Analysis of serpentinophytes from north-east of Portugal for trace metal accumulation--relevance to the management of mine environment

Using Mediterranean Native Plants for the Phytoremediation of Mining Sites: An Overview of the Past and Present, and Perspectives for the Future

Mining exploitation in the Mediterranean Basin has left evident scars on the environment, and poses serious risks for human health and biodiversity, especially when mine wastes are left abandoned. This review analysed the main issues of metal(loid)s pollution related to mine exploitation in the Mediterranean Basin. Here, a list of Mediterranean native plant species studied for phytoremediation is given and, considering their biological forms, vegetational types, and ecology, we categorised them into halotolerant and hydro/hygrophilous vegetation, annual and perennial meadows, garrigues and maquis, and high maquis and woods. The main conclusions of the review are as follows: (1) plant communities established on mine environments are often rich in endemic taxa which ensure a high biodiversity and landscape value, and can help in the psychophysical health of local inhabitants; (2) political and land management should take greater account of the use of native plants for the remediation of contaminated soils; (3) a multidisciplinary approach that includes, among others, studies on biochemical response to metal(loid)s as well as the application of innovative soil amendments gives better results; (4) phytoextraction applications require a detailed recovery plan that takes into consideration several issues, including the negative influence on biodiversity due to extensive use of monotypic plantations, disposal of harvested hazardous plants, and the risk of phytoextracts entering the food chain; and (5) more studies are necessary to increase knowledge and to detect suitable species-especially halophytic ones-for phytoremediation purposes.

Ni, Cr and Co Phytoremediations by Alyssum murale Grown in the Serpentine Soils Around Guleman Cr Deposits, Elazig Turkey

Serpentine soils containing high levels of nickel and other metals are particularly preferred by some plants that accumulate nickel in their bodies. In this study, the Ni, Co, and Cr accumulation capacities of A. murale grown in Guleman's serpentine soils were measured. In this respect, 12 A. murale and their soils were collected from the mining site and surroundings. Afterwards, the collected samples were measured in order to evaluate the translocation and accumulation amounts of Ni, Cr, and Co. For that, soil and plant samples were analyzed using inductively coupled plasma mass spectroscopy (ICP-MS). The mean Ni concentrations in the soil, roots, and shoots of A. murale were measured as 2475, 7384, and 7694 mg/kg, respectively. The mean Cr concentrations in the soil, roots, and shoots of A. murale were measured as 742, 33, and 8.4 mg/kg while the mean Co concentrations of A. murale in the soil, roots, and shoots were 166, 10.2, and 23.5 mg/kg, respectively. Then, ECR and ECS values were calculated for Ni, Co, and Cr. The results indicated that A. murale grown in Guleman's serpentine soils may be helpful for the rehabilitation studies of mining soils contaminated by Ni and can be utilized for phytoextraction.

Nickel hyperaccumulation, elemental profiles and agromining potential of three species of Odontarrhena from the ultramafics of Western Iran

The profiles of trace and major elements in three Odontarrhena species from the ultramafics of Western Iran (O. callichroa, O. penjwinensis and O. inflata) were evaluated to provide detailed information on their soil-plant relationships and potentials for agromining. The mean concentrations of Ni in leaf dry matter of these three species were 877, 3,270 and 2,720 mg kg^-1, respectively. The mean concentrations of total soil Ni at sites Mazi Ban, Kamyaran and Ghala Ga were 1,470, 2,480, 1,030 mg kg^-1, respectively. The Bioconcentration Factor (BCF) for Ni was >1 in O. penjwinensis and O. inflata, but not in O. callichroa. A positive relationship between shoot Ni and soil pH was found for all three species. They display Ni hyperaccumulation in the leaves, but with pronounced variation in the Ni concentrations attained. Odontarrhena penjwinensis emerged as the most promising potential candidate for future Ni agromining. The progress made in this study will enable further consideration of the three Odontarrhena species, especially O. penjwinensis, for any future commercial Ni agromining of the serpentinic ultramafic soils in Western Iran.

The Impact of Pb from Ammunition on the Vegetation of a Bird Shooting Range

Hunting with lead ammunition represents a source of heavy metal pollution to the environment that can be potentially high at the local scale. Intensive hunting of small game species can concentrate high levels of ammunition discharging in small areas. This type of hunting is a relevant economic resource for private landowners in some regions of Spain, and current legislation allows the use of lead ammunition in these scenarios. It becomes, therefore, highly relevant to study whether this activity may pose concerns to the conservation of the environment in the areas where it takes place. Using a red-legged partridge (Alectoris rufa) shooting range as a study area, we examined the effect of intensive hunting on this species on the vegetation present. We found significantly higher lead levels in the sprouts of plants of shooting areas related to control sites of the same property where partridge shooting does not occur. We found differences in the presence of lead between sprouts of different plant species. In addition, old sprouts of existing vegetation in shooting areas also showed higher lead levels than newly emerged sprouts of the same plants. These results demonstrate the impact of lead ammunition on vegetation in terms of persistence over time and differences between species. Further analyses using chemical and ecotoxicological data are necessary to evaluate the extent of environmental pollution risks. Our results provide new support in favor of the use of alternative ammunition, with particular emphasis on scenarios where hunting activity is intensive.

Metal accumulation by Alyssum serpyllifolium subsp. malacitanum Rivas Goday (Brassicaceae) across different petrographic entities in South-Iberian ultramafic massifs: plant-soil relationships and prospects for phytomining

To date, studies of hyperaccumulation in plant tissues on ultramafic rocks have not considered the great diversity of petrographic entities in the world's outcrops. One of them is the one that we studied in Spain with more than eight petrographic entities and different soils. Our hypothesis is that the different chemical compositions of the soils in ultramafic rocks significantly affect the hyperaccumulation of metals by specialized plants, which may have consequences for phytomining. For this purpose, individuals, populations, and different soils have been tested and the results have been subjected to the corresponding statistical tests. The obtained knowledge reflects the different behavior of the studied plant not only for the Ni: the obtained results for Sr and for Ba revealed interesting results for the hyperaccumulation in Alyssum of both metals.

Phytoremediation potential of the naturally occurring wetland species in protected Long Beach in Ulcinj, Montenegro

Long Beach, situated in southern Montenegro, is subject to considerable biogenic and abiogenic influences. Thus, analyzing total heavy metal content in soil and plants in this region is, while challenging, highly important in order to assess the level for determining the soil degradation level and the phytoremediation potential of naturally growing salt marsh species. This area together with a Bojana river and backshore forms a real vegetation mosaic where habitats of various types coexist. Therefore, it represents good model system. In the present study, the levels of As, Al, B, Cd, Co, Cr, Cu, Hg, Fe, Mn, Mo, Ni, Pb and Zn in coastal soils as well as in eight salt marsh plants: Bolboschoenus maritimus, Juncus acutus, Juncus anceps, Juncus articulatus, Juncus gerardii, Juncus maritimus, Scirpus holoschoenus and Schoenus nigricans, were investigated in order to identify the plant species that can be used for the remediation of polluted sites, especially those located along the coastline. The obtained results show that species J. gerardii, J. articulatus and B. maritimus can be clearly separated from J. acutus, J. anceps, J. maritimus, S. holoschoenus and Sh. nigricans based on the degree of heavy metal accumulation in various organs. Moreover, analyses revealed that the bioaccumulation factor of underground organs is significantly higher relative to that of the aboveground parts for almost all investigated metals and species. The bioaccumulation factor had the highest value in the underground organs of J. gerardii and B. maritimus, where a value of 3.37 was measured for B and 2.54 for Hg, respectively. Hence, as all investigated species are "underground accumulators" for most of the analyzed metals, they could be useful for phytostabilization and phytoremediation of B and Hg in particular. Moreover, each plant species can be used in the phytoremediation process targeting specific heavy metals.

