Camille Dumat

Foliar Lead Uptake by Lettuce Exposed to Atmospheric Fallouts

Metal uptake by plants occurs by soil-root transfer but also by direct transfer of contaminants from the atmosphere to the shoots. This second pathway may be particularly important in kitchen gardens near industrial plants. The mechanisms of foliar uptake of lead by lettuce ( Lactuca sativa ) exposed to the atmospheric fallouts of a lead-recycling plant were studied. After 43 days of exposure, the thoroughly washed leaves contained 335 +/- 50 mg Pb kg(-1) (dry weight). Micro-X-ray fluorescence mappings evidenced Pb-rich spots of a few hundreds of micrometers in diameter located in necrotic zones. These spots were more abundant at the base of the central nervure. Environmental scanning electron microscopy coupled with energy dispersive X-ray microanalysis showed that smaller particles (a few micrometers in diameter) were also present in other regions of the leaves, often located beneath the leaf surface. In addition, submicrometric particles were observed inside stomatal openings. Raman microspectrometry analyses of the leaves identified smelter-originated Pb minerals but also secondary phases likely resulting from the weathering of original particles. On the basis of these observations, several pathways for foliar lead uptake are discussed. A better understanding of these mechanisms may be of interest for risk assessment of population exposure to atmospheric metal contamination.

Review of Pb availability and toxicity to plants in relation with metal speciation; role of synthetic and natural organic ligands

Biogeochemical behavior of lead (Pb), a persistent hazardous pollutant of environmental concern, strongly depends on its chemical speciation. Therefore, in this review, link between Pb speciation: presence of organic ligands and its environmental behavior has been developed. Both, biogeochemical and ecotoxicological data are discussed in environmental risk assessment context and phytoremediation studies. Three kinds of organic ligands selected for this review include: (1) ethylene diamine tetra-acetic acid (EDTA), (2) low molecular weight organic acids (LMWOAs) and (3) humic substances (HSs). The review highlights the effect of Pb speciation on: (i) Pb fate and behavior in soil; (ii) Pb plant uptake and accumulation in different plant parts; and (iii) Pb-induced phyto-toxicity. Effects of organic ligands on Pb speciation are compared: how they can change Pb speciation modifying accordingly its fate and biogeochemistry in soil-plant system? EDTA forms soluble, stable and phytoavailable Pb-chelates due to high binding Pb affinity. LMWOAs can solubilize Pb in soil by decreasing soil pH or increasing soil organic contents, but have little effect on its translocation. Due to heterogeneous structure, HSs role is complex. In consequence Pb speciation knowledge is needed to discuss phyto-toxicity data and improved soil phytoremediation techniques.

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

Fine and ultrafine metallic particulate matters (PMs) are emitted from metallurgic activities in peri-urban zones into the atmosphere and can be deposited in terrestrial ecosystems. The foliar transfer of metals and metalloids 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 from the 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 (PbCO(3) and organic Pb). Some compounds were internalized in their primary form (PbSO(4)) 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.

Lead-induced genotoxicity to Vicia faba L.roots in relation with metal cell uptake and initial speciation

Formation of organometallic complexes in soil solution strongly influence metals phytoavailability. However, only few studies deal with the influence of metal speciation both on plant uptake and genotoxicity. In the present study, Vicia faba seedlings were exposed for 6h in controlled hydroponic conditions to 5 μM of lead nitrate alone and chelated to varying degrees by different organic ligands. Ethylenediaminetetraacetic acid and citric acid were, respectively, chosen as models of humic substances and low weight organic acids present in natural soil solutions. Visual Minteq software was used to estimate free lead cations concentration and ultimately to design the experimental layout. For all experimental conditions, both micronucleus test and measure of lead uptake by plants were finally performed. Chelation of Pb by EDTA, a strong chelator, dose-dependently increased the uptake in V. faba roots while its genotoxicity was significantly reduced, suggesting a protective role of EDTA. A weak correlation was observed between total lead concentration absorbed by roots and genotoxicity (r(2)=0.65). In contrast, a strong relationship (r(2)=0.93) exists between Pb(2+) concentration in exposure media and genotoxicity in the experiment performed with EDTA. Citric acid induced labile organometallic complexes did not demonstrate any significant changes in lead genotoxicity or uptake. These results demonstrate that metal speciation knowledge could improve the interpretation of V. faba genotoxicity test performed to test soil quality.

A field study of lead phytoextraction by various scented Pelargonium cultivars.

