Heavy metal accumulation and phytostabilization potential of dominant plant species growing on manganese mine tailings

Screening plants that are hypertolerant to and excluders of certain heavy metals plays a fundamental role in a remediation strategy for metalliferous mine tailings. A field survey of terrestrial higher plants growing on Mn mine tailings at Huayuan, Hunan Province, China was conducted to identify candidate species for application in phytostabilization of the tailings in this region. In total, 51 species belonging to 21 families were recorded and the 12 dominant plants were investigated for their potential in phytostabilization of heavy metals. Eight plant species, Alternanthera philoxeroides, Artemisia princeps, Bidens frondosa, Bidens pilosa, Cynodon dactylon, Digitaria sanguinalis, Erigeron canadensis, and Setaria plicata accumulated much lower concentrations of heavy metals in shoots and roots than the associated soils and bioconcen- tration factors （BFs） for Cd, Mn, Pb and Zn were all 〈 1, demonstrating a high tolerance to heavy metals and poor metals translocation ability. The field investigation also found that these species grew fast, accumulated biomass rapidly and developed a vegetation cover in a relatively short time. Therefore, they are good candidates for phytostabilization purposes and could be used as pioneer species in phytoremediation of Mn mine tailings in this region of South China.

Arsenic uptake by arbuscular mycorrhizal maize (Zea mays L.) grown in an arsenic-contaminated soil with added phosphorus

The effects of arbuscular mycorrhizal （AM） fungus （Glomus mosseae） and phosphorus （P） addition （100 mg/kg soil） on arsenic （As） uptake by maize plants （Zea mays L.） from an As-contaminated soil were examined in a glasshouse experiment. Non-mycorrhizal and zero-P addition controls were included. Plant biomass and concentrations and uptake of As, P, and other nutrients, AM colonization, root lengths, and hyphal length densities were determined. The results indicated that addition of P significantly inhibited root colonization and development of extraradical mycelium. Root length and dry weight both increased markedly with mycorrhizal colonization under the zero-P treatments, but shoot and root biomass of AM plants was depressed by P application. AM fungal inoculation decreased shoot As concentrations when no P was added, and shoot and root As concentrations of AM plants increased 2.6 and 1.4 times with P addition, respectively. Shoot and root uptake of P, Mn, Cu, and Zn increased, but shoot Fe uptake decreased by 44.6%, with inoculation, when P was added. P addition reduced shoot P, Fe, Mn, Cu, and Zn uptake of AM plants, but increased root Fe and Mn uptake of the nonmycorrhizal ones. AM colonization therefore appeared to enhance plant tolerance to As in low P soil, and have some potential for the phytostabilization of As-contaminated soil, however, P application may introduce additional environmental risk by increasing soil As mobility.

Restoration potential of pioneer plants growing on lead-zinc mine tailings in Lanping, southwest China

This study focused on the restoration potential of ten pioneer plants (Artemisia roxburghiana, Artemisia tangutica, Carex inanis, Cyperaceae hebecarpus, Plantago depresa, Cynoglossum lanceolatum, Potentilla saundesiana, Coriaria sinica, Oxyria sinensis, and Miscanthus nepalensis) during the early phase of Pb-Zn mine tailings phytostabilization, in Lanping, China. The concentrations of heavy metals (Pb, Zn, and Cu) and soil fertility (the available N, P, K, and organic matter) in the rhizosphere of these spe...

