Selection of Salinity-Adapted Endorhizal Fungal Consortia from Two Inoculum Sources and Six Halophyte Plants.

Soil salinity is a limiting factor in crop productivity. Inoculating crops with microorganisms adapted to salt stress is an alternative to increasing plant salinity tolerance. Few studies have simultaneously propagated arbuscular mycorrhizal fungi (AMF) and dark septate fungi (DSF) using different sources of native inoculum from halophyte plants and evaluated their effectiveness. In alfalfa plants as trap culture, this study assessed the infectivity of 38 microbial consortia native from rhizosphere soil (19) or roots (19) from six halophyte plants, as well as their effectiveness in mitigating salinity stress. Inoculation with soil resulted in 26-56% colonization by AMF and 12-32% by DSF. Root inoculation produced 10-56% and 8-24% colonization by AMF and DSF, respectively. There was no difference in the number of spores of AMF produced with both inoculum types. The effective consortia were selected based on low Na but high P and K shoot concentrations that are variable and are relevant for plant nutrition and salt stress mitigation. This microbial consortia selection may be a novel and applicable model, which would allow the production of native microbial inoculants adapted to salinity to diminish the harmful effects of salinity stress in glycophyte plants in the context of sustainable agriculture.

Citrate-coated cobalt ferrite nanoparticles for the nano-enabled biofortification of wheat.

A pot experiment was conducted in an open greenhouse to explore the use of citrate-coated cobalt ferrite nanoparticles (CoFe2O4 NPs) as a source for Fe fortification of three wheat lines (Triticum aestivum L.). Two of the three wheat lines tested differ in their efficiency concerning Zn storage in their grains (efficient and inefficient), and one had inefficient P-absorption. The NPs were supplied by foliar or soil application of Fe at 330 mg L-1, and 46 or 68 mg kg-1 soil, respectively. A positive control (Fe-EDTA salt, a conventional iron fertilizer) and a negative control (no fertilization) were also included to compare the efficiency of NP fertilization. Soil fertilization with NPs improved the grain yield and Fe concentration in the grains compared with the foliar application of NPs and conventional Fe fertilizer. Application of soil NPs at 68 mg kg-1 increased the grain yield by 52% and 21% compared with the control and soil Fe-EDTA treatments, respectively. Likewise, grain Fe concentration increased by 96% and 72% compared with the control and soil Fe-EDTA treatments, respectively. The phytic acid concentration in grains and the phytic acid:Fe ratio decreased by 6% and 62%, respectively, due to the soil application of NPs (68 mg Fe per kg). The Fe grain concentration of lines inefficient for Zn storage and P-uptake in plants from soil fertilized with NPs (68 mg Fe per kg) was 1.37 and 0.26 fold above the target biofortification concentration (60 mg Fe per kg). Cobalt concentration in grains ranged from 9 to 16 mg kg-1. These concentrations were below the maximum allowable limit of Co in grains (50 mg kg-1) recommended by FAO and the WHO. Our results showed that Fe supplied as NPs may improve the nutritional quality of wheat grains, and the economic yield. However, there remains a long way to go to achieve effective and economic use of nanotechnology for the nutritional development of wheat.

Trace element adsorption from acid mine drainage and mine residues on nanometric hydroxyapatite.

Mining Ag, Cu, Pb, and Zn sulfides by flotation produces great volume of residues, which oxidized through time and release acid solutions. Leachates from tailing heaps are a concern due to the risk of surface water pollution. Hydroxyapatite nanoparticles may remove trace elements from acid leachate collected from an oxidized tailing heap (pH ranged 1.69 ± 0.3 to 2.23 ± 0.16; [SO42-] = 58 ± 0.67 to 60.69 ± 0.39 mmol). Based on the batch experiments under standard conditions, the average removal efficiency was 96%, 92%, 86%, and 67% for Cd, Pb, Zn, and Cu, respectively. The Zn adsorption was modeled by the Freundlich equation, but Cd, Cu, and Pb isotherms do not fit to Freundlich nor Lagmuir equations. Adsorption and other mechanisms occur during trace elements removal by hydroxyapatite. In the polymetallic system, trace elements saturate the specific surface of hydroxyapatite in the following order Zn, Cd, Cu, and Pb. The pH values must be higher than 7.5 to adsorb trace elements. The dose of 3.8% of hydroxyapatite to acid mine drainage removed efficiently > 80% of the soluble Fe, Cu, Mn, Zn, Cd, Ni, and Pb: 4020.0, 37.3, 34.8, 432.0, 4.4, 0.7, and 0.11 mg L-1 from leachate A and 3357.1, 46.6, 27.8, 569.0, 4.7, 0.6, and 1.7 from leachate B, respectively. The application of 0.7% of hydroxyapatite decreased the extractable Pb in unoxidized tailing heaps from 272 to 100 mg kg-1. It is likely to use hydroxyapatite to control trace element mobility from mine residues to surrounding soils and surface water.

