Spectral data of tropical soils using dry-chemistry techniques (VNIR, XRF, and LIBS): A dataset for soil fertility prediction.

Proximal soil sensing technologies, such as visible and near infrared diffuse reflectance spectroscopy (VNIR), X-ray fluorescence spectroscopy (XRF), and laser-induced breakdown spectroscopy (LIBS), are dry-chemistry techniques that enable rapid and environmentally friendly soil fertility analyses. The application of XRF and LIBS sensors in an individual or combined manner for soil fertility prediction is quite recent, especially in tropical soils. The shared dataset presents spectral data of VNIR, XRF, and LIBS sensors, even as the characterization of key soil fertility attributes (clay, organic matter, cation exchange capacity, pH, base saturation, and exchangeable P, K, Ca, and Mg) of 102 soil samples. The samples were obtained from two Brazilian agricultural areas and have a wide variation of chemical and textural attributes. This is a pioneer dataset of tropical soils, with potential to be reused for comparative studies with other datasets, e.g., comparing the performance of sensors, instrumental conditions, and/or predictive models on different soil types, soil origin, concentration range, and agricultural practices. Moreover, it can also be applied to compose soil spectral libraries that use spectral data collected under similar instrumental conditions.

Simplifying Sample Preparation for Soil Fertility Analysis by X-ray Fluorescence Spectrometry.

Portable X-ray fluorescence (pXRF) sensors allow one to collect digital data in a practical and environmentally friendly way, as a complementary method to traditional laboratory analyses. This work aimed to assess the performance of a pXRF sensor to predict exchangeable nutrients in soil samples by using two contrasting strategies of sample preparation: pressed pellets and loose powder (<2 mm). Pellets were prepared using soil and a cellulose binder at 10% w w-1 followed by grinding for 20 min. Sample homogeneity was probed by X-ray fluorescence microanalysis. Exchangeable nutrients were assessed by pXRF furnished with a Rh X-ray tube and silicon drift detector. The calibration models were obtained using 58 soil samples and leave-one-out cross-validation. The predictive capabilities of the models were appropriate for both exchangeable K (ex-K) and Ca (ex-Ca) determinations with R2 ≥ 0.76 and RPIQ > 2.5. Although XRF analysis of pressed pellets allowed a slight gain in performance over loose powder samples for the prediction of ex-K and ex-Ca, satisfactory performances were also obtained with loose powders, which require minimal sample preparation. The prediction models with local samples showed promising results and encourage more detailed investigations for the application of pXRF in tropical soils.

Melted Paraffin Wax as an Innovative Liquid and Solid Extractant for Elemental Analysis by Laser-Induced Breakdown Spectroscopy.

This work proposes a new development in the use of melted paraffin wax as a new extractant in a procedure designed to aggregate the advantages of liquid phase extraction (extract homogeneity, fast, and efficient transfer, low cost and simplicity) to solid phase extraction. As proof of concept, copper(II) in aqueous samples was converted into a hydrophobic complex of copper(II) diethyldithiocarbamate and subsequently extracted into paraffin wax. Parameters which affect the complexation and extraction (pH, DDTC, and Triton X-100 concentration, vortex agitation time and complexation time) were optimized in a univariate way. The combination of the extraction proposed procedure with laser-induced breakdown spectroscopy allowed the precise copper determination (coefficient of variation = 3.1%, n = 10) and enhanced detectability because of the concentration factor of 18 times. A calibration curve was obtained with a linear range of 0.50-10.00 mg L-1 (R2 = 0.9990, n = 7), LOD = 0.12 mg L-1, and LOQ = 0.38 mg L-1 under optimized conditions. An extraction procedure efficiency of 94% was obtained. The accuracy of the method was confirmed through the analysis of a reference material of human blood serum, by the spike and recovery trials with seawater, tap water, mineral water, and alcoholic beverages and by comparing with those results obtained by graphite furnace atomic absorption spectrometry.

Mercury Amalgam Diffusion in Human Teeth Probed Using Femtosecond LIBS.

