Geochemical signatures and natural background values of rare earth elements in soils of Brazilian Amazon.

Rare earth elements (REEs) are generally defined as a homogenous group of elements with similar physical-chemical properties, encompassing Y and Sc and the lanthanides elements series. Natural REEs contents in soils depend on the parent material, the soil genesis processes and can be gradually added to the soil by anthropogenic activities. The REEs have been considered emerging pollutants in several countries, so the establishment of regulatory guidelines is necessary to avoid environmental contamination. In Brazil, REE soils data are restricted to some regions, and knowledge about them in the Amazon soils is scarce, although this biome covers more than 40% of the Brazilian territory. Thus, the objectives of this study were to determine the REE content in soils of two hydrographic basins (Solimões and Rio Negro) of the Amazon biome, establish their Quality Reference Values (QRV) and to investigate the existence of enrichment of REEs in urban soils. The ΣREE(Y + Sc) content of Solimões surface samples was 109.28 mg kg-1 and the ΣREE(Y + Sc) content in the subsurface samples was 94.11 mg kg-1. In soils of Rio Negro basin, the ΣREE(Y + Sc) was 43.95 15 mg kg-1 surface samples and 38.40 mg kg-1 in subsurface samples. The ΣREE(Y + Sc) in urban topsoils samples was 38.62 mg kg-1. The REEs contents pattern in three studied areas are influenced in different amplitude by natural soil properties. The REEs content in urban topsoils were slightly higher than the Rio Negro pristine soils, but the ecological risk was low. QRVs recommend for Solimões soils ranged from 0.01 (Lu) to 145.6 mg kg-1 (Ce) and for Rio Negro soils ranged from 0.05 (Lu) to 15.8 mg kg-1 (Ce).

Preparation and evaluation of hydrocalumite-iron oxide magnetic intercalated with dodecyl sulfate for removal of agrichemicals.

The magnetic adsorbent prepared with hydrocalumite-iron oxide (HC/Fe) modified with dodecyl sulfate (DS) was examined for the removal of the agrichemicals atrazine (ATZ) and chlorpyrifos (CPF) from aqueous solution. The adsorbent HC-DS/Fe was characterized by infrared spectroscopy (IR), Raman spectroscopy, X-ray diffractometry (XRD) and atomic absorption spectrometry. The effects of adsorbent dosage, contact time, pH and initial concentration of ATZ and CPF were evaluated. HC-DS/Fe presented a maximum adsorption capacity for ATZ of 4.5 mg g-1 (30 min) and for CPF of 72.9 mg g-1 (210 min) at 25 °C. HC-DS/Fe can be readily removed from the aqueous solution by magnetization because of its magnetic properties. The free energy variation for HC-DS/Fe during the adsorption of the ATZ was -48.78 to -53.91 kJ mol-1 and for the CPF of -55.79 to -59.28 kJ mol-1, suggesting the spontaneity of the adsorption process. The positive value of △H suggests an endothermic process for the interaction of ATZ and CPF by HC-DS/Fe. This adsorbent showed satisfactory results when used in the treatment of a sample of river water, fortified with the agrichemicals chlorpyrifos, atrazine, thiamethoxam and acetamiprid.

Simplex-Centroid mixture design applied to arsenic (V) removal from waters using synthetic minerals.

