Localization of mercury and gold in cassava (Manihot esculenta Crantz).

The potential of cassava (Manihot esculenta Crantz.) for simultaneous Hg and Au phytoextraction was explored by investigating Hg and Au localization in cassava roots through Micro-Proton Induced X-Ray Emission, High-Resolution Transmission Electron Microscopy (HR-TEM) and X-Ray Diffractometry (XRD). The effect of Hg and Au in the cyanogenic glucoside linamarin distribution was also investigated using Matrix Assisted Laser Desorption Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (MALDI-FT-ICR-MS) imaging. Hg was located mainly in the root vascular bundle of plants grown in 50 or 100 µmol L-1 Hg solutions. Au was localized in the epidermis and cortex or in the epidermis and endodermis for 50 and 100 µmol L-1 Au solutions, respectively. For 50 µmol L-1 solutions of both Hg and Au, the two metals were co-localized in the epidermis. When the Hg concentrations were increased to 100 µmol L-1, Au was still localized to a considerable extent in the epidermis while Hg was located in all root parts. HR-TEM and XRD revealed that Au nanoparticles were formed in cassava roots. MALDI-FT-ICR-MS imaging showed linamarin distribution in the roots of control and plants and metal-exposed plants thus suggesting that linamarin might be involved in Hg and Au uptake and distribution.

Localization of nickel in the hyperaccumulator plant Breynia cernua (Poir.) Mull.Arg. discovered in the nickeliferous laterites of Zambales, the Philippines.

A newly discovered nickel (Ni) hyperaccumulator plant, Breynia cernua (Phyllanthaceae) from the nickeliferous laterites of Acoje, Zambales, has elevated Ni concentrations. Its computed bioaccumulation factor is 1.7 and the translocation factor is 4.6. Leaf tissues which contain the highest Ni concentrations were analyzed using optical microscopy and Scanning Electron Microscopy with Energy-Dispersive X-ray (SEM/EDX). The results indicated that most of the Ni are stored in the epidermal cells of the leaves, followed by the mesophyll cells then the vascular bundles. The accumulation of Ni found in the subcellular locations, probably in the vacuoles, may prevent phytotoxicity that could affect the normal function of other cellular structures. A possible resistance mechanism through strain avoidance towards Ni accumulation makes B. cernua capable of tolerating elevated Ni concentrations in its tissues. The tolerance of B. cernua to Ni phytotoxicity suggests possible applications of this hyperaccumulator plant in phytoextraction technology.

Copper uptake by Pteris melanocaulon Fée from a Copper-Gold mine in Surigao del Norte, Philippines.

The ability of some plants to take up metal contaminants in the soil has been of increasing interest as an environmental approach to pollution clean-up. This study aimed to assess the ability of Pteris melanocaulon for copper(Cu) uptake by determining the Cu levels in the fern vis-à-vis surrounding soil and the location of Cu accumulation within its biomass. It also aimed to add information to existing literature as P. melanocaulon are found to be less documented compared to other fern metal accumulators, such as P. vittata. The P. melanocaulon found in the Suyoc Pit of a Copper-Gold mine in Placer, Surigao del Norte, Philippines exhibited a high Bioaccumulation Factor(BF) of 4.04 and a low Translocation Factor(TF) of 0.01, suggesting more Cu accumulation in the roots (4590.22 ± 385.66 µg g(-1) Cu). Noteworthy was the Cu concentration in the rhizome which was also high (3539.44 ± 1696.35 µg g(-1) Cu). SEM/EDX analyses of the Cu content in the roots indicated high elemental %Cu in the xylem (6.95%) than in the cortex (2.68%). The high Cu content in the roots and rhizomes and the localization of Cu in the xylem manifested a potential utilization of the fern as a metallophyte for rhizofiltration and phytostabilization.

Succulent species differ substantially in their tolerance and phytoextraction potential when grown in the presence of Cd, Cr, Cu, Mn, Ni, Pb, and Zn.

