensors have been increasingly used for a variety of purposes worldwide, with great interest on portable X-ray fluorescence (pXRF) spectrometry applications in Soil Science. pXRF provides rapid, inexpensive, non-destructive, and environmentally-friendly elemental analysis in soils, rocks, sediments, plant tissues, water, and other matrices. While temperate regions concentrate the largest number of studies involving pXRF for soil characterization, tropical regions have recently demonstrated increasing interests in—and acceptance of—pXRF applications for soil-related studies due to the wide range of purposes in which this equipment can be utilized. However, the lack of a standard methodology for tropical soil analysis via pXRF coupled with the recognized variation of results according to the procedures used during analyses underlie the need for routine protocols for improving pXRF analyses in tropical environments. Besides establishing such a standard methodology, this review elucidates the main differences between soils from tropical and temperate regions that are key in pXRF research, presents state-of-the-art achievements in pXRF analysis, and envisions applications of pXRF in tropical soils.

In this study, a novel analytical method which consists of a combination of Fast Sequential Flame Atomic Absorption Spectrometry (FS-FAAS) and Continuous Flow Hydride Generation Atomic Absorption Spectrometry (CF-HGAAS) is proposed. The method developed was employed for the sequential determination of As and Sb at sub-μg L−1 levels in bottled mineral waters. A strong enhancement in the analytical throughput was obtained when compared with the traditional mono-element CF-HGAAS with a quartz tube atomizer (QTA). Variables which would affect the method performance such as Ar flow rate, HCl and NaBH4 concentrations as well as delay and integration time were optimized. A flame atomic absorption spectrometer working in fast sequential mode was used in all experiments. After just 20 s of read delay, As and Sb were sequentially determined in 6 s (3 s each element). A 26−2 fractional factorial design was employed for studies of potential interferents with transition metals that could be present in mineral water samples. Limits of detection obtained for As and Sb were 0.15 and 0.14 μg L−1, respectively. The accuracy of the proposed method was checked by the use of 2 certified reference materials: Trace elements in water (NIST 1643e) and Trace metals in drinking water (HPS TMDW). Good agreement between certified and found concentrations was observed. Finally, As and Sb were determined in commercial bottled mineral water samples. Adequate sensitivity, high throughput and minimization of reagents and sample consumption are the attractive features of this new method.

The ability to provide a fast and multielemental analytical response directly from a solid sample makes both laser-induced breakdown spectroscopy (LIBS) and X-ray fluorescence spectrometry (XRF) very versatile tools for plant nutrition diagnosis. This review focuses on the main developments and advances in LIBS and XRF in the analysis of plant materials over the last ten years. Fundamental aspects and instrumentation are given for both techniques. The developments in the quantitative analysis of plant leaves are discussed, with special emphasis on the key aspects and challenges concerning field sampling protocols, sample preparation, and calibration strategies. Microchemical imaging applications by LIBS and XRF (including synchrotron radiation) are also presented in a broader selection of plant compartments (e.g., leaves, roots, stems, and seeds). Challenges, expectations and complementarities of LIBS and XRF towards plant nutrition diagnosis are thoroughly discussed.

About one-third of organic agriculture production in Brazil is carried out by smallholders, who seek to use low-cost organic fertilizers in their crops. In this study, we evaluated the nest refuse of leaf-cutting ants (NR) in the formulation of growing substrates for lettuce (Lactuca sativa) and arugula (Eruca sativa) seedlings. A completely randomized design with six treatments and four repetitions was applied. The treatments were basis growing substrate (CONT), commercial substrate (TropstratoHT®—TROP), and four formulations using NR of two species of leaf-cutting ants associated with 75 or 85% (volume fraction) of CONT. Substrates were submitted to chemical analysis for determination of macro- and micronutrients while plant vigor was evaluated considering plant height (PH), root length (RL), stem diameter (SD), dry mass (DM), and number of leaves (NL) at 15, 20, 25, and 30 days after sowing. The data were submitted to a chemometric evaluation by means of principal component analysis (PCA). Treatments with 25% of NR resulted in lettuce seedlings from 42 to 53% higher and with a twofold increase of dry mass compared to the commercial substrate (TROP) (P

An adequate concentration of zinc in seeds can help in the initial development of plants. ZnO-coating can provide this nutrient to plants from the early stages of growth. However, there is a pressing need for additional studies to enable its safe use. This study aimed to evaluate the elemental distribution over ZnO-treated maize seeds stored for up to 12 months, as well as to map Zn species in the internal seed tissues. Synchrotron radiation micro-X-ray fluorescence spectrometry (SR μ-XRF) and micro-X-ray absorption near-edge spectroscopy (μ-XANES) were used as analytical tools for this purpose. The highest Zn accumulation site in micro-sized ZnO treated maize seeds is the embryo, mainly close to the black layer. The distribution pattern of Zn, S and P does not change in maize seeds treated with ZnO. Zn mass fractions in the embryo, pericarp and endosperm suggest that after 12 months of storage, Zn absorption is observed in ZnO-treated seeds. In the Zn hotspot, this element is in the form of phytate and in more readily bioavailable forms, such as Zn3(PO4)2 and cysteine. These findings can yield valuable insights into the advantages of using advanced microanalytical tools to provide important information regarding potential nutrient bioavailability to those interested in biofortification studies.