Arsenic (As) is a toxic and carcinogenic element. Therefore, it is necessary to carry out research on As-contaminated water management in order to achieve the World Health Organization (WHO) standard for drinking water (0.010 mg L-1). A Simplex-Centroid mixture design (SCMD) was used to determine the best mineral composition for both maximum adsorption capacity of As(V) (MAC-As) and residual concentration of As(V) (RC-As), using synthetic poorly crystallized aluminum hydroxide (pAlHyd), calcined layered double hydroxide (cLDH), and two-line ferrihydrite (2ℓFh). The analysis of variance results and the predicted values of models showed a good agreement with the experimental data, indicating that SCMD is a reliable method to optimize As removal through determination of the best mineral composition. The ability of pure synthetic minerals to remove As from water was different among those mixtures thereof, which indicate that the mineral components interacted with each other. Results showed that cLDH was the best As adsorbent. However, it showed a RC-As higher than the WHO standard. The pAlHyd and 2ℓFh exhibited smaller MAC-As, but they lowered RC-As to below 0.010 mg L-1, showing no direct relationship between high MAC-As and low RC-As. Therefore, mineral compositions which combine high adsorption capacity with low residual concentration should work better for removing As from drinking water, ensuring it meets the WHO potability standard. Ternary diagrams for MAC-As and RC-As showed that the best combination for maximizing MAC-As and reducing RC-As should be a mixture of 75-90% of cLDH, 10-20% of pAlHyd, and 0-5% of 2ℓFh.

Iron oxide/carbon nanotubes/chitosan magnetic composite film for chromium species removal.

An adsorbent in the form of a CLCh/MWCNT/Fe film was prepared using multiple walled carbon nanotubes (MWCNT) doped with magnetic iron oxide and deposited in crosslinked chitosan (CLCh). The CLCh/MWCNT/Fe was characterized by Inductively Coupled Plasma Mass Spectrometry (ICP-MS), nitrogen (N2) adsorption/desorption, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectrometry (EDS), Infrared Spectroscopy (IR) and Raman Spectroscopy. The CLCh/MWCNT/Fe film presented a maximum adsorption capacity for Cr(III) of 66.25 mg/g (150 min) and for Cr(VI) of 449.30 mg/g (60 min) at 25 °C. The CLCh/MWCNT/Fe can be easily removed from the aqueous solution by a mechanical separation or by magnetization due to its magnetic properties. In ten consecutive reutilization adsorption cycles the CLCh/MWCNT/Fe film presented efficiency losses of only 12% and 6% for the removal of Cr(III) and Cr(VI), respectively.

Heterogeneous photocatalysis using TiO2 modified with hydrotalcite and iron oxide under UV-visible irradiation for color and toxicity reduction in secondary textile mill effluent.

The objective of this study was to evaluate ADMI color removal from a biologically treated textile mill effluent by heterogeneous photocatalysis with UV-visible irradiation (UV-vis) using a novel catalyst composed of TiO2 supported on hydrotalcite and doped with iron oxide (HT/Fe/TiO2). Simulated biological treatment of solutions of the dyes (50 mg/L) used in the greatest amounts at the mill where the textile effluent was collected resulted in no color removal in reactive dye solutions and about 50% color removal in vat dye solutions, after 96 h, indicating that the secondary effluent still contained a large proportion of anionic reactive dyes. Photocatalytic treatments were carried out with TiO2 and HT/Fe/TiO2 of Fe:Ti molar ratios of 0.25, 0.5, 0.75 and 1, with varying catalyst doses (0-3 mg/L), initial pH values (4-10) and UV-vis times (0-6 h). The highest ADMI color removal with unmodified TiO2 was found at a dose of 2 g/L and pH 4, an impractical pH value for industrial application. The most efficient composite was HT/Fe/TiO2 1 at pH 10, also at a dose of 2 g/L, which provided more complete ADMI color removal, from 303 to 9 ADMI color units (96%), than unmodified TiO2, from 303 to 37 ADMI color units (88%), under the same conditions. Hydroxyl radicals were responsible for the color reduction, since when 2-propanol, an OH scavenger, was added color removal was very low. For this reason, the HT/Fe/TiO2 1 composite performed better at pH 10, because the higher concentration of hydroxide ions present at higher pH favored hydroxyl radical formation. COD reductions were relatively low and similar, approximately 20% for both catalysts after 6 h under UV-vis, because of the low initial COD (78 mg/L). Secondary effluent toxicity to Daphnia similis (EC50 = 70.7%) was reduced by photocatalysis with TiO2 (EC50 = 95.0%) and the HT/Fe/TiO2 1 composite (EC50 = 78.6%). HT/Fe/TiO2 1 was reused five times and still lowered secondary effluent ADMI color below local discharge limits. Benefits of the HT/Fe/TiO2 1 catalyst compared to TiO2 include its lower bandgap energy (2.34 eV vs 3.25 eV), higher ADMI color removal and its magnetic nature that facilitated its recovery and would reduce treatment costs.