Root and Shoot Response to Nickel in Hyperaccumulator and Non-Hyperaccumulator Species

The soil-root interface is the micro-ecosystem where roots uptake metals. However, less than 10% of hyperaccumulators' rhizosphere has been examined. The present study evaluated the root and shoot response to nickel in hyperaccumulator and non-hyperaccumulator species, through the analysis of root surface and biomass and the ecophysiological response of the related aboveground biomass. Ni-hyperaccumulators Alyssoides utriculata (L.) Medik. and Noccaea caerulescens (J. Presl and C. Presl) F.K. Mey. and non-hyperaccumulators Alyssum montanum L. and Thlaspi arvense L. were grown in pot on Ni-spiked soil (0-1000 mg Ni kg^-1, total). Development of root surfaces was analysed with ImageJ; fresh and dry root biomass was determined. Photosynthetic efficiency was performed by analysing the fluorescence of chlorophyll a to estimate the plants' physiological conditions at the end of the treatment. Hyperaccumulators did not show a Ni-dependent decrease in root surfaces and biomass (except Ni 1000 mg kg^-1 for N. caerulescens). The non-hyperaccumulator A. montanum suffers metal stress which threatens plant development, while the excluder T. arvense exhibits a positive ecophysiological response to Ni. The analysis of the root system, as a component of the rhizosphere, help to clarify the response to soil nickel and plant development under metal stress for bioremediation purposes.

Ultramafic geoecosystems as a natural source of Ni, Cr, and Co to the environment: A review

Ultramafic soils are in equal parts fascinating and dangerous. Developed on rocks derived predominately from the Earth's mantle and metamorphosed at the ocean floors, ultramafic soils form in the places where tectonic forces brought these rocks from mantle depths to the surface. As it is common in nature, both ultramafic rocks and soils are site-specific, and vary in character and composition; however, they have one thing in common, they are enriched in certain elements and three metals in particular form an "ultramafic" triad: Ni, Cr, and Co. These three metals are far from being human-friendly and strict legislative limits are established for maximum allowable concentrations of these metals in soils, but mostly in the case when the metals are of anthropogenic origin. However, ultramafic soils are a natural phenomenon where increased metal content is not the result of pollution, but rather referred as a peculiar geochemical background, therefore there is no reason for their remediation. At the same time, it is not that easy to actually find an ultramafic soil that does not overstep the limits (for the sake of this paper we use median world Regulatory Guidance Values - RGVs). Often, mobile Ni and Co concentrations are above the guidelines when doing tests to estimate the bioavailable fraction (EDTA and DTPA), and high concentrations of Ni are also commonly present in excluder plants (also edible ones). Also waters in ultramafic areas often exceed Ni and Cr(VI) limits. It is therefore expected that the ultramafic metals are present in the food chain and they might constitute a potential health risk. Thus, there is a need for additional research focused on assessment of the potential health consequences of chronic high exposure on naturally occurring Ni, Cr, and Co.

Biomagnetic monitoring of atmospheric heavy metal pollution using pine needles: the case study of Isfahan, Iran

Atmospheric deposition particles are fine-sized having a high adsorption capacity. Therefore, they can easily transfer the contamination to other areas. Plants can absorb certain pollutants using their leaves and then accumulate them in their biomass. In this study, the spatial and temporal variability of air pollution was assessed using pine needles as the bioindicators of atmospheric pollution. The magnetic susceptibility (MS) at low and high frequencies (χlf, χhf) and the concentration of selected heavy metals of pine needles (Pinus mugo) were estimated in order to address the possible relationships between needles' MS and the heavy metal concentration in the city of Isfahan, central Iran. In addition, the relationship between the heavy metal concentration of pine needles and that of the atmospheric dust was examined using the published data. Tree pine needles were monthly sampled, from April to December 2015 (T1-T9), during 9 months, from 30 different sites in the Isfahan city. There were two treatments including washed + unwashed (WU) and washed + washed (WW). The heavy metal total concentrations including Zn, Fe, Cu, Co, Pb, and Ni were measured. The mean concentrations of Fe, Zn, Pb, Cu, Ni, and Co were 80.4, 3.9, 1.8, 1.4, 0.6, and 0.3 mg kg-1, respectively. The results revealed that the concentration of heavy metals and MS in the pine needles followed the order Fe > Zn > Pb > Cu > Ni > Co. Also, the heavy metal concentration in the pine needles with different treatments had the following trend: WU > WW. It was shown that there was a significant correlation (p < 0.01) between the heavy metal concentrations and the leaf MS values of the pine needles and the concentration of heavy metals in atmospheric dust. Besides, similar trends were detected for the spatial variability of heavy metals and the pine needles' MS. In general, it could be concluded that the biomagnetic approach could serve as a comparatively fast and low-cost method to detect highly polluted urban areas with selected heavy metals, particularly the areas which are under the influence of anthropogenic and other traffic-related sources.

Bacterial community diversity in the rhizosphere of nickel hyperaccumulator plant species from Borneo Island (Malaysia)

The Island of Borneo is a major biodiversity hotspot, and in the Malaysian state of Sabah, ultramafic soils are extensive and home to more than 31 endemic nickel hyperaccumulator plants. The aim of this study was to characterize the structure and the diversity of the rhizosphere bacterial communities of several of these nickel hyperaccumulator plants and factors that affect these bacterial communities in Sabah. The most abundant phyla were Proteobacteria, Acidobacteria and Actinobacteria. At family level, Burkholderiaceae and Xanthobacteraceae (Proteobacteria phylum) were the most abundant families in the hyperaccumulator rhizospheres. Redundancy analysis based on soil chemical analyses and relative abundances of the major bacterial phyla showed that abiotic factors of the studied sites drove the bacterial diversity. For all R. aff. bengalensis rhizosphere soil samples, irrespective of studied site, the bacterial diversity was similar. Moreover, the Saprospiraceae family showed a high representativeness in the R. aff. bengalensis rhizosphere soils and was linked with the nickel availability in soils. The ability of R. aff. bengalensis to concentrate nickel in its rhizosphere appears to be the major factor driving the rhizobacterial community diversity unlike for other hyperaccumulator species.

Occurrence and cycling of trace elements in ultramafic soils and their impacts on human health: A critical review

The transformation of trace metals (TMs) in natural environmental systems has created significant concerns in recent decades. Ultramafic environments lead to potential risks to the agricultural products and, subsequently, to human health. This unique review presents geochemistry of ultramafic soils, TM fractionation (i.e. sequential and single extraction techniques), TM uptake and accumulation mechanisms of ultramafic flora, and ultramafic-associated health risks to human and agricultural crops. Ultramafic soils contain high levels of TMs (i.e. Cr, Ni, Mn, and Co) and have a low Ca:Mg ratio together with deficiencies in essential macronutrients required for the growth of crops. Even though a higher portion of TMs bind with the residual fraction of ultramafic soils, environmental changes (i.e. natural or anthropogenic) may increase the levels of TMs in the bioavailable or extractable fractions of ultramafic soils. Extremophile plants that have evolved to thrive in ultramafic soils present clear examples of evolutionary adaptations to TM resistance. The release of TMs into water sources and accumulation in food crops in and around ultramafic localities increases health risks for humans. Therefore, more focused investigations need to be implemented to understand the mechanisms related to the mobility and bioavailability of TMs in different ultramafic environments. Research gaps and directions for future studies are also discussed in this review. Lastly, we consider the importance of characterizing terrestrial ultramafic soil and its effect on crop plants in the context of multi-decadal plans by NASA and other space agencies to establish human colonies on Mars.