Given the large variety of raw materials used in manufacturing micronutrient fertilizers, the quantitative determination of Cd, Cr, Ni and Pb in such complex matrices is challenging and often impairs the routine analysis even in modern laboratories. In the present work, a LIBS method for the direct analysis of pelletized test samples was developed to find a solution where the optimization relied on both analytical sensitivity and limit of detection by combining Doehlert experimental design with Derringer's desirability function. The test samples were analyzed in the form of pressed pellets prepared from a large variety of laboratory samples previously comminuted in a planetary ball mill. LIBS experiments were carried out with a Q-switched Nd:YAG laser at 1064 nm, and a spectrometer with Echelle optics and an intensified charged-coupled device. The optimized operating conditions were thus found with laser pulses of 25 J cm−2 (750 μm laser spot size), 30 accumulated laser pulses per site, 2.5 μs gate delay, and 10.0 μs integration time gate. Cd, Cr, Ni and Pb mass fractions, obtained by a validated reference method based on microwave-assisted acid digestion and ICP OES measurements, were used to build the calibration models. Linear correlation coefficients between the analyte mass fractions and the corresponding emission intensities ranged from 0.9980 for Pb to 0.9999 for Cr, and the limits of detection were 5 mg kg−1 Cd, 7 mg kg−1 Cr, 15 mg kg−1 Ni and 50 mg kg−1 Pb. The coefficients of variation of measurements (n = 10 sites per pellet, 30 laser pulses per site) varied from 0.5% (Ni, Pb) to 15% (Cd, Cr). The proposed method simplifies the analytical sequence and complies with the purpose of fast and accurate assessment of inorganic contamination profiles in micronutrient fertilizers.

Pellets of sieved plant materials (150, 106, 75, 53 and 20 μm sieve apertures) were prepared and analyzed by laser-induced breakdown spectroscopy (LIBS), and the results for Ca, K, Mg, P, B and Mn were discussed as a function of particle size distribution. This parameter is of key importance for appropriate test sample presentation in the form of pressed pellets for quantitative analysis by LIBS. Experiments were carried out with a Q-switched Nd:YAG laser at 1064 nm, and a spectrometer with Echelle optics and an intensified charge-coupled device. Results indicated that smaller particles yielded up to 50% emission signal intensities' enhancement and attained better measurements' precision (site-to-site variation). Moreover, matrix effects were reduced by analyzing pellets prepared from 95 = 102 μm) and by using a 50 J cm − 2 laser fluence (220 mJ per pulse; 750 μm laser spot size). The preparation of pellets from laboratory samples with monomodal particle size distributions, where most particles were smaller than 100 μm, was decisive for improving analyte micro-homogeneity within the test samples and for attaining lower coefficients of variation of measurements, typically lower than 10% (n = 10 sites per pellet; 20 laser pulses per site).

Building on the successful experience in operating the DarkSide-50 detector, the DarkSide Collaboration is going to construct DarkSide-20k, a direct WIMP search detector using a two-phase Liquid Argon Time Projection Chamber (LAr TPC) with an active (fiducial) mass of 23 t (20 t). This paper describes a preliminary design for the experiment, in which the DarkSide-20k LAr TPC is deployed within a shield/veto with a spherical Liquid Scintillator Veto (LSV) inside a cylindrical Water Cherenkov Veto (WCV). This preliminary design provides a baseline for the experiment to achieve its physics goals, while further development work will lead to the final optimization of the detector parameters and an eventual technical design. Operation of DarkSide-50 demonstrated a major reduction in the dominant 39Ar background when using argon extracted from an underground source, before applying pulse shape analysis. Data from DarkSide-50, in combination with MC simulation and analytical modeling, shows that a rejection factor for discrimination between electron and nuclear recoils of $>3 \times 10^{9}$ is achievable. This, along with the use of the veto system and utilizing silicon photomultipliers in the LAr TPC, are the keys to unlocking the path to large LAr TPC detector masses, while maintaining an experiment in which less than $< 0.1$ events (other than $\nu$ -induced nuclear recoils) is expected to occur within the WIMP search region during the planned exposure. DarkSide-20k will have ultra-low backgrounds than can be measured in situ, giving sensitivity to WIMP-nucleon cross sections of $1.2 \times 10^{-47}$ cm2 ( $1.1 \times 10^{-46}$ cm2) for WIMPs of 1 TeV/c2 (10 TeV/c2) mass, to be achieved during a 5 yr run producing an exposure of 100 t yr free from any instrumental background.

The accumulation and spatial distribution of arsenic and phosphorus in the As-hyperaccumulator fern Pityrogramma calomelanos were investigated by micro-energy dispersive X-ray fluorescence spectrometry (μ-EDXRF). Ferns were grown in half-strength Hoagland nutrient solution without and with 1.0, 10 or 30 × 10−3 mol L−1 As during three weeks. Microchemical As and P maps in different areas of the pinna were obtained by μ-EDXRF, and the same elements were also determined in pelletized powdered samples from the pinna, stipe and root. The reference method for the determination of As and P in the fern samples was a validated method based on microwave-assisted acid digestion followed by ICP OES analysis. Correlations between X-ray characteristic emission intensities and the corresponding As and P mass fractions obtained from the analysis of pelletized test samples exhibited linear correlation coefficients higher than 0.98 (n = 42). Better root mean square errors of prediction (RMSEPs) were obtained when different calibration models were built with pinna, stipe and root test samples separately. Arsenic was accumulated mainly in the pinna midrib, secondary veins, and apical and marginal regions of the pinnule of P. calomelanos, causing alterations in the P distribution. The proposed μ-EDXRF method is an appropriate analytical tool for simultaneously mapping As and P in P. calomelanos. In addition, useful information for either environmental monitoring or phytoremediation studies regarding As contamination is properly obtained.

