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Abstract: The occurrence of mining areas in the vicinities of salt marshes may affect their ecological functions and facilitate the transfer of pollutants into the food chain. The mobilisation of metals in salt marsh soils is controlled by abiotic (pH, redox potential) and biotic (influence of rhizosphere) factors. The effect of the rhizosphere of two plant species (Sarcocornia fruticosa and Phragmites australis) and different flooding regimes on potentially harmful metals and As mobilisation from salt marsh soil polluted by mining activities were investigated (total concentrations: 536mgkg−1 As, 37mgkg−1 Cd, 6746mgkg−1 Pb, 15,320mgkg−1 Zn). The results show that the changes in redox conditions (from 300mV to −100mV) and pH after flooding and rewetting periods may mobilise the contaminant elements into soil solution (e.g., 100μgL−1 Cd, 30μgL−1 Pb, 7mgL−1 Zn), where they are available for plants or may be leached from the soil. Drying periods generated peaks of concentrations in the soil solution (up to 120μgL−1 Cd and 50μgL−1 Pb). The risk assessment of As and metal-polluted salt marshes should take into account flood dynamics in order to prevent metal(loid) mobilisation. [ABSTRACT FROM AUTHOR]

Neutron Radiography (NR) is a valuable non-invasive tool to study in situ root development in soil. However, there is a lacuna of quantitative information on its capabilities and limitations. We combined neutron radiography with image analysis techniques to quantify the neutron absorption coefficients ( Σ) of various root-growth media for a range of water contents ( θ) in the presence and absence of plant roots with various rooting systems. Plants were grown in aluminium containers (170 × 150 × 12 mm) and were imaged using NR, as well as X-Ray radiography and an optical scanner. Sandy soil was the best medium for NR because it supported plant growth at θ that gave a good contrast for root visualisation. After correction for neutron scattering, we obtained a linear correlation between Σ and soil θ. The minimum detectable root thickness in neutron radiographs was found to be 0.2 mm in these containers. Combining NR with X-Ray radiography could provide information on soil structure in addition to revealing root structure and development. [ABSTRACT FROM AUTHOR]

Mine tailings are an environmental problem in Southern Spain because wind and water erosion of bare surfaces results in the dispersal of toxic metals over nearby urban or agricultural areas. Revegetation with tolerant native species may reduce this risk. We grew two grasses, Lygeum spartum and Piptatherum miliaceum, and the crop species Cicer arietinum (chickpea) under controlled conditions in pots containing a mine tailings mixed into non-polluted soil to give treatments of 0%, 25%, 50%, 75% and 100% mine tailings. We tested a neutral (pH 7.4) mine tailings which contained high concentrations of Cd, Cu, Pb and Zn. Water-extractable metal concentrations increased in proportion to the amount of tailings added. The biomass of the two grasses decreased in proportion to the rate of neutral mine-tailing addition, while the biomass of C. arietinum only decreased in relation to the control treatment. Neutron radiography revealed that root development of C. arietinum was perturbed in soil amended with the neutral tailings compared to those of the control treatment, despite a lack of toxicity symptoms in the shoots. In all treatments and for all metals, the plants accumulated higher concentrations in the roots than in shoots. The highest concentrations occurred in the roots of P. miliaceum (2500mgkg−1 Pb, 146mgkg−1 Cd, 185mgkg−1 Cu, 2700mgkg−1 Zn). C. arietinum seeds had normal concentrations of Zn (70–90mgkg−1) and Cu (6–9mgkg−1). However, the Cd concentration in this species was ∼1mgkg−1 in the seeds and 14.5mgkg−1 in shoots. Consumption of these plant species by cattle and wild fauna may present a risk of toxic metals entering the food chain. [Copyright &y& Elsevier]