Cow manure and cow manure-derived biochar application as a soil amendment for reducing cadmium availability and accumulation by Brassica chinensis L. in acidic red soil

Organic amendment is a promising,in situ phytostabilization approach to alleviate the phytotoxic effects of heavy metal contaminated soils.The aim of this study was to evaluate the feasibility of cow manure（CM）and its derived biochar（CMB）as a soil amendment on cadmium（Cd）availability and accumulation in low and high Cd-accumulating cultivars of Brassica chinensis L.grown in an acidic red soil.CM and CMB were applied to Cd-contaminated acidic red soil at the rates of 0,3.0and 6.0%（w/w）.Application of CMB was significantly more effective than that of CM,as it reduced the availability of Cd in soil by 34.3–69.9%and its bioaccumulation in the low Cd accumulator,Aijiaoheiye 333,by 51.2 and 67.4%,respectively.The addition of CMB significantly increased the extractability and accumulation of trace metals（Zn,Mn,Fe,and Cu）by plants and improved plant biomass production.CMB application,combined with utilizing low Cd accumulating cultivars represents a new,sustainable strategy to alleviate the toxic effects on Cd and improve food safety.

Progresses in restoration of post-mining landscape in Africa

Mining alters the natural landscape and discharges large volumes of wastes that pose serious pollution hazards to the environment, to human health and to agriculture. As a result, the recent 2 decades have witnessed a global surge in research on post-mining landscape restoration, yielding a suite of techniques including physical, chemical, biological(also known as phytoremediation) and combinations. Despite the long history of mining in Africa, no systematic review has summarized advances in restoration research and practices after mining disturbance. Thus, the aim of this review was to document the state-of-knowledge and identify gaps in restoration of postmining landscape in Africa through literature review. We found that:(1) there has been substantial progress in identifying species suitable for phytoremediation;(2) few studies evaluated the feasibility of organic amendments to promote autochthonous colonization of mine wastelands or growth of planted species; and(3) restoration of limestone quarries in Kenya, sand mining tailings in South Africa,and gold mine wasteland in Ghana are successful cases of large-scale post-mining restoration practices in Africa.However, the pace of post-mining landscape restoration research and practice in Africa is sluggish compared to other parts of the global south. We recommend:(1)mainstreaming the restoration of mine wastelands in national research strategies and increased development planning to make the mining sector ‘‘Green'';(2) inventory of the number, area, and current status of abandoned mine lands;(3) expanding the pool of candidate species for phytostabilization;(4) further evaluating the phytostabilization potential of organic amendments, e.g., biochar;(5)assessing the impacts of mining on regional biodiversity.

Physico-chemical characteristics and heavy metal concentrations of copper mine wastes in Zambia:implications for pollution risk and restoration

Soil characterization is a vital activity to develop appropriate and effective restoration protocols for mine wastelands while insights into the total content of heavy metals in the soil is an important step in estimating the hazards that the metals may pose to the vital roles of soil in the ecosystem.This study addressed the following research questions:(1)To what extent do the physico-chemical characteristics vary between mine waste sediments and the nearby forest soil?(2)Are the concentrations of heavy metals high enough to be considered as toxic?and(3)Are heavy metals present in mine waste sediments potential sources of pollution?We hypothesized that the physicochemical characteristics of mine waste sediments are less favorably for plant establishment and growth while the concentrations of heavy metals are very high,thus restricting the success of revegetation of mine waste lands.Mine waste sediments were sampled following a diagonal transect across tailings dams,overburden dump sites and the local forest soil from the top layer(0-20 cm)using a closed auger.Samples were analyzed for arsenic,barium,lead,cadmium,cobalt,copper,chromium,nickel,vanadium,and zinc as well as for soil physico-chemical properties.The mine waste sediments were dominated by silt whilst the forest soil by sand particles,with significantly high bulk density in the former.Both the forest soil and overburden sediments were acidic than the alkaline tailings dam sediment.Total organic carbon and nitrogen contents were significantly low in mine wasteland substrates but the concentration of Ca and Mg were significantly higher in tailings dam substrate than the forest soil.The concentrations of available P,K and Na were similar across sites.The mean concentrations of heavy metals were significantly(p<0.01)higher in mine waste sediments than the forest soil;except for cadmium(p=0.213).The order of contamination by heavy metals on the tailings was Cu>Co>Ba>Ni>As>Zn>Pb>Cr>V>Cd,and that on the overburdens was Cu>Co>Ba>Ni>Zn>Cr>Pb>V>As>Cd.The pollution load index(PLI)was nearly twice higher for the tailings dam(8.97)than the overburden(5.84).The findings show that the copper mine wastes(the tailings dams and overburden waste rock sites)are highly contaminated by heavy metals;which,in turn,might pose serious hazards to human health and agricultural productivity.In addition,poor macro-nutrient availability,substrate compaction and soil acidity(particularly on overburden sites)coupled with toxic level of heavy metals would be the main challenges for successful phytostabilization of copper mine wastelands.