Microsampling strategies were evaluated for the direct analysis of dried sugar cane leaves by energy-dispersive X-ray fluorescence spectrometry (EDXRF) and laser-induced breakdown spectroscopy (LIBS). The analysis by EDXRF was carried out by irradiating each leaf fragment in its middle portion with a collimated 5 mm X-ray spot size for 50 s, allowing the determination of P, K, Ca, S, Fe, Mn and Si. EDXRF was also useful to conclude that 15 leaf fragments (37.5% of the recommended sampling area) were enough for attaining a representative analytical response from the whole diagnostic leaf. Regarding LIBS, which employs a substantial smaller ablation area (i.e., 750 µm laser spot size), sampling strategies were defined by taking into account the microchemical distribution of P, Ca, Mg, Fe, Mn, B and Si in a 9 mm × 9 mm leaf fragment area. The proposed sampling protocol relied on the interrogation (rastering) of 3 equally spaced sampling lines in each leaf fragment with 48 accumulated laser pulses per line (Nd:YAG at 1064 nm, 5 ns, 10 Hz, 50 J cm−2) perpendicular to the leaf midrib. This strategy enabled the simultaneous determination of P, K, Ca, Mg, Fe, Cu, Mn, Zn, B and Si by LIBS. Cross-validation between LIBS and EDXRF for P, K, Ca, Fe, Mn and Si predicted mass fractions presented high linear correlation coefficients of up to 0.9778 (selecting 15 leaf fragments per diagnostic leaf from 10 different sugar cane varieties). The results provide insights into a novel and promising strategy for direct and fast plant nutrition diagnosis, fostering further studies for in situ analysis of fresh leaves, strengthening the implementation of Precision Agriculture and Green Chemistry concepts.

On November 5, 2015, after the collapse of the Fundao tailings dam, a massive amount of iron mine waste was released into the Doce River system in southeast Brazil. The aim of our study was to determine the mass fractions of potentially toxic elements in soil affected by the deposition of material by the waste wave. A preliminary screening was performed with portable X-ray fluorescence spectrometry (PXRF) and principal component analysis (PCA). The EPA 3050B method was further applied to digest the samples for quantitative determination of As, Ba, Cr, Cu, Mn, Ni, Pb, V, and Zn by inductively coupled plasma mass spectrometry. PCA was useful to classify the mine waste samples based on the Fe signal from the PXRF spectra, in spite of the heterogeneous nature of the material discharged into the Doce River system. The anomalous levels of As (up to 164 mg kg−1) and Mn (as high as 2410 mg kg−1) found in some mine waste and affected soil samples are within the background ranges typically observed in the soils of the Iron Quadrangle region. The toxicity characteristic leaching procedure shows no evidence of hazards regarding As, but a high natural background level of Mn was found in the mobile fraction. This preliminary environmental assessment highlights the importance of evaluation of long-term effects on soil directly impacted, as well as on the aquatic biota of the Doce River system and adjacent coastal environment given the large affected area, which includes regions with varying background levels of toxic elements.

Laser-induced breakdown spectroscopy (LIBS) and energy dispersive X-ray fluorescence spectrometry (EDXRF) were evaluated for the determination of P, K, Ca, Mg, S, Fe, Cu, Mn and Zn in pressed pellets of wheat flours. EDXRF and LIBS calibration models were built with analytes mass fractions determined by inductively coupled plasma optical emission spectrometry after microwave-assisted acid digestion in a set of 25 wheat flour laboratory samples. Test samples consisted of pressed pellets prepared from wheat flour mixed with 30% mm − 1 cellulose binder. Experiments were carried out with a LIBS setup consisted of a Q-switched Nd:YAG laser and a spectrometer with Echelle optics and ICCD, and a benchtop EDXRF system fitted with a Rh target X-ray tube and a Si(Li) semiconductor detector. The correlation coefficients from the linear calibration models of P, K, Ca, Mg, S, Fe, Mn and Zn determined by LIBS and/or EDXRF varied from 0.9705 for Zn to 0.9990 for Mg by LIBS, and from 0.9306 for S to 0.9974 for K by EDXRF. The coefficients of variation of measurements varied from 1.2 to 20% for LIBS, and from 0.3 to 24% for EDXRF. The predictive capabilities based on RMSEP (root mean square error of prediction) values were appropriate for the determination of P, Ca, Mg, Fe, Mn and Zn by LIBS, and for P, K, S, Ca, Fe, and Zn by EDXRF. In general, results from the analysis of NIST SRM 1567a Wheat flour by LIBS and EDXRF were in agreement with their certified mass fractions.

The analytical performances of benchtop and handheld energy dispersive X-ray fluorescence spectrometry (EDXRF) systems were evaluated aiming at the direct and simultaneous determination of P, K, Ca, S, Fe, Mn, and Si in plant materials. Pressed pellets of comminuted leaves from 23 varieties of sugar cane were used as laboratory samples. Both systems presented similar figures of merit, and were able to provide useful data for plant nutrition diagnosis. Linear correlation between the elemental mass fractions in the test samples and characteristic X-ray intensities was obtained for all analytes with both types of equipment. Correlation coefficients from 0.9601 to 0.9918 and from 0.9094 to 0.9948 were attained for benchtop and handheld EDXRF, respectively. The coefficient of variation of measurements carried out in 3 different test samples was also appropriate, being lower than 13% for all analytes. Limits of detection were comparable for both systems (20 mg kg−1 for Fe and Mn, and approximately 0.1 g kg−1 for P, K, Ca, S and Si) and permit the evaluation of the mineral nutrition status of sugar cane crop taking into account the critical levels of these elements. The handheld system is a cost-effective and appealing option for those who intend to carry out faster in situ and laboratory analysis with equivalent performance of the benchtop equipment.

