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This study investigates the effectiveness of using nanoscale zero-valent iron (nZVI) to immobilise Pb/Zn in two different soils (acidic and calcareous) and the effects of nZVI treatment on soil physico-chemical and biological properties. Soil samples spiked with Pb(II) or Zn(II) were treated with commercial nZVI suspension at a dose of 20% (28-36 mg Fe(0)/g soil) for 72 h and one month. Sequential extraction procedures showed a significant decrease of Pb/Zn bound to exchangeable and carbonate fractions and an increase of residual fraction after the treatment with nZVI. There were no significant differences in the distribution of Pb/Zn in the soil fractions between the contact times studied; the immobilisation of Pb/Zn with nZVI in the described conditions was stable at least for a month. Better immobilisation results were found for Pb than for Zn. No negative effects on soil physico-chemical and biological properties were observed. In fact, the application of nZVI stimulated the soil respiration and the dehydrogenase activity in both soils, especially in the case of Pb, probably due to the higher immobilisation percentages. These results suggest that the use of nZVI to remediate polluted soils with Pb or Zn is a promising in situ strategy, and more research is required both in the laboratory and field to investigate the effects of such a treatment to the soil ecosystem.

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The tolerance of the metallophyte Silene vulgaris, a plant suitable for the phytostabilisation of metal(loid)contaminated soils, to arsenic (As), mercury (Hg) and cadmium (Cd) was evaluated in a semi-hydroponic culture system under controlled environmental conditions. The appearance of oxidative stress, alteration of photochemical processes and modification of biothiol content were studied as physiological parameters of metal(loid) stress in plants treated with 0, 6 and 30 mM (As, Hg or Cd) for 7 days. In spite of the metal(loid) excluder behaviour of S. vulgaris, Cd was translocated to the aerial part of the plant at a higher rate than Hg or As. The major toxic effects were observed in roots, where lipid peroxidation was increased in a dose-dependent manner. Redox enzymes such as glutathione reductase (GR) were severely inhibited by Hg, whereas GR was overexpressed. The accumulation of Cd produced a remarkable production of phytochelatins (PCs) in roots, whereas Hg and As led to modest PCs synthesis. There was a severe loss of chlorophyll content in Cd-treated plants, accompanied with a significant decrease in photosystem II efficiency (WPSII) and photochemical quenching (qP). Similar negative effects were observed in Hg-and Asexposed plants, but to a lesser degree. The exposure to the highest dose of each toxic element (30 mM) caused depletion of the light harvesting complex b1 protein. In conclusion, specific stress signatures to each metal(loid) were observed, with As being the least toxic element, suggesting that different mechanisms of tolerance were exerted. These results could be applied in future experiments to select tolerant ecotypes to optimize the phytostabilisation of metal(loid) multipolluted soils.

Phytomanagement could be a viable alternative in areas polluted with wastes from chromium-using industries. This study investigated the ability of Silene vulgaris to take up Cr(III) and Cr(VI) with special attention on the mechanism used by this species to tolerate high doses of Cr(VI). Plants were grown semihydroponically with different concentrations of either Cr(III) or Cr(VI). A combination of synchrotron X-ray spectroscopic techniques, scanning electron and light microscopy and infrared spectroscopy were used to determine the distribution and speciation of Cr. S. vulgaris accumulated more Cr when grown with Cr(VI) resulting in an overall reduction in biomass. Starch accumulation in leaves may be attributed to an impartment between carbon utilization and assimilation resulted from stunted plant growth but not the complete inhibition of photosynthesis indicating that S. vulgaris possess tolerance mechanisms that allows it to survive in Cr(VI) rich environments. These primary tolerance mechanisms are (a) the total reduction of Cr(VI) to Cr(III) in the rhizosphere or just after uptake in the fine lateral root tips and (b) chelation of Cr(III) to the cell wall both of which reduce metal interference with critical cell functions. These mechanisms make S. vulgaris suitable for in situ remediation of Cr polluted soils.

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