Phytoextraction to promote sustainable development

Mining makes a positive contribution to the economy of Indonesia. Significant earnings accrue through the export of tin, coal, copper, nickel and gold. Of these commodities, gold carries the highest unit value. But not all gold mining is regulated. Indonesia has a significant Artisanal and Small Scale Gold Mining (ASGM) industry, defined as any informal and unregulated system of gold mining. These operations are often illegal, unsafe and are environmentally and socially destructive. New technology is needed to support the sustainable exploitation of gold and other precious metal resources in locations where ASGM is currently practised. This technology must be simple, cheap, easy to operate and financially rewarding. A proven option that needs to be promoted is phytoextraction. This is technology where plants are used to extract metals from waste rock, soil or water. These metals can subsequently be recovered from the plant in pure form, and sold or recycled. Gold phytoextraction is a commercially available technology, while international research has shown that phytoextraction will also work for mercury. In the context of ASGM operations, tailings could be contained in specific ‘farming areas’ and cropped using phytoextraction technology. The banning of ASGM operations is not practicable or viable. Poverty would likely become more extreme if a ban were enforced. Instead, new technology options are essential to promote the sustainable development of this industry. Phytoextraction would involve community and worker engagement, education and employment. New skills in agriculture created through application of the technology would be transferrable to the production of food, fibre and timber crops on land adjacent to the mining operations. Phytoextraction could therefore catalyse sustainable development in artisanal gold mining areas throughout Indonesia

Thiosulphate assisted phytoextraction of mercury contaminated soils at the Wanshan Mercury Mining District, Southwest China

Wanshan, known as the “Mercury Capital” of China, is located in the Southwest of China. Due to the extensive mining and smelting works in the Wanshan area, the local ecosystem has been serious contaminated with mercury. In the present study, a number of soil samples were taken from the Wanshan mercury mining area and the mercury fractionations in soils were analyzed using sequential extraction procedure technique. The obtained results showed that the dominate mercury fractions (represent 95% of total mercury) were residual and organic bound mercury. A field trial was conducted in a mercury polluted farmland at the Wanshan mercury mine. Four plant species Brassica juncea Czern. et Coss.var. ASKYC (ASKYC), Brassica juncea Czern. et Coss.var.DPDH (DPDH), Brassica juncea Czern. et Coss.var.CHBD(CHBD), Brassica juncea Czern. et Coss.var.LDZY (LDZY) were tested their ability to extract mercury from soil with thiosulphate amendment. The results indicated that the mercury concentration in the roots and shoots of the four plants were significantly increased with thiosulphate treatment. The mercury phytoextraction yield of ASKYC, DPDH, CHBD and LDZY were 92, 526, 294 and 129 g/ha, respectivel

Nickel and Cobalt Phytoextraction by the Hyperaccumulator Berkheya coddii: Implications for Polymetallic and Phytoremediation

We investigated the potential of the South African high-biomass Ni hyperaccumulator Berkheya coddii to phytoextract Co and/or Ni from artificial metalliferous media. Plant accumulation of both metals from single-element substrates indicate that the plant/media metal concentration quotient (bioaccumulation coefficient) increases as total metal concentrations increase. Cobalt was readily taken up by B. coddii with and without the presence of Ni. Nickel uptake was, however, inhibited by the presence of an equal concentration of Co. Bioaccumulation coefficients of Ni and Co for the single element substrates (total metal concentration of 1000 μg g-1) were 100 and 50, respectively. Cobalt phytotoxicity was observed above a total Co concentration in plant growth media of 20 μg g-1. Elevated Co concentrations significantly decreased the biomass production of B. coddii without affecting the bioaccumulation coefficients. The mixed Ni-Co substrate produced bioaccumulation coefficients of 22 for both Ni and Co. Cobalt phytotoxicity in mixed Ni-Co substrate occurred above a total Co concentration of 15 μg g-1. When grown in the presence of both Ni and Co, the bioaccumulation coefficients of each metal were reduced, as compared to single-element substrate. This may indicate competition for binding sites in the root zone. The interference relationship between Ni and Co uptake demonstrated by B. coddii suggests a significant limitation to phytoextraction where both metals are present

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