Abstract: Mine tailings are ubiquitous in the landscapes of mined areas. Metal solubilities were compared in two chemically distinct mine tailings from the old Mining District of Cartagena-La Unión (SE Spain). One of the tailings was acidic (pH 3.0) with 5400mg/kg Zn, 1900mg/kg As and 7000mg/kg Pb. The other was neutral (pH 7.4) with 9100mg/kg Zn, 5200mg/kg Pb and 350mg/kg As. In samples from the acidic tailings, more than 15% of the Zn and 55% of the Cd were extractable with 0.1M NaNO3, and distilled water. In the neutral tailings, using the same reagents, less than 1% of the metals were extractable. A sequential extraction procedure revealed that the sum of the residual and the Fe oxide fractions of Cu, Zn and Pb comprised 80–95% in the acidic tailings and 70–90% in the neutral tailings. The acidic mine tailings had a higher metal solubility, resulting in more metal leaching in the short-term, but also a higher fraction of inert metal. In contrast, in the neutral tailings, the metals were evenly distributed between, oxides and the residual fraction. This implies lower metal mobility in the short-term, but that metal mobility may increase in the long-term. When applied to mine tailings, sequential extractions may provide misleading results because the strong cation exchange capacity of some extractants may induce pH changes and thereby significantly change metal solubility. [Copyright &y& Elsevier]

Abstract: Abandoned industrial sites have traditionally constituted an important source of environmental problems. However, such sites are considered in many cases a historic heritage, and in this way, have been protected with different legal dispositions. Mining activities can be considered a special type of industrial site in that they encompass not only architectural but also landscape elements related to geology or topography. The necessity of developing new economic opportunities in these places, whose economy has been traditionally based on the “mining monoculture”, has resulted in the creation of a cultural revival in some mining sites. Nevertheless, these new economic potentials must be compatible with the obligation to maintain a low environmental risk in sites where the heavy metal concentrations are very high. The Cartagena–La Unión Mining District in Southern Spain is an example of such a case. This paper reviews the environmental situation in that area and the initiatives for establishing a cultural tourism. The goal of this paper is to incite the public debate about the balance between environmental risks, cultural safeguarding and economic development. [Copyright &y& Elsevier]

Mine tailings are typical elements in post-mining landscapes which usually have high heavy metal contents and are affected by intensive erosion processes, above all in arid and semiarid areas. Revegetation of these sites is considered a low cost and suitable technology to effect surface stabilization. Spontaneous plant communities that colonize tailings in Southern Spain showed different behavior depending on the pH: in neutral tailings the plant communities were formed by less number of plant species than in acid tailings but they had less seasonal variations, showing a stable development. This spontaneous vegetation, that is adapted to metal toxicity and to drought, allows reducing air borne and water erosion, and may mitigate the spread of the contamination to the nearby areas. [Copyright &y& Elsevier]

Abstract: Mine tailings are one of the main environmental problems in post-mining landscapes and their removal is often complicated due to their high heavy metal content and dimensions. In this sense, using plant species for in situ stabilization may be an interesting and low cost option. Moreover, there are some plant species that have adapted to these conditions and are usually present at these contaminated sites. In this study, a mine tailing located in South-East Spain was investigated in order to establish lines for further phytostabilization research. A plot sampling design was carried out in order to characterize the soil properties. In addition, two plant species that have naturally colonized some parts of the tailing, Hyparrhenia hirta and Zygophyllum fabago, were sampled, including the analyses of their respective rhizospheric soils. The results of plot soil samples showed pH values from ultra acid to slightly alkaline. The electrical conductivity values were around 4dSm−1 in plots with vegetation and 8dSm−1 in the plot without vegetation. Total metal concentrations were high (4000mgkg−1 for Pb, 9000–15000mgkg−1 for Zn). DTPA- and water-extractable Zn were 5% and 3% of the total, respectively. H. hirta accumulated around 150mgkg−1 Pb in both shoots and roots. Zn concentration was 750mgkg−1 in Z. fabago shoots. DTPA-extractable Zn and Cu were positively correlated to plant uptake. [Copyright &y& Elsevier]

Abstract: Mine tailings are a characteristic of landscapes where mineral extraction has occurred. These tailings usually contain high heavy metal concentrations and have low fertility. In arid and semiarid zones, erosion may be an additional problem. The removal of these tailings is often impractical due to their large volumes. Therefore, a need exists to develop in situ low cost technologies to effect surface stabilization. The use of vegetation can be an attractive option, since there are some native plant species that can colonize parts of these polluted sites unaided. Some edaphic factors were investigated, including heavy metal concentrations, in three mine tailings from a semiarid mining zone in Southeast Spain. High total metal concentrations were found: 5000–8000 mg/kg for lead and 7600–12300 mg/kg for zinc. Two of these mine tailings had pH values between 6 and 7, while the other was acidic, with a pH of 2.5. Metal solubility was pH dependent, with more than 10% of the total zinc soluble in the acid substrate and less than 1% in the neutral substrates. The metal concentrations (copper, lead and zinc) in shoots of native vegetation colonizing in these sites were studied. No species of hyperaccumulators were found. The highest concentrations were found in Zygophyllum fabago, with 530 mg/kg zinc, Helichrysum decumbens with 390 mg/kg lead, and Tamarix sp. with 11 mg/kg copper. An analysis of the rhizospheric soil of these plants indicated that Lygeum spartum grew in pH 3 soil and had low metal concentration in shoots (40 mg/kg zinc and 41 mg/kg lead). [Copyright &y& Elsevier]