Rhizosphere response to nickel in a facultative hyperaccumulator

This study faces the characterization of the culturable microbiota of the facultative Ni-hyperaccumulator Alyssoides utriculata to obtain a collection of bacterial and fungal strains for potential applications in Ni phytoextraction. Rhizosphere soil samples and adjacent bare soil associated with A. utriculata from serpentine and non-serpentine sites were collected together with plant roots and shoots. Rhizobacteria and fungi were isolated and characterized genotypically and phenotypically. Plants and soils were analyzed for total element concentration using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Serpentine and non-serpentine sites differ in terms of elements concentration in soil, plant roots and shoots. Ni and Co are significantly higher on serpentine site, while Ca is more abundant in non-serpentine site. Bacteria and fungi were significantly more abundant in rhizosphere than in bare soil and were dominated by genera Arthrobacter, Bacillus and Streptomyces, Penicillium and Mucor. The genus Pseudomonas was only found in rhizospheric serpentine soils (<2% of total serpentine isolates) and with Streptomyces sp. showed highest Ni-tolerance up to 15 mM. The same occurred for Trichoderma strain, belonging to the harzianum group (<2% of the total microfungal count) and Penicillium ochrochloron (<10% of the total microfungal count, tolerance up to Ni 20 mM). Among serpentine bacterial isolates, 8 strains belonging to 5 genera showed at least one PGPR activity (1-Aminocyclopropane-1-Carboxylic Acid (ACC) deaminase activity, production of indole-3-acetic acid (IAA), siderophores and phosphate solubilizing capacity), especially genera Pantoea, Pseudomonas and Streptomyces. Those microorganisms might thus be promising candidates for employment in bioaugmentation trials.

Trace elements in Plantago lanceolata L., a plant used for herbal and food preparations: new data and literature review

Plantago lanceolata L. is a common grassland and roadside plant, widely used in many countries in food and herbal preparations. In this study, samples of this wild plant were collected from rural, suburban/urban, and industrial environments; the concentrations of As, Cd, Co, Cu, Fe, Mn, Ni, P, Pb, V, and Zn were measured in the edible parts of the plant (leaves), in the roots, and in the soils in order to calculate the bioaccumulation and translocation factors. The data obtained were compared with literature data available. Except for samples collected near mines and smelting plants, where Cd, Pb, and Zn concentrations were up to 15 times higher, in all other cases, no differences were observed with respect to samples from rural areas, except for Pb concentration, which was 3 times higher in urban areas. In the samples collected in our study area, the metal content does not pose particular health risks; however, even within a quite restricted region like the investigated area, high metal concentrations, possibly due to the presence of particular substrates, were observed in some samples collected from areas considered "clean" and suitable for wild food plant gathering.

Neglected Mediterranean plant species are valuable resources: the example of Cistus ladanifer

The combination of genotypic selection, targeted and improved cultivation, and processing techniques for specific applications gives C. ladanifer the potential to be used as a valuable resource in Mediterranean areas with poor agronomic advantages. Cistus ladanifer (rockrose) is a perennial shrub, well adapted to the Mediterranean climate and possibly to upcoming environmental changes. As a sequence to a thorough review on taxonomic, morphological, chemical and competitive aspects of C. ladanifer, the research team focuses here on the economic potential of C. ladanifer: from production to applications, highlighting also known biological activities of extracts and their compounds. The use of this natural resource may be a viable solution for poor and contaminated soils with no need for large agricultural techniques, because this species is highly resistant to pests, diseases and extreme environmental factors. In addition, this species reveals interesting aptitudes that can be applied to food, pharmaceutical, phytochemical and biofuel industries. The final synthesis highlights research lines toward the exploitation of this neglected resource, such as selection of plant lines for specific applications and development of agronomic and processing techniques.

The interaction of heavy metals and metalloids in the soil-plant system in the São Domingos mining area (Iberian Pyrite Belt, Portugal)

São Domingos belongs among the most important historic Iberian Pyrite Belt Cu mines. The anthrosoil is contaminated by a very high content of heavy metals and metalloids. The study was focused on evaluating the interaction of some chemical elements (Ca, Mg, Fe, Mn, Cu, Pb, Zn, Ag, Cd, Ni, Co, As, Sb) in the system soil vs. five autochthonous dominant plant species: Pinus pinaster Aiton, Quercus rotundifolia Lam., Agrostis sp., Juncus conglomeratus L. and Juncus effusus L. The plants are heavily contaminated by Cu, Pb, As and Zn. The bioconcentration factor proved that they exhibit features of metal tolerant excluders. The trees are accumulators of Ag, whereas the graminoids are hyper-accumulators of Ag and Juncus effusus of Co. The translocation factor confirmed that the selected elements are immobilised in the roots except for Mn and Zn in Pinus pinaster and Mn in Quercus rotundifolia and Juncus conglomeratus. The bioaccumulation of Mn, Zn and Cu at low pH increases. The increased content of Ca and Mg in the soil inhibits, in the case of some metals and metalloids, their intake to plants. Although the studied plants, despite their fitness and vitality at the contaminated sites, are not suitable for phytoextraction (except Co and Ag), they can be used for phytostabilisation at the mining habitats.

Plant and Soil Metal Concentrations in Serpentine Soils and Their Influence on the Diet of Extensive Livestock Animals

Background:

Grazing circuits and resources consumed differ strongly throughout the year and within a territory. For this reason, animals’ diet composition, as well as their exposure to metals, is variable. No studies have been performed on how habitat use affects the metal concentrations to which sheep and goats reared in serpentine soil areas are exposed.

Objective:

The aim of the present study was to investigate the metal exposure of grazing animals raised in a serpentine soil area of the north-east of Portugal, taking into account the spatial distribution of metal concentrations in soils and plants.

Methods:

The habitat use and foraging behaviour of six flocks of sheep and goats were studied. The concentrations of Ca, Mg, Mn, Cr and Ni were determined in the soils and plant species most consumed by those animals.

Results:

The highest Mg, Mn, Cr and Ni concentrations were found in the soils of the ultramafic complex. Ni concentrations above the recommended threshold for agricultural soils (30 μg/g) were found in some sites. A positive correlation between Ni concentration in soils and plants was found (0.634). Ni concentrations higher than 10 µg/g were found in some samples of the following plant species:Sorghum × drummondii(Steud.) Millsp. & Chase,Quercus rotundifoliaLam.,Cytisus multiflorus(L’Hér.) Sweet,Cistus ladaniferL. andErica scopariaL. Significant differences (p ≤ 0.05) in metal concentrations of the plants most consumed by each flock were observed.

Conclusion:

Grazing circuits have an important role in the metal exposure of animals raised in this serpentine soil area.

Modeling of Cd adsorption to goethite-bacteria composites

The accurate modeling of heavy metal adsorption in complex systems is fundamental for risk assessments in soils and associated environments. Bacteria-iron (hydr)oxide associations in soils and sediments play a critical role in heavy metal immobilization. The reduced adsorption of heavy metals on these composites have been widely reported using the component additivity (CA) method. However, there is a lack of a mechanism model to account for these deviations. In this study, we established models for Cd adsorption on goethite-Pseudomonas putida composites at 1:1 and 5:1 mass ratios. Cadmium adsorption on the 5:1 composite was consistent with the additivity method. However, the CA method over predicted Cd adsorption by approximately 8% on the 1:1 composite at high Cd concentration. The deviation was corrected by adding the site blockage reactions between P. putida and goethite. Both CA and "CA-site masking" models for Cd adsorption onto the composites were in line with the ITC data. These results indicate that CA method in simulating Cd adsorption on bacteria-iron oxides composites is limited to low bacterial and Cd concentrations. Therefore the interfacial complexation reactions that occur between iron (hydr)oxides and bacteria should be taken into account when high concentrations of bacteria and heavy metals are present.

