RESUMO
The present study proposes a maize sprouts hydroponic growth model to evaluate the As, Cd, Cr and Pb translocation from multinutrient fertilizer and to do speciation of As and Cr in this fertilizer and As in parts of plant in order to predict their phytoavailability. X-ray absorption near edge structure (XANES) was employed to speciate As and Cr directly on fertilizer solid sample. Arsenate (AsV) and a solid solution of FeCrO3 were the major species identified in the samples. The sprouts were hydroponically cultivated in water, fertilizer slurry and fertilizer extract media. Concentrations of As, Cd and Pb measured on leaves of maize sprouts ranged from 0.061 to 0.31 mg kg-1, whereas Cr was not translocated to the aerial parts of sprouts. High performance liquid chromatographic with inductively coupled plasma mass spectrometry (HPLC-ICP-MS) analysis was used to determine As speciation in maize sprouts, as well as in the fertilizer extracts and slurries. Arsenate was the only species identified in the initial fertilizer extract and this information is in agreement with the XANES results. However, the reduction of arsenate to arsenite was observed in extracts and slurries collected after sprout growth, probably due to the action of exudates secreted by plant roots. Arsenite was the predominant species identified in sprouts, the high phosphate concentration in the medium may have contributed to reduce arsenate phytoavailability.
Assuntos
Fertilizantes , Zea mays , Cádmio , Hidroponia , Chumbo , MineraisRESUMO
The sequential extraction procedure of the Community Bureau of Reference (BCR) was applied to investigate the mobility of potentially toxic elements (As, Cd, Cr, and Pb) and nutrients (P, Ca, Mg, Cu, Fe, Mn, and Zn) in a multinutrient mineral fertilizer based on phosphate rocks supplemented with 10% (w w-1) micronutrient mixture (raw material used as a micronutrient source). For both samples, As and Cd were more mobile, whereas Cr remained in the solid residue. A higher mobility of Pb was observed in the micronutrient mixture; however, the high concentration of P (8.3% w w-1) in the fertilizer could have decreased Pb mobility as a result of Pb3(PO4)2 formation. The nutrients had great mobility, except Fe, which remained almost totally in the residual fraction in both samples. X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy analyses of solid residues showed that the ways in which elements were distributed in the sample particles could affect their mobility.