Soil pollution by heavy metals/metalloids (HMMs) is a problem worldwide. To prevent dispersion of contaminated particles by erosion, the maintenance of a vegetative cover is needed. Successful plant establishment in multi-polluted soils can be hampered not only by HMM toxicities, but also by soil nutrient deficiencies and the co-occurrence of abiotic stresses. Some plant species are able to thrive under these multi-stress scenarios often linked to marked fluctuations in environmental factors. This study aimed to investigate the metabolic adjustments involved in Zygophyllum fabago acclimative responses to conditions prevailing in HMM-enriched mine-tailings piles, during Mediterranean spring and summer. To this end, fully expanded leaves, and rhizosphere soil, of three contrasting mining and non-mining populations of Z. fabago grown spontaneously in south-eastern Spain were sampled in two consecutive years. Approximately 50 biochemical, physiological and edaphic parameters were examined, including leaf redox components, primary and secondary metabolites, endogenous levels of salicylic acid, and physicochemical properties of soil (fertility parameters and total concentration of HMMs). Multivariate data analysis showed a clear distinction in antioxidative/oxidative profiles between and within the populations studied. Levels of chlorophylls, proteins and proline characterized control plants whereas antioxidant capacity and C- and S-based antioxidant compounds were biomarkers of mining plants. Seasonal variations were characterized by higher levels of alkaloids and PAL and soluble peroxidase activities in summer, and by soluble sugars and hydroxycinnamic acids in spring irrespective of the population considered. Although the antioxidant systems are subjected to seasonal variations, the way and the intensity with which every population changes its antioxidative/oxidative profile seem to be determined by soil conditions. In short, Z. fabago displays a high physiological plasticity that allow it to successfully shift its metabolism to withstand the multiple stresses that plants must cope with in mine tailings piles under Mediterranean climatic conditions. [ABSTRACT FROM AUTHOR]

Trace elements (TEs) occur at low concentrations (<1000 mg kg-1) in organisms, yet they have a large biological effect, both as essential nutrients and environmental contaminants. Phytomanagement describes the manipulation of soil-plant systems to affect the fluxes of TEs in the environment with the goal of remediating contaminated soils, recovering valuable metals, or increasing micronutrient concentrations in crops. Phytomanagement includes all biological, chemical, and physical technologies employed on a vegetated site. Successful phytomanagement should either cost less than other remediation or fortification technologies, or be a profitable operation, by producing valuable plant biomass products. This may include bioenergy or timber production on contaminated land, a practice that does not reduce food production. We review the components of phytomanagement and the underlying biogeochemical processes, with a view to elucidating situations where this technology may be successfully applied and identifying future research needs. Many full-scale operations have proved the efficacy of plants to reduce contaminant mobility in soils (phytostabilization), particularly when used in combination with other technologies. As a stand-alone technology, the oft-touted use of plants to extract TEs from contaminated soils (phytoextraction) or low-grade ore bodies (phytomining) is unsuitable for most, if not all, sites due to low-extraction rates and problems caused by site heterogeneity, the limited rooting depth of plants and the presence of contaminant mixtures. Unsubstantiated claims about phytoextraction have tarnished the reputation of all “phyto” technologies. Nevertheless, phytoextraction, as part of a larger environmental toolkit, has a role in phytomanagement. The growth, or lack thereof, of profitable companies that provide phytomanagement will indicate its value. A critical knowledge gap in phytomanagement is the integration of the processes that affect plant-TE interactions and the biophysical processes affecting TE fluxes in the root zone, especially the effect of roots on contaminant fluxes. [ABSTRACT FROM AUTHOR]