We evaluated the new on site soil conditions and their potential risks immediately after a fire that completely destroyed the Brazilian Antarctic Station, on February 2012. The investigated variables were the concentration of potentially toxic elements (Cd, Cr, Cu, Mn, Ni, Pb, V and Zn) in soil samples collected close to the station and inside the burnt station's ruins. Soil samples collected 4 years before the fire were used as reference samples for comparative purposes. Principal Component Analysis (PCA) and μ-X-Ray Fluorescence were used as preliminary tools to provide fast and reliable qualitative information about soil pollution. Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES) was chosen for the quantitative determination of the chemical elements under study. A Toxicity Characteristic Leaching Procedure was applied to access the potential mobility of the chemical elements in the environment. We found high pseudototal concentrations of Cu, Pb and Zn in soils collected within the station's ruins reaching the alarming levels of 34,000 ± 4,000, 13,700 ± 500 and 42,200 ± 1,700 mg kg− 1, respectively. A point that deserves a close and special attention is the possible contamination of nearby lakes that supply the station with water, due to the high leachable Pb and Zn concentrations of the contaminated soil. Also, attention should be given to the possible development of melting channels carrying contaminated water to the coastal marine ecosystem. Due to its high risk of contamination, a complete clean-up procedure ought to be carried out, with barriers to avoid leaching/washing, removal of all debris and underlying soil, and careful disposal of the contaminated material, followed by remediation.

In this study, we proposed a straightforward approach that could be used for Cr redox speciation in soil samples from remote places. For this aim, soil samples under strong anthropogenic impact, from the vicinity of the Brazilian Antarctic Station were studied. Control samples with no direct impact, were also collected further (4 km) from the station. A preliminary laboratory evaluation for Cr (VI) presence was performed using X-ray absorption spectroscopy. The proposed method was based on a hot alkaline extraction to promote the quantitative extraction of Cr (VI) from soil samples. The colorimetric reagent 1,5-diphenylcarbazide (DPC) was added to the extracts to form a violet complex with Cr (VI). A simple and inexpensive commercial scanner was used to acquire the digital images of the formed complex. Partial Least Squares models were constructed with the following average color descriptors: red (R), green (G), blue (B), hue (H), saturation (S), value (V), relative color descriptors (r, g and b) and luminosity (L). The results obtained with this scanner approach were consistent with the official method that uses a spectrophotometer at 540 nm. Besides that, this is the first study that reports Cr redox speciation in soils from Antarctica, which is regarded as the less polluted place on the Earth.

In spite of the importance of Si for improving the productivity of many important crops, such as those from the Poaceae family (e.g. sugar cane, maize, wheat, rice), its quantitative determination in plants is seldom carried out and restricted to few laboratories in the world. There is a survey of methods in the literature, but most of them are either laborious or difficult to validate in view of the low availability of reference materials with a certified Si mass fraction. The aim of this study is to propose a method for the direct determination of Si in pellets of plant materials by laser-induced breakdown spectroscopy (LIBS). The experimental setup was designed by using a Q-switched Nd:YAG laser at 1064 nm (5 ns, 10 Hz) and the emission signals were collected by lenses into an optical fiber coupled to an Echelle spectrometer equipped with an intensified charge-coupled device. Experiments were carried out with leaves from 24 sugar cane varieties, with mass fractions varying from ca. 2 to 10 g kg − 1 Si. Pellets prepared from cryogenically ground leaves were used as test samples for both method development and validation of the calibration model. Best results were obtained when the test samples were interrogated with laser fluence of 50 J cm − 2 (750 μm spot size) and measurements carried out at Si I 212.412 nm emission line. The results obtained by LIBS were compared with those from inductively coupled plasma optical emission spectrometry after oven-induced alkaline digestion, and no significant differences were observed after applying the Student's t -test at 95% confidence level. The trueness of the proposed LIBS method was also confirmed from the analysis of CRM GBW 07603 (Bush branches and leaves).

The anthropogenic effects of Antarctic refuge buildings and research stations on the surrounding soils are scarcely investigated, especially when the structures are small-sized, and sporadically used or visited. The Coppermine Peninsula (Robert Island, South Shetland Islands archipelago) possesses one of the richest flora in Antarctica, being classified as an Antarctic Specially Protected Area (ASPA). There, a small refuge (Luis Risopatron) has been seasonally occupied for scientific purposes since 1957, although no studies on the anthropic disturbances in the surroundings soils are reported. The aim of this study was the determination of the potentially toxic metals (Cd, Cr, Cu, Mn, Ni, Pb, V, and Zn) mass fractions in surface soils (n = 40) collected at the surroundings of the Luis Risopatron refuge. Enrichment factors (EF) and geoaccumulation index (I geo) were also calculated, using Zr as the reference element, in order to evaluate the anthropogenic impacts of these small buildings in the studied area. The main contaminants were Pb and Zn, which presented EF and I geo values ranging from 1.0 to 18.3 and from −1.8 to 3.5. The mass fractions of these elements determined after an aqua regia extraction varied from 5.4 to 102 mg kg−1 Pb and from 43 to 210 mg kg−1 Zn. These results highlight that a small refuge can show environmental disturbance from low to moderate, with few hotspots with heavily contaminated soils. Environmental monitoring strategy for similar refuges anywhere in Antarctica is recommended.