Strategies of heavy metal uptake by three Armeria species growing on different geological substrates in Serbia

This study surveyed three species of the genus Armeria Willd. from five ultramafic outcrops, two non-ultramafic (schist) soils, and one tailing heap of an abandoned iron-copper mine from Serbia. Similarities and differences among the three Armeria species growing on different geological substrates in the ability to control uptake and translocate nine metals were examined. Chemical characteristics of the soil and plant samples (concentrations of P₂O_5, K₂O, Ca, Fe, Mn, Ni, Zn, Cu, Cr, Co, Cd, and Pb) are presented. In order to assess accumulative potential of these three Armeria species, biological concentration, accumulation, as well as translocation factors were used. Three investigated Armeria species growing on eight different localities showed large differences in heavy metal uptake, translocation, and accumulation. The differences were present among the plant samples of the same species and even more among three different Armeria species and were primarily the result of the different contents of available heavy metals in the investigated soils. Additionally, differences might be the consequence of diverse responses and possible presence of supplementary resistance mechanisms in the plants from the ultramafic soils. None of the three Armeria species showed shoot hyperaccumulative potential for any of the investigated heavy metals and they could be considered as root accumulators, considering their potential to accumulate medium to large amounts of Zn (BCF up to 134), Cr (BCF up to 148), and Cd (BCF up to 9) in their roots.

Response of spontaneous plants from an ex-mining site of Elba island (Tuscany, Italy) to metal(loid) contamination

The release of large amounts of toxic metals in the neighboring sites of abandoned mine areas represents an important environmental risk for the ecosystem, because it adversely affects soil, water, and plant growth. The aim of the present study was to investigate the metal(loid) (As, Cr, Cu, Ni, Pb, and Zn) contents of native Mediterranean plants grown on the ex-mining area of Elba island (Italy), with the prospective of its recovery by further phytoremediation technology. Soil samples were collected and characterized for metal(loid) content in total and potentially available (EDTA-extractable) fractions. Arsenic was particularly high, being 338 and 2.1 mg kg^-1 as total and available fractions, respectively. Predominant native species, namely Dittrichia viscosa L. Greuter, Cistus salviifolius L., Lavandula stoechas L., and Bituminaria bituminosa L., were analyzed for metal content in the different plant organs. D. viscosa exhibited the highest metal(loid) content in the leaves and the singular behavior of translocating arsenic to the leaves (transfer factor about 2.06 and mean bioconcentration factor about 12.48). To assess the healthy status of D. viscosa plants, the leaves were investigated further. The activities of the main antioxidant enzymes and the levels of secondary metabolites linked to oxidative stress in plants from the ex-mining area were not significantly different from those of control plants, except for a lower content of carotenoids, indicating that native plants were adapted to grow in these polluted soils. These results indicate that D. viscosa can be suitable for the revegetation of highly metal-contaminated areas.

Evolution of nickel hyperaccumulation and serpentine adaptation in the Alyssum serpyllifolium species complex

Metal hyperaccumulation is an uncommon but highly distinctive adaptation found in certain plants that can grow on metalliferous soils. Here we review what is known about evolution of metal hyperaccumulation in plants and describe a population-genetic analysis of the Alyssum serpyllifolium (Brassicaceae) species complex that includes populations of nickel-hyperaccumulating as well as non-accumulating plants growing on serpentine (S) and non-serpentine (NS) soils, respectively. To test whether the S and NS populations belong to the same or separate closely related species, we analysed genetic variation within and between four S and four NS populations from across the Iberian peninsula. Based on microsatellites, genetic variation was similar in S and NS populations (average Ho=0.48). The populations were significantly differentiated from each other (overall FST=0.23), and the degree of differentiation between S and NS populations was similar to that within these two groups. However, high S versus NS differentiation was observed in DNA polymorphism of two genes putatively involved in adaptation to serpentine environments, IREG1 and NRAMP4, whereas no such differentiation was found in a gene (ASIL1) not expected to play a specific role in ecological adaptation in A. serpyllifolium. These results indicate that S and NS populations belong to the same species and that nickel hyperaccumulation in A. serpyllifolium appears to represent a case of adaptation to growth on serpentine soils. Further functional and evolutionary genetic work in this system has the potential to significantly advance our understanding of the evolution of metal hyperaccumulation in plants.

Selection of native plants with phytoremediation potential for highly contaminated Mediterranean soil restoration: Tools for a non-destructive and integrative approach

The aim of this study was to develop an effective and non-destructive method for the selection of native Mediterranean plants with phytoremediation potential based on their spontaneous recovery capacities. The study site consisted in a mixed contaminated soils (As, Cu, Pb, Sb, Zn) in the vicinity of a former lead smelting factory abandoned since 1925 in the Calanques National Park (Marseille, southeastern France). We developed an integrated characterization approach that takes into account topsoil metal(loid)s (MM) contamination, plant community composition and structure and mesologic parameters without using destructive methods. From a statistical selection of significant environmental descriptors, plant communities were described and interpreted as the result of spontaneous recovery under multiple stresses and local conditions (both natural and anthropogenic). We collected phytoecological and MM topsoil data using field monitoring and geographic information system (GIS) on a pollution hotspot where natural plant communities occur. The results of the multivariate analysis performed between species and descriptors indicated that a century of MM pollution pressure produced a significant correlation with plant community dynamics in terms of composition, diversity and structure, leading to the co-occurrence of different plant succession stages. Thus, these successions seemed linked to the variability of anthropogenic disturbance regimes within the study site. We recorded high topsoil contamination heterogeneity at the scale both of the plot and of the whole study area that suggested a heterogeneous MM distribution pattern dependent on the source of contaminants and site environmental variability. We identified 4 spontaneous plant communities co-occurring through a MM contamination gradient that could be used later from degraded to reference communities to define ecological restoration target combined to phytoremediation applications with respect to local conditions. Our results suggested that some of the native plant species such as Coronilla juncea and Globularia alypum might be tolerant to high mixed MM soil concentrations and they could thus be used for phytostabilization purposes in polluted Mediterranean areas in regard to their life-traits. Our non-destructive methodology led both to the selection of tolerant native plant species and communities and identification of highly polluted priority intervention areas through the study site where phytostabilization should be implemented. Furthermore, by analyzing succession dynamics linked to contamination patterns throughout the area and spontaneous recovery of native tolerant vegetation, our methodology opens up broad perspectives and research fields for ecological restoration for Mediterranean protected and contaminated areas based on ecosystem trajectories and new approaches for the integrative management of polluted soils.

Characterization of cadmium-resistant bacteria and their potential for reducing accumulation of cadmium in rice grains

Cadmium (Cd) pollution is a serious widespread environmental problem that not only destroys the microbial ecology of soil and decreases crop production, but also poses a serious risk to human health. Many methods have been used for the remediation of Cd pollution but none of these is totally satisfactory. Microbial remediation strategies have attracted increasing interest since they are environmentally friendly and cost-effective. In the present study, three Cd-resistant bacteria were isolated and evaluated for potential application in Cd bioremediation. Based on their morphological, physiological and biochemical characteristics, together with 16S rDNA gene sequence analyses, bacteria were identified as Stenotrophomonas acidaminiphila (2#), Pseudomonas aeruginosa (9#) and Delftia tsuruhatensis (12#). Pseudomonas aeruginosa showed very high tolerance to metals, especially Cd (2200mg/L), Zn (1800mg/L) and Pb (1200mg/L), and is thought to be a multi-metal-resistant bacterium. Pseudomonas aeruginosa was also sensitive to 13 different antibiotics. The effects of the bacterial strains on the growth of rice plants and their ability to reduce Cd accumulation from Cd-contaminated soils in pot experiments were also evaluated. For Oryza sativa L. A grown in contaminated soil (3mg/kg Cd), the accumulation of Cd was decreased by 31.2 and 25.5% in brown rice and polished rice, respectively, by strain 9#; Pseudomonas aeruginosa was more effective in reducing Cd accumulation in rice grains than a mixture of strains. For Oryza sativa L. B, a mixture of strains acting synergistically was more effective than a single strain in reducing Cd accumulation; treatment with mixed strains (strains+3mg/kg Cd) resulted in 41.3, 35.9, and 32.6% reductions in Cd accumulation in unhulled rice, brown rice and polished rice, respectively. Although different results were obtained for two rice varieties, it can still be concluded that Cd-resistant bacteria are suitable for reducing Cd accumulation in rice grains and show potential for bioremediation of Cd-contaminated soils.

