Browsing by Author "Slaveykova, V. I."
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- Effect of humic acid on Cd(II), Cu(II), and Pb(II) uptake by freshwater algae: kinetic and cell wall speciation considerationsPublication . Lamelas, C.; Pinheiro, J. P.; Slaveykova, V. I.The present study examines the effect of humic acid on the uptake kinetics of Cd(II), Cu(II), and Pb(II) by the freshwater alga Chlorella kesslerii. The results demonstrated that the relative proportion of Pb in the cell wall layer is greater than that of the internalized Pb, while internalized Cd and Cu were comparable or greater than the adsorbed metal concentration. In the presence of 10 mg L-1 humic acid (HA), Cd and Cu uptake kinetics were consistent with that predicted by measured free metal concentrations. For Pb, the uptake flux and amount of lead bound to internalization and adsorption sites were an order of magnitude higher than those found at the same free lead ion concentrations in the presence of citric acid. Chemodynamic modeling suggested that the enhancement of the Pb uptake flux in the presence of HA originates from an increasing amount of Pb bound to the internalization sites through a ternary complex formation between lead-humic acid complex and internalization sites. Cell wall speciation calculations indicated that the lead-humic acid complex is the predominant species in the cell wall layer, while for Cu(II) and Cd(II) metal bound to the internalization (Cu) and adsorption (Cd) sites significantly dominated over the M-HA complex. The findings of the work show the relevance of the cell wall layer concentration and speciation and its key role in defining the local equilibrium conditions between metal and internalizations sites. The results of the present kinetic study have important consequences for improvement of the mechanistic understanding of the role of dissolved organic matter in metal uptake in phytoplankton and biogeochemical cycling of metals in the surface waters.
- Interactions of core-shell quantum dots with metal resistant bacterium Cupriavidus metallidurans: Consequences for Cu and Pb removalPublication . Slaveykova, V. I.; Pinheiro, J. P.; Floriani, M.; Garcia, M.In the present study we address the interactions of carboxyl-CdSe/ZnS core/shell quantum dots (QDs),as a model of water dispersible engineered nanoparticles, and metal resistant bacteria Cupriavidusmetallidurans, largely used in metal decontamination. The results demonstrate that QDs with averagehydrodynamic size of 12.9 nm adhere to C. metallidurans. The percentage of bacterial cells displayingQD-fluorescence increased proportionally with contact time and QD concentration in bacterial mediumdemonstrating the association of QDs with the metal resistant bacteria. No evidence of QD internalizationinto bacterial cytoplasm was found by transmission electron microscopy with energy dispersive X-rayspectrometry, however QD clusters of sizes between 20 and 50 nm were observed on the bacterial sur-face and in the bacterial periplasmic compartment; observations consistent with the losses of membraneintegrity induced by QDs. The presence of 20 nM QDs induced about 2-fold increase in Cu and Pb uptakefluxes by C. metallidurans exposed to 500 nM Pb or Cu, respectively. Overall, the results of this work sug-gest that when present in mixture with Cu and Pb, low levels of QDs originating from possible incidentalrelease or QD disposal could increase metal accumulation in metal resistant bacterium.
- Modeling of Cd uptake and efflux kinetics in metal-resistant bacterium cupriavidus metalliduransPublication . Hajdu, R.; Pinheiro, J. P.; Galceran, J.; Slaveykova, V. I.The Model of Uptake with Instantaneous Adsorption and Efflux, MUIAE, describing and predicting the overall Cd uptake by the metal-resistant bacterium Cupriavidus metallidurans CH34, is presented.MUIAEtakes into account different processes at the bacteria-medium interface with specific emphasis on the uptake and efflux kinetics and the decrease in bulk metal concentration. A single set of eight parameters provides a reasonable description of experimentally determined adsorbed and internalized Cd, as well as the evolution of dissolved Cd concentrations with time, for an initial Cd concentration between 10-8 and 10-4 M, covering the situation of contaminated environments and heavily polluted effluents. The same set of parameters allowed successful prediction of the internalized and adsorbed Cd as a function of the measured free Cd ion concentration in the presence of natural and anthropogenic ligands. The findings of the present study reveal the key role of Cd efflux and bulk depletion on the overall Cd uptake by C. metallidurans, and the need to account for these processes to understand and improve the efficiency of the metal removal from the contaminated environment.