The X-ray fluorescence (XRF) is an analytical technique for determination of elemental composition of different materials. In soils, the XRF has many pedological, environmental and agronomic applications, mainly after the emergence of portable equipments (pXRF). This technique has been recently adopted and successfully used for soil characterization worldwide, but very rare works have been carried out in soils of developing countries. The soil characterization includes the complete elemental composition determination (nutrients, trace and rare-earth elements) and allows estimating some soil physical and chemical properties. In Brazil, this technique is still incipient, mainly the use of pXRF, however, it can greatly contribute to soil characterization in-field or in-lab conditions and also replacing methods of soil analyses considered non-environmentally friendly. This review summarizes the XRF technique including principles and the main applications of pXRF in soils highlighting its potential for tropical Soil Science.Index terms: Soil analyses; soil morphometrics; soil characterization. RESUMOFluorescência de raios-X (FRX) é uma técnica analítica para determinação da composição elementar de diferentes materiais. Em solos, a FRX apresenta muitas aplicações pedológicas, ambientais e agronômicas, principalmente após a emergência de equipamentos portáteis (pXRF). Essa técnica tem sido utilizada com sucessso no mundo todo para caracterização do solo, entretanto, são raros os trabalhos em solos de países em desenvolvimento. A caracterização do solo inclui a determinação completa da composição elementar (nutrientes, elementos-traço e terras-raras) e permite a estimativa de atributos químicos e físicos do solo. No Brasil, a FRX é ainda incipiente, principalmente o uso do pXRF, entretanto, essa técnica pode contribuir grandemente para a caracterização do solo no campo, em condições laboratoriais e, também, substituindo alguns métodos de análise do solo considerados não prejudicial ao ambiente. Esta revisão sumariza a técnica de FRX incluindo princípios e as principais aplicações do pXRF, destacando seu potencial de uso na Ciência do Solo tropical. Termos para indexação:Análise do solo; morfometria do solo; caracterização do solo.
Core Ideas We verified the effect of soil moisture on portable X‐ray fluorescence (pXRF) results with undisturbed soil samples. Heavy oxides (Fe and Ti) are much less affected by soil moisture than light oxides (Si and Al). The power model described the effect of soil moisture on pXRF results for SiO2 and Al2O3 well A practical correction factor for SiO2 and Al2O3 was proposed for accurate in‐field measurements Portable X‐ray fluorescence (pXRF) has been used in many countries to assess the total elemental composition of soils and has agronomic, pedological, and environmental applications. This technique is still incipient in tropical developing countries like Brazil but has potential to improve and decrease the costs of research. Soil moisture is one of the most important factors influencing pXRF results. This pilot study evaluated how soil moisture affects elemental concentrations of oxides common in Brazilian soils (SiO2, Al2O3, Fe2O3, TiO2, and P2O5) as assessed by pXRF. Undisturbed soil samples were collected from the surface and subsurface horizons of six representative Brazilian soils (representing ∼40% of the country) with variable texture, weathering, or leaching status. Soil moisture ranged from complete saturation to oven‐dry. During drying, six pXRF measurements were made and oxide contents were recorded. In all soils, the P2O5 content was below the pXRF detection limit, and SiO2 and Al2O3 were strongly influenced by soil water content. As soil moisture increased, SiO2 and Al2O3 contents decreased (described by a power model, y = a – bxc). The TiO2 content was much less affected by soil moisture, whereas Fe2O3 was not significantly affected by soil moisture. Soil texture and weathering status are closely related to variation in the SiO2 and Al2O3 contents determined by the pXRF with soil moisture. These findings are critical to the appropriate application of pXRF in tropical countries featuring oxide‐laden soils. For in‐field measurement of oxides affected by soil moisture (Si and Al), a practical correction factor was determined.
This study evaluated Cd and Pb accumulation by castor bean (Ricinus communis cv. Guarany) plants grown in nutrient solution, aiming to assess the plant's ability and tolerance to grow in Cd- and Pb-contaminated solutions for phytoremediation purposes. The plants were grown in individual pots containing Hoagland and Arnon's nutrient solution with increasing concentrations of Cd and Pb. The production of root and shoot dry matter and their contents of Cd, Pb, Ca, Mg, Cu, Fe, Mn, and Zn were evaluated in order to calculate the translocation and bioaccumulation factors, as well as toxicity of Cd and Pb. Cadmium caused severe symptoms of phytotoxicity in the plant's root and shoot, but no adverse effect was observed for Pb. Castor bean is an appropriate plant to be used as indicator plant for Cd and tolerante for Pb in contaminated solution and it can be potentially used for phytoremediation of contaminated areas.
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