Mutielemental concentration and physiological responses of Lavandula pedunculata growing in soils developed on different mine wastes

This study aimed to: i) evaluate the accumulation and translocation patterns of potentially hazardous elements into the Lavandula pedunculata and their influence in the concentrations of nutrients; and ii) compare some physiological responses associated with oxidative stress (concentration of chlorophylls (Chla, Chlb and total), carotenoids, and total protein) and several components involved in tolerance mechanisms (concentrations of proline and acid-soluble thiols and total/specific activity of catalase (CAT) and superoxide dismutase (SOD)), in plants growing in soils with a multielemental contamination and non-contaminated. Composite samples of soils, developed on mine wastes and/or host rocks, and L. pedunculata (roots and shoots) were collected in São Domingos mine (SE of Portugal) and in a reference area with non-contaminated soils, Corte do Pinto, with the same climatic conditions. São Domingos soils had high total concentrations of several hazardous elements (e.g. As and Pb) but their available fractions were small (mainly <5.8 % of the total). Translocation behaviour of elements was not clear according to the physiological importance of the elements. In general, plant shoots from São Domingos had the highest elements concentrations, but only As, Mn and Zn reached phytotoxic concentrations. Concentration of Chlb in shoots from São Domingos was higher than those from Corte do Pinto. No significant differences were obtained between concentrations of Chla, total protein, proline and acid-soluble thiols in shoots collected in both areas, as well as SOD activity (total and specific) and specific CAT activity. Total CAT activity varied with population being lower in the shoots of the plants from São Domingos, but no correlation was obtained between this enzymatic activity and the concentrations of the studied elements in shoots. Lavandula pedunculata plants are able to survive in soils developed on different mine wastes with multielemental contamination and low fertility showing no symptoms (visible and physiological) of phytotoxicity or deficiency.

The hyperaccumulator Sedum plumbizincicola harbors metal-resistant endophytic bacteria that improve its phytoextraction capacity in multi-metal contaminated soil

Endophyte-assisted phytoremediation has recently been suggested as a successful approach for ecological restoration of metal contaminated soils, however little information is available on the influence of endophytic bacteria on the phytoextraction capacity of metal hyperaccumulating plants in multi-metal polluted soils. The aims of our study were to isolate and characterize metal-resistant and 1-aminocyclopropane-1-carboxylate (ACC) utilizing endophytic bacteria from tissues of the newly discovered Zn/Cd hyperaccumulator Sedum plumbizincicola and to examine if these endophytic bacterial strains could improve the efficiency of phytoextraction of multi-metal contaminated soils. Among a collection of 42 metal resistant bacterial strains isolated from the tissues of S. plumbizincicola grown on Pb/Zn mine tailings, five plant growth promoting endophytic bacterial strains (PGPE) were selected due to their ability to promote plant growth and to utilize ACC as the sole nitrogen source. The five isolates were identified as Bacillus pumilus E2S2, Bacillus sp. E1S2, Bacillus sp. E4S1, Achromobacter sp. E4L5 and Stenotrophomonas sp. E1L and subsequent testing revealed that they all exhibited traits associated with plant growth promotion, such as production of indole-3-acetic acid and siderophores and solubilization of phosphorus. These five strains showed high resistance to heavy metals (Cd, Zn and Pb) and various antibiotics. Further, inoculation of these ACC utilizing strains significantly increased the concentrations of water extractable Cd and Zn in soil. Moreover, a pot experiment was conducted to elucidate the effects of inoculating metal-resistant ACC utilizing strains on the growth of S. plumbizincicola and its uptake of Cd, Zn and Pb in multi-metal contaminated soils. Out of the five strains, B. pumilus E2S2 significantly increased root (146%) and shoot (17%) length, fresh (37%) and dry biomass (32%) of S. plumbizincicola as well as plant Cd uptake (43%), whereas Bacillus sp. E1S2 significantly enhanced the accumulation of Zn (18%) in plants compared with non-inoculated controls. The inoculated strains also showed high levels of colonization in rhizosphere and plant tissues. Results demonstrate the potential to improve phytoextraction of soils contaminated with multiple heavy metals by inoculating metal hyperaccumulating plants with their own selected functional endophytic bacterial strains.

Nickel phytoremediation potential of the Mediterranean Alyssoides utriculata (L.) Medik

This study investigated the accumulation and distribution of nickel in the leaves and roots of the Mediterranean shrub Alyssoides utriculata to assess its potential use in phytoremediation of Ni contaminated soils. Total (AAS and ICP-MS) Ni, Ca and Mg contents were analyzed in the plants and related to their bioavailability (in EDTA) in serpentine and non-serpentine soils. To find the relationships between the soil available Ni and the Ni content of this species, we also evaluated possible interactions with Ca and Mg. The bioaccumulation factor (BF) and the translocation factor (TF) were determined to assess the tolerance strategies developed by A. utriculata and to evaluate its potential for phytoextraction or phytostabilization. The leaf Ni is higher than 1000 μg g(-1) which categorizes the species as a Ni-hyperaccumulator and a great candidate for Ni-phytoextraction purposes. In addition to the accumulation of Ni, the leaf Mg is also correlated with soil bioavailable concentrations. The Ca uptake and translocation were significantly lower in serpentine plants (higher Ni), as such, the leaf Ca is probably greatly influenced either by the soil's Ni or the soil Ca/Mg ratio. The BFs and TFs are strongly higher than 1 and generally did not significantly differed between plants from serpentine (higher Ni) and non-serpentine soils (lower Ni). The present study highlights for the first time that A. utriculata could be suitable for cleaning Ni-contaminated areas and provides a contribution to the very small volume of data available on the potential use of native Mediterranean plant species from contaminated sites in phytoremediation technologies.

Seedling emergence, growth and trace elements tolerance and accumulation by Lamiaceae species in a mine soil

The potential use of three Laminaceae species (Lavandula dentata, Rosmarinus officinalis and Thymus vulgaris) for the phytostabilisation of a trace elements contaminated (acid) soil has been evaluated. These species were grown in mine tailing soil unamended (TS) and amended with calcium carbonate and pig manure (ATS), and unpolluted substrate for control (CT); plant growth, root characterisation, soil trace elements contents and their accumulation in plants were measured. Results indicated that seed emergence was independent from substrate characteristics, but seedlings died in TS with 40% survival in ATS. The biomass of L. dentata and T. vulgaris and root development in R. officinalis were negatively affected when grown in TS but without differences between ATS and CT. Applicating amendments reduced soil exchangeable and extractable fractions concentrations of trace elements in ATS compared with TS. The establishment of L. dentata and R. officinalis were related to trace elements immobilisation. Trace element concentrations in plants grown in tailing soils were similar to those reported for control, although applicating amendments reduced Zn accumulation in all species, and favoured increased absorption and aerial translocation of As and Pb by L. dentata and T. vulgaris; nonetheless, levels were below toxicity thresholds. Thus, these species fulfill the criteria for phytostabilisation purposes, aided by employing amendments.