Changes in fatty acid in Tecoma stans grown in mine residues after compost amendment.

Amendment tailing heaps with compost may deplete metal(loid)s concentration and improve the conditions for plant development. This research aimed to compare the Tecoma stans ability to grow on soil from the Sonora desert and mining waste (MW) after amendment with compost. Amendment the MW, with compost, decreased soluble As, Cd, Cu, Mn, Pb, and Zn up to 47, 33, 11, 34, 69, and 34%, respectively; increased ten times the leaves weight, and thirteen times the leaf area of the plants. Arsenic, Cd, Pb, Cu, and Zn in plants tissues decreased 27, 28, 27, 12, and 11%, respectively. The bioaccumulation and translocation factors were lower than one, so T. stans do not accumulate these elements. Polyunsaturated fatty acids 18:2ω6 and 18:3ω3 were increased, suggesting lower alteration of thylakoidal membrane integrity due to compost treatment. But, the amendment to the tailing was not enough to deplete the abiotic stress.

Amendment mine tailing with vermicompost depletes changes in polyunsaturated fatty acid of Tecoma stans.

Bioaccessibility of potentially toxic elements in mine residue particles.

Mining companies used to abandon tailing heaps in countryside regions of Mexico and other countries. Mine residues (MRs) contain a high concentration of potentially toxic elements (PTE). The wind can disperse dust particles (<100 µm) and once suspended in the atmosphere, can be ingested or inhaled; this is a common situation in arid climates. Nowadays, there is little information on the risk of exposure to PTEs from particulate matter dispersed by wind. The pseudo-total PTE in bulk and fractionated MR after aqua regia digestion, the inhalable bioaccessibility with Gamble solution (pH = 7.4), and the gastric bioaccessibility with 0.4 M glycine solution at pH 1.5 were determined. As and Pb chemical species were identified by X-ray absorption near-edge structure (XANES) spectroscopy. The highest rate of dispersion was observed with 74-100 µm particles (104 mg m-2 s-1); in contrast, particles <44 µm had the lowest rate (26 mg m-2 s-1). The highest pseudo-total As (35 961 mg kg-1), Pb (3326 mg kg-1), Cd (44 mg kg-1) and Zn (up to 4678 mg kg-1) concentration was in the <20 µm particles and As in the 50-74 µm (40 236 mg kg-1) particles. The highest concentration of inhaled bioaccessible As (343 mg kg-1) was observed in the <20 µm fraction and the gastric bioaccessible As was 744 mg kg-1, Pb was 1396 mg kg-1, Cd was 19.2 mg kg-1, and Zn was 2048 mg kg-1. The predominant chemical As species was arsenopyrite (92%), while 54% of Pb was in the adsorbed form. Erodible particle matter is a potential risk for humans in case of inhalation or ingestion.

Metal(loid) bioaccessibility of atmospheric particulate matter from mine tailings at Zimapan, Mexico.