Plants for the phytoextraction of heavy metals should have the ability to accumulate high concentrations of such metals and exhibit multiple tolerance traits to cope with adverse conditions such as coexistence of multiple heavy metals, high salinity, and drought which are the characteristics of many contaminated soils. This study compared 14 succulent species for their phytoextraction potential of Cd, Cr, Cu, Mn, Ni, Pb, and Zn. There were species variations in metal tolerance and accumulation. Among the 14 succulent species, an Australian native halophyte Carpobrotus rossii exhibited the highest relative growth rate (20.6-26.6 mg plant(-1) day(-1)) and highest tolerance index (78-93%), whilst Sedum "Autumn Joy" had the lowest relative growth rate (8.3-13.6 mg plant(-1) day(-1)), and Crassula multicava showed the lowest tolerance indices (<50%). Carpobrotus rossii and Crassula helmsii showed higher potential for phytoextraction of these heavy metals than other species. These findings suggest that Carpobrotus rossii is a promising candidate for phytoextraction of multiple heavy metals, and the aquatic or semiterrestrial Crassula helmsii is suitable for phytoextraction of Cd and Zn from polluted waters or wetlands.

Performance measurement via sap flow monitoring of three eucalyptus species for mine site and dryland salinity phytoremediation.

Monitoring of trees with reliable technology is essential in phytoremediation. Sap flow instrumentation on three Eucalyptus species at a mine site in western Victoria, Australia, was used to determine which species is best suited to meet the goals of a phytoremediation project. Specifically, the aim of the monitoring was to determine which species could better tolerate the hypersaline soil, potentially lower saline ground water, and cope with expected hotter and drier weather given climate change scenarios. Over a summer period, average daily water use of E. cladocalyx was approximately six times greater than E. melliodora and four times greater than E. polybractea. During a three day heat wave event, E. cladocalyx was found to have a higher tolerance to extreme temperature. The optimal VPD/temperature for tree transpiration was 2.6 kPa/26.2 °C for E. cladocalyx, 2.1 kPa/23.9 °C for E. melliodora, and 2.0 kPa/23.2 °C for E. polybractea. Through sap flow monitoring, it was determined that E. cladocalyx could better tolerate saline soils, hotter and drier weather, and had greater potential to lower saline ground water.

Rinorea niccolifera (Violaceae), a new, nickel-hyperaccumulating species from Luzon Island, Philippines.

A new, nickel-hyperaccumulating species of Rinorea (Violaceae), Rinorea niccolifera Fernando, from Luzon Island, Philippines, is described and illustrated. This species is most similar to the widespread Rinorea bengalensis by its fasciculate inflorescences and smooth subglobose fruits with 3 seeds, but it differs by its glabrous ovary with shorter style (5 mm long), the summit of the staminal tube sinuate to entire and the outer surface smooth, generally smaller leaves (3-8 cm long × 2-3 cm wide), and smaller fruits (0.6-0.8 cm diameter). Rinorea niccolifera accumulates to >18,000 µg g(-1) of nickel in its leaf tissues and is thus regarded as a Ni hyperaccumulator.

Australian native plant species Carpobrotus rossii (Haw.) Schwantes shows the potential of cadmium phytoremediation.

