Procédé de phytoextraction couplé à la bioaugmentation d'un sol agricole polycontaminé par du chrome, du mercure et du plomb

Agricultural soils have been contaminated for many years by both direct pesticides and fertilizer supplies, and indirect contaminations originated from industrial activities. The agricultural soil used in the present study was collected in the Thur valley (Haut-Rhin, France), and contains chromium (488 mg/kg), mercury (13 mg/kg) and lead (381 mg/kg). Phytoextraction is a soft-cleaning technology, cost-effective and non-destructive for biological life in soil. Nevertheless the low availability of metals in soil along with the slowness of the phytoextraction rocess represent limiting factors that are likely to reduce its efficiency. A new technology named rhizoremediation, which associate bioaugmentation and phytoremediation, was tested in this study in order to enhance the phytoextraction rate. Our results showed that Cr and Pb availability in soil was enhanced, as the result of the bioaugmentation of soil with microorganisms producing siderophores, especially with the Pseudomonas species. The siderophore production with Pseudomonas species was optimized with the addition of carbon substrates. Immobilization of bacterial cells in Ca-alginate beads supplied with skim milk enhanced the siderophore production in a metal-containing media and improved the bacterial survival in soil. More than 90% of Cr, Fe and Pb and more than 40% of Hg were adsorbed onto Ca-alginate beads surface, which decrease metal toxicity for immobilized or free cells, and create an iron deficiency inside the beads, which enhanced siderophores production by microorganisms. The selected icroorganisms were inoculated in the contaminated soil, with maize as a model plant. The bioaugmentation of soil pots with immobilized cells of P. aeruginosa and skim milk enhanced the amount of metal accumulated in leaves by a factor of 5.4 and 3.8 for Cr and Pb respectively compared to non-bioaugmented pots. Soil bioaugmentation with free cells of R. metallidurans supplied with skim milk enhanced Cr extraction by leaves by a factor of 5.2.Les sols agricoles sont depuis de nombreuses années contaminés directement par apports d'intrants (pesticides, fertilisants) mais également de façon indirecte en raison de la proximité de certaines installations industrielles. Notre étude porte sur des sols agricoles à l'aval de la vallée de la Thur (Haut-Rhin), polycontaminés par du chrome (488 mg/kg), du mercure (13 mg/kg) et du plomb (381 mg/kg). La phytoextraction est une méthode innovante, employée pour ses propriétés respectueuses de la vie biologique du sol et son faible coût. La faible disponibilité des métaux dans le sol (notamment Cr, Hg et Pb), et par conséquent le temps de décontamination, constitue la principale limite de cette technique. La bioaugmentation couplée à la phytoremédiation (rhizoremédiation) est une technique récente qui a été testée pour cette étude de façon à accroître la vitesse de phytoextraction. Les résultats ont montré que les microorganismes producteurs de sidérophores, notamment les Pseudomonas, étaient potentiellement intéressants pour augmenter la mobilité du chrome et du plomb dans le sol. La production de sidérophores par des cellules libres ou immobilisées de Pseudomonas cultivées en présence de divers substrats carbonés a été optimisée. L'immobilisation des microorganismes dans des billes d'alginate de calcium enrichies en lait écrémé a montré que les microorganismes étudiés produisaient plus de sidérophores en présence de métaux et que leur survie dans le sol était accrue. Les billes de Ca-alginate adsorbent plus de 90% de Cr, Fe et Pb ainsi que plus de 40% de Hg, ce qui diminue la toxicité métallique pour les cellules libres ou immobilisées, et crée également un déficit en Fe dans les billes, stimulant ainsi la production de sidérophores par les microorganismes. Les microorganismes sélectionnés ont ensuite été inoculés dans le sol contaminé, cultivé avec du maïs comme plante modèle. La bioaugmentation des pots de sol avec Pseudomonas aeruginosa co-immobilisé dans des billes de Ca-alginate avec du lait écrémé a permis de multiplier le prélèvement de Cr par les feuilles de maïs par 5,4 et celui du Pb par 3,8 par rapport aux pots non bioaugmentés. L'inoculation du sol enrichi en lait écrémé avec des cellules libres de R. metallidurans a permis d'augmenter le rélèvement foliaire de Cr par 5,2

Brassica juncea tested on urban soils moderately contaminated by lead: Origin of contamination and effect of chelates

International audienc

<i>Brassica juncea</i> tested on urban soils moderately contaminated by lead: Origin of contamination and effect of chelates

<p>Urban garden soils are a potential repository of heavy metal pollution, resulting from either anthropogenic or geogenic origin. The efficiency of phytoextraction was compared on two garden soils with the same texture and topsoil Pb concentration (170 mg kg⁻¹) but not the same origin: one geogenic, the other anthropogenic. Two varieties of <i>Brassica juncea</i> were tested with citric acid (25 mmol kg⁻¹) or ethylenediaminetetraacetic acid (EDTA, 2.5 mmol kg⁻¹). Geogenic Pb was shown to be two times less available than anthropogenic Pb, as a result of which the phytoextraction efficiency was reduced by 59%. Pb mobility in the soil was solely enhanced with EDTA, which increased the Pb concentration in shoots of <i>B. juncea</i> by between 14 and 26 times in comparison with the control. The highest Pb concentration in shoots still remained low, however (<i>i.e.</i>, 45 mg kg⁻¹ dry weight). Regardless of the chelates introduced, <i>B. juncea</i> 426308 accumulated roughly twice as much lead as <i>B. juncea</i> 211000, but only for the anthropogenic contaminated soil. Under these conditions, the amount of Pb accumulated by <i>B. juncea</i> (even when assisted by EDTA) was not high enough to envision achieving soil clean-up within a reasonable time frame.</p