Metal(loid)s are contaminants of concern emitted as particulate matter (PM) from several pollution sources. The objective was to characterize potential exposure from local airborne metal(loid)s in a community in proximity to mine tailings. Air samples were collected weekly at five sites around the municipal mine tailings using two Hi-volume samplers for simultaneously collecting PM10 and PM2.5. Total suspended particulates (TSP), concentrations, speciation, and bioaccessibility of metal(loid)s were quantified. The size and form of particles were determined by scanning electron microscopy. The concentration of TSP (µg m-3) in the airborne samples ranged from 21.2 to 64.6 for PM2.5 and 23.6 to 80.1 for PM10. The profiles of analyzed quasi-total metal(loid) concentration from all sampling sites were similar between these aerosols PM sizes except at site 2 for Cd, at site 3 for Cu, and site 4 for Zn. The order of quasi-total metal(loid) concentration, in the airborne samples for both PM sizes, was As > Zn > Fe > Pb > Cu > Mn > Cd. As speciation included As-sulfite, As(III)-O, and As(V)-O with less concentration of As(III)-O in both PM sizes. Bioaccessible metal(loid) concentrations were very high and represented a great percentage from the quasi-total airborne concentrations, for instance, 10% and 37% for Pb and 8% and 6% for As in pulmonary and gastric bioaccessible concentrations, respectively. Knowing the toxic effects of these pollutants, there is an urgent need to establish environmental regulation of bioaccessible pollutant concentrations from PM dislodged from uncovered metal(loid) mine tailings affecting not only nearby human populations but also possible long-distance ecosystem transport.

Afforestation may influence changes in tailing heaps in a long time.

A soil and plant survey was carried out in a tailing heap afforested 30 years ago to gain information about the changes in the tailing and metal uptake by plants. A poor development of Technosol was found. It was observed accumulation of OM spatio temporarily. Metal concentrations in the soil profile varied between plots. Extractable Pb concentrations ranged from 0.4 to 2.9%; extractable Cd varied 9.7-46% of the total concentration. PCA analysis shows DTPA-Zn and DTPA-Cu, Na, K, and OM have the widest concentrations range between soil layers. Casuarina equisetifolia and Pennisetum clandestinum formed a pristine uniform litter layer, whereas Eucalyptus camaldulensis did not form a litter layer. Casuarina equisetifolia has a higher population density (756 p ha-1) compared to Populus nigra (528 p ha-1) and E. camaldulensis (621 p ha-1). Pennisetum clandestinum grew successfully and covered the tailing, but Cd and Pb concentrations were above the domestic animal toxicity limits, 0.5 and 10 mg kg-1, respectively. Populus nigra absorbed more Zn than Casuarina equisetifolia and Eucalyptus camaldulensis. Trees species did not accumulate high foliar Cu and Zn concentrations, but Pb (47.7-124.3 mg kg-1) and Cd (5.7-26.8 mg kg-1) concentrations are over those reported for mature leaf tissues. HighlightsPennisetum clandestinum formed soil cover on remediated plots.Casuarina equisetifolia was efficient in forming a litter soil horizon.Trasdescantia fluminensis accumulated Pb.Populus nigra accumulated Zn and Cd from the tailing heap.

Screening bacterial phosphate solubilization with bulk-tricalcium phosphate and hydroxyapatite nanoparticles.

Phosphate-solubilizing bacteria can release phosphorus (P) from insoluble minerals and benefit either soil fitness or plant growth. Bulk sized P compounds have been suggested but little is known about solubilization of nanosized materials such as hydroxyapatite nanoparticles (HANP). A screening of the initial 43 strains from vanilla rhizospheres for phosphate solubilization with bulk Ca3(PO4)2 was carried out. Subsequently, 6 strains were selected on bulk rock phosphate (RP) and HANP. Two kinetics experiments were run out regarding evaluation at 5, 10 and 20 days after inoculation (dai). Bacterial biomass production was similar in both experiments; the lowest biomass was found at 20 dai. In all cases, bacteria reduced the original culture medium pH; which was related with phosphate solubilization from the production of organic acids. Citric acid was produced by all strains. Enterobacter cloacae CP 31 was the most interesting bacterium: produced the lowest culture pH at 20 dai (4) with both Ca3(PO4)2 and RP, and 3.7 at 10 dai with HANP correlating with high soluble P concentration (536, 64 and 13 mg L-1 with these P sources, respectively). This bacterium should be tested as an inoculant in plants to reveal its potential as plant promoter growth and HANP to suggest its role in the potential use of nano-P fertilizers.

Phytotoxicity and upper localization of Ag@CoFe2O4 nanoparticles in wheat plants.