Serpentine bacteria influence metal translocation and bioconcentration of Brassica juncea and Ricinus communis grown in multi-metal polluted soils

The aim of this study was to assess the effects of inoculation of rhizosphere or endophytic bacteria (Psychrobacter sp. SRS8 and Pseudomonas sp. A3R3, respectively) isolated from a serpentine environment on the plant growth and the translocation and accumulation of Ni, Zn, and Fe by Brassica juncea and Ricinus communis on a multi-metal polluted serpentine soil (SS). Field collected SS was diluted to 0, 25, 50, and 75% with pristine soil in order to obtain a range of heavy metal concentrations and used in microcosm experiments. Regardless of inoculation with bacteria, the biomass of both plant species decreased with increase of the proportion of SS. Inoculation of plants with bacteria significantly increased the plant biomass and the heavy metal accumulation compared with non-inoculated control in the presence of different proportion of SS, which was attributed to the production of plant growth promoting and/or metal mobilizing metabolites by bacteria. However, SRS8 showed a maximum increase in the biomass of the test plants grown even in the treatment of 75% SS. In turn, A3R3 showed maximum effects on the accumulation of heavy metals in both plants. Regardless of inoculation of bacteria and proportion of SS, both plant species exhibited low values of bioconcentration factor (<1) for Ni and Fe. The inoculation of both bacterial strains significantly increased the translocation factor (TF) of Ni while decreasing the TF of Zn in both plant species. Besides this contrasting effect, the TFs of all metals were <1, indicating that all studied bacteria-plant combinations are suitable for phytostabilization. This study demonstrates that the bacterial isolates A3R3 and SRS8 improved the growth of B. juncea and R. communis in SS soils and have a great potential to be used as inoculants in phytostabilization scenarios of multi-metal contaminated soils.

Improvement of Ni phytostabilization by inoculation of Ni resistant Bacillus megaterium SR28C

The use of metal tolerant plants for the phytostabilization of metal contaminated soil is an area of extensive research and development. In this study the effects of inoculation of Ni-resistant bacterial strains on phytostabilization potential of various plants, including Brassica juncea, Luffa cylindrica and Sorghum halepense, were studied. A Ni-resistant bacterial strain SR28C was isolated from a nickel rich serpentine soil and identified as Bacillus megaterium based on the morphological features, biochemical characteristics and partial 16S rDNA sequence analysis. The strain SR28C tolerated concentrations up to 1200 mg Ni L(-1) on a Luria-Bertani (LB) agar medium. Besides, it showed high degree of resistance to various metals (Cu, Zn, Cd, Pb and Cr) and antibiotics (ampicillin, tetracycline, streptomycin, chloramphenicol, penicillin and kanamycin) tested. In addition, the strain bound considerable amounts of Ni in their resting cells. Besides, the strain exhibited the plant growth promoting traits, such as solubilization of phosphate and production of indole-3-acetic acid (IAA) in modified Pikovskayas medium and LB medium, respectively in the absence and presence of Ni. Considering such potential, the effects of SR28C on the growth and Ni accumulation of B. juncea, L. cylindrica and S. halepense, were assessed with different concentrations of Ni in soil. Inoculation of SR28C stimulated the biomass of the test plants grown in both Ni contaminated and non-contaminated soils. Further, SR28C alleviated the detrimental effects of Ni by reducing its uptake and translocation to the plants. This study suggested that the PGPB inoculant due to its intrinsic abilities of growth promotion and attenuation of the toxic effects of Ni could be exploited for phytostabilization of Ni contaminated site.

Could an abandoned mercury mine area be cropped?

The Almadén area (Spain) is known for its high natural mercury background as well as for the anthropogenic impact due to mining activities. After the end of these activities, appropriate alternative use of the soil has to be found, and agricultural activities stand out as an environmentally-friendly and potentially profitable alternative, giving to the soil a sustainable use without risks for human or animal health according to current legislation. Experiments performed at different scales (involving hydroponics, growth in pots and lysimeters) allow recommendations to be made regarding the adequacy of cultivation of different crops for animal or human consumption before they are sown in the field. Regarding crops for animal feeding, mercury accumulation in vegetative organs represents a higher potential risk for animals. Nevertheless, seeds and fruits can be used, both for human and animal consumption. Finally, this work will lead the way to obtain a scientific basis for elaborating a list of recommendations on sustainable and safe alternative land use, according to current international legislation.

Phytoremedial assessment of flora tolerant to heavy metals in the contaminated soils of an abandoned Pb mine in Central Portugal

Significant accumulation of heavy metals in soils and flora exists around the abandoned Barbadalhos Pb mine in Central Portugal. Soil and plant samples [49 species] were collected from two line transects, LT 1 and LT 2, in the mineralized and non-mineralized area, respectively to gain a comprehensive picture of heavy metals in soils and flora to assess its potential for phytoremediation. Phytosociological inventories of the vegetation were made using the Braun-Blanquet cover-abundance scale. Metal concentrations in soil ranged from (in mg kg(-1)): 98-9330 [Pb], 110-517 [Zn], 7.1-50 [Co], 69-123 [Cr], 31-193 [Cu], 33400-98500 [Fe], 7.7-51 [Ni], 0.95-13 [Ag], 2.8-208 [As], and 71-2220 [Mn] along LT 1; and 24-93 [Pb], 30-162 [Zn], 3.7-34 [Co], 61-196 [Cr], 21-46 [Cu], 24100-59400 [Fe], 17-87 [Ni], 0.71-1.9 [Ag], 4.3-12 [As], and 44-1800 [Mn] along LT 2. Plant metal content ranged from (in mg kg(-1)): 1.11-548 [Pb], 7.06-1020 [Zn], 0.08-2.09 [Co], 0.09-2.03 [Cr], 2.63-38.5 [Cu], 10.4-4450 [Fe], 0.38-8.9 [Ni], and 0.03-1.9 [Ag] along LT 1; and 0.94-11.58 [Pb], 2.83-96.5 [Zn], 0.12-1.44 [Co], 0.21-1.49 [Cr], 1.61-22.7 [Cu], 4.6-2050 [Fe], 0.51-4.81 [Ni], and 0.02-0.31 [Ag] along LT 2. Plants with highest uptake of metals were: Cistus salvifolius (548 mg Pb kg(-1)), Digitalis purpurea (1017 mg Zn kg(-1) and 4450 mg Fe kg(-1)). Mentha suavolens and Ruscus ulmifolius were seen to hyperaccumulate Ag (1.9 and 1 mg Ag kg(-1), respectively). More metals and higher concentrations were traced in plants from LT 1, especially for Pb and Zn.

Intrinsic characteristics of Cr⁶⁺-resistant bacteria isolated from an electroplating industry polluted soils for plant growth-promoting activities

The Cr(6+)-resistant plant growth-promoting bacteria was isolated from soil samples that were collected from an electroplating industry at Coimbatore, India, that had tolerated chromium concentrations up to 500 mg Cr(6+)/L in Luria-Bertani medium. Based on morphology, physiology, and biochemical characteristics, the strain was identified as Bacillus sp. following the Bergey's manual of determinative bacteriology. Evaluation of plant growth-promoting parameters has revealed the intrinsic ability of the strain for the production of indole-3-acetic acid (IAA), siderophore, and solubilization of insoluble phosphate. Bacillus sp. have utilized tryptophan as a precursor for their growth and produced IAA (122 μg/mL). Bacillus sp. also exhibited the production of siderophore that was tested qualitatively using Chrome Azurol S (CAS) assay solution and utilized the insoluble tricalcium phosphate as the sole source of phosphate exhibiting higher rate of phosphate solubilization after 72 h of incubation (1.45 μg/mL). Extent of Cr(6+) uptake and accumulation of Cr(6+) in the cell wall of Bacillus sp. was investigated using atomic absorption spectrophotometer and scanning electron microscope-energy dispersive spectroscopy, respectively. The congenital capability of this Cr(6+)-resistant plant growth-promoting Bacillus sp. could be employed as bacterial inoculum for the improvement of phytoremediation in heavy metal contaminated soils.

