Impact of the earthworm Lumbricus terrestris (L.) on As, Cu, Pb and Zn mobility and speciation in contaminated soils

To assess the risks that contaminated soils pose to the environment properly a greater understanding of how soil biota influence the mobility of metal(loid)s in soils is required. Lumbricus terrestris L. were incubated in three soils contaminated with As, Cu, Pb and Zn. The concentration and speciation of metal(loid)s in pore waters and the mobility and partitioning in casts were compared with earthworm-free soil. Generally the concentrations of water extractable metal(loid)s in earthworm casts were greater than in earthworm-free soil. The impact of the earthworms on concentration and speciation in pore waters was soil and metal specific and could be explained either by earthworm induced changes in soil pH or soluble organic carbon. The mobilisation of metal(loid)s in the environment by earthworm activity may allow for leaching or uptake into biota

Bioavailability in soils

The consumption of locally-produced vegetables by humans may be an important exposure pathway for soil contaminants in many urban settings and for agricultural land use. Hence, prediction of metal and metalloid uptake by vegetables from contaminated soils is an important part of the Human Health Risk Assessment procedure. The behaviour of metals (cadmium, chromium, cobalt, copper, mercury, molybdenum, nickel, lead and zinc) and metalloids (arsenic, boron and selenium) in contaminated soils depends to a large extent on the intrinsic charge, valence and speciation of the contaminant ion, and soil properties such as pH, redox status and contents of clay and/or organic matter. However, chemistry and behaviour of the contaminant in soil alone cannot predict soil-to-plant transfer. Root uptake, root selectivity, ion interactions, rhizosphere processes, leaf uptake from the atmosphere, and plant partitioning are important processes that ultimately govern the accumulation ofmetals and metalloids in edible vegetable tissues. Mechanistic models to accurately describe all these processes have not yet been developed, let alone validated under field conditions. Hence, to estimate risks by vegetable consumption, empirical models have been used to correlate concentrations of metals and metalloids in contaminated soils, soil physico-chemical characteristics, and concentrations of elements in vegetable tissues. These models should only be used within the bounds of their calibration, and often need to be re-calibrated or validated using local soil and environmental conditions on a regional or site-specific basis.Mike J. McLaughlin, Erik Smolders, Fien Degryse, and Rene Rietr

Electronic stress tensor analysis of molecules in gas phase of CVD process for GeSbTe alloy

We analyze the electronic structure of molecules which may exist in gas phase of chemical vapor deposition process for GeSbTe alloy using the electronic stress tensor, with special focus on the chemical bonds between Ge, Sb and Te atoms. We find that, from the viewpoint of the electronic stress tensor, they have intermediate properties between alkali metals and hydrocarbon molecules. We also study the correlation between the bond order which is defined based on the electronic stress tensor, and energy-related quantities. We find that the correlation with the bond dissociation energy is not so strong while one with the force constant is very strong. We interpret these results in terms of the energy density on the "Lagrange surface", which is considered to define the boundary surface of atoms in a molecule in the framework of the electronic stress tensor analysis.Comment: 32 pages, 9 figure

Metal and metalloid foliar uptake by various plant species exposed to atmospheric industrial fallout: Mechanisms involved for lead

Fine and ultrafine metallic particulatematters (PMs) are emitted frommetallurgic activities in peri-urban zones into the atmosphere and can be deposited in terrestrial ecosystems. The foliar transfer ofmetals andmetalloids and their fate in plant leaves remain unclear, although this way of penetration may be a major contributor to the transfer of metals into plants. This study focused on the foliar uptake of various metals and metalloids from enriched PM(Cu, Zn, Cd, Sn, Sb, As, and especially lead (Pb)) resulting fromthe emissions of a battery-recycling factory.Metal and metalloid foliar uptake by various vegetable species, exhibiting different morphologies, use (food or fodder) and life-cycle (lettuce, parsley and rye-grass) were studied. The mechanisms involved in foliar metal transfer from atmospheric particulate matter fallout, using lead (Pb) as a model element was also investigated. Several complementary techniques (micro-X-ray fluorescence, scanning electron microscopy coupled with energy dispersive X-ray microanalysis and time-of-flight secondary ion mass spectrometry) were used to investigate the localization and the speciation of lead in their edible parts, i.e. leaves. The results showed lead-enriched PM on the surface of plant leaves. Biogeochemical transformations occurred on the leaf surfaces with the formation of lead secondary species (PbCO3 and organic Pb). Some compounds were internalized in their primary form (PbSO4) underneath an organic layer. Internalization through the cuticle or penetration through stomata openings are proposed as two major mechanisms involved in foliar uptake of particulate matter

Electronic structure and magnetism of Fe3−x_{3-x}Vx_{x}X (X = Si, Ga and Al) alloys by the KKR-CPA method