Environmental concern related to Ag+ release from conventional AgNPs is expected to be prevented once contained into a magnetic core like magnetite or CoFe2O4. Accordingly, we obtained CoFe2O4 NPs by microwave-assisted synthesis, which AgNO3 addition rendered Ag@CoFe2O4 NPs. NPs were characterized, and before exploring potential applications, we carried out 7-day wheat toxicity assays. Seed germination and seedling growth were used as toxicity endpoints and photosynthetic pigments and antioxidant enzymes as oxidative stress biomarkers. Total Fe, Co, and Ag determination was initial indicative of Ag@CoFe2O4 NPs uptake by plants. Then NPs localization in seedling tissues was sought by scanning electron microscopy (SEM) and darkfield hyperspectral imaging (DF-HSI). Not any silver ion (Ag+) was detected into the ferrite structure, but results only confirmed the presence of metallic silver (Ag0) adsorbed on the CoFe2O4 NPs surface. Agglomerates of Ag@CoFe2O4 NPs (~10 nm) were fivefold smaller than CoFe2O4 NPs, and ferrimagnetic properties of the CoFe2O4 NPs were conserved after the formation of the Ag@CoFe2O4 composite NPs. Seed germination was not affected by NPs, but root and shoot lengths of seedlings diminished 50% at 54.89 mg/kg and 168.18 mg/kg NPs, respectively. Nonetheless, hormesis was observed in roots of plants exposed to lower Ag@CoFe2O4 NPs treatments. Photosynthetic pigments and the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), guaiacol peroxidase (GPX), and ascorbate peroxidase (APX) indicated oxidative damage by reactive oxygen species (ROS) generation. SEM suggested NPs presence in shoots and roots, whereas DF-HSI confirmed some Ag@CoFe2O4 NPs contained in shoots of wheat plants.

Phytoremediation assisted by mycorrhizal fungi of a Mexican defunct lead-acid battery recycling site.

A field experiment was conducted during 15 months to study the effects of four arbuscular mycorrhizal fungi (AMF) on the growth of Ricinus communis accession SF7. Plants were established on amended soil (vermicompost:sawdust:soil 1:1:1) severely polluted by lead-acid batteries (LAB) located at Mexico State, Mexico. Plants inoculated with Acaulospora sp., Funneliformis mosseae and Gigaspora gigantea had 100% survival in comparison to non-inoculated plants (57%). These same AMF enhanced palmitic and linoleic acids content in seeds of R. communis. Acaulospora sp. modified rhizosphere soil pH and decreased 3.5 folds Pb foliar concentrations while F. mosseae BEG25 decreased three times Pb soil availability in comparison to non-inoculated plants. Spatial changes in Pb soil availability were observed at the end of this research. No fungal effect on P, Ca, Cu foliar concentrations, soluble sugars, proline, chlorophyll or on the activity of two oxidative stress enzymes was observed. Mycorrhizal colonization from the inoculated fungi was between 40% and 60%, while colonization by native fungi was between 16% and 22%. A similar percentage of foliar total phenolic compounds was observed in non-mycorrhizal plants and those inoculated with G. gigantea and Acaulospora sp. This is the first research reporting effects of AMF on R. communis (castor bean) shrubs when grown on a LAB recycling site suggesting the use of Acaulospora sp. and F. mosseae BEG25 in phytostabilization to ameliorate Pb pollution and decreasing its ecological risk.

Leaf Epiphytic Bacteria of Plants Colonizing Mine Residues: Possible Exploitation for Remediation of Air Pollutants.