A portable energy dispersive X-ray fluorescence spectrometer was evaluated in the in situ analysis of fresh sugar cane leaves for real time plant nutrition diagnosis. Fresh leaf fragments (n = 10 sugar cane varieties; 20 fragments per leaf; 2 measurement sites per fragment) were irradiated and the averaged data from X-ray characteristic emission lines intensities (for K, Ca, S and Si Kα lines) were in close agreement with mass fraction data obtained by a validated comparative method. The linear correlation coefficients (r) ranged from 0.9575 for Ca to 0.9851 for Si. The obtained limits of detection were at least two-fold lower than the critical nutrient levels. Manganese can also be properly determined, but validation still requires more robust calibration models. The proposed method is a straightforward approach towards the fast evaluation of the nutritional profile of plants avoiding time-consuming steps, which involve drying, grinding, weighing, and acid digestion.

The Black Hills State University Underground Campus (BHUC) houses a low background counting facility on the 4850' level of the Sanford Underground Research Facility. There are currently four ultra-low background, high-purity germanium detectors installed in the BHUC and it is anticipated four more detectors will be installed within a year. In total, the BHUC will be able to accommodate up to twelve detectors with space inside a class 1000 cleanroom, an automated liquid nitrogen fill system, on-site personnel assistance and other required utilities.

In this study, two methods were developed for the sequential determination of As and Sb, Bi and Pb using fast sequential continuous flow hydride generation atomic absorption spectrometry. Limits of detection obtained for As and Sb were 0.15 and 0.16 μg L−1 and for Bi and Pb were 0.60 and 0.77 μg L−1, respectively. Arsenic, Sb, and Bi were free from the influence of possible interferents in the levels investigated, but Pb showed a significant analytical signal decrease when Co, Cu, Fe, Ni, and HNO3 were presented in the solutions. The methods were applied to the analysis of water from the Tiete River (Sao Paulo State, Brazil), sea water from Praia Grande—Ubatuba (Sao Paulo State), chicken feed, trace elements in water (NIST 1643e), and trace metals in drinking water (HPS TMDW). The obtained recoveries varied from 88 (for As) to 116 % (for Bi).

Leaf-cutting ants are responsible for carrying out an important ecological process in neotropical ecosystems: the cycling of elements. However, although several studies have demonstrated the accumulation of organic matter inside colonies, little is known about the dynamics of nutrients and its residence time in nest refuse compared to the leaf material harvested by ants. This study compares the nutrient content of nest refuse and leaf material of the leaf-cutting ant Atta sexdens during states of decomposition in a transitional environment between forest and shrub vegetation in Northeastern Brazil. The decomposition rate of the refuse material was two-fold faster than the substrate harvested. In addition, there was a substantial difference in chemical and structural characteristics between both substrates. Refuse material showed higher contents of Ca whereas leaf fragments had a higher P content, more organic carbon (OC), and a higher lignin/cellulose ratio. During the period of decomposition in the field, only OC content decreased simultaneously in both substrates, indicating that changes had occurred mainly in the structure of the substrates with a low transference rate of most nutrients to the surrounding soil. A higher lignin/cellulose ratio in the leaf material may explain the higher residence time of this substrate in the environment. Results indicate that colonies of A. sexdens accelerate the decomposition of organic matter, perhaps due to reduced lignin–cellulose ratio. Organic carbon may be mineralized in the first days after the disposal of the refuse material into the nest chambers.

Este estudo foi centrado na avaliacao quimica de amostras de solos provenientes de diversas estacoes de pesquisa na Antartica. Amostras de solos de referencia foram coletadas em locais com minimo impacto antropico, distantes das estacoes de pesquisa. Locais selecionados nas vizinhancas das estacoes Frei Montalva e Escudero (Chile), Grande Muralha (China), Bellingshausen (Russia) e Artigas (Uruguai) foram os pontos a priori supostamente antropizados deste estudo. O procedimento de extracao sequencial (SEP) baseado no protocolo proposto pelo BCR (Community Bureau of Reference) foi aplicado para a determinacao de Cu, Mn e Zn. Com o auxilio dos metodos PCA (analise de componentes principais) e PARAFAC (analise de fatores paralelos) foram extraidas informacoes significativas a partir dos dados brutos obtidos com SEP. As amostras de solos afetadas pelas estacoes de pesquisa estao associadas com elevadas concentracoes de metais pesados (especialmente Cu e Zn, dentre os elementos investigados, nas fracoes mais labeis de SEP aplicado). Este indicio de contaminacao esta relacionado com o uso de oleo diesel para geracao de energia pelas estacoes antarticas. The aim of this study was to carry out a broad chemical investigation of selected soil samples from Antarctica, near different Antarctic scientific stations. Soil samples collected in background reference sites, with minimal human impact, far away from the stations were used as control samples. Anthropogenic places at the vicinity of the following stations Frei Montalva and Escudero (Chile), Great Wall (China), Bellingshausen (Russia) and Artigas (Uruguay) were studied as a priori human impacted sites. The sequential extraction procedure (SEP) based on the BCR (Community Bureau of Reference) protocol was applied for Cu, Mn and Zn determination. With the help of PCA (principal component analysis) and PARAFAC (parallel factor analysis) methods, meaningful information was extracted from the raw data obtained from SEP procedure. Soil samples affected by the scientific stations are associated with higher heavy metal contents (especially Cu and Zn, between the investigated metals, in the most labile fractions of the SEP applied). This pollution signal is associated with diesel use for the energy generation by the Antarctic stations.