Many polluted sites are typically characterized by contamination with multiple heavy metals, drought, salinity, and nutrient deficiencies. Here, an Australian native succulent halophytic plant species, Carpobrotus rossii (Haw.) Schwantes (Aizoaceae) was investigated to assess its tolerance and phytoextraction potential of Cd, Zn, and the combination of Cd and Zn, when plants were grown in soils spiked with various concentrations of Cd (20-320 mg kg(-1) Cd), Zn (150-2,400 mg kg(-1) Zn) or Cd + Zn (20 + 150, 40 + 300, 80 + 600 mg kg(-1)). The concentration of Cd in plant parts followed the order of roots > stems > leaves, resulting in Cd translocation factor (TF, concentration ratio of shoots to roots) less than one. In contrast, the concentration of Zn was in order of leaves > stems > roots, with a Zn TF greater than one. However, the amount of Cd and Zn were distributed more in leaves than in stems or roots, which was attributed to higher biomass of leaves than stems or roots. The critical value that causes 10% shoot biomass reduction was 115 µg g(-1) for Cd and 1,300 µg g(-1) for Zn. The shoot Cd uptake per plant increased with increasing Cd addition while shoot Zn uptake peaked at 600 mg kg(-1) Zn addition. The combined addition of Cd and Zn reduced biomass production more than Cd or Zn alone and significantly increased Cd concentration, but did not affect Zn concentration in plant parts. The results suggest that C. rossii is able to hyperaccumulate Cd and can be a promising candidate for phytoextraction of Cd from polluted soils.

Phytotoxicity of biosolids and screening of selected plant species with potential for mercury phytoextraction.

Mercury contaminated stockpiles of biosolids (3.5-8.4 mg kg(-1) Hg) from Melbourne Water's Western Treatment Plant (MW-WTP) were investigated to evaluate the possibility for their phytoremediation. Nine plant species (Atriplex codonocarpa, Atriplex semibaccata, Austrodanthonia caespitosa, Brassica juncea, Brassica napus, Gypsophila paniculata, Sorghum bicolor, Themeda triandra and Trifolium subterraneum) were screened for phytoextraction potential in Hg-contaminated biosolids from MW-WTP. In addition, the same plant species were germinated and grown in two other substrates (i.e. potting mix and potting mix spiked with mercury(II)). Growth measurements and the mercury uptake for all three substrates were compared. Some plant species grown in potting mix spiked with mercury(II) grew more vigorously than in the other two substrates and showed higher levels of sulphur in their tissues. These results suggested that the mercury stress activated defence mechanisms and it was hypothesised that this was the likely reason for the enhanced production of sulphur compounds in the plant species studied which stimulated their growth. Some species did not grow in biosolids because of the combined effect of high mercury toxicity and high salt content. Atriplex conodocarpa and Australodanthonia caespitose proved to be the most suitable candidates for mercury phytoextraction because of their ability to translocate mercury from roots to the above-ground tissues.

Phytostabilisation of arsenical gold mine tailings using four Eucalyptus species: growth, arsenic uptake and availability after five years.

Arsenic (As) contamination is a worldwide problem. Where arsenic is highly concentrated and confined within a limited area, such as in many mine tailings facilities, phytostabilisation is an attractive technology for long-term remediation. Important characteristics of a plant to be useful for phytostabilisation include As tolerance and low levels of As accumulation, as well as the ability to limit As availability. Performance needs to be monitored over the long term to ensure an ongoing vegetation community, though this is rarely done. In this study, the suitability of four Eucalyptus species (E. cladocalyx, E. melliodora, E. polybractea, E. viridis) for the phytostabilisation of arsenical, sulphidic gold mine tailings was assessed after five years. All four species accumulated low As concentrations, the highest being recorded in mature leaves, ranging from 0.29 to 5.14 microg g(-1) As. E. polybractea had significantly higher foliar As than the other three species but there was also great variation within the species. Between 5-10 times lower concentrations were recorded in stem samples and no As was detected in young leaf tips. There was also significant variation in the growth of trees upon the site. Eucalyptus cladocalyx grew significantly taller than other species although greater variation was detected within the species than between. The variation in tree heights was not correlated with As concentrations in either stems or leaves. Arsenic availability was determined to depths of 2.2 m and found to be low when compared to total As in the tailings. Importantly, no effect of trees on As availability or soil pH was detected. We conclude that E. cladocalyx, in particular is an ideal candidate for the long-term phytostabilisation of As-contaminated land and mine tailings. The variation detected in both As accumulation and growth is also promising for the selection of desirable traits.