Plant surfaces are known as an important sink for various air pollutants, including particulate matter and its associated potentially toxic elements (PTE). Moreover, leaves surface or phylloplane is a habitat that harbors diverse bacterial communities (epiphytic). However, little is known about their possible functions during phytoremediation of air pollutants like PTE. The study of leaf epiphytic bacteria of plants colonizing mine residues (MR) containing PTE is thus a key to understand and exploit plant-epiphytic bacteria interactions for air phytoremediation purposes. In this research, we aimed (i) to characterize the functions of epiphytic bacteria isolated from the phylloplane of Brickellia veronicifolia, Flaveria trinervia, Gnaphalium sp., and Allionia choisyi growing spontaneously on multi-PTE contaminated MR and (ii) to compare these against the same plant species in a non-polluted control site (NC). Concentrations (mg kg-1) of PTE on MR leaf surfaces of A. choisyi reached up to 232 for Pb, 13 for Cd, 2,728 for As, 52 for Sb, 123 for Cu in F. trinervia, and 269 for Zn in Gnaphalium sp. In the four plant species, the amount of colony-forming units per cm2 was superior in MR leaves than in NC ones, being A. choisyi the plant species with the highest value. Moreover, the proportion of isolates tolerant to PTE (Zn, Cu, Cd, and Sb), UV light, and drought was higher in MR leaves than in those in NC. Strain BA15, isolated from MR B. veronicifolia, tolerated 150 mg Zn L-1, 30 mg Sb L-1, 25 mg Cu L-1; 80 mg Pb L-1, and was able to grow after 12 h of continuous exposition to UV light and 8 weeks of drought. Plant growth promotion related traits [N fixation, indole acetic acid (IAA) production, and phosphate solubilization] of bacterial isolates varied among plant species isolates and between MR and NC sampling condition. The studied epiphytic isolates possess functions interesting for phytoremediation of air pollutants. The results of this research may contribute to the development of novel and more efficient inoculants for microbe-assisted phytoremediation applied to improve air quality in areas exposed to the dispersion of metal mine tailings.

Seed Endophyte Microbiome of Crotalaria pumila Unpeeled: Identification of Plant-Beneficial Methylobacteria.

Metal contaminated soils are increasing worldwide. Metal-tolerant plants growing on metalliferous soils are fascinating genetic and microbial resources. Seeds can vertically transmit endophytic microorganisms that can assist next generations to cope with environmental stresses, through yet poorly understood mechanisms. The aims of this study were to identify the core seed endophyte microbiome of the pioneer metallophyte Crotalaria pumila throughout three generations, and to better understand the plant colonisation of the seed endophyte Methylobacterium sp. Cp3. Strain Cp3 was detected in C. pumila seeds across three successive generations and showed the most dominant community member. When inoculated in the soil at the time of flowering, strain Cp3 migrated from soil to seeds. Using confocal microscopy, Cp3-mCherry was demonstrated to colonise the root cortex cells and xylem vessels of the stem under metal stress. Moreover, strain Cp3 showed genetic and in planta potential to promote seed germination and seedling development. We revealed, for the first time, that the seed microbiome of a pioneer plant growing in its natural environment, and the colonisation behaviour of an important plant growth promoting systemic seed endophyte. Future characterization of seed microbiota will lead to a better understanding of their functional contribution and the potential use for seed-fortification applications.

Microscopic characterization of orchid mycorrhizal fungi: Scleroderma as a putative novel orchid mycorrhizal fungus of Vanilla in different crop systems.

Vanilla is an orchid of economic importance widely cultivated in tropical regions and native to Mexico. We sampled three species of Vanilla (V. planifolia, V. pompona, and V. insignis) in different crop systems. We studied the effect of crop system on the abundance, type of fungi, and quality of pelotons found in the roots using light and electron microscopy and direct sequencing of mycorrhizal structures. Fungi were identified directly from pelotons obtained from terrestrial roots of vanilla plants in the flowering stage. Root samples were collected from plants in crop systems located in the Totonacapan area in Mexico (states of Puebla and Veracruz). DNA was extracted directly from 40 pelotons and amplified using ITS rRNA sequencing. Peloton-like structures were observed, presenting a combination of active pelotons characterized by abundant hyphal coils and pelotons in various stages of degradation. The most active pelotons were observed in crop systems throughout living tutors (host tree) in comparison with roots collected from dead or artificial tutors. Fungi identified directly from pelotons included Scleroderma areolatum, a common ectomycorrhizal fungus that has not been reported as a mycorrhizal symbiont in orchids. Direct amplification of pelotons also yielded common plant pathogens, including Fusarium and Pyrenophora seminiperda, especially in those sites with low colonization rates, and where large numbers of degraded pelotons were observed. This research reports for the first time the potential colonization of Vanilla by Scleroderma, as a putative orchid mycorrhizal symbiont in four sites in Mexico and the influence of crop system on mycorrhizal colonization on this orchid.

Jatropha curcas and assisted phytoremediation of a mine tailing with biochar and a mycorrhizal fungus.