In this work the diffusion of mercury and other elements from amalgam tooth restorations through the surrounding dental tissue (dentin) was evaluated using femtosecond laser-induced breakdown spectroscopy (fs-LIBS). To achieve this, seven deciduous and eight permanent extracted human molar teeth with occlusal amalgam restorations were half-sectioned and analyzed using pulses from a femtosecond laser. The measurements were performed from the amalgam restoration along the amalgam/dentin interface to the apical direction. It was possible to observe the presence of metallic elements (silver, mercury, copper and tin) emission lines, as well as dental constituent ones, providing fingerprints of each material and comparable data for checking the consistence of the results. It was also shown that the elements penetration depth values in each tooth are usually similar and consistent, for both deciduous and permanent teeth, indicating that all the metals diffuse into the dentin by the same mechanism. We propose that this diffusion mechanism is mainly through liquid dragging inside the dentin tubules. The mercury diffused further in permanent teeth than in deciduous teeth, probably due to the longer diffusion times due to the age of the restorations. It was possible to conclude that the proposed femtosecond-LIBS system can detect the presence of metals in the dental tissue, among the tooth constituent elements, and map the distribution of endogenous and exogenous chemical elements, with a spatial resolution that can be brought under 100 µm.

Direct determination of the nutrient profile in plant materials by femtosecond laser-induced breakdown spectroscopy.

Femtosecond laser-induced breakdown spectroscopy (fs-LIBS) has been used for the first time for quantitative determination of nutrients in plant materials from different crops. A highly heterogeneous population of 31 samples, previously analyzed by inductively coupled plasma optical emission spectroscopy, covering a wide range of matrices was interrogated. To tackle the analysis, laser-induced plasmas under argon atmosphere of pellets prepared from sieved cryogenically ground leaves were studied. Predictive functions based on univariate and multivariate modeling of optical emissions associated to macro- (Ca, Mg, and P) and micronutrients (Cu, Fe, Mn and Zn) were designed. Hierarchical cluster analysis was performed to select representative calibration (n(cal)=17) and validation (n(val)=14) datasets. The predictive performance of calibration functions over fs-LIBS data was compared with that attained on spectral information from nanosecond LIBS (ns-LIBS) operating at different wavelengths (1064 nm, 532 nm, and 266 nm). Findings established higher accuracy and less uncertainty on mass fractions quantification from fs-LIBS, whatever the modeling approach. Quality coefficients below 20% for the accuracy error on mass fractions' prediction in unknown samples, and residual predictive deviations in general above 5, were obtained. In contrast, only multivariate modeling satisfactorily handled the non-linear variations of emissions in ns-LIBS, leading to 2-fold decrease in the root mean square error of prediction (RMSEP) of Ca, Mg, P, Cu, Fe, Mn and Zn in comparison with the univariate approach. But still, an averaged quality coefficient about 35% and residual predictive deviations below 3 were found. Similar predictive capabilities were observed when changing the laser wavelength. Although predicted values by ns-LIBS multivariate modeling exhibit better agreement with reference mass fractions as compared to univariate functions, fs-LIBS conducts better quantification of nutrients in plant materials since it is less dependent on the chemical composition of the matrices.

Evaluation of grinding methods for pellets preparation aiming at the analysis of plant materials by laser induced breakdown spectrometry.

It has been demonstrated that laser induced breakdown spectrometry (LIBS) can be used as an alternative method for the determination of macro (P, K, Ca, Mg) and micronutrients (B, Fe, Cu, Mn, Zn) in pellets of plant materials. However, information is required regarding the sample preparation for plant analysis by LIBS. In this work, methods involving cryogenic grinding and planetary ball milling were evaluated for leaves comminution before pellets preparation. The particle sizes were associated to chemical sample properties such as fiber and cellulose contents, as well as to pellets porosity and density. The pellets were ablated at 30 different sites by applying 25 laser pulses per site (Nd:YAG@1064 nm, 5 ns, 10 Hz, 25J cm(-2)). The plasma emission collected by lenses was directed through an optical fiber towards a high resolution echelle spectrometer equipped with an ICCD. Delay time and integration time gate were fixed at 2.0 and 4.5 µs, respectively. Experiments carried out with pellets of sugarcane, orange tree and soy leaves showed a significant effect of the plant species for choosing the most appropriate grinding conditions. By using ball milling with agate materials, 20 min grinding for orange tree and soy, and 60 min for sugarcane leaves led to particle size distributions generally lower than 75 µm. Cryogenic grinding yielded similar particle size distributions after 10 min for orange tree, 20 min for soy and 30 min for sugarcane leaves. There was up to 50% emission signal enhancement on LIBS measurements for most elements by improving particle size distribution and consequently the pellet porosity.