Removal of Cu, Cr, Ni, Zn, and Cd from electroplating wastes and synthetic solutions by vermicompost of cattle manure.

This study was undertaken to evaluate the retention of Cu, Cr, Ni, Zn, and Cd under laboratory conditions from synthetic solution and electroplating wastes by vermicompost. A glass column was loaded with vermicompost, and metal solutions were passed through it. Metal concentrations were then measured in the eluate in order to evaluate the amounts retained by the vermicompost. Measurements of pH, metal concentrations, moistness, organic matter and ash contents, and infrared and XRD spectroscopy were used for vermicompost characterisation. Vermicompost residues obtained from this process were used for plant nutrition in eroded soil collected from a talus near a highway. Metal retention (in g of metal/kg of vermicompost) from effluents ranged from 2 for Cr and Zn to 4 in the case of Ni. In synthetic solutions, the values for metal retention were 4 for Cd and Zn, 6 for Cu and Ni, and 9 for Cr. The results also showed that metal concentrations in the purified effluents were below the maximum values established for waste discharges into rivers by the Brazilian Environmental Standards. The relatively high available Cd concentration of the vermicompost residue resulted in plant damage. This effect was attributed to the presence of Cd in the synthetic solution passed through the vermicompost. The data obtained do not give a complete picture of using vermicompost in cultivated lands, but such values as are determined do show that it can be suitable to remove heavy metals from industrial effluents.

[Selenium concentration in food consumed in Brazil]. / Concentrações de selênio em alimentos consumidos no Brasil.

OBJECTIVE: To determine the selenium content of foods consumed in Brazil. METHODS: The project was carried out between 1993 and 1999. The food samples were collected in stores in several Brazilian states. The levels of selenium were determined by hydride generation atomic absorption spectrophotometry and by wet oxidation. RESULTS: The highest levels of selenium were found in animal products, especially fish, and in wheat products. We found that plant products generally had selenium levels of less than 5.0 micrograms/100 g. CONCLUSIONS: In Brazil a diet rich in animal products, especially fish, is important in ensuring consumption of the recommended levels of selenium.

Concentracoes de selenio em alimentos consumidos no Brasil / Selenium content of Brazilian foods

Objective. To determine the selenium content of foods consumed in Brazil. Methods. The project was carried out between 1993 and 1999. The food samples were collected in stores in several Brazilian states. The levels of selenium were determined by hydride generation atomic absorption spectrophotometry and by wet oxidation. Results. The highest levels of selenium were found in animal products, especially fish, and in wheat products. We found that plant products generally had selenium levels of less than 5.0 µg/100 g. Conclusions. In Brazil a diet rich in animal products, especially fish, is ensuring consumption of the recommended levels of selenium

Objetivo. Determinar os teores de selênio em alimentos consumidos no Brasil. Métodos. O trabalho foi desenvolvido de 1993 a 1999. As amostras de alimentos foram coletadas no comércio varejista em vários estados do Brasil. Os teores de selênio foram determinados por meio de espectrofotometria de absorção atômica, utilizando-se a técnica de geração de hidretos, e oxidação da matéria orgânica por via úmida. Resultados. Os teores mais elevados de selênio foram encontrados nos produtos de origem animal, sobretudo nos pescados, e nos produtos derivados do trigo. Observou-se que os teores de selênio nos alimentos de origem vegetal foram, de modo geral, inferiores a 5,0 µg/100g. Conclusões. No Brasil, a presença de pescados, principalmente, e de outros produtos de origem animal é importante na dieta para garantir o consumo dos teores recomendados de selênio.