Leaf-cutting ants perform a vital role in the cycling of carbon and nutrients in tropical ecosystems. Nests have high levels of organic matter and refuse dumps host up to two times more soil micro-organisms than non-nest soil. The increased levels of organic matter in the soil of nests, however, can affect CO2 emissions from soil and alter the balance of atmospheric CO2. We aimed at assessing the effect of nests of the leaf-cutting ant Acromyrmex balzani on CO2 emissions in a coastal area of Northeast Brazil. Results show that A. balzani nests emitted up to four times more CO2 than the surrounding soil and emissions were positively correlated with soil moisture and soil organic matter (SOM) content. In addition, field experiments demonstrated that refuse material has a lower residence time than the leaf material brought to the colonies. Despite the high density of nests and high content of SOM compared to adjacent control soil, CO2 emissions by A. balzani nests represent only 0.3% of the total CO2 efflux by the studied ecosystem. Although these effluxes account for a relative small portion of the total soil CO2 emission, they are still important for the understanding of C balance, especially when one considers the thousands of tons of CO2 emitted each day, across entire Neotropical regions where leaf-cutting ants occur.

This paper presents some recent applications of Flame Atomic Absorption Spectrometry (FAAS) to different matrices and samples. The time window selected was from 2006 up to March, 2011, and several aspects related to food, biological fluids, environmental, and technological samples analyses were reported and discussed. In addition, the chemometrics application for FAAS methods development was also taken into account, as well as the use of metal tube atomizers in air/acetylene flame. Preconcentration methods coupled to FAAS were discussed, and several approaches related to speciation, flotation, ionic liquids, among others were discussed. This paper can be interesting for researchers and FAAS users in order to see the state of the art of this technique.

The combined use of internal standardization with collision and reaction interface in an inductively coupled plasma quadrupole mass spectrometer (ICP-QMS-CRI) was evaluated. The behavior of several elements (Ba, Cd, Co, Cr, Cu, Li, Mn, Mo, Pb, Sb, V and Zn) was studied by introducing H2 or He through the skimmer and sampler cones of the CRI device and by using In, Rh and Sc as internal standards. Certified reference material of trace elements in water (NIST 1643e) was used to evaluate the performance of the method. A vinegar sample and mixed food diet standard reference material were directly introduced into the equipment as complex matrices for Cr and V determinations. Improvements in accuracy and precision were attained combining both strategies. The introduction of H2 through the skimmer cone was the best way to overcome polyatomic ions formation and to improve SBR and BEC values for several elements. The use of Sc as internal standard improved the performance of ICP-QMS-CRI.

Technosols are anthropogenic soils that may be strongly impacted by heavy metal deposition, which have not yet been described in Antarctica. In this paper, we present a chemical study of what is supposedly the oldest manmade soil from Antarctic Peninsula, developed in the vicinity of Trinity House and Nordenskjold Hut at Hope Bay. Chemical and morphological soil attributes indicate that a former ornithogenic site (penguin rookery) was further subjected to human disturbance, following local exploration since 1903. We detected very high amounts of heavy metals such as Cd, Cu, Pb, and Zn. For the most impacted site, pseudototal concentrations of these elements reach 47, 2,082, 19,381, and 5,225 mg kg−1, respectively. Enrichment factors were calculated using Zr as reference element, and high values were found for these contaminated sites, qualifying some of them as extremely polluted. Also, both the mobilizable and mobile fraction of Cd and Pb indicate the need of intervention in the affected area. These findings are all consistent with the human impacts and strong contamination. Strong positive correlation between the pseudototal concentrations of Cd, Cu, Mn, Ni, Pb, and Zn indicates a similar source of pollution. These soils may represent the oldest Technosols in Antarctic Continent.

As formigas cortadeiras (Atta e Acromyrmex) são consideradas importantes pragas na agricultura e silvicultura, mas pouco se sabe sobre os reais danos dessas espécies. Uma forma bastante difundida de avaliação do dano é por meio do cálculo da taxa de conversão, dividindo-se o peso do material cortado pelo peso de lixo produzido pelas colônias. Foi levantada a hipótese de que a qualidade do substrato cortado pode influenciar no forrageamento das operárias, alterando a taxa de conversão e dificultando as estimativas de dano. A taxa de conversão de oito colônias de Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae) foi calculada com duas espécies vegetais com diferentes concentrações de lignina e celulose, para testar essa hipótese. Colônias mantidas com folhas de baixa qualidade (razão lignina/celulose elevada) tiveram maior forrageamento e produziram mais lixo. Entretanto, a taxa de conversão das colônias foi semelhante com essas duas plantas (média = 1,54). Esse valor está dentro da variação encontrada para outras espécies no campo (1,5-1,8), indicando um fator semelhante de conversão entre os gêneros Atta e Acromyrmex. O consumo médio de material vegetal, em termos de pesos seco e fresco, de uma colônia de A. sexdens rubropilosa com 4.500 operárias, foi estimado em 520 e 1.100 g/ano, respectivamente. Leaf-cutting ants (Atta and Acromyrmex) are important pests in agriculture and forestry, although few data exist on the actual damage caused by these species. A model used to evaluate damage by leaf-cutting ants are estimates of the conversion factor, which is the ratio between the weight of material cut by the ants and the refuse produced by the colonies. The hypothesis that substrate quality influences foraging by workers, modifying the conversion factor and impairing damage estimates was put forward. To test this hypothesis, the conversion factor was calculated for eight colonies of Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae), using two plant species, with different lignin and cellulose concentrations. Colonies maintained with low quality leaves (high lignin/cellulose ratio) presented higher foraging activity and produced more refuse than colonies maintained with high quality leaves. However, the conversion factors obtained for the two groups of leaf-cutting ant colonies (average = 1.54) was within the variation found for other species in the field (1.5 – 1.8), indicating a similar conversion factor in Atta and Acromyrmex. The average consumption in both dry and fresh weight of plant material of a colony of Atta sexdens rubropilosa with 4,500 workers was estimated as 520 and 1,100 g/year, respectively.