Preliminary study on Cd accumulation characteristics in Sansevieria trifasciata Prain

Phytoremediation techniques to clean heavy metal pollution soil depend on identifying plant species that can act as phytoremediators.One important approach to screening potential phytoremediators is to evaluate characteristics of heavy metal accumulation.In this study,we performed firsthand analysis of Cd tolerance and accumulation characteristics of three Sansevieria trifasciata cultivars by pot experiment.Plant growth results showed that all three S.trifasciata cultivars can tolerate 50 mg kg^-1 soil Cd concentration.After growth under 50 mg kg^-1 soil Cd concentration for 4 months,the Cd bioconcentration factors in the shoots of S.‘Trifasciata’,S.trifasciata‘Laurentii’,and S.trifasciata‘Silver Hahnii’were 1.26,1.30,and 1.19,while those in the roots were 12.53,11.43,and 5.45,respectively.This result reveals the considerably low translocation factors of 0.10,0.12,and 0.22 for S.‘Trifasciata’,S.trifasciata‘Laurentii’,and S.trifasciata‘Silver Hahnii’,respectively.These results suggest that all three S.trifasciata cultivars had high Cd absorption capacities but low Cd translocation capacities.In combination with total Cd accumulation distribution and plant growth characteristics,S.trifasciata can be designed as a phytostabilizer in Cd-contaminated soils in its cultivation regions.Meanwhile,the mechanism of high Cd tolerance and accumulation characteristics in the roots of S.trifasciata should be explored.This study provides new resources for dealing with Cd-contaminated soils and exploring Cd tolerance and accumulation mechanisms in plants.

Differential expression of zinc accumulation during two growing seasons of Acacia victoriae

It is important to understand seasonal heavy metal accumulation in different parts of plants in order to develop the best phytoremediation practices for con- taminated soils. For this purpose we exposed, 1 year old A. victoriae seedlings to ZnSO4 in 4 different concentrations： 0, 50, 250 and 500 mg Zn L-1 for 45 days over two growing seasons. Subsequently, bioaccumulation of Zn in different plant tissues （roots, shoots and leafs） was assessed by Atomic Absorption Spectroscopy （AAS） for two peri- ods. In addition, various growth attributes （dry biomass, shoot and root lengths, plant appearance） and functional traits （leaf area, chlorophyll a, b and total） were measured. The accumulation of Zn was influenced by the Zn con- centration in the growth medium and the number of growing seasons. The amounts of Zn concentrated in the root tissues might indicate A. victoriae as a good option for phytostabilization of soils contaminated by Zn. We rec- ommend that if A. victoriae is used for phytoextraction purposes, then it should be harvested at the end of the first growing season （fall） because at this time the concentra- tions of Zn in the above-ground parts will be maximal.

