International audience | Growth in the presence of sucrose was shown to confer to Arabidopsis thaliana (thale cress or mustard weed) seedlings, under conditions of in vitro culture, a high level of tolerance to the herbicide atrazine and to other photosynthesis inhibitors. This tolerance was associated with root-to-shoot transfer and accumulation of atrazine in shoots, which resulted in significant decrease of herbicide levels in the growth medium. In soil microcosms, application of exogenous sucrose was found to confer tolerance and capacity to accumulate atrazine in Arabidopsis thaliana plants grown on atrazine-contaminated soil, and resulted in enhanced decontamination of the soil. Application of sucrose to plants grown on herbicide-polluted soil, which increases plant tolerance and xenobiotic absorption, thus appears to be potentially useful for phytoremediation.

International audience | Phytoremediation is of great interest to remediate soil contaminated with hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4,6-trinitrotoluene (TNT). The ability of 4 agronomic plants (maize, soybean, wheat and rice) to take up these explosives and their fate in plants were investigated. Plants were grown for 42 days on soil contaminated with [14C]RDX or [14C]TNT. Then, each part was analyzed for its radioactivity content and the percentage of bound and soluble residues was determined following extractions. Extracts were analyzed by radio-HPLC. More than 80% of uptaken RDX was translocated to aerial tissues, up to 64.5 mg g−1 of RDX. By contrast, TNT was little translocated to leaves since less than 25% of uptaken TNT was accumulated in aerial parts. Concentrations of TNT residues were 20 times lower than for RDX uptake. TNT was highly metabolized to bound residues (more than 50% of radioactivity) whereas RDX was mainly found in its parent form in aerial parts.

International audience | Phytoremediation is an emerging strategy to remediate soils contaminated with pollutants like explosives in which plants will uptake, degrade and/or accumulate pollutants. To implement this technology on a site contaminated with RDX, we chose rice, which is able to grow in lagoons, and we tested its ability to grow in soils with high levels of RDX and to decrease RDX concentrations in soil. Rice was grown for 40 days in soil contaminated with increasing [14C]RDX concentrations. Emergence and growth were not affected by RDX. Total chlorophyll content decreased with RDX concentrations of over 500 mg kg−1. Amounts of chlorophyll were correlated with the appearance of necrosis in leaf extremities. After 40 days, rice translocated 89% of uptaken radioactivity to leaves with 90% in leaf extremities. Analyzes of leaf extracts showed that 95% of radioactivity was RDX in its parent form. Necrosis appears to be a phytotoxic symptom of RDX accumulation.

For most trace elements, the technique of phytoextraction needs significant improvements to become practically feasible. Calculations for Cd revealed that the amount of Cd taken up by Thlaspi caerulescens or Salix spp. needs at least to be the double of the present amount to slightly decrease the Cd concentration in the upper 0.5 m of the soil within a period of 10 years. Additionally, metals taken up by the plants might pose an important risk. Alternatives as bioavailable contaminant stripping and phytostabilization might be more appropriate. Phytoextraction efficiency should be improved and associated risks need more attention before phytoextraction can be established as a commercial technology.

The growth of transgenic canola (Brassica napus) expressing a gene for the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase was compared to non-transformed canola exposed to flooding and elevated soil Ni concentration, in situ. In addition, the ability of the plant growth-promoting bacterium Pseudomonas putida UW4, which also expresses ACC deaminase, to facilitate the growth of non-transformed and transgenic canola under the above mentioned conditions was examined. Transgenic canola and/or canola treated with P. putida UW4 had greater shoot biomass compared to non-transformed canola under low flood-stress conditions. Under high flood-stress conditions, shoot biomass was reduced and Ni accumulation was increased in all instances relative to low flood-stress conditions. This is the first field study to document the increase in plant tolerance utilizing transgenic plants and plant growth-promoting bacteria exposed to multiple stressors. Using transgenic plants and plant growth-promoting bacteria as phytoremediation methods increased plant tolerance at a metal-contaminated field site under low flood conditions.

This study examined the effects of heavy metals and plant arsenic uptake on soil arsenic distribution. Chemical fractionation of an arsenic-contaminated soil spiked with 50 or 200 mg kg-1 Ni, Zn, Cd or Pb was performed before and after growing the arsenic hyperaccumulator Pteris vittata L for 8 weeks using NH4Cl (water-soluble plus exchangeable, WE-As), NH4F (Al-As), NaOH (Fe-As), and H2SO4 (Ca-As). Arsenic in the soil was present primarily as the recalcitrant forms with Ca-As being the dominant fraction (45%). Arsenic taken up by P. vittata was from all fractions though Ca-As contributed the most (51-71% reduction). After 8 weeks of plant growth, the Al-As and Fe-As fractions were significantly (p < 0.01) greater in the metal-spiked soils than the control, with changes in the WE-As fraction being significantly (p = 0.007) correlated with plant arsenic removal. The plant's ability to solubilize soil arsenic from recalcitrant fractions may have enhanced its ability to hyperaccumulate arsenic. Arsenic taken up by P. vittata was from all fractions with most from the Ca-fraction.