Soil pollution is an important ecological problem worldwide. Phytoremediation is an environmental-friendly option for reducing metal pollution. A greenhouse experiment was conducted to determine the growth and physiological response, metal uptake, and the phytostabilization potential of a nontoxic Jatropha curcas L. genotype when grown in multimetal-polluted conditions. Plants were established on a mine residue (MR) amended or not amended with corn biochar (B) and inoculated or not inoculated with the mycorrhizal fungus Acaulospora sp. (arbuscular mycorrhizal fungus, AMF). J. curcas was highly capable of growing in an MR and showed no phytotoxic symptoms. After J. curcas growth (105 days), B produced high desorption of Cd and Pb from the MR; however, no increases in metal shoot concentrations were observed. Therefore, Jatropha may be useful for phytostabilization of metals in mine tailings. The use of B is recommended because improved MR chemical properties conduced to plant growth (cation-exchange capacity, organic matter content, essential nutrients, electrical conductivity, water-holding capacity) and plant growth development (higher biomass, nutritional and physiological performance). Inoculation with an AMF did not improve any plant growth or physiological plant characteristic. Only higher Zn shoot concentration was observed, but it was not phytotoxic. Future studies of B use and its long-term effect on MR remediation should be conducted under field conditions.

Riparian plants on mine runoff in Zimapan, Hidalgo, Mexico: Useful for phytoremediation?

Dispersion and runoff of mine tailings have serious implications for human and ecosystem health in the surroundings of mines. Water, soils and plants were sampled in transects perpendicular to the Santiago stream in Zimapan, Hidalgo, which receives runoff sediments from two acidic and one alkaline mine tailing. Concentrations of potentially toxic elements (PTE) were measured in water, soils (rhizosphere and non-rhizosphere) and plants. Using diethylenetriaminepentaacetic acid (DTPA) extractable concentrations of Cu, Zn, Ni, Cd and Pb in rhizosphere soil, the bioconcentration and translocation factors were calculated. Ruderal annuals formed the principal element of the herbaceous vegetation. Accumulation was the most frequent strategy to deal with high concentrations of Zn, Cu, Ni, Cd and Pb. The order of concentration in plant tissue was Zn>Pb>Cu>Ni>Cd. Most plants contained concentrations of PTE considered as phytotoxic and behaved as metal tolerant species. Rorippa nasturtium-aquaticum accumulated particularly high concentrations of Cu. Parietaria pensylvanica and Commelina diffusa, common tropical weeds, behaved as Zn hyperaccumulators and should be studied further.

Inhibition of microorganisms involved in deterioration of an archaeological site by silver nanoparticles produced by a green synthesis method.

The Citadel, part of the pre-Hispanic city of Teotihuacan and listed as a World Heritage Site, harbors irreplaceable archaeological walls and murals. This city was abandoned by the 7th century and its potential deterioration represents a noteworthy loss of the world's cultural heritage. This research consisted of isolation and identification of bacteria and fungi contributing to this deterioration from walls of a pre-Hispanic city. In addition, silver nanoparticles (AgNP) produced, using a green synthesis method, were tested as potential inhibitors of microbes. AgNP of different sizes and concentrations were tested using in situ assays. Leaf aqueous extracts from two plants species (Foeniculum vulgare and Tecoma stans) and two extraction procedures were used in the NP synthesis. The potential of AgNP as preventive/corrective treatments to protect stucco materials from biodeterioration, as well as the microbial inhibition on three stone materials (stucco, basalt and calcite) was analyzed. Twenty-three bacterial species belonging to eight genera and fourteen fungal species belonging to seven genera were isolated from colored stains, patinas and biofilms produced on the surfaces of archaeological walls from the pre-Hispanic city, Teotihuacan. AgNP from F. vulgare were more effective for in vitro microbial growth inhibition than those from T. stans. Bacteria were less sensitive to AgNP than fungi; however, sensitivity mainly depended on the microbial strain and the plant extract used to prepare AgNP. The use of AgNP as a preventive or corrective treatment to decrease microbial colonization in three kinds of stone used in historical walls was successful. Calcite was more colonized by Alternaria alternata, but less by Pectobacterium carotovorum. This is the first study at different scales (in vitro and tests on different stone types) of inhibition of biodeterioration-causing microorganisms isolated from an archaeological site by green synthesized AgNP.