Phytomanagement of tailings requires the use of soil conditioners to favour plant establishment, but their benefits on soil microbial composition need to be assessed. The goal of this work was to evaluate the effect of two organic amendments, manure compost and biochar, on soil bacterial and fungal composition at metallic mine tailings. The addition of compost caused stronger effects in most of soil parameters and microbial composition than biochar, especially at the initial stage of the experiment. However, the higher dependence on labile organic carbon for some bacterial groups at the treatments containing compost determined their decay along time (Flavobacteriales , Sphingobacteriales) and the appearance of other taxa more dependent on recalcitrant organic matter (Xanthomonadales , Myxococcales). Biochar favoured bacterial decomposers (Actinomycetales) specialised in high lignin and other recalcitrant carbon compounds. Unlike bacteria, only a few fungal orders increased their relative abundances in the treatments containing compost (Sordariales and Microascales) while the rest showed a decrease or remained unaltered. The mix biochar-compost may result the best option to support a more diverse microbial population in terms of soil functionality that is able to decompose both labile and recalcitrant carbon compounds. This may favour the resilience of the system against environmental stressors. [Display omitted] • Compost increased dissolved nitrogen and organic carbon in comparison to biochar. • Shifts in bacterial orders were related to decreases in dissolved organic carbon. • Unlike bacteria, fungal composition was less impacted by compost. • Mix compost-biochar may support higher functionality of the microbial composition. [ABSTRACT FROM AUTHOR]

Phytomanagement is considered a suitable option in line with nature-based solutions to reduce environmental risks associated to metal(loid) mine tailings. We aimed at assessing the effectiveness of biochar from pruning trees combined with compost from urban solid refuse (USR) to ameliorate the conditions of barren acidic (pH ~5.5) metal(loid) mine tailing soils (total concentrations in mg kg−1: As ~220, Cd ~40, Mn ~1800, Pb ~5300 and Zn ~8600) from Mediterranean semiarid areas and promote spontaneous plant colonization. Two months after amendment addition were enough to observe improvements in chemical and physico-chemical tailing soil properties (reduced acidity, salinity and water-soluble metals and increased organic carbon and nutrients content), which resulted in lowered ecotoxicity for the soil invertebrate Enchytraeus crypticus. Recalcitrant organic carbon provided by biochar remained in soil whereas labile organic compounds provided by USR were consumed over time. These improvements were consistent for at least one year and led to lower bulk density, higher water retention capacity and higher scores for microbial/functional-related parameters in the amended tailing soil. Spontaneous growth of native vegetation was favored with amendment addition, but adult plants of remarkable size were only found after three years. This highlights the existence of a time-lag between the positive effects of the amendment on tailing soil properties being observed and these improvements being translated into effective spontaneous plant colonization. [Display omitted] • Combination of biochar and urban solid refuse improved metal(loid) mine tailing soil. • Amendment improvements in tailing physico-chemistry and nutrients sustained over time. • Greater scores for microbial/functional-related parameters in amended tailing soil. • Spontaneous colonization by surrounding native vegetation in amended tailing soil. • Time-lag between evident tailing soil improvements and effective plant colonization. [ABSTRACT FROM AUTHOR]

Phytomanagement has been considered a feasible technique to decrease the environmental risks associated to mine tailings and its implementation relies on a suitable plant species selection. The goal of this study was to identify the edaphic factors, including microbiology, affecting the establishment of plant species with contrasting growth patterns during the phytomanagement of mine tailings. For this purpose, a comprehensive rhizosphere characterization was performed in an early ruderal colonizer, Zygophyllum fabago and two late successional tree species, Pinus halepensis and Tetraclinis articulata, growing at a mine tailings pile in southeast Spain. The neutral pH of the tailings determined low 0.01 M CaCl 2 metal extractable concentrations (e.g. <10 μg kg−1 Pb and Cd). Thus, other soil properties different from metal concentrations resulted more determining to explain plant establishment. Results revealed that Z. fabago selectively colonized tailings patches characterized by high salinity (3.5 dS m−1) and high silt percentages (42%), showing a specific halotolerant rhizospheric microbial composition, such as the bacterial Sphingomonadales and Cytophagales orders and the fungal Pleosporales and Hyprocreales orders. The two tree species grew at moderate salinity areas of the tailings pile (1.7 dS m−1) with high sand percentages (85%), where Actinomycetales was the most abundant bacterial order (>10% abundance). The contrasting mycorrhizal behaviour of both tree species (ectomycorrhizal for P. halepensis and endomycorrhizal for T. articulata) could explain the differences found between their fungal rhizospheric composition. In terms of phytomanagement, the selective plant species colonization following specific soil patches at mine tailings would increase their biodiversity and resilience against environmental stressors. • Ruderal Zygophyllum fabago colonized high salinity patches at tailings. • Trees established at the lower salinity areas of the tailings. • Actinomycetales bacterial order was the most abundant at tailings rhizospheres. • Fungal composition at trees was determined by their endo/ecto mycorrhizal behaviour. [ABSTRACT FROM AUTHOR]