Phytoremediation Potential of Vetiver Grass (Vetiveria Zizanioides) in Two Mixed Heavy Metal Contaminated Soils from the Zoundweogo and Boulkiemde Regions of Burkina Faso (West Africa)

In the agricultural regions of Burkina Faso, urban solid waste fertilizers were usually applied. This activity is likely to contaminate the soils and expose populations to serious diseases. This study aims to assess rate of heavy metal (Cd, Cu, Mn, Pb, Zn, Ni, Cr) contamination in both agricultural lixisol and vertisol and to evaluate the removal efficiency of heavy metals using Vetiver grass on different two mixed heavy metal contaminated soils. A pot experiment was conducted to compare the metal accumulation and overall efficiency of metal uptake by different plant parts (roots and shoots) on both tropical soils. After 3 and 6 months growing on laboratory conditions, Vetiver grass plants were harvested and heavy metal concentrations in shoot and root parts determined by Inductively Coupled Plasma - Atomic Emission Spectroscopy. The results indicate that at 3 and 6 moths, the shoot and root concentrations of heavy metals in Vetiver grass harvested in lixisol were higher than vertisol. For different plant parts, all metal concentrations were higher in root than in shoot, except Cu and Pb. At the 3 and 6 months, the BCF values > 1 for Cd, Cu and Zn in both soils showed Vetiver grass as an effective phyto-stabilizer for these metals. However, the TF values > 1 for Cd (lixisol), Mn, Zn Ni and Cr (vertisol) indicated the efficiency of Vetiver for phytoextraction. The results of this study showed that Vetiver is more effective in lixisol, but it can be used for remediation of both studied tropical soils from agricultural region of Burkina Faso. Nevertheless, considering the special limitations of the experimental conditions, further field monitoring is necessary to demonstrate the phytoremediation efficiency of Vetiver in agricultural soils under the climatic conditions of Burkina Faso.

Lupinus microcarpus Growing in Arsenic—Agricultural Soils from Chile: Toxic Effects and It Potential Use as Phytoremediator Plant

Arsenic (As) is the most important contaminant of the environment in northern Chile. The purpose of the present work is to study As-toxicity symptoms on Lupino microcarpus (lupine), an annual legume plant that constitutes part of the desert community of the pre-Andean area of the Antofagasta Region, Chile. This plant species is cultivated in As-agricultural soil collected from Chiu Chiu (northern Chile) which is classified as arid soils. Control soil (0 - 20 cm depth) is collected from an area located in the central zone of Chile, which is classified as molli soil. The main physic-chemical characteristics of As-soil and the control soil are determined. Eighteen plastic pots of 1.6 L (fifteen for experimental and three for control) are filled with As-soil and control soil treatments. Two plants are cultivated in each pot and then separated leaves and roots for As-analysis. Visual As-toxicity symptoms such as foliar chlorosis, necrosis of the leaf tips and margins, leaf wilting and stunted are determined. Total As concentrations in soils where lupine is cultivated, reach levels between 5.3 - 14.2 mg·kg-1 d.w. (control soil As-level: 3.1 mg·kg-1). Roots show higher As-concentration than leaves, both experimental plants as control plants (2.28 - 9.1 mg·kg-1 d.w., and 0.76 mg·kg-1 d.w., respectively) and low values of transport index (TI) (0.16 - 0.34). All of visual As-toxicity symptoms determined is showed by lupin cultivated in As-agricultural soils. Neither control lupin plant suffers any toxicity symptoms. The results indicate that lupine plants do not resist contamination and accumulated higher levels of As in roots. Lupine can be used in the phytostabilisation of As immobilizing it by microbial activity in agricultural soil.

Assessment of Seedling Establishment and Growth Performance of <i>Leucaena leucocephala</i>(Lam.) De Wit., <i>Senna siamea</i>(Lam.) and <i>Eucalyptus grandis</i>W. Hill ex Maid. in Amended and Untreated Pyrite and Copper Tailings