Metal concentrations in the soils and native plants surrounding the old flotation tailings pond of the copper mining and smelting complex Bor (Serbia)

In this study concentrations of metals in the native plants and soils surrounding the old flotation tailings pond of the copper mine were determined. It has been established that the soil is heavily contaminated with copper, iron and arsenic, the mean concentrations being 1585.6, 29,462.5 and 171.7 mg kg(-1) respectively. All the plants, except manganese, accumulated metallic elements in concentrations which were either in the range of critical and phytotoxic values (Pb and As) or higher (Zn), and even much higher (Cu and Fe) than these values. Otherwise, the accumulation of Mn, Pb and As was considerably lower than that of Cu, Fe and Zn. In most plants the accumulation of target metals was highest in the root. Several plant species showed high bioaccumulation and translocation factor values, which classify them into species for potential use in phytoextraction. The BCF and TF values determined in Prunus persica were 1.20 and 3.95 for Cu, 1.5 and 6.0 for Zn and 1.96 and 5.44 for Pb. In Saponaria officinalis these values were 2.53 and 1.27 for Zn, and in Juglans regia L. they were 8.76 and 17.75 for Zn. The translocation factor in most plants, for most metals, was higher than one, whereas the highest value was determined in Populus nigra for Zn, amounting to 17.8. Among several tolerant species, the most suitable ones for phytostabilization proved to be Robinia pseudoacacia L. for Zn and Verbascum phlomoides L., Saponaria officinalis and Centaurea jacea L. for Mn, Pb and As.

Inoculation of endophytic bacteria on host and non-host plants--effects on plant growth and Ni uptake

Among a collection of Ni resistant endophytes isolated from the tissues of Alyssum serpyllifolium, four plant growth promoting endophytic bacteria (PGPE) were selected based on their ability to promote seedling growth in roll towel assay. Further, the PGPE screened showed the potential to produce plant growth promoting (PGP) substances and plant polymer hydrolyzing enzymes. These isolates were further screened for their PGP activity on A. serpyllifolium and Brassica juncea under Ni stress using a phytagar assay. None of the four isolates produced any disease symptoms in either plant. Further, strain A3R3 induced a maximum increase in biomass and Ni content of plants. Based on the PGP potential in phytagar assay, strain A3R3 was chosen for studying its PGP effect on A. serpyllifolium and B. juncea in Ni contaminated soil. Inoculation with A3R3 significantly increased the biomass (B. juncea) and Ni content (A. serpyllifolium) of plants grown in Ni contaminated soil. The strain also showed high level of colonization in tissue interior of both plants. By 16S rRNA gene sequencing analysis, A3R3 was identified as Pseudomonas sp. Successful colonization and subsequent PGP potentiality of Pseudomonas sp. A3R3 indicate that the inoculation with PGPE might have significant potential to improve heavy metal phytoremediation.

Comparison of element concentrations in fir and rhododendron leaves and twigs along an altitudinal gradient

Concentrations of 23 elements (Ca, K, Mg, P, Al, Cu, Fe, Mn, Mo, Na, Ni, Zn, Ag, Ba, Be, Cd, Co, Cr, Pb, Sb, Th, Tl, and V) in leaf and twig samples of a fir (Abies fabri) and a rhododendron (Rhododendron williamsianum) collected along an altitudinal gradient on Mount Gongga, China, are reported in the present study. Most of the macronutrients (K and P), micronutrients (Fe, Zn, Cu, Na, Ni, Mo, and Al), and trace elements (Pb, Tl, Ag, Cd, Ba, Co, V, Be, and Cr) are significantly enriched in fir when compared to rhododendron; however, Ca, Mg, Mn, Ba, and Cd are more enriched in rhododendron than in fir. Most of the elements in both plants are more significantly enriched in twigs than in leaves. The relationship between element concentration in plants and altitudinal gradient is nonlinear. Altitudes of 3,200 and 3,400 m are turning points for fir and rhododendron growth, respectively. Concentrations of all trace elements in the two plants along the altitudinal gradient are well below the toxic level in plants. No known industrial sources of the elements investigated exist in the Mount Gongga area, China. Element concentrations in the present study are higher than those found in mosses collected from the same area, indicating that the area is not contaminated. The element concentrations that we observed in plant samples were due to soil uptake. The pronounced differences between the two species are due to the different uptake characteristics of fir and rhododendron.

Nickel speciation in the xylem sap of the hyperaccumulator Alyssum serpyllifolium ssp. lusitanicum growing on serpentine soils of northeast Portugal

Nickel speciation was studied in the xylem sap of Alyssum serpyllifolium ssp. lusitanicum, a Ni-hyperaccumulator endemic to the serpentine soils of northeast Portugal. The xylem sap was collected from plants growing in its native habitat and characterized in terms of carboxylic and amino acids content. The speciation of nickel was studied in model and real solutions of xylem sap by voltammetric titrations using Square Wave Voltammetry (SWV). The results showed that Ni transport in the xylem sap occurs mainly as a free hydrated cation (about 70%) and complexed with carboxylic acids, mainly citric acid (18%). Altogether, oxalic acid, malic acid, malonic acid and aspartic acid complexed less than 13% of total Ni. A negligible amount bounded to the amino acids, like glutamic acid and glutamine (<1%). Histidine did not play a role in Ni translocation in the xylem sap of A. serpyllifolium under field conditions. Amino acids are one of the main forms of N transport in the xylem sap, and under field conditions, N is usually a limited nutrient. We hypothesize that the translocation of Ni in the xylem sap as a free ion or chelated with carboxylic acids is 'cheaper' in terms of N resources.

Verbascum bombyciferum Boiss. (Scrophulariaceae) as possible bio-indicator for the assessment of heavy metals in the environment of Bursa, Turkey

In this study, we determined the heavy metal content (Cd(2+), Cr(3+), Cu(2+), Fe(3+), Ni(2+), Pb(2+), and Zn(2+)) in the soil surrounding the roots and different organs of Verbascum bombyciferum Boiss. (Scrophulariaceae), which is endemic to Uludağ Mountain, Bursa, Turkey. Plant samples were collected from roadsides, and heavy metal accumulation capabilities were tested. This is one of the pioneer species of ruderal plant communities on roadsides, building sites, rubbish dumps, etc. Different organs of plant samples (roots, stems, leaves, and flowers) and their soils were analyzed by inductively couple plasma optical emission spectroscopy for their heavy metal contents. Some of the analyzed heavy metals (Cd(2+), Cr(3+), Pb(2+), and Zn(2+)) were usually increased depending on the traffic in the sample sites, and this variation was also reflected in heavy metal content of plant samples. Our results show that this plant can be used as a bio-indicator species in the monitoring of increased Cd(2+), Cr(3+), Pb(2+), and Zn(2+) in the environment. We also concluded that V. bombyciferum have the capability of Cd(2+), Cr(3+), Cu(2+), Ni(2+), Pb(2+), and Zn(2+) accumulation.

Biotechnological applications of serpentine soil bacteria for phytoremediation of trace metals

Serpentine or ultramafic soils are produced by weathering and pedogenesis of ultramafic rocks that are characterized by high levels of Ni, Cr, and sometimes Co, but contain low levels of essential nutrients such as N, P, K, and Ca. A number of plant species endemic to serpentine soils are capable of accumulating exceptionally high concentrations of Ni, Zn, and Co. These plants are known as metal "hyperaccumulators." The function of hyperaccumulation depends not only on the plant, but also on the interaction of the plant roots with rhizosphere microbes and the concentrations of bioavailable metals in the soil. The rhizosphere provides a complex and dynamic microenvironment where microorganisms, in association with roots, form unique communities that have considerable potential for the detoxification of hazardous materials. The rhizosphere bacteria play a significant role on plant growth in serpentine soils by various mechanisms, namely, fixation of atmospheric nitrogen, utilization of 1-aminocyclopropane-1-carboxylic acid (ACC) as the sole N source, production of siderophores, or production of plant growth regulators (hormones). Further, many microorganisms in serpentine soil are able to solubilize "unavailable" forms of heavy metal-bearing minerals by excreting organic acids. In addition, the metal-resistant serpentine isolates increase the efficiency of phytoextraction directly by enhancing the metal accumulation in plant tissues and indirectly by promoting the shoot and root biomass of hyperaccumulators. Hence, isolation of the indigenous and stress-adapted beneficial bacteria serve as a potential biotechnological tool for inoculation of plants for the successful restoration of metal-contaminated ecosystems. In this study, we highlight the diversity and beneficial features of serpentine bacteria and discuss their potential in phytoremediation of serpentine and anthropogenically metal-contaminated soils.

