Browsing by Author "Bali, R"

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    Biogenic Pt uptake and nanoparticle formation in Medicago sativa and Brassica juncea
    (Springer, 2010-10) Bali, R; Siegele, R; Harris, AT
    The ability of the facultative metallophyte plants, Medicago sativa (M. sativa) and Brassica juncea (B. juncea) to accumulate and translocate platinum (Pt) from aqueous substrates is reported. The influence of Pt concentration in the substrate (5, 10, 20, 40 and 80 ppm), exposure time (24, 48 and 72 h) and substrate pH (2, 3, 5, 7 and 9) was determined. In both plants the concentration of Pt increased with substrate concentration and exposure time. Greater accumulation was detected in the roots of M. sativa than B. juncea, up to a maximum of 94.19 mg Pt g−1 (dry biomass) compared with 38.5 mg Pt g−1 (dry biomass) following exposure to 80 ppm Pt after 72 h exposure, respectively. However, at lower substrate concentrations (5 and 20 ppm) greater quantities of Pt were detected in the shoots of B. juncea, ranging between 0.02 and 0.32 mg Pt g−1 (dry biomass) at 5 ppm across the different time intervals studied, compared with 0.02−0.14 mg Pt g−1 (dry biomass) for M. sativa, suggesting B. juncea to be a better translocator of Pt under idealised conditions at low concentrations. Higher Pt uptake was also observed in acidic media, with a maximum at pH 2 for M. sativa and pH 3 for B. juncea, indicating the role of net surface charge on the bioaccumulation of Pt. Once sequestered Pt(II) was reduced to Pt(0) due to the action of local metabolites. TEM images of M. sativa root samples showed the in vivo formation of Pt nanoparticles between 3 and 100 nm in size and of varying morphologies in the epidermal root cells. In vivo Pt distribution profiles were assessed using proton induced X-ray emission (μ-PIXE) spectroscopy, which showed even distribution across all tissue systems (epidermal, cortical and vascular) within the roots of both M. sativa and B. juncea. © 2010, Springer. The original publication is available at www.springerlink.com
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    Biogenic separation, accumulation and cellular distribution of Cu, Co, and Ni in medicago sativa under idealized conditions
    (Taylor & Francis, 2010-06) Bali, R; Siegele, R; Harris, AT
    The limits of uptake of Co, Ni, and Cu by the common metallophyte, Medicago sativa, were assessed using hydroponic growth and metal uptake experiments. The influence of the growth substrate metal concentration (500 and 1000 ppm) and exposure time, i.e., the time plants were exposed to the metal solution (24, 48, or 72 h) was investigated. The combined roots and shoots of Medicago sativa accumulated up to 2.2 wt-% Co, 2.0 wt-% Ni, and 3.5 wt-% Cu, when exposed to aqueous solutions containing 1000 ppm Co for 48 h, 1000 ppm Ni for 72 h, and 1000 ppm Cu for 72 h, respectively. The distribution of the sequestered metals was assessed using proton induced that X-ray emission spectroscopy (μ-PIXE), which indicated that translocation mechanism was most likely xylem loading. However, the rate of translocation of the metal from the roots to the plant stem was different for each metal, suggesting differing mechanisms for each. Collectively, these results suggest the separation and removal of the heavy metals Cu, Co, and Ni from contaminated substrates using Medicago sativa is a viable technology. © 2010, Taylor & Francis Ltd.
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    Phytoextraction of Au: uptake, accumulation and cellular distribution in Medicago sativa and Brassica juncea
    (Elsevier, 2010-01-15) Bali, R; Siegele, R; Harris, AT
    The influence of metal concentration, solution pH and exposure time on the phytoextraction (i.e. separation using vascular plants) of Au was investigated for the known metallophytes Brassica juncea (BJ) and Medicago sativa (MS). Metal uptake was inferred using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and in vivo localisation and distribution using proton induced X-ray emission spectroscopy (μ-PIXE). MS roots accumulated a maximum of 287 mg Au g−1 (dry biomass) and BJ roots a maximum of 227 mg Au g−1 (dry biomass), both when exposed to a 10,000 ppm aqueous solution of KAuCl4. MS was found to accumulate comparatively greater quantities of Au than BJ across higher substrate concentrations (40–10,000 ppm Au) whereas BJ was found to be a better accumulator of Au at lower concentrations (5–20 ppm Au). In general MS showed an increase in Au uptake with an increase in Au substrate concentration and the time exposed, whereas for BJ the maximum uptake was observed after 48 h of exposure at higher concentrations (100–10,000 ppm), and then decreased at longer exposure times. The uptake ratio (UR), defined as the ratio of Au concentration in plant tissues to the concentration in the substrate, increased with increasing concentration and exposure time, to a maximum of 995 for MS roots after 72 h exposure. Metal translocation from roots to shoots in BJ increased with increasing substrate concentration, however in the shoots, metal uptake increased from 24 to 48 h and then decreased at 72 h, indicating some threshold level had been reached and metal was then being excluded from the cells, possibly through the phloem to the Au solution. Elemental distribution maps of plant tissues measured using μ-PIXE, show Au present across the entire sample, ranging from the epidermis and cortex, with the greatest concentration occurring within the central stele. This result is suggestive of xylem loading. These results collectively suggest that the separation of Au using vascular plants for applications in mining (phytomining) and remediation (phytoremediation) are viable technologies. © 2010, Elsevier Ltd.