Enhanced phytoextraction of uranium and selected heavy metals by Indian mustard and ryegrass using biodegradable soil amendments

The applicability of biodegradable amendments in phytoremediation to increase the uptake of uranium (U), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb) and zinc (Zn) by Indian mustard (Brassica juncea) and ryegrass (Lolium perenne) was tested in a greenhouse experiment. Plants were cultivated during one month on two soils with naturally or industrially increased contaminant levels of U. Treatments with citric acid, NH₄-citrate/citric acid, oxalic acid, S,S-ethylenediamine disuccinic acid (EDDS) or nitrilotriacetic acid (NTA) at a rate of 5 mmol kg^− 1 dry soil caused increases in soil solution concentrations that were up to 18 times higher for U and up to 1570 times higher for other heavy metals, compared to the controls. Shoot concentrations increased to a much smaller extent. With EDDS, 19-, 34-, and 37-fold increases were achieved in shoots of Indian mustard for U, Pb and Cu, respectively. The increases in plant uptake of Cd, Cr and Zn were limited to a factor of four at most. Ryegrass generally extracted less U and metals than Indian mustard. Despite a marked increase of U and metal concentrations in shoots after addition of amendments, the estimated time required to obtain an acceptable reduction in soil contaminant concentrations was impractically long. Only for Cu and Zn in one of the studied soils, could the Flemish standards for clean soil theoretically be attained in less than 100 years.     

Phytoextraction of gold and copper from mine tailings with Helianthus annuus L. and Kalanchoe serrata L.

To examine the feasibility of gold phytoextraction, and the corresponding uptake of copper that is induced at the same time, field and laboratory scale experiments were carried out using mine tailings from the Magistral mine in Sinaloa State, Mexico. The locally available plant species Helianthus annuus L. (sunflower) and Kalanchoe serrata L. (magic tower) were used in this work, in combination with the chemical amendments: sodium cyanide (NaCN), ammonium thiocyanate (NH₄SCN), ammonium thiosulphate (NH₄)₂S₂O₃, and thiourea [SC (NH₂)₂] to promote gold uptake. The results show that for K. serrata, average copper concentrations were increased to above 4 mg/kg and gold concentrations to above 9 mg/kg in the dry matter of aerial tissues. For H. annuus average copper concentrations were increased to 118 mg/kg in roots, 141 mg/kg in stem and, 119 mg/kg in leaves while average gold concentrations were increased to 15 mg/kg in leaves, 16 mg/kg in roots and, 21 mg/kg in plant stems. Poor health of plants after treatment with chemicals to induce gold uptake could be a function of toxic concentrations of other trace elements such as copper in the plants. Our results confirm that phytoextraction technology can be used to recover precious metals from mine tailings, and that at the current market price for gold, this recovery may be economic. However, our results also highlight the differential response of plant species to copper and gold in the ground, and the importance of choosing the correct chemical to induce metal uptake.     

尾矿污染区的植物修复研究进展

植物修复是尾矿污染区土壤修复的常用技术。该技术可在稳定被污染土壤及防止地下水二次污染的同时修复污染土壤,既不破坏污染土壤结构,又减少修复费用,因此已成为重金属污染修复技术的研究热点。尾矿污染区植物修复有两种主要作用方式:植物萃取和植物稳定。本文对不同气候条件下两种植物修复方法的优缺点及其适用条件进行了讨论,并对植物修复技术最新研究动态和今后研究方向进行了阐述。     

含砷金矿蜈蚣草除砷应用前景探讨

含砷金矿通常为难浸提金矿,因而选用经济、环保、有效的除砷预处理方法成为提高金回收提取效率的关键。综述了目前砷金矿预处理方法的优缺点和植物提取及砷转化的研究现状,结合超积累植物蜈蚣草在土壤砷污染植物修复方面的应用,提出了在砷金矿区种植砷超积累植物蜈蚣草来提取去除砷的设想,分析表明,植物预处理方法对于含砷较高的原矿、精矿,以及品位较低的含砷尾矿中的金回收具有广阔的应用前景。     