We present first principles charge- and spin-selfconsistent electronic structure computations on the Heusler-type disordered alloys Fe$_{3-x}$V$_{x}$X for three different metalloids X=(Si, Ga and Al). In these calculations we use the methodology based on the Korringa-Kohn- Rostoker formalism and the coherent-potential approximation (KKR-CPA), generalized to treat disorder in multi-component complex alloys.Comment: RevTeX, 17 pages, 15 figures, to appear in Phys. Rev. B on Nov. 15 199

Impacts of epigeic, anecic and endogeic earthworms on metal and metalloid mobility and availability

The introduction of earthworms into soils contaminated with metals and metalloids has been suggested to aid restoration practices. Eisenia veneta (epigeic), Lumbricus terrestris (anecic) and Allolobophora chlorotica (endogeic) earthworms were cultivated in columns containing 900 g soil with 1130, 345, 113 and 131 mg kg1 of As, Cu, Pb and Zn, respectively, for up to 112 days, in parallel with earthworm-free columns. Leachate was produced by pouring water on the soil surface to saturate the soil and generate downflow. Ryegrass was grown on the top of columns to assess metal uptake into biota. Different ecological groups affected metals in the same way by increasing concentrations and free ion activities in leachate, but anecic L. terrestris had the greatest effect by increasing leachate concentrations of As by 267%, Cu by 393%, Pb by 190%, and Zn by 429% compared to earthworm-free columns. Ryegrass grown in earthworm-bearing soil accumulated more metal and the soil microbial community exhibited greater stress. Results are consistent with earthworm enhanced degradation of organic matter leading to release of organically bound elements. The degradation of organic matter also releases organic acids which decrease the soil pH. The earthworms do not appear to carry out a unique process, but increase the rate of a process that is already occurring. The impact of earthworms on metal mobility and availability should therefore be considered when inoculating earthworms into contaminated soils as new pathways to receptors may be created or the flow of metals and metalloids to receptors may be elevated

Tolerance Threshold and Phyto-assessment of Cadmium and Lead in Vetiver Grass, Vetiveria zizanioides (Linn.) Nash

Various types of plant species have been extensively used for heavy metals phyto-remediation without taking into consideration its tolerance threshold. In this study, Vetiver grass, Vetiveria zizanioides (Linn.) Nash was evaluated under five different sets of contaminated spiked cadmium (5Cd, 10Cd, 50Cd, 100Cd and 150Cd mg/kg) and lead (50Pb, 100Pb, 200Pb, 400Pb and 800Pb mg/kg) concentration levels in soil. The growth performance, metal tolerance and phyto-assessment of Cd and Pb in the roots and tillers were assessed using flame atomic absorption spectrometry (FAAS). Tolerance index (TI), translocation factor (TF), biological transfer factor (BTF), biological accumulation coefficient (BAC) and metal uptake efficacy were used to determine the Cd and Pb translocation capability in Vetiver grass. Significantly higher (p\u3c0.05) accumulation of Cd and Pb was recorded in the roots of all spiked treatments. Furthermore, strong and significantly positive correlations were exhibited between the increased levels of spiked heavy metal concentrations with both Cd (r=0.975) and Pb (r=0.952) accumulations. The results of this study showed Vetiver grass as an effective phyto-stabilizer for both Cd and Pb. Nevertheless, the growth of Vetiver grass was restricted when the tolerance threshold of 100 mg/kg (dry weight basis) Cd was exceeded in the contaminated soil

Long-term field metal extraction by pelargonium:phytoextraction efficiency in relation to plant maturity

The long length of periods required for effective soil remediation via phytoextraction constitutes a weak point that reduces its industrial use. However, these calculated periods are mainly based on short-term and/or hydroponic controlled experiments. Moreover, only a few studies concern more than one metal, although soils are scarcely polluted by only one element.In this scientific context, the phytoextraction of metals and metalloids (Pb, Cd, Zn, Cu,and As) by Pelargonium was measured after a long-term field experiment. Both bulk and rhizosphere soils were analyzed in order to determine the mechanisms involved in soil-root transfer. First, a strong increase in lead phytoextraction was observed with plant maturity, significantly reducing the length of the period required for remediation. Rhizosphere Pb, Zn, Cu, Cd, and As accumulation was observed (compared to bulk soil), indicating metal mobilization by the plant, perhaps in relation to root activity. Moreover, metal phytoextraction and translocation were found to be a function of the metals’ nature. These results, taken altogether, suggest that Pelargonium could be used as a multi-metal hyperaccumulator under multi-metal soil contamination conditions, and they also provide an interesting insight for improving field phytoextraction remediation in terms of the length of time required, promoting this biological technique