The use of a vegetation cover for the management of heavy metal contaminated soils needs prior investigations on the plant species the best sustainable. In this work, behaviors of Trifolium repens and Lolium perenne, growing in a metal-polluted field located near a closed lead smelter, were investigated through Cd, Pb and Zn-plant metal concentrations and their phytotoxicity. In these plant species, metals were preferentially accumulated in roots than in shoots, as follow: Cd > Zn > Pb. Plant exposure to such metals induced oxidative stress in the considered organs as revealed by the variations in malondialdehyde levels and superoxide dismutase activities. These oxidative changes were closely related to metal levels, plant species and organs. Accordingly, L. perenne seemed to be more affected by metal-induced oxidative stress than T. repens. Taken together, these findings allow us to conclude that both the plant species could be suitable for the phytomanagement of metal-polluted soils. Usefulness of Trifolium repens and Lolium perenne for the phytomanagement of heavy metal-contaminated soils.

Boron (B) is a widespread environmental contaminant that is mobile relative to other trace elements. We investigated the potential of hybrid poplar (Populus sp.) for B phytomanagement using a lysimeter experiment and a field trial on B-contaminated wood-waste. In both studies, poplars enhanced evapotranspiration from the wood-waste, reduced B leaching, and accumulated B in the aerial portions of the tree. When grown in a substrate containing 30 mg/kg B, poplar leaves had an average B concentration of 845 mg/kg, while the stems contained 21 mg/kg B. Leaf B concentrations increased linearly with leaf age. A decomposition experiment revealed that abscised leaves released 14% of their B during the winter months. Fertiliser application enhanced tree growth without decreasing the leaf B concentrations. Harvesting alternate rows of trees on a contaminated site would reduce leaching from the site while removing B. Harvested plant material may provide bioenergy, stock fodder, or an amendment for B-deficient soils. Poplars reduce boron leaching from contaminated sites.

Phytoremediation is potentially effective for managing excessive selenium (Se) in drainage sediment residing in the San Luis Drain in central California. This 2-year field study examined the feasibility of amending drainage sediment (containing 4.78 mg Se g 1) with methionine and casein to enhance volatilization without or with vegetation of Sporobolus airoides. Results show that without organic amendments, rates of Se volatilization were less than 25 mgm 2 d 1 in all plots. After amending the sediment with 71.4 mg methionine kg 1 soil, Se volatilization rates were 434 107 mgm 2 d 1 in vegetated plots and 289 117 mgm 2 d 1 in irrigated bare plots.With the amendment of 572 mg casein kg 1 soil, rates increased to 346 103 mgm 2 d 1 in irrigated bare plots and to 114 55 mgm 2 d 1 in vegetated plots. Both methionine and casein promoted biological remediation of Se via volatilization most effectively during the warmest months.

With a view to the selection of plants for the re-vegetation of contaminated, semi-arid land, two populations of the perennial species Bituminaria bituminosa (Fabaceae) from the south of Spain were studied: one (“LA”) from a non-contaminated soil and the other (“C2”) from a similar soil having elevated total levels of Pb and Zn (1,112 and 4,249 μg g-¹, respectively). For sand-cultured plants receiving nutrient solution, flow cytometry showed that heavy metals, at the concentrations measured in aqueous extracts from contaminated soils, had only slight genotoxic effects on root tip cell nuclei. Both populations were also grown in both soils, in two pot experiments. In the first, shoot biomass of LA and C2 in the contaminated soil was decreased to similar extents, with respect to the “clean” soil. Tissue heavy metal concentrations were unlikely to have been phytotoxic, except in the case of shoot Zn for population LA, but there were tissue deficiencies of P and K for populations LA and C2, respectively. In the second pot assay, the stimulation of growth by NPK fertiliser confirmed that even though this soil had high total heavy metal levels, nutrient availability was the principal factor limiting growth. The lesser transport of heavy metals (Cd, Mn and Zn) to the shoot by the population from the contaminated site is a factor that should be considered when selecting B. bituminosa lines for the phytostabilisation of such sites.