Multi-dose applying EDTA to decrease the potential groundwater contamination using rainbow pink (Dianthus chinensis) for enhanced phytoextraction

Synthetic chelating agents are used to increase the phytoextraction of metals from contaminated soils, however the increased bioavailability of the metals may increases the potential risk of groundwater contamination. In this study, 4 mmol EDTA kg⁻¹ was applied using four application methods to a Cd-, Zn-, and Pb-contaminated soil to evaluate the effects of multi-dose EDTA application on the metals concentrations in the soil solution, soil (as extracted by different methods), and shoots of rainbow pink (Dianthus chinensis). Results showed that application of 4 mmol kg⁻¹ one time or application of 2 mmol kg⁻¹ two times, significantly decreased the concentration of Cd, Zn, and Pb in the soil solution at the end of experiment (42nd day) compared with the application of 0.67 mmol kg⁻¹ six times during 6 weeks experiments. Application of 2 mmol kg⁻¹ two times significantly decreased the deionized water-extractable Cd and Pb concentrations in the soil compared with the application of 0.67 mmol kg⁻¹ six times. However, there were no any effects of the different application methods on the concentration and total removal of Cd, Zn, and Pb in the shoots of rainbow pink. Results revealed that application of 2 mmol kg⁻¹ two times was effective to decrease the potential groundwater contamination.     

Ammonium thiosulphate enhanced phytoextraction from mercury contaminated soil--results from a greenhouse study

According to the 'hard and soft' acid-base principle, mercury is a 'soft metal' and will preferentially form soluble chemical complexes with sulphur-containing ligands. In this work mercury uptake by Chenopodium glaucum L. growing on mercury-contaminated soil was promoted using ammonium thiosulphate. The relative geochemical fractionation of mercury in the soil was subsequently investigated as a function of plant growth with and without thiosulphate amendment. The results indicate that the solubility of mercury is significantly increased through the application of thiosulphate to the soil. Substantially higher mercury levels were found in C. glaucum L. treated with 2 g kg(-1) thiosulphate of soil when compared to the non-treated plants. Compared with initial soil, soluble and exchangeable fractions were increased both in planted and planted treated plants. However, no significant difference was observed between the soils of the planted and planted treated plants. The oxide-bound mercury concentration was significantly decreased for the planted soil (treated and non-treated) at the end of the experiment. Moreover, this fraction was highly correlated with the plant tissue mercury concentration. Taken together, thiosulphate assisted phytoextraction could be used to reduce environmental risk apparent for mercury-contaminated soil through reducing the oxide bound fractions, while managing the bioavailable fractions (compared with no treated plant).     

The effect of EDDS addition on the phytoextraction efficiency from Pb contaminated soil by Sedum alfredii Hance

Present study reports the results of three pot experiments, conducted to investigate the chelate-assisted phytoextraction of Pb contaminated soils. The optimum phytoextraction was observed when 2.5 mM ethylene diamine disuccinic acid (EDDS) was added in single dosage for 14 days to low Pb soil (treated with 400 mg kg⁻¹ soil). On the contrary, for high Pb soil (treated with 1200 mg kg⁻¹ soil), 5 mM EDDS concentration in single dosage for 10 days produced better results. Post-harvest effects of EDDS on the concentrations of available Pb and dissolved organic carbon (DOC) were significantly higher as compared with check (CK i.e. without EDDS addition), and consequently decreased with the passage of time. Our results suggested that chelate-assisted phytoextraction was more suitable for slightly contaminated soils.     