Mining activities on metal sulphide ores are considered one of the most environmentally damaging anthropogenic activities worldwide, mainly due to the production of metal(loid)- enriched tailings. The objective of the work was to elucidate which factors, including edaphic, vegetation and microbiological aspects, determine soil functionality in the phytomagement of mine tailings piles in semiarid areas. For this purpose, a field study was conducted using a transect experimental design in a former mining area located in southern Spain. Soil characteristics, including edaphic parameters, bacterial and fungal compositions, were determined. The variation in edaphic parameters (pH, electrical conductivity, organic carbon, particle size distribution, etc) through the deterioration transect caused a decrease in plant and microbial diversities, as well as in microbial productivity measured by enzymatic activities. Variation in bacterial relative abundances through the transect was better explained by soil fertility related factors, such as organic matter, pH, salinity, enzymatic activities or microbial biomass (which in turn were related to the presence of plants), than by metals concentrations. The presence of vegetation at the tailings allowed the transition from lithotrophic bacterial orders which dominated in bare tailings areas (e.g. Acidimicrobiales , Chromatiales) to organotrophic oriented orders (e.g. Cytophagales , Actinomycetales). Vegetated patches at the tailings pile and its borders shared some organotrophic bacteria with control forest samples (e.g. Rhizobiales), indicating that natural plant mediated successional processes might stimulate biogeochemical cycles similar to those occurring at non-polluted systems. This functionality of the impacted sites, which include unfavourable edaphic conditions, should be taken into account in the phytomanagement of mine tailings, since it may support its long-term sustainability. Unlike bacteria, variations in fungal relative abundances through the transect were not clearly explained by soil parameters or the presence of plants. Other factors related to spatial distribution or the type of organic substrates may be more determinant in the case of fungi. Image 1 • A gradient determined by organic matter, salinity and metal concentrations occurred. • Bacterial abundance was better explained by fertility factors than by metals. • Plants caused transition from lithotrophic to organotrophic bacterial orders. • Variation in fungal abundance was less dependent on soil factors. [ABSTRACT FROM AUTHOR]

Abstract The suitable phytomanaging of mine tailings not only requires an improvement of soil fertility but also the assessment of the biotic interactions between the selected plant species. This study aimed to evaluate the effect of an organic amendment on the response of two plant species of contrasting habit, a tree, Pinus halepensis and a grass, Piptatherum miliaceum growing on a metal(loid)-contaminated substrate collected from mine tailings. Pots containing single plant individuals or their combination, with and without organic amendment (at 10% rate), were established and grown in a greenhouse for 13 months. Plant biomass, foliar ionome, leaf δ15N and metal(loid) concentrations were measured at the end of the experiment. The amendment alleviated P deficiency in the substrate and strongly stimulated biomass production by both plant species (10-fold for pine; 90-fold for the grass), leading to more balanced N/P ratios in leaves (especially for the grass). Co-culture with the grass negatively affected pine growth, decreasing total biomass and leaf δ15N values and inducing severe N deficiency (leaf N/P ratio<10). In contrast, co-culture with pine improved the nutrient status and growth of the grass, but only under non-amended conditions. Needle metal(loid) concentrations in P. halepensis were affected by both amendment addition and co-culture with the grass. High biomass growth with low metal(loid) concentrations in P. miliaceum leaves for the amended treatment makes this grass species suitable for the phytomanagement of metal(loid) polluted tailings, since it achieves high biomass production together with low concentrations of metal(loid)s in edible/senescent parts. Highlights • Co-culture modulated plant performance in amended treatments. • Co-culture with the grass P.miliaceum negatively affected pine (P.halepensis) growth. • P.miliaceum showed higher competitive ability when co-cultured with P.halepensis. [ABSTRACT FROM AUTHOR]