Growth and survival performance of Leucaena leucocephala (Lam.) De Wit., Senna siamea Lam. and Eucalyptus grandis W. Hill ex Maid. in amended and untreated pyrite and copper tailings were evaluated under field conditions. The physico-chemical characteristics of the pyrite soil and tailings were determined. Growth in height, basal diameter and later dbh, relative growth rate due to height (RGRh) and basal diameter (RGRd) and survival were determined every after six months. A split block experimental design was used and the data collected were analyzed using a statistical package R, with an additional package lme4. Tailings and pyrite soils had extremely low pH, poor nutritional status, low organic matter content and elevated concentrations of available heavy metals as compared to the unpolluted soils and treated pyrite soil and copper tailings. Growth performance was extremely poor on the untreated pyrite soil and copper tailings for all the species but significantly enhanced by the application of compost and limestone. Treatment had a significant effect on all parameters at all sites. Eucalyptus grandis displayed a higher potential of phytomass accumulation than Leucaena leucocephala and Senna siamea. Even though Leucaena leucocephala grew fastest reaching reproductive maturity in 7 months after planting, relative growth rates of the three species were not significantly different at all sites. The three species can be used for phytostabilisation of the tailings at Kilembe tailings dam sites (KTDS) after treatment while at Low polluted pyrite trail site (LPPTS) and Highly polluted pyrite trail sites (HPPTS) Senna siamea is more suitable as Eucalyptus grandis and Leucaena leucocephala are susceptible to attacks by Syncerus caffer (Buffalos) and Kobus kob thomasi (Uganda Kob).

Tolerance of Chrysantemum maximum to heavy metals:The potential for its use in the revegetation of tailings heaps

To find if ornamental plants are applicable to the remediation of metal-polluted areas, the tolerance of chrysanthemum plants （Chysanthemum maximum） var. Shasta to different metals under hydroponic conditions was studied. Their responses as influenced by the mycorrhizal fungus Glomus mosseae （Nicol. ＆ Gerd.） Gerdemann ＆ Trappe BEG25 on substrates containing mine residues were also investigated. Our results showed that chrysanthemum is a metal-tolerant plant under hydroponic conditions, plants behaving as Pb-excluders, whereas Cd, Cu and Ni were accumulated in roots. Low accumulation in flowers was observed for Cd and Cu but it was concentration-dependent. Ni and Pb were not translocated to flowers. Shoot biomass was not significantly affected by the different rates of mine residue addition for both mycorrhizal and non-mycorrhizal plants. Mycorrhizal plants accumulated less Pb and Cu in both shoots and roots than non-mycorrhizal plants. Chysanthemum could be a prospective plant for revegetation of tailings and the use of inoculation may decrease plant metal accumulation in polluted soils.

Contrasting soil fungal communities at different habitats in a revegetated copper mine wasteland

Little is known about the responses of soil fungal communities to revegetation of mine wastelands,representing a major gap in the knowledge needed to improve the performances of revegetation schemes for mine wastelands.To shed some light on this matter,we reestablished 4000 m^(2) of vegetation on an extremely acidic(pH 2.5)copper mine tailings pond and collected soil samples from three different types of habitats:amended layer of the reclaimed tailings(ALRT),unamended layer of the reclaimed tailings(ULRT),and unreclaimed tailings(UT).Soil fungal communities in the 120 samples collected in two consecutive years were characterized via high-throughput sequencing.The fungal diversities at ALRTand ULRT were found to be significantly higher than those at UT.Ascomycota whose relative abundance ranged from 74.5% to 98.4% was the most predominant phylum across all habitats,exhibiting the lowest predominance at ALRT.Two acidophilic fungal genera,Acidomyces and Acidiella,dominated UT with relative abundances being as high as 37.8% and 15.2%,respectively.In contrast,three genera with plant growth-promoting species(Talaromyces,Trichoderma and Penicillium)were abundant at ULRT and ALRT.Remarkably,their relative abundances at ULRTcould be up to 29.0%,26.9% and 9.7%,respectively.The three types of habitats differed considerably in the overall soil fungal community composition at species level,which became more pronounced as time progressed.The abovementioned differences between habitats in soil fungal community features were related to the reduced availability of soil copper and zinc.These results improved our understanding of fungal ecology of mine wastelands.