Phytoremediation appears to be a promising technique for metal soil clean up, although its successful application on a large scale still remains a challenge. Field experiments for six scented Pelargonium cultivars, conducted on two Pb-contaminated calcareous and acidic soils, revealed vigorous plant growth, with no symptoms of morpho-phytotoxicity in spite of high Pb accumulation levels. Lead contents in the harvestable parts of all plants grown on the acidic and more contaminated soil were significantly higher than those grown on the calcareous soil. Three cultivars (Attar of Roses, Clorinda and Atomic Snowflake) are Pb-hyperaccumulator plants: they accumulated more than 1,000 mg Pb kg(-1)DW, with high biomass produced.

Study of lead phytoavailability for atmospheric industrial micronic and sub-micronic particles in relation with lead speciation

Particles from channelled emissions of a battery recycling facility were size-segregated and investigated to correlate their speciation and morphology with their transfer towards lettuce. Microculture experiments carried out with various calcareous soils spiked with micronic and sub-micronic particles (1650+/-20mg Pb kg(-1)) highlighted a greater transfer in soils mixed with the finest particles. According to XRD and Raman spectroscopy results, the two fractions presented differences in the amount of minor lead compounds like carbonates, but their speciation was quite similar, in decreasing order of abundance: PbS, PbSO(4), PbSO(4) x PbO, alpha-PbO and Pb(0). Morphology investigations revealed that PM(2.5) (i.e. Particulate Matter 2.5 composed of particles suspended in air with aerodynamic diameters of 2.5 microm or less) contained many Pb nanoballs and nanocrystals which could influence lead availability. The soil-plant transfer of lead was mainly influenced by size and was very well estimated by 0.01M CaCl(2) extraction.

Heavy-Metal-Induced Reactive Oxygen Species: Phytotoxicity and Physicochemical Changes in Plants

As a result of the industrial revolution, anthropogenic activities have enhanced there distribution of many toxic heavy metals from the earths crust to different environmental compartments. Environmental pollution by toxic heavy metals is increasing worldwide, and poses a rising threat to both the environment and to human health.Plants are exposed to heavy metals from various sources: mining and refining of ores, fertilizer and pesticide applications, battery chemicals, disposal of solid wastes(including sewage sludge), irrigation with wastewater, vehicular exhaust emissions and adjacent industrial activity.Heavy metals induce various morphological, physiological, and biochemical dysfunctions in plants, either directly or indirectly, and cause various damaging effects. The most frequently documented and earliest consequence of heavy metal toxicity in plants cells is the overproduction of ROS. Unlike redox-active metals such as iron and copper, heavy metals (e.g, Pb, Cd, Ni, AI, Mn and Zn) cannot generate ROS directly by participating in biological redox reactions such as Haber Weiss/Fenton reactions. However, these metals induce ROS generation via different indirect mechanisms, such as stimulating the activity of NADPH oxidases, displacing essential cations from specific binding sites of enzymes and inhibiting enzymatic activities from their affinity for -SH groups on the enzyme.Under normal conditions, ROS play several essential roles in regulating the expression of different genes. Reactive oxygen species control numerous processes like the cell cycle, plant growth, abiotic stress responses, systemic signalling, programmed cell death, pathogen defence and development. Enhanced generation of these species from heavy metal toxicity deteriorates the intrinsic antioxidant defense system of cells, and causes oxidative stress. Cells with oxidative stress display various chemical,biological and physiological toxic symptoms as a result of the interaction between ROS and biomolecules. Heavy-metal-induced ROS cause lipid peroxidation, membrane dismantling and damage to DNA, protein and carbohydrates. Plants have very well-organized defense systems, consisting of enzymatic and non-enzymatic antioxidation processes. The primary defense mechanism for heavy metal detoxification is the reduced absorption of these metals into plants or their sequestration in root cells.Secondary heavy metal tolerance mechanisms include activation of antioxidant enzymes and the binding of heavy metals by phytochelatins, glutathione and amino acids. These defense systems work in combination to manage the cascades of oxidative stress and to defend plant cells from the toxic effects of ROS.In this review, we summarized the biochemiCal processes involved in the over production of ROS as an aftermath to heavy metal exposure. We also described the ROS scavenging process that is associated with the antioxidant defense machinery.Despite considerable progress in understanding the biochemistry of ROS overproduction and scavenging, we still lack in-depth studies on the parameters associated with heavy metal exclusion and tolerance capacity of plants. For example, data about the role of glutathione-glutaredoxin-thioredoxin system in ROS detoxification in plant cells are scarce. Moreover, how ROS mediate glutathionylation (redox signalling)is still not completely understood. Similarly, induction of glutathione and phytochelatins under oxidative stress is very well reported, but it is still unexplained that some studied compounds are not involved in the detoxification mechanisms. Moreover,although the role of metal transporters and gene expression is well established for a few metals and plants, much more research is needed. Eventually, when results for more metals and plants are available, the mechanism of the biochemical and genetic basis of heavy metal detoxification in plants will be better understood. Moreover, by using recently developed genetic and biotechnological tools it may be possible to produce plants that have traits desirable for imparting heavy metal tolerance.