The objective of this work was to evaluate the effects of plant interactions (intra- and interspecific) on the growth and metal(loid) uptake of the tree species Pinus halepensis to determine its suitability for the phytomanagement of semiarid mine tailings. The pioneer tailings colonizer grass Piptatherum miliaceum was selected for assessing interspecific interactions. The experiment was conducted following a pot experimental design employing mine tailings soil. Pots containing single individuals of P. halepensis or P. miliaceum and pots containing combinations with pines (two pines per pot, or one pine and one grass per pot) were used. The analyses included the determination of plant biomass, foliar element status and stable isotope composition, metal(loid) uptake and its translocation to different plant organs. P. halepensis strongly favoured the growth of P. miliaceum by increasing 9-fold the latter's biomass and alleviating its P limitation. In this interspecific treatment P. halepensis showed a strong N limitation (N/P = 7), which negatively affected its growth, (to about half the biomass of that obtained for the other treatments) and exhibited a significant increase in some metals translocation (especially Cd) into aerial parts. Interestingly, P. miliaceum showed a decrease in the root to leaves translocation factor for most of metals when growing together with pines. The effects of the intraespecific combination on growth and metal uptake in P. halepensis were less relevant than those obtained for the interspecific one. Further research should be focused on testing the behaviour of plant co-cultures under the addition of N or P amendments which could alleviate the negative effects of plant competition. [ABSTRACT FROM AUTHOR]

Urban organic waste materials may find a potential use as amendments in agricultural or environmental fields. However, before being applied in field practices, urban organic wastes must meet some environmental and legal requirements. The objective of this work was to assess the metal (Cd, Cu, Mn, Pb and Zn) extractability in two amended degraded semiarid soils (a former agricultural soil and a mine tailings soil) employing an urban organic waste amendment. A seven-steps sequential extraction procedure was performed in order to determine the changes in metal (Cd, Cu, Mn, Pb and Zn) fractionation, after two weeks and after eight months of soil incubation in pots. The urban organic waste increased organic carbon at both soils but it did not affected pH. At both soils, the addition of the amendment increased the labile fractions of metals, especially Cu (up to 13% of total content). In the amended agricultural soil the incubation favoured the fractions associated to Mn oxides (for Mn and Zn) and organic matter (for Cu), probably due to the higher buffer capacity of the soil (pH ~ 8, high CaCO 3 , loam texture). In the amended mine tailings soil, with lower buffer capacity (pH ~ 7, low CaCO 3 , loamy sand texture), there was a redistribution into more labile fractions associated to carbonates (Mn, Pb and Zn). In low buffer capacity soils, such as the case of the mine tailings soil, the changes generated by the mineralisation of the organic matter may alter heavy metal fractionation promoting the increase of carbonate bound fractions, which could be easily mobilisable. The assessment of the long-term dynamics of organic matter mineralisation and its relation to metal geochemistry is necessary to provide a safe employment of this urban organic waste for restoring degraded soils. [ABSTRACT FROM AUTHOR]

Many soils polluted by antimony (Sb) are subject to fluctuating waterlogging conditions; yet, little is known about how these affect the mobility of this toxic element under field conditions. Here, we compared Sb leaching from a calcareous shooting range soil under drained and waterlogged conditions using four large outdoor lysimeters. After monitoring the leachate samples taken at bi-weekly intervals for >1.5 years under drained conditions, two of the lysimeters were subjected to waterlogging with a water table fluctuating according to natural rainfall water infiltration. Antimony leachate concentrations under drained conditions showed a strong seasonal fluctuation between 110 μg L −1 in summer and <40 μg L −1 in winter, which closely correlated with fluctuations in dissolved organic carbon (DOC) concentrations. With the development of anaerobic conditions upon waterlogging, Sb in leachate decreased to 2–5 μg L −1 Sb and remained stable at this level. Antimony speciation measurements in soil solution indicated that this decrease in Sb(V) concentrations was attributable to the reduction of Sb(V) to Sb(III) and the stronger sorption affinity of the latter to iron (Fe) (hydr)oxide phases. Our results demonstrate the importance of considering seasonal and waterlogging effects in the assessment of the risks from Sb-contaminated sites. [ABSTRACT FROM AUTHOR]