The soils developed under High Altitude Rocky Complexes in Brazil are generally of very low chemical fertility, with low base saturation and high exchangeable aluminium concentration. This stressful condition imposes evolutionary pressures that lead to ecological success of plant species that are able to tolerate or accumulate high amounts of aluminium. Several analytical methods are currently available for elemental mapping of biological structures, such as micro-X-ray fluorescence (μ-EDX) and histochemical tests. The aim of this study was to combine μ-EDX analysis and histochemical tests to quantify aluminium in plants from High Altitude Rocky Complexes, identifying the main sites for Al-accumulation. Among the studied species, five showed total Al concentration higher than 1000 mg kg−1. The main Al-hyperaccumulator plants, Lavoisiera pectinata, Lycopodium clavatum and Trembleya parviflora presented positive reactions in the histochemical tests using Chrome Azurol and Aluminon. Strong positive correlations were observed between the total Al concentrations and data obtained by μ-EDX analysis. The μ-EDX analysis is a potential tool to map and quantify Al in hyperaccumulator species, and a valuable technique due to its non-destructive capacity. Histochemical tests can be helpful to indicate the accumulation pattern of samples before they are submitted for further μ-EDX scrutiny. Solos associados aos Complexos Rupestres de Altitude no Brasil destacam-se pela baixa fertilidade química, baixa saturação de bases e elevados teores de alumínio trocável. Esta condição estressante impõe pressões evolutivas que determinam o sucesso ecológico de espécies capazes de tolerar ou acumular grandes quantidades de alumínio. Vários métodos analíticos são utilizados para mapeamento de elementos químicos em estruturas biológicas, como microfluorescência de raios-X (μ-EDX) e testes histoquímicos. O objetivo do presente trabalho foi combinar a μ-EDX e testes histoquímicos para quantificar o teor de Al em espécies vegetais de Complexos Rupestres de Altitude, e identificar os principais sítios de bioacumulação de Al. Cinco das espécies investigadas apresentaram concentração total de Al maior que 1000 mg kg−1. As principais hiperacumuladoras de Al, Lavoisiera pectinata, Lycopodium clavatum e Trembleya parviflora, apresentaram reação positiva nos testes histoquímicos com Chrome Azurol e Aluminon. Alta correlação positiva foi observada entre as concentrações totais de Al e as magnitudes de sinal obtidas por μ-EDX. A análise com o uso da μ-EDX mostrou-se uma ferramenta promissora para mapear e quantificar Al em espécies hiperacumuladoras, constituindo uma importante técnica não destrutiva. Testes histoquímicos podem ser úteis na identificação de padrões de acumulação de Al em amostras vegetais antes de serem submetidas a uma minuciosa análise com a μ-EDX.

As saúvas (Atta spp.) estão amplamente distribuídas pelo continente Sul-Americano e são consideradas importantes componentes do ecossistema neotropical. Diversos estudos têm demonstrado o efeito de formigueiros no enriquecimento do solo e na facilitação ao estabelecimento de espécies vegetais. Possivelmente o enriquecimento do solo seja devido ao acúmulo de matéria orgânica decomposta em câmaras de descarte (lixo) no interior das colônias. Entretanto, pouco se sabe sobre a composição química do lixo de formigas cortadeiras. O objetivo do presente trabalho foi comparar os teores de nutrientes do lixo produzido por colônias de Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae), em laboratório, mantidas com folhas de duas espécies de plantas. Os tratamentos foram dois tipos de substrato (Acalypha sp. ou Bauhinia sp.), repetidos quatro vezes. Oito colônias foram divididas em dois grupos (n = 4), e cada grupo foi mantido com apenas um tratamento. Após 30 dias de experimento, as amostras de folhas e lixo foram secas em estufa (70 ºC) e submetidas à digestão ácida, para determinação das concentrações de N, P, K, S, Ca e Mg. Diferenças nas concentrações dos macronutrientes entre os tratamentos (lixo ou folha) foram comparadas por meio de ANOVA e teste T. As concentrações de nutrientes no lixo foram sempre maiores do que nas folhas, independentemente da espécie cortada. Folhas de Acalypha sp. apresentaram concentrações significativamente maiores do que folhas de Bauhinia sp. com relação aos teores de P, Ca, Mg e S; entretanto, as concentrações do lixo em todos os formigueiros foram muito próximas, indicando incorporação adicional de nutrientes por meio do fungo, excreções e, ou, cadáveres no lixo. Esses resultados indicam que, independentemente do substrato cortado, o lixo produzido apresenta maiores concentrações de nutrientes do que as folhas, sendo importante locus de reciclagem de nutrientes no ecossistema. O lixo pode ser uma das principais razões para o aumento da concentração de nutrientes em solos de formigueiros. Leaf-cutting ants (Atta spp.) are widely distributed in South America, and are considered to be important components of the neotropical ecosystems. Several studies have demonstrated the effect of ant-nesting in soil enrichment, thus facilitating vegetation succession. Possibly, this enrichment is due to decomposed organic matter concentration after disposal of nest refuse in the deep soil by the colonies. However, little is known about the chemical composition of refuse material produced by leaf-cutting ants. The present work aimed to compare the macronutrient concentration in nest refuse and leaves of two different harvested plants (Acalypha sp. or Bauhinia sp.) in colonies of Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae) maintained in laboratory. Eight colonies were divided into two groups (n = 4), and each one was maintained with only one feed type. After 30 days of experiment, samples of leaves and refuse were oven-dried at 70 ºC and subjected to acid digestion for chemical determination of total N, P, K, S, Ca and Mg. Differences in concentrations of macronutrients in both leaves and refuse were compared using ANOVA and T test. Nutrient concentration in the refuse material was consistently higher than in leaves, for both plants. Acalypha sp. leaves showed greater nutrient concentration than those of Bauhinia sp., while the concentration of all refuses were very similar. This indicates an additional enrichment of nutrients in the refuse material by either ant carcasses, fungus cycling or excretions. Results suggest that nests of leaf-cutting ant are important loci of nutrient recycling of the ecosystem. Moreover, the refuse may represent an important factor for chemical enrichment in soils influenced by leaf-cutting ants.