Determination of nickel, calcium and magnesium in xylem sap by flame atomic absorption spectrometry using a microsampling technique

INTRODUCTION

Knowledge of xylem sap chemical composition is important to the understanding of translocation, detoxification and tolerance mechanisms. However, the small amount of sample available often hampers its characterisation. Hence, low volume consumption techniques are needed for xylem sap analysis.

OBJECTIVE

To develop a microsampling technique for the determination of elements in xylem sap from different plants by flame atomic absorption spectrometry (FAAS).

METHODOLOGY

The microsampling device was optimised in terms of sample volume and integration time. The analytical characteristics of the microsampling technique (micro-FAAS) were established and compared with those of FAAS with traditional continuous nebulisation. The method was validated by means of an independent technique.

RESULTS

Ca, Mg and Ni were determined in a 50 microL aliquot of xylem sap solution/element that was introduced directly into the flame via the microsampling accessory. Good precision was obtained with relative standard deviations of 1.1, 0.6 and 2.3% for Ca, Mg and Ni, respectively. Matrix effects resulting from the physical characteristics of the samples and possible chemical interferences caused by phosphate and/or sulphate were ruled out.

CONCLUSION

A simple, rapid and reproducible microsampling technique coupled to FAAS was developed and successfully applied in the determination of Ca, Mg and Ni in xylem sap.

Endophytic bacteria and their potential to enhance heavy metal phytoextraction

Pollution of soils with heavy metals is becoming one of the most severe environmental and human health hazards. Due to its widespread contamination finding innovative ways to clean metal pollutant has become a priority in the remediation field. Phytoremediation, the use of plants for the restoration of environments contaminated with pollutants is a relatively new technology that is more benign than current engineering solutions to treat contaminated sites. Recently, the benefits of combining endophytic bacteria with plants for increased remediation of pollutants have been successfully tried for toxic metal removal from contaminated soils. Endophytic bacteria reside within plant hosts without causing disease symptoms. Further, the metal resistant endophytes are reported to be present in various hyperaccumulator plants growing on heavy metal contaminated soils and play an important role in successful survival and growth of plants. Moreover, the metal resistant endophytes are reported to promote plant growth by various mechanisms such as nitrogen fixation, solubilization of minerals, production of phytohormones, siderophores, utilization of 1-aminocyclopropane-1-carboxylic acid as a sole N source and transformation of nutrient elements. In this review we highlight the diversity and plant growth promoting features of metal resistant endophytic bacteria and discuss their potential in phytoextraction of heavy metals from contaminated soils.

Rhizosphere microbial densities and trace metal tolerance of the nickel hyperaccumulator Alyssum serpyllifolium subsp. lusitanicum

In this study we determine culturable microbial densities (total heterotrophs, ammonifiers, amylolytics and cellulolytics) and bacterial resistance to Co, Cr, and Ni in bulk and rhizosphere soils of three populations of the Ni-hyperaccumulator Alyssum serpyllifolium subsp. lusitanicum and the excluder Dactylis glomerata from ultramafic sites (two populations in Northeast (NE) Portugal (Samil (S), Morais (M)) and one population in Northwest (NW) Spain (Melide (L)). The relationship between bioavailable metal concentrations (H2O-soluble) and microbial densities were analysed. Significant differences in microbial densities and metal-resistance were observed between the two species and their three populations. The hyperaccumulator showed higher microbial densities (except cellulolytics) and a greater rhizosphere effect, but this was only observed in S and M populations. These populations of A. serpyllifolium also showed selective enrichment of Ni-tolerant bacteria at the rhizosphere where Ni solubility was enhanced (densities of Ni-resistant bacteria were positively correlated with H2O-soluble Ni). These rhizobacteria could solubilise Ni in the soil and potentially improve phytoextraction strategies.

Isolation and characterization of Ni mobilizing PGPB from serpentine soils and their potential in promoting plant growth and Ni accumulation by Brassica spp

The study was undertaken to assess the effects of Ni mobilizing bacteria on the plant growth and the uptake of Ni by Brassica juncea and Brassica oxyrrhina. Among a collection of Ni resistant bacterial strains isolated from the non-rhizosphere and rhizosphere soils of Alyssum serpyllifolium and Astragalus incanus at a serpentine site in Bragança, north-east of Portugal, nine strains were selected based on their ability to solubilize Ni in soil. Further assessment on plant growth-promoting parameters revealed the intrinsic ability of the Ni mobilizing strains to produce indole-3-acetic acid (IAA), siderophores, utilize 1-aminocyclopropane-1-carboxylic acid (ACC) as the sole N source and solubilize insoluble phosphate. All of the strains tested positive for IAA production and phosphate solubilization. In addition, all the strains, except SRS5 exhibited significant levels of siderophore production. Besides, five isolates showed positive for ACC deaminase activity. In pot experiments, inoculation of plants with Ni mobilizing strains increased the biomass of both B. juncea and B. oxyrrhina. Among the strains, Pseudomonas sp. SRI2, Psychrobacter sp. SRS8 and Bacillus sp. SN9 showed maximum increase in the biomass of the test plants. In addition, the strain SN9 significantly increased the Ni concentration in the root and shoot tissues of B. juncea and B. oxyrrhina. Further, a significantly positive correlation was observed between the bacterial Ni mobilization in soil and the total Ni uptake in both plant species. The findings, therefore, revealed that inoculation of Ni mobilizing plant growth-promoting bacterial strain SN9 increases the efficiency of phytoextraction directly by enhancing Ni accumulation in plant tissues and indirectly by promoting the shoot and root biomass of B. juncea and B. oxyrrhina.

Heavy metals distribution in soils surrounding an abandoned mine in NW Madrid (Spain) and their transference to wild flora

The present work concerns the distribution and mobility of heavy metals (Fe, Mn, Cu, Zn and Cd) in the surrounding soils of a mine site and their transfer to wild flora. Thus, soils and plants were sampled from a mining valley in NW Madrid (Spain), and total and extractable heavy metals were analysed. Soils affected by mining activities presented total Cd, Cu and Zn concentrations above toxic thresholds. The percentage of extractable element was highest for Cd and lowest for Cu. A highly significant correlation was observed between the total and extractable concentrations of metals in soils, indicating that, among the factors studied, total metals concentration is the most relevant for heavy metals extractability in these soils. (NH(4))(2)SO(4)-extractable metal concentrations in soils are correlated better with metal concentrations in several plant species than total metals in soils, and thus can be used as a suitable and robust method for the estimation of the phytoavailable fraction present in soils. Twenty-five vascular plant species (3 ferns and 22 flowering plants) were analysed, in order to identify exceptional characteristics that would be interesting for soil phytoremediation and/or reclamation. High Cd and Zn concentrations have been found in the aerial parts of Hypericum perforatum (Cd), Salix atrocinerea (Cd, Zn) and Digitalis thapsi (Cd, Zn). The present paper is, to the best of our knowledge, the first report of the metal accumulation ability of the two latter plant species. The phytoremediation ability of S. atrocinerea for Cd and Zn was estimated, obtaining intervals of time that could be considered suitable for the phytoextraction of polluted soils.