Phytomanagement in terms of phytostabilisation has been proposed as a suitable technique to decrease the environmental risks of metal(loid) enriched mine tailings. Nevertheless, at these sites some issues must be solved to assure the long-term establishment of vegetation ( e.g. salinity, low fertility, metal(loid) phytotoxicity, etc.) The objective of this study was to assess the effects of the addition of a municipal solid waste on a mine tailings soil and on the growth and metal(loid) accumulation of a grass plant species ( Piptatherum miliaceum ). In addition, the effects of intra-specific interactions were evaluated. A pot experiment was performed during 8 months, including two soil treatments: the mine soil and its combination with municipal solid wastes. For each treatment, pots without plants, pots with one plant, and pots with two plants were arranged. The addition of municipal solid wastes improved the soil fertility and plant growth in the mine soil, but also increased the mobile fractions of Zn, Pb, Cd, Mn and Ni. Plants in the amended treatments showed better nutritional status (higher P and K). Stable isotope δ 15 N was associated to the better nutritional status, while δ 13 C and δ 18 O indicated higher photosynthetic efficiency and stomatal conductance in amended treatments. Although the accumulation in leaves of most metal(loid)s decreased with the municipal waste application, the concentrations in both treatments did not exceed toxic limits for fodder. There was an effect of intra-specific competition in plant growth, probably due to lack of nutrients in the mining soil or limited pots volume in the treatments with municipal waste. [ABSTRACT FROM AUTHOR]

Plant selection is a critical issue for the long-term success of phytomanagement projects. The presence of “microenvironments” related to salinity in mine tailings under semiarid climates make halophytes a suitable alternative for phytostabilisation. The goal of this work was to assess the criteria for plant species selection for the phytostabilisation of mining wastes in semiarid areas, focusing on the suitability of the employment of spontaneous halophyte plant species. For this purpose, a comprehensive soil below-plant and plant survey including spontaneous halophyte and non-halophyte plant species were performed in an extensive area covered by mining wastes in SE Spain. The soil samples collected below halophyte plants showed higher electrical conductivity, organic carbon and water extractable salts concentrations than the non-halophyte ones. Zygophyllum fabago and Limonium cossonianum were the most suitable species to colonize the salty micro niches at the tailings while Tamarix canariensis and Atriplex halimus showed the best soil fertility indicators under moderate electrical conductivity values. In general, the halophyte species showed lower metal(loid) concentrations in leaves or shoots than the non-halophyte ones ( e.g . Cistus monspeliensis , Dittrichia viscosa and Helichrysum decumbens ). Oppositely, the leaves of halophyte plant species, specially A. halimus and Z. fabago , showed higher accumulation of Na and Cl which may be of interest to effect the long term desalination of the tailings. The interest of employing halophytes is not only focused on metal(loid)s tolerance but also in the high potential for soil improvement (organic matter accumulation, desalination). The positive effects of combining halophyte with non-halophyte plant species may enhance the long-term sustainability of the plant community. [ABSTRACT FROM AUTHOR]

The goal of this work was to assess the selection of the most suitable combination of plant species for the phytomanagement of mine tailings, by comparing among different plant life-forms (grasses, shrubs and trees). A comparison on induced rhizosphere changes generated by four plant species (the grass Piptatherum miliaceum, the shrub Helichrysum decumbens, and the trees, Pinus halepensis and Tetraclinis articulata) and high density vegetation patches (fertility islands) at a mine tailing located at Southeast Spain and the description of their physiological status employing stable isotopes analyses were carried out. The edaphic niches for plant growth were determined by salinity, organic matter and total soil nitrogen while metal(loid)s concentrations played a minor role. Induced changes in plant rhizospheres had a significant impact in soil microbiology. While grasses and shrubs may play an important role in primary ecological succession, trees seem to be the key to the development of fertility islands. The low δ15N values (−8.00‰) in P. halepensis needles may reflect higher ectomycorrhizal dependence. Large differences in leaf δ18O among the plant species indicated contrasting and complementary water acquisition strategies. Leaf δ13C values (−27.6‰) suggested that T. articulata had higher water use efficiency than the rest of species (−29.9‰). The implement of a diverse set of plant species with contrasting life forms for revegetating tailings may result in a more efficient employment of water resources and a higher biodiversity not only in relation to flora but soil microbiology too. [Copyright &y& Elsevier]

Highlights: [•] CaCl2-extractable Cu was correlated with dissolved organic carbon. [•] CaCl2-extractable concentrations did not correlate with metal uptake. [•] Pinus halepensis may be used to phytostabilise metal polluted soils in semiarid areas. [•] Areas surrounding tailings were impacted by high metal(loid) concentrations. [Copyright &y& Elsevier]