Cadmium-induced physiological response and antioxidant enzyme changes in the novel cadmium accumulator, Tagetes patula

The accumulation and effect of cadmium (Cd) on the growth and enzymatic activities changes of antioxidants in Tagetes patula, French marigold, were investigated to reveal the physiological mechanisms corresponding to its Cd tolerance and accumulation. Hydroponically grown T. patula plants were treated with different concentrations of Cd (0, 10, 25, 50 μM Cd Cl(2)) at various regime of times. T. patula accumulated Cd to a maximum of 450 mg Cd kg(-1) dry weight (DW) in shoot and 3500 mg Cd kg(-1) DW in root after 14 days' exposure at 10 and 50 μM Cd Cl(2), respectively. The translocation factors of Cd were greater than 1 in plants exposed to 10 μM Cd Cl(2). Toxic effects were gradually observed with increasing Cd concentration (25 and 50 μM) accompanied with the reduction of biomass, chlorophyll content, decrease of cell viability and the increase level of lipid peroxidation. In leaves of T. patula, the activities of ascorbate peroxidase (APX), glutathione reductase (GR) and superoxide dismutase (SOD) were induced by Cd. However, in roots, activities of APX, GR, SOD and catalase (CAT) were significantly reduced by 25 and 50 μM Cd treatment but not 10 μM Cd. In-gel zymography analysis revealed that Cd induced the enzymatic activities of APX, MnSOD, CuZnSOD and different isozymes of GR in leaves. These results indicate that T. patula is a novel Cd accumulator and able to tolerate with Cd-induced toxicity by activation of its antioxidative defense system.     

Enhanced heavy metal phytoextraction by Echinochloa crus-galli using root exudates

Heavy metal uptake and growth by Echinochloa crus-galli were investigated to determine if the use of root exudates enhanced phytoextraction. E. crus-galli were planted in soils contaminated with 600 mg kg^− 1 Pb, 40 mg kg^− 1 Cd and 100 mg kg^− 1 Cu. E. crus-galli were then cultivated with and without root exudates from Belamcanda chinensis for 4 weeks. The growth of E. crus-galli in metal-contaminated soils that contained root exudates showed increased roots and shoots when compared to E. crus-galli grown without root exudates (p < 0.05). In addition, the accumulation of metal in E. crus-galli that was cultivated with the root exudates was two- to fourfold higher than in plants that were cultivated without the root exudates. The exchangeable soil fraction in the rhizosphere of E. crus-galli grown with root exudates was greater than when E. crus-galli was grown without root exudates. Finally, the BCF and TF values of Cd, Cu and Pb were greater when the root exudates were added (p < 0.05). Taken together, these results indicate that root exudates can be used as a natural chelating agent to enhance phytoextraction.     

Effect of mycorrhizal fungi on the phytoextraction of weathered p,p-DDE by Cucurbita pepo

Field experiments were conducted to assess the impact of inoculation with mycorrhizal fungi on the accumulation of weathered p,p'-DDE from soil by three cultivars of zucchini (Cucurbita pepo spp. pepo cv Costata Romanesco, Goldrush, Raven). Three commercially available mycorrhizal products (BioVam, Myco-Vam, INVAM) were inoculated into the root system of the zucchini seedlings at planting. In agreement with our previous findings, plants not inoculated with fungi accumulated large but variable amounts of contaminant, with root bioconcentration factors (BCFs, ratio of p,p'-DDE, on a dry weight basis, in the root to that in the soil) ranging from 10 to 48 and stem BCFs ranging from 5.5 to 11. The total amount of contaminant phytoextracted during the 62 day growing season ranged from 0.72-2.9%. The effect of fungal inoculation on the release of weathered p,p'-DDE from soil and on the subsequent uptake of the parent compound by zucchini appeared to vary at the cultivar level. For Goldrush, fungal inoculation generally decreased tissue BCFs but because of slightly larger biomass, did not significantly impact the percent contaminant phytoextracted. Alternatively, for Costata, BioVam and Myco-Vam generally enhanced p,p'-DDE accumulation from soil, and increased the amount of contaminant phytoextracted by up to 34%. For Raven, BioVam reduced contaminant uptake whereas Myco-Vam and INVAM increased contaminant phytoextraction by 53 and 60%, respectively. The data show that fungal inoculation may significantly increase the remedial potential of C. pepo ssp. pepo. The apparent cultivar specific response to mycorrhizal inoculation is unexpected and the subject of ongoing investigation.