Technosols on mining wastes in the subarctic: Efficiency of remediation under Cu-Ni atmospheric pollution

Tne copper-nickel factory's emissions in the Murmansk region,Russia,led to the degradanon of plant cover and topsoil with the subsequent formation of industrial barrens.In this study,the industrial barrens were remediated by means of Technosol engineering,when grasses were sown on the two different types of mining wastes (carbonatite and serpentinite-magnesite) covered by hydroponic vermiculite.The serpentinite-magnesite waste was significantly different from the carbonatite waste in the content of silicon (Si) and manganese (Mn),pH,and texture.Both wastes had an alkaline pH level and high content of calcium (Ca) and magnesium (Mg).The vegetation and Technosol properties at the remediated sites were analyzed in 2017 and compared to the initial state (2010 year) to assess the efficiency of the long-term remediation.The quality and sustainability of Technosols based on the serpentinite-magnesite wastes were substantially higher compared to the carbonatite-based Technosol.Biomass and a projective cover of the grass community depended on Si content in the original mining waste and were found to be higher in the serpentinite-magnesite Technosol.The content of organic carbon and its fractions,microbial biomass and basal respiration after seven years of Technosol evolution was comparable to natural values.These parameters were directly related to plant cover state and were inversely proportional to copper (Cu) content in Technosol.The Technosol development led to the reduction of nickel (Ni) and Cu migration in soil-plant ecosystems due to neutralization and adsorption properties of mining wastes and phytostabilization by underground parts of grass communities.The Technosol development in its early stage of pedogenesis indicates the efficiency of applied remediation technology to the degraded acidic soil under the conditions of industrial atmospheric pollution.

Contribution of arbuscular mycorrhizal fungi and soil amendments to remediation of a heavy metal-contaminated soil using sweet sorghum

Owing to their potential advantages such as waste reduction,recycling,and economic attributes,fast-growing bioenergy crops have the capacity to effectively phytoremediate heavy metal-contaminated soils.However,little is known about the role of microbial and chemical amendments in phytoremediation using bioenergy crops.Here,we studied the contributions of inoculation with the arbuscular mycorrhizal fungus(AMF)Acaulospora mellea ZZ and three soil amendments,i.e.,hydroxyapatite(HAP),manure,and biochar,at doses of 0.1%and 1%(weight:weight)to heavy metal phytoremediation using sweet sorghum grown on an abandoned agricultural soil,with environmentally realistic contamination(2.6 mg kg^(-1) Cd,1796 mg kg^(-1) Pb,and 1603 mg kg^(-1) Zn),in a plant growth chamber.Mycorrhizal colonization,plant biomass and metal accumulation,metal availability,and soil pH were determined in harvested seedlings 12 weeks after sowing.The results showed that root colonization by indigenous AMF decreased by 28%-46%with HAP,but increased after manure and biochar applications as compared to the no amendment control(CK).The AMF inoculation increased root colonization rates by 16%^(-1)28%and in particular,alleviated the inhibition of HAP.The remediation effects were highly dependent on the amendment type and dose.Among the three soil amendments,HAP was the most effective in promoting plant growth and phytostabilization of Cd,Pb,and Zn and phytoextraction of Cd,particularly at a dose of 1%.Compared to CK,1%HAP decreased DTPA-extractable Cd,Pb,and Zn concentrations in soil by 31%-43%,30%-38%,and 22%-23%,respectively.Manure and biochar also exerted positive effects on heavy metal immobilization,as indicated by lower DTPA extractability,but only the 1%manure treatment showed plant growth-promoting effect.The AMF inoculation did not affect plant growth,but increased soil pH and induced synergistic interactions with amendments on the immobilization of Cd and Pb.In conclusion,soil amendments,particularly HAP,produced positive impacts and synergistic interactions with AMF on the phytostabilization of heavy metals using sweet sorghum.Accordingly,sweet sorghum combined with soil amendments and AMF may be an effective strategy for heavy metal phytoremediation.