EDTA-Enhanced Phytoremediation of Heavy Metals: A Review

The increase in heavy metal terrestrial ecosystems’ contamination through anthropogenic activities is a widespread and serious global problem due to their various environmental and human implications. For these reasons, several techniques, including phytoremediation of heavy metals, have been extensively studied. In spite of significant recent advancement, ethylene diamine tetraacetic acid (EDTA)-enhanced heavy metal phytoextraction as well as related ecological risks are still topical and remain an important area of research. In fact, EDTA favors the solubilization of metals and metalloids in soils, and was therefore extensively studied during the last two decades in order to improve phytoextraction efficiency and reduce treatment duration. This review highlights the recent findings (2010–2012) and mechanisms behind EDTA-enhanced (1) solubilization of heavy metals in soil, (2) mobilization/transport of soluble metals towards plant root zone, and (3) metal absorption by plant roots and translocation towards aerial parts. The review also presents potential risks associated with EDTA-enhanced phytoextraction: (1) environmental persistence of EDTA and/or metal-EDTA complex; (2) potential toxicity of EDTA and/or metal-EDTA complex to plants; and (3) leaching and contamination of groundwater. Moreover, field-scale cost of EDTA-enhanced remediation and the role of EDTA in time required for heavy metal remediation is discussed.

Foliar heavy metal uptake, toxicity and detoxification in plants: a comparison of foliar and root metal uptake

Anthropologic activities have transformed global biogeochemical cycling of heavy metals by emitting considerable quantities of these metals into the atmosphere from diverse sources. In spite of substantial and progressive developments in industrial processes and techniques to reduce environmental emissions, atmospheric contamination by toxic heavy metals and associated ecological and health risks are still newsworthy. Atmospheric heavy metals may be absorbed via foliar organs of plants after wet or dry deposition of atmospheric fallouts on plant canopy. Unlike root metal transfer, which has been largely studied, little is known about heavy metal uptake by plant leaves from the atmosphere. To the best of our understanding, significant research gaps exist regarding foliar heavy metal uptake. This is the first review regarding biogeochemical behaviour of heavy metals in atmosphere-plant system. The review summarizes the mechanisms involved in foliar heavy metal uptake, transfer, compartmentation, toxicity and in plant detoxification. We have described the biological and environmental factors that affect foliar uptake of heavy metals and compared the biogeochemical behaviour (uptake, translocation, compartmentation, toxicity and detoxification) of heavy metals for root and foliar uptake. The possible health risks associated with the consumption of heavy metal-laced food are also discussed.

Influence of soil ageing on bioavailability and ecotoxicity of lead carried by process waste metallic ultrafine particles

Ultrafine particulate matters enriched with metals are emitted into the atmosphere by industrial activities and can impact terrestrial and aquatic ecosystems. Thus, this study investigated the environmental effects of process particles from a lead-recycling facility after atmospheric deposition on soils and potential run-off to surface waters. The toxicity of lead-enriched PM for ecosystems was investigated on lettuce and bacteria by (i) germination tests, growth assays, lead transfer to plant tissues determination and (ii) Microtox analysis. The influence of ageing and soil properties on metal transfer and ecotoxicity was studied using three different soils and comparing various aged, spiked or historically long-term polluted soils. Finally, lead availability was assessed by 0.01 M CaCl(2) soil extraction. The results showed that process PM have a toxic effect on lettuce seedling growth and on Vibrio fischeri metabolism. Soil-PM interactions significantly influence PM ecotoxicity and bioavailability; the effect is complex and depends on the duration of ageing. Solubilisation or stabilisation processes with metal speciation changes could be involved. Finally, Microtox and phytotoxicity tests are sensitive and complementary tools for studying process PM ecotoxicity.