Cryosols from Maritime Antarctica have been less studied than soils from continental areas of Antarctica. In this work X-ray diffraction, difference X-ray diffraction, differential thermal analysis, thermogravimetry, transmission electron microscopy/energy dispersive spectroscopy and selective chemical dissolution were used to characterize the clay fraction of basaltic, acid sulfate and ornithogenic Cryosols from ice-free areas of Admiralty Bay, King George Island. Non-crystalline phases are important soil components and reach >75% of the clay fraction for some ornithogenic soils. Randomly interstratified smectite-hydroxy-Al-interlayered smectite is the main clay mineral of basaltic soils. Kaolinite, chlorite and regularly interstratified illite-smectite predominate in acid sulfate soils. Jarosite is also an important component of the clay fraction in these soils. Crystalline Al and Fe phosphates occur in the clay at sites directly affected by penguin activity and the chemical characteristics of these ornithogenic sites are controlled by highly reactive, non-crystalline Al, Si, Fe and P phases. Chemical weathering is an active process in Cryosols in Maritime Antarctica and is enhanced by the presence of sulfides for some parent materials, and faunal activity.

An analytical procedure relying on micro-energy dispersive X-ray fluorescence spectrometry (μ-EDX) was evaluated for the quantitative determination of macro-, micronutrients and beneficial elements in pressed pellets of plant materials. For testing purposes, leaves from 23 varieties of sugar cane, previously analyzed by validated reference methods, based on wet decomposition procedures followed by ICP OES measurements were used. Linear correlations between analyte mass fractions in the tested samples and the corresponding μ-EDX intensities were obtained for P, K, Ca, S, Fe, Mn and Si with regression coefficients ranging from 0.9501 to 0.9933. Furthermore, the coefficients of variation of results in the 0.3 to 16% range (n = 3 sampling lines, 30 sampling sites per line), the spatial resolution of 50 μm per site and the suitable detection limits for these analytes were additional features that demonstrated the performance of the proposed procedure as a useful tool for plant nutrient diagnosis. In addition, the results also indicate that μ-EDX can be recommended as a cross-validation method for analysis of plant materials, owing to its inherent non-destructive capability and, particularly, when dealing with analytes' micro-heterogeneity evaluation within the samples.

A method for direct determination of Pb by LA-ICP-MS in lichen samples collected in a heavily anthropogenically impacted area of Maritime Antarctica was developed. The lichen samples were cryogenically ground and digested with nitric acid and hydrogen peroxide. Lead determination by solution-based ICP-MS was validated by the use of 2 certified reference materials. Once the Pb concentrations were measured with adequate accuracy and precision, a method for its direct determination by LA-ICP-MS was developed. The laser ablation parameters were optimized by the use of a Doehlert design matrix. The final optimized conditions were: laser energy (60%), spot size (150 μm) and repetition rate (10 Hz). Lead concentration of the analyzed lichen samples were plotted against the intensity of the lead isotopes (208Pb, 207Pb and 206Pb) determined by LA-ICP-MS. Satisfactory linear correlation factors were obtained when 13C was used as internal standard. Lead distribution profiles in lichen thalli cross-sections were also obtained. By these results, LA-ICP-MS emerges as a potential analytical tool for Pb concentration estimation in lichen samples. Minimum amount of sample required, bioimaging capability, high analytical throughput, and minimization of waste generation are the major analytical features of this approach. The significant differences between the Pb concentration in the lichen samples from the control site (1.12 ± 0.05 mg kg−1) and from the impacted points (mean = 5.03 ± 0.57 mg kg−1) permitted qualify these organisms as good biomonitors. Elemental bioimaging of lichens demonstrated that the medulla region of lichen thalli is consistently the main atmospheric lead bioaccumulating lichen tissue.