Chelate-assisted phytoextraction of lead using Fagopyrum esculentum: laboratory vs. field experiments

International audienceThe development of more sustainable remediation techniques has been receiving greater attention, as an alternative to soil excavation plan in urban gardens. An in situ phytoextraction experiment with buckwheat (Fagopyrum esculentum) was performed with a 5 mmol kg(-1) citric acid (CA) application. Joint experiments under laboratory conditions were conducted using various cultivars of F. esculentum in two soils with a Pb contamination of either geogenic or anthropogenic origin and various chelate concentrations. Results show that a minimum dose of 50 mmol kg(-1) of CA is required to lower soil pH and raise the concentration of mobile Pb-CaCl2 for both soils. Consequently, Pb shoot uptake is increased from 6.3 to 8.9 times depending on soil type. Phytoextraction efficiency is found to be 1.3 to 2.0 times higher in the anthropogenic contaminated soil than in the soil with geogenic Pb. A scale effect has also been identified since Pb root accumulation under laboratory conditions was 2.4 times higher than in the field experiment. Despite an increase in the Pb extraction rate with CA, buckwheat appears to lack the efficiency needed to remove Pb in moderately contaminated soils. The calculated remediation period would last 166 years to remove the mobile Pb fraction

The PvdRT-OpmQ efflux pump controls the metal selectivity of the iron uptake pathway mediated by the siderophore pyoverdine in Pseudomonas aeruginosa

International audienc

The Pseudomonas aeruginosa Pyochelin-Iron Uptake Pathway and Its Metal Specificity▿

Pyochelin (Pch) is one of the two major siderophores produced and secreted by Pseudomonas aeruginosa PAO1 to assimilate iron. It chelates iron in the extracellular medium and transports it into the cell via a specific outer membrane transporter, FptA. We used the fluorescent properties of Pch to show that this siderophore chelates, in addition to Fe3+ albeit with substantially lower affinities, Ag+, Al3+, Cd2+, Co2+, Cr2+, Cu2+, Eu3+, Ga3+, Hg2+, Mn2+, Ni2+, Pb2+, Sn2+, Tb3+, Tl+, and Zn2+. Surprisingly, the Pch complexes with all these metals bound to FptA with affinities in the range of 10 nM to 4.8 μM (the affinity of Pch-Fe is 10 nM) and were able to inhibit, with various efficiencies, Pch-55Fe uptake in vivo. We used inductively coupled plasma atomic emission spectrometry to follow metal uptake by P. aeruginosa. Energy-dependent metal uptake, in the presence of Pch, was efficient only for Fe3+. Co2+, Ga3+, and Ni2+ were also transported, but the uptake rates were 23- to 35-fold lower than that for Fe3+. No uptake was seen for all the other metals. Thus, cell surface FptA has broad metal specificity at the binding stage but is much more selective for the metal uptake process. This uptake pathway does not appear to efficiently assimilate any metal other than Fe3+

Trace elements in urban garden and health risks

12th Urban Environment Symposium, OSLO, NORVEGE, 01-/06/2016 - 03/06/2016During the last century, global urban populations have increased very rapidly. In the context of global changes and with the need of food supply and recreation areas for these urban populations, green areas are developing. Thus, allotment gardens are expanding worldwide. However, the garden location and soil quality, which have not been taken into account beforehand, can induce health risks.For many years, the city of Nantes supports the allotment gardening. Attentive to the potential health risks associated with this practice, for instance the consumption of vegetables grown on contaminated soil, the parks and gardens and environment department has launched a program to check the soil quality of its 24 gardens towards pollutants. In case of soil and vegetable contamination, soil management is foreseen.In this study, three gardens were investigated (Eglantiers, Contrie and Batignolles). Soil and vegetables samples were analyzed. The spatial distribution (horizontal and vertical) of As, Cu, Pb, and Zn, in the plots of the garden, was determined, completed by a historical analysis of the site. The studied elements were quantified using a portable X-ray fluorescence spectrometer. To assess the transfer of trace elements in vegetables, its accumulation in vegetable samples was assessed after a digestion with aqua regia and a determination by atomic absorption.Trace elements contents were mapped. Significant As and Pb anomalies were observed in several plots of the different gardens. Moreover, the results showed different origins for the pollution and different levels of vegetable transfer. The results for vegetables were compared with the European regulation that defines the maximum authorized concentration of some trace elements in vegetables destined to human consumption. Some concentrations in vegetables exceeded the threshold level (e.g. Pb 0.1 mg kg-1 fresh matter (FM))