Variation in the distribution of trace elements in renal cell carcinoma.

The development of cancer is a complex, multistage process during which a normal cell undergoes genetic changes that result in phenotypic alterations and in the acquisition of the ability to invade other sites. Inductively coupled plasma optical emission spectroscopy was used to estimate the contents of Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, P, Pb, and Zn in healthy kidney and renal cell carcinoma (RCC), and significant differences were found for all elements. Along with the progression of the malignant disease, a progressive decrease of Cd and K was observed. In fact, for Cd, the concentration in stage T4 was 263.9 times lower than in stage T1, and for K, the concentration in stage T4 was 1.73 times lower than in stage T1. Progressive accumulation was detected for P, Pb, and Zn in stage T4. For P, the concentration in stage T4 was 11.1 times higher than in stage T1; for Pb, the concentration in stage T4 was 232.7 times higher than in T1; and for Zn, the concentration in T4 was 8.452 times higher than in T1. This study highlights the marked differences in the concentrations of selected trace metals in different malignant tumor stages. These findings indicate that some trace metals may play important roles in the pathogenesis of RCC.

Evaluation of femtosecond laser-induced breakdown spectroscopy for analysis of animal tissues.

The aim of this work was to evaluate the performance of femtosecond laser-induced breakdown spectroscopy (fs-LIBS) for the determination of elements in animal tissues. Sample pellets were prepared from certified reference materials, such as liver, kidney, muscle, hepatopancreas, and oyster, after cryogenic grinding assisted homogenization. Individual samples were placed in a two-axis computer-controlled translation stage that moved in the plane orthogonal to a beam originating from a Ti:Sapphire chirped-pulse amplification (CPA) laser system operating at 800 nm and producing a train of 840 microJ and 40 fs pulses at 90 Hz. The plasma emission was coupled into the optical fiber of a high-resolution intensified charge-coupled device (ICCD)-echelle spectrometer. Time-resolved characteristics of the laser-produced plasmas showed that the best results were obtained with delay times between 80 and 120 ns. Data obtained indicate both that it is a matrix-independent sampling process and that fs-LIBS can be used for the determination of Ca, Cu, Fe, K, Mg, Na, and P, but efforts must be made to obtain more appropriate detection limits for Al, Sr, and Zn.

Lead contents in the surface enamel of deciduous teeth sampled in vivo from children in uncontaminated and in lead-contaminated areas.

This study aimed to: (1) measure lead contents in the surface enamel of two populations consisting of 4-6-year-old children, one from an apparently uncontaminated area (Ribeirão Preto, São Paulo State, SP, Brazil, n=247) and the other from an area notoriously contaminated with lead (Bauru, São Paulo State, Brazil, n=26); (2) compare biopsy depths between the two populations; (3) correlate biopsy depth with lead content; (4) stratify samples according to biopsy depth to compare lead contents in samples from similar biopsy depths. A surface enamel acid-etch microbiopsy was performed in vivo on a single upper deciduous incisor for each sample. Lead was measured by graphite furnace atomic absorption spectrometry (GFAAS) while phosphorus was measured colorimetrically to establish biopsy depth. Samples from both populations were classified into categories of similar biopsy depths based on biopsy depth quartiles. Median lead contents were statistically different between the Ribeirão Preto population (206 microg/g, range: 5-1399 microg/g) and the Bauru population (786 microg/g, range: 320-4711 microg/g) (p<0.001); however, biopsy depth did not differ between the Ribeirão Preto (3.9 microm, Standard Deviation, SD=0.9) and Bauru (3.8 microm, SD=0.9) populations (p=0.7940). Pearson's correlation coefficient for biopsy depths versus log10 lead values was -0.29 for Ribeirão Preto and -0.18 for Bauru. Lead contents were statistically different between the two populations for all quartiles of biopsy depth. These findings suggest that lead accumulated in the surface enamel of deciduous teeth is linked to the environment in which people reside, indicating that this tissue should be further explored as an accessible biomarker of lead exposure.

Mercury distribution in medium-size rivers and reservoirs of the Sao Paulo state (southeast Brazil).