Phytobarriers: Plants capture particles containing potentially toxic elements originating from mine tailings in semiarid regions.

Retention of particles containing potentially toxic elements (PTEs) on plants that spontaneously colonize mine tailings was studied through comparison of washed and unwashed shoot samples. Zn, Pb, Cd, Cu, Ni, Co and Mn concentrations were determined in plant samples. Particles retained on leaves were examined by Scanning Electronic Microscopy and energy dispersive X-Ray analysis. Particles containing PTEs were detected on both washed and unwashed leaves. This indicates that the thorough washing procedure did not remove all the particles containing PTEs from the leaf surface, leading to an overestimation of the concentrations of PTEs in plant tissues. Particularly trichomes and fungal mycelium were retaining particles. The quantity and composition of particles varied among plant species and place of collection. It is obvious that plants growing on toxic mine tailings form a physical barrier against particle dispersion and hence limit the spread of PTEs by wind.

Wild flora of mine tailings: perspectives for use in phytoremediation of potentially toxic elements in a semi-arid region in Mexico.

The aim of this research was to identify wild plant species applicable for remediation of mine tailings in arid soils. Plants growing on two mine tailings were identified and evaluated for their potential use in phytoremediation based on the concentration of potentially toxic elements (PTEs) in roots and shoots, bioconcentration (BCF) and translocation factors (TF). Total, water-soluble and DTPA-extractable concentrations of Pb, Cd, Zn, Cu, Co and Ni in rhizospheric and bulk soil were determined. Twelve species can grow on mine tailings, accumulate PTEs concentrations above the commonly accepted phytotoxicity levels, and are suitable for establishing a vegetation cover on barren mine tailings in the Zimapan region. Pteridium sp. is suitable for Zn and Cd phytostabilization. Aster gymnocephalus is a potential phytoextractor for Zn, Cd, Pb and Cu; Gnaphalium sp. for Cu and Crotalaria pumila for Zn. The species play different roles according to the specific conditions where they are growing at one site behaving as a PTEs accumulator and at another as a stabilizer. For this reason and due to the lack of a unified approach for calculation and interpretation of bioaccumulation factors, only considering BCF and TF may be not practical in all cases.

Localization and speciation of arsenic in Glomus intraradices by synchrotron radiation spectroscopic analysis.

The protective mechanisms employed by arbuscular mycorrhizal fungi (AMF) to reduce the toxic effects of arsenic on host plants remain partially unknown. The goal of this research was identifying the in situ localization and speciation of arsenic (As) in the AM fungus Rhizophagus intraradices [formerly named Glomus intraradices] exposed to arsenate [As(V)]. By using a two-compartment in vitro fungal cultures of R. intraradices-transformed carrot roots, microspectroscopic X-ray fluorescence (µ-XRF), and microspectroscopic X-ray absorption near edge structure (µ-XANES), we observed that As(V) is absorbed after 1 h in the hyphae of AMF. Three hours after exposure a decrease in the concentration of As was noticed and after 24 and 72 h no detectable As concentrations were perceived suggesting that As taken up was pumped out from the hyphae. No As was detected within the roots or hyphae in the root compartment zone three or 45 h after exposure. This suggests a dual protective mechanism to the plant by rapidly excluding As from the fungus and preventing As translocation to the plant root. µ-XANES data showed that gradual As(V) reduction occurred in the AM hyphae between 1 and 3 h after arsenic exposure and was completed after 6 h. Principal component analysis (PCA) and linear combination fitting (LCF) of µ-XANES data showed that the dominant species after reduction of As(V) by R. intraradices extra-radical hyphal was As(III) complexed with a reduced iron(II) carbonate compound. The second most abundant As species present was As(V)-iron hydroxides. The remaining As(III) compounds identified by the LCF analyses suggested these molecules were made of reduced As and S. These results increase our knowledge on the mechanism of As transport in AMF and validate our hypotheses that R. intraradices directly participates in arsenic detoxification. These fungal mechanisms may help AMF colonized plants to increase their tolerance to As at contaminated sites.

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

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