The aim of this work was to investigate mercury (Hg) levels in six meso-scale watersheds (Upper Paranapanema, Aguapeí, Peixe, São José dos Dourados, Mogi-Guaçu, and Piracicaba) of the São Paulo state to contribute to a more comprehensive understanding of Hg contamination in Brazil. Water, sediment, bivalves, and fish samples were collected during 2001 at 11 sites. Fish were also collected in the Jurumirim and Salto Grande Reservoirs which are 39 and 52 yr old since impoundment, respectively. Results showed that Hg concentrations were low in almost all samples, except fish from Jurumirim Reservoir (total mercury [T-Hg] = 1.14 +/- 0.55 mg kg(-1) wet wt.). In spite of industrialization and high population, the results showed that there was no important source of Hg contamination in the investigated areas. The higher concentrations found in fish from Jurumirim seem to be the result of processes that favor Hg mobilization and methylation as a consequence of the impoundment of the reservoir area. The same levels were not observed in the Salto Grande Reservoir, probably because these are no longer significant due to the long time since the impoundment. To understand the dynamics of methylmercury (MeHg) production and its accumulation in fish, further studies are needed in the Jurumirim Reservoir. The results show that even at low T-Hg concentrations in sediment and water, concentrations in fish can reach values that pose concerns for consumption. This emphasizes the importance of designing an optimized biomonitoring program that can provide warning of biogeochemical conditions that promote formation of MeHg.

In vivo studies on lead content of deciduous teeth superficial enamel of preschool children.

The amount of lead in the superficial enamel of deciduous teeth from 4- and 5-year-old children was determined by means of an enamel biopsy followed by lead analysis by graphite furnace atomic absorption spectrometry. Children examined in this study (n=329) attended public preschools in the city of Piracicaba, SP, Brazil. The selection of preschools was based on geographical location: some were located in an industrial area of the city, whereas others were located in an area devoid of industries. The objectives of this study were (1) to test whether enamel biopsies were an appropriate method for lead content population screening in young children; (2) to verify the lead content of superficial enamel of preschool children's deciduous teeth and to compare the results obtained from children exposed to different environments; (3) to analyze how biopsy depth correlated with lead content and affected comparisons between groups. An adhesive tape with a central hole (diameter=1.6 mm) was placed on one of the upper central incisors. Five microliters of 1.6 M l(-1) HCl in 70% glycerol (v/v) were applied to this area for 20 s, followed by a rinse with 5-microl ultrapurified water for 10 s. It was shown that the technique was feasible for population studies on young children. The lead concentration in enamel biopsies from the industrial area children (median: 169 ppm Pb) was significantly higher than that from the children living far from industries (118.1 ppm Pb) (P<0.0001). Analysis of the data showed that biopsies deeper than 3.9 microm gave more reliable results for comparisons between groups. To our knowledge, this study is the first to use an enamel microbiopsy to characterize a large sample of young children in vivo for lead monitoring in teeth.

Concentração de chumbo em dentes decíduos de pré-escolares de Piracicaba, SP, Brasil - Estudo piloto / Analysis of lead levels in deciduous teeth of preschool children from Piracicaba, SP, Brazil - A pilot study

O chumbo (Pb) é um metal tóxico ao organismo humano que pode ficar incorporado no tecido dentário. A origem ambiental de Pb está relacionada à poluição, principalmente industrial. Sabe-se que alguns defeitos de esmalte estão associados à presença de Pb, e aqueles por sua vez seriam indicadores de um maior risco de cárie. O objetivo desta pesquisa foi verificar a concentração de Pb no esmalte de dentes decíduos de crianças de duas pré-escolas de regiões distintas da cidade de Piracicaba, uma industrial e outra livre de indústrias. Para a determinação da quantidade de chumbo nos dentes decíduos foi utilizada uma técnica de biópsia de esmalte. A concentração de Pb encontrada nos dentes das crianças da região industrial foi maior que a da não industrial, entretanto a diferença não foi estatisticamente significativa (p maior 0,05). Como a diferença encontrada foi de 37 por cento, ela pode ter significado biológico justificando a necessidade de um estudo epidemiológico delineado para inclusive avaliar a significância estatística. (Apoio financeiro, FAPESP processos 99